Methods for preparing sulfilimines and sulfoximines from thioethers using o-(diphenylphosphinyl)hydroxyl amine (DPPH), and amatoxin analogs prepared from such methods

Abstract

The present disclosure relates to methods for preparing sulfilimines and sulfoximines from thioethers using O-(diphenylphosphinyl)hydroxyl amine (DPPH), and methods for preparing amatoxin analogs, such as, the compound of Formula I(a'), which can be prepared from said sulfilimine and sulfoximine preparation methods as well as conjugates comprising said amatoxin analogs and their use, for example, in the treatment of cancer:, wherein A is S+(NH2)Q-, S=NH or S(O)=NH and Q is a counteranion.

Description

METHODS FOR PREPARING SULFILIMINES AND SULFOXIMINES AND AMATOXIN ANALOGS THAT CAN BE PREPARED FROM SUCH METHODS CROSS-REFERENCE TO RELATED APPLICATIONS

[0001] The present application claims the benefit of priority from co-pending U.S. provisional application no.63 / 542,354 filed on October 4, 2023, the contents of which are incorporated herein by reference in their entirety. FIELD

[0002] The present disclosure relates to methods for preparing sulfilimines and sulfoximines and amatoxin analogs that can be prepared from such methods as well as to conjugates comprising such amatoxin analogs and their use, for example, in the treatment of cancer. BACKGROUND

[0003] The diversity of sulfur-based molecular constellations (Scheme 1), along with the potential for stereogenicity at sulfur-IV / VI centers, opens new chemical space in the design of pharmaceuticals and agrochemicals (Tilby & Willis, 2021; Wojaczyńska & Wojaczyński, 2020).Scheme 1. Diverse S(IV / VI) centered sulfur constellations.

[0004] Whilst sulfoxides, sulfones, and sulfonamides have been mainstays in medicinal chemistry for over a century (Zhao et al., 2019), sulfoximine-bearing bio-actives (Scheme 2) (Mäder & Kattner, 2020; Han et al., 2021) have recently sparked acute interest in new S- imination methods, whereby sulfoximines are accessed from thioethers either via iminating sulfoxides or oxidizing sulfilimines (Scheme 3) (Bull et al., 2017; Andresini et al., 2021). Of recent interest are sulfondiimines that also arise from sulfilimines (Passia et al., 2022).

[0005] Notwithstanding burgeoning interest in various S(VI)-motifs, sulfilimines, known since 1922 (Mann & Pope, 1922), are themselves versatile and configurationally stable S(IV) motifs that are valued as building blocks (Tian et al., 2019; Xie & Sun, 2021; Haut et al., 2021; Cheng et al., 2022), directing groups (Yoshida et al., 2015; Tian et. al., 2020; Hayashi et al., 2016), chiral auxiliaries, and chiral ligands (Taylor, 1999; Takada et al., 2000; Thakur et al., 2004). Signifying biological relevance, sulfilimine staple was discovered in collagen(Vanacore et al., 2009). In proteins, sulfilimine salts generated from S-methylcysteines have been exploited to give dehydroalanines for bioconjugation (Bernardes et al., 2008). Both free-NH sulfilimines and free-NH sulfoximines undergo Chan-Lam coupling whereby such N-substitution enables subsequent bioconjugation (Meng et al., 2022; Ding et al., 2022). Alternatively, N-substituted sulfilimines have been installed directly to enable bioconjugation (Lin et al., 2017; Lin et al., 2020; Elledge et al., 2020). Unquestionably, therefore, access to these S-motifs depends on robust S-imination methods.Scheme 2. Chemical structures of selected clinical drug candidates / prospects and agrochemicals bearing sulfoximines or sulfondiimine moieties.Scheme 3. Ex pl sy routes to i inesf in [O] and [N]represent different electrophilic O / N- nsfer reagents; RAis SO2Ar, CF3CO, ROCO; RBis tosyl (Ts), CN, ROCO, alkyl, (Ns); RCis H, alkyl, Ts, Ns.

[0006] N-substituted / protected sulfilimines are readily procured (Bizet et al., 2015); chloramine-T (Na N-chloro-para-toluene sulfonamidate) readily affords N-tosyl sulfilimines (Tsujihara et al., 1969; Marzinzik & Sharpless, 2001), and transition metal catalysis has expanded access to N-substituted sulfilimines with diverse iminating reagents including organoazides (Liu & Che, 2010; Farwell et al., 2014; Uchida & Katsuki, 2014), 1,4,2-dioxazol-5-one (Bizet et al., 2014; Yoshitake et al., 2020), N-halo-carbamates, N- sulfonyl-carbamates (Takada et al., 1997), and imino-iodinanes (van Leest et al., 2021; Okamura & Bohm, 2004; Cho & Bolm, 2005; Mancheño & Bolm, 2006). However, for metal-free imination, oxaziridines are amongst the few biomolecule-compatible reagents capable of late-stage S-imination; these provide N-carbamoyl sulfilimines and have been appended with handles e.g. alkynes for subsequent bioconjugation (Lin et al., 2017).

[0007] However, for drug development, access to free-NH sulfur(IV / VI) motifs, including sulfoximines and sulfondiimines, is important to obviate the need for subsequent N-deprotection. Hence, the direct generation of a free-NH sulfilimine (R2S=NH) is of considerable interest. Historically, direct imination of thioethers and sulfoxides was achieved with hydrazoic acid generated from azide salts and strong acid e.g. H2SO4 (Bizet et al., 2015; Misani et al., 1951). Subsequently, electrophilic iminating agents, e.g. hydroxylamine-O- sulfonic acid (HOSA), O-mesitylene-sulfonylhydroxyl amine (MSH) (Tamura et al., 1975) and 2,4-dinitrophenylhydroxyl amine (DPH) (Tamura et al., 1973) found use. Yet, reports of explosive decomposition limit the commercial availability of MSH (Mendiola et al., 2009) and limit scalability of reactions. Similarly, DPH, and its by-product 2,4-dinitrophenol (DNP), carry explosion risk, and both are toxic (Ma et al., 2017). Transition metals, affording safety and greater chemical diversity, catalyze direct imination of sulfoxides; such include Rh / DPH (Miao et al., 2014), and Fe / 4-nitroarylhydroxylammonium triflate (Yu et al., 2018). For metal-free access to sulfoximines, reports feature [PhI(OAc)2] / NH4H2NCO2(Zenzola et al., 2016) and other hypervalent iodine agents (Koser et al., 1987). With respect to sulfoximines, N-substituted sulfilimines are readily oxidized in good yield (Mancheño et al., 2010; Gaggero et al., 1997; Johnson & Kirchhoff, 1979; Huang & Swern, 1979; Mancheño et al., 2007; Lebel et al., 2014; Greenwood & Ellman, 2023; Akutagawa et al., 1984), yet free-NH sulfilimines are oxidized in variable if not lower yields, accompanied by sulfoxide and sulfone by-products (Yoshimura et al., 1976). Scheme 4 shows exemplary synthetic approaches to free-NH sulfilimines and sulfoximines.Scheme 4. Comparative synthetic approaches to free-NH sulfilimines and sulfoximines.

[0008] A survey of the vast literature indicates that standard reagents / methods have not found use in late-stage S-imination in the context of complex molecules to give free-NH sulfilimines. As a large number of natural products and bioactive agents present sulfoxides (Wojaczyńska & Wojaczyński, 2023), the potential for replacing a sulfoxide with a free-NH sulfilimine intrigues. Yet to the best of the inventors’ knowledge, no study has evaluated the potential bioisosterism of sulfilimines, the study of which would benefit from a late-stage S-imination reaction. Ideally, such would proceed under mild, metal-free, and biomolecule-compatible conditions.

[0009] Diphenyl-phoshinylhydroxylamine (DPPH) has previously found applications as an aminating reagent in the context of carbon and nitrogen nucleophiles. For example, DPPH has been reported in electrophilic imination reactions on carbon anions (Harger, 1981; Colvin et al., 1982; Smulik & Vedejs, 2003; Laulhe et al., 2012; Ong et al., 2022; Saito, 2022; Erdik, 2004). This reagent is commercially available and can conveniently be synthesized in the lab on gram-scale (Laulhé & Nantz, 2011; Tamas, 2020).

[0010] Amatoxins are one of the most notorious sulfoxide-bearing classes of natural products (Wieland et al., 1978; Lindell et al., 1970) and unnatural amatoxin-sulfones are also cytotoxic (Wieland et al., 1983). The amatoxin family of cytotoxic peptide bicycles are marked by a unique tryptathionine crosslink comprising a cysteine and tryptophan. These toxins are highly selective allosteric inhibitors of RNA polymerase II (Lindell et al., 1970) and now show great promise as payloads in ADC therapy (Pahl et al., 2018; Figueroa- Vazquez, et al., 2021; Moldenhauer et al., 2012). The oxidation state and the stereochemical configuration of the sulfur atom has a pronounced effect on toxicity; the naturally occurring α-amanitin features an (R)-sulfoxide, whilst unnatural (S)-sulfoxide diastereomer is 8-foldless cytotoxic (Wieland et al., 1983). Both the unnatural sulfone and the thioether are surprisingly as toxic as the (R)-sulfoxide (Matinkhoo et al., 2018). Prior work on stereoselective sulfoxidation of thioether precursors of amanitin and related synthetic amatoxins led to stereo-defined sulfoxides along with sulfones on the more synthetically tractable 5-hydroxy-tryptathionine bearing toxin; all of these show comparable cytotoxicities (IC50 about 1µM on HEK cells) with respect to natural α-amanitin-based congeners (containing the 6-hydroxy-tryptathionine) (Pryyma et al., 2020). There has been a long- standing interest in amatoxins (see also, for example: Matinkhoo et al., 2018; Pryyma et al., 2020; Todorovic et al., 2022), and the prospect of installing such S-N constellations on such a toxin may be desirable. However, it was unknown whether replacing the sulfoxide with a sulfilimine would maintain the cytotoxicity of an amatoxin. Additionally, the toxin’s electron-rich and therefore oxidatively delicate (hydroxy)tryptathionine (Ttn) staple poses an appreciable chemical challenge that would befall any electrophilic S-imination method. SUMMARY

[0011] The present disclosure includes an amatoxin analog comprising a tryptathionine bridge of the Formula:, wherein A is S+(NH2)Q–, S=NH or S(O)=NH; Q is a counteranion; R2aand R2bare each independently H or C1-10alkyl; or R2aand R2btogether with the carbon atom to which they are attached, together form C3-10cycloalkyl; each R7is independently OR ^, N(R ^)2, NO2, CN, COOR ^, N3, NR ^NR ^, ON(R ^)2, NR ^-OR ^, SeR ^, SO3R ^, P(O)(OR ^)2, C(O)N(R ^)2, CHO, B(OR ^)2, CH3, CH2OH, or halo; r is an integer from 0 to 4; and each R ^ is independently H, C1-20alkyl, C2-20alkenyl, C2-20alkynyl, C3- 20cycloalkyl, C6-30aryl, heterocycloalkyl or heteroaryl, wherein one or more available carbon atoms in the C1-20alkyl, C2-20alkenyl and C2-20alkynyl is optionally replaced by a heteroatom, and wherein the C1-C2-20alkenyl, C2-20alkynyl, C3-20cycloalkyl, C6-30aryl, heterocycloalkyl and heteroaryl is optionally further substituted with one or more groups selected from OR ^ ^, halo, azide and nitrile, wherein R ^ ^ is independently H, C1-20alkyl, C2-20alkenyl, C2-20alkynyl, C3-20cycloalkyl, C6-30aryl, heterocycloalkyl or heteroaryl, or a pharmaceutically acceptable salt thereof, wherein in the amatoxin analog or the pharmaceutically acceptable salt thereof, one or more available hydrogens is / are optionally replaced with deuterium and / or one or more available hydrogens is / are optionally replaced with fluorine and / or one or more available atoms is / are optionally replaced with its radioactive isotope.

[0012] In an embodiment, the amatoxin analog is a compound of Formula I:, wherein A is S+(NH2)Q–, S=NH or S(O)=NH; Q is a counteranion; X1and X2are each independently (CH2)m, CHCH3, CHCH2CH3, C(CH3)2 or NR ^; R1is CH(Z-CH3)2, wherein one or more available hydrogens is / are optionally substituted with SH; or R1is C3-10cycloalkyl, wherein one or more available hydrogens on the C3-10cycloalkyl is / are optionally substituted with C1-10alkyl and / or one or more available carbon atoms in the C3-10cycloalkyl is / are optionally replaced by O; and wherein one or more single bonds between two available carbon atoms in R1is / are optionally replaced by a double bond;R2aand R2bare each independently H or C1-10alkyl; or R2aand R2btogether with the carbon atom to which they are attached, together form C3-10cycloalkyl; R3is OR ^, NH(OR ^), NH-NHR ^ or N(R ^)2; R4is H or OH; R5and R6are each independently H, OR ^, NHR ^ or halo; each R7is independently OR ^, N(R ^)2, NO2, CN, COOR ^, N3, NR ^NR ^, ON(R ^)2, NR ^-OR ^, SeR ^, SO3R ^, P(O)(OR ^)2, C(O)N(R ^)2, CHO, B(OR ^)2, CH3, CH2OH, or halo; each Z is independently (CH2)nO(CH2)p, (CH2)nSe(CH2)p or (CH2)q; each m is independently an integer from 1 to 5; each n is independently an integer from 0 to 4; each p is independently an integer from 0 to 4; n + p in each Z, is independently ^ 4; each q is independently an integer from 0 to 4; r is an integer from 0 to 4; and each Rʹ is independently H, C1-20alkyl, C2-20alkenyl, C2-20alkynyl, C3- 20cycloalkyl, C6-30aryl, heterocycloalkyl or heteroaryl, wherein one or more available carbon atoms in the C1-20alkyl, C2-20alkenyl and C2-20alkynyl is optionally replaced by a heteroatom, and wherein the C1-20alkyl, C2-20alkenyl, C2-20alkynyl, C3-20cycloalkyl, C6-30aryl, heterocycloalkyl and heteroaryl is optionally further substituted with one or more groups selected from ORʹʹ, halo, azide and nitrile, wherein Rʹʹ is independently H, C1-20alkyl, C2-20alkenyl, C2-20alkynyl, C3-20cycloalkyl, C6-30aryl, heterocycloalkyl or heteroaryl, or a pharmaceutically acceptable salt thereof; wherein in the compound of Formula I or the pharmaceutically acceptable salt thereof, one or more available hydrogens is / are optionally replaced with deuterium and / or one or more available hydrogens is / are optionally replaced with fluorine and / or one or more available atoms is / are optionally replaced with its radioactive isotope.

[0013] In an embodiment, the amatoxin analog has one or more of the following:(i) R1other than (ii) X1other than CH2; (iii) X2other than CH2;(iv) R2aother than H; and (v) R2bother than H.

[0014] In an embodiment, the amatoxin analog is a compound of Formula I(a):wherein A is S+(NH2)Q–, S=NH or S(O)=NH; Q is a counteranion; R1is CH(Z-CH3)2, wherein one or more available hydrogens is / are optionally substituted with SH; or R3is C3-10cycloalkyl,wherein each Z isindependently(CH2)nO(CH2)por(CH2)q;R3is OR ^, NH(OR ^), NH-NHR ^ or N(R ^)2; R4is H or OH; R5and R6are each independently H, OR ^, NHR ^ or halo; each R7is independently OR ^, N(R ^)2, NO2, CN, COOR ^, N3, NR ^NR ^, ON(R ^)2, NR ^-OR ^, SeR ^, SO3R ^, P(O)(OR ^)2, C(O)N(R ^)2, CHO, B(OR ^)2, CH3, CH2OH, or halo; each n is independently 0, 1, or 2; each p is independently 0, 1, or 2; each q is independently 0, 1, or 2; r is an integer from 0 to 4; and each Rʹ is independently H, C1-20alkyl, C2-20alkenyl, C2-20alkynyl, C3- 20cycloalkyl, C6-30aryl, heterocycloalkyl or heteroaryl, wherein one or more available carbon atoms in the C1-20alkyl, C2-20alkenyl and C2-20alkynyl is optionally replaced by a heteroatom, and wherein the C1-20alkyl, C2-20alkenyl, C2-20alkynyl, C3- 20cycloalkyl, C6-30aryl, heterocycloalkyl and heteroaryl is optionally further substituted with one or more groups selected from ORʹʹ, halo, azide and nitrile, wherein Rʹʹ is independently H, C1-20alkyl, C2-20alkenyl, C2-20alkynyl, C3-20cycloalkyl, C6-30aryl, or heteroaryl,or a pharmaceutically acceptable salt thereof; wherein in the compound of Formula I(a) or the pharmaceutically acceptable salt thereof, one or more available hydrogens is / are optionally replaced with deuterium and / or one or more available hydrogens is / are optionally replaced with fluorine and / or one or more available atoms is / are optionally replaced with its radioactive isotope.

[0015] In an embodiment, the amatoxin analog of Formula I(a) has the following stereochemistry:.

[0016] In an embodiment, the amatoxin analog of Formula I(a) has the following stereochemistry:.

[0017] In an embodiment, R1is CH(CH3)(CH2CH3).

[0018] In an embodiment, R3is OH or NH2. In another embodiment, R3is -N(R ^)2, wherein one R ^ is H and the other R ^ is C1-20alkyl substituted with -N3.

[0019] In an embodiment, R4, R5and R6are each OH.

[0020] In an embodiment, r is 1.

[0021] In an embodiment, R7is 5-OH.

[0022] In an embodiment, A is S+(NH2)Q–. In another embodiment, A is S=NH. In another embodiment, A is S(O)=NH.

[0023] In an embodiment, A is (R)-A. In another embodiment, A is (S)-A.

[0024] In an embodiment, th amatoxin analog is:, or a pharmaceutically acceptable salt thereof.

[0025] In an embodiment, the amatoxin analog is not in the form of a salt. In another embodiment, the amatoxin analog is in the form of a pharmaceutically acceptable salt of the amatoxin analog.

[0026] The present disclosure also includes an amatoxin-linker construct comprising an amatoxin analog as described herein (which may include pharmaceutically acceptable salts thereof) coupled to a linker, wherein the linker comprises a reactive group R8for conjugating the amatoxin-linker construct to a target-binding moiety.

[0027] In an embodiment, the linker is coupled to the amatoxin analog or the salt thereof at a site indicated by A, R3, R4, R5, R6and / or R7in an amatoxin analog as described herein. In another embodiment, the linker is coupled to the amatoxin analog or the salt thereof through a moiety obtained from the reaction of A, R3, R4, R5, R6and / or R7as described herein with a complementary functional group on the linker. In another embodiment, R3comprises an N3 moiety, the complementary functional group on the linker is an alkyne, and the linker is coupled to the amatoxin analog or the salt thereof through a 1,2,3-triazole. In another embodiment, the linker is coupled to the amatoxin analog or the salt thereof through a moiety obtained from the reaction of A with a complementary functional group on the linker. In another embodiment, the moiety obtained from the reaction of the nitrogen of A with the complementary functional group on the linker is an S-N-carbamoyl group.

[0028] The present disclosure also includes a conjugate comprising a target-binding moiety conjugated to an amatoxin analog as described herein or an amatoxin-linker construct as described herein.

[0029] In an embodiment, the target-binding moiety is a peptide, an oligonucleotide, a lipid, a lipid carrier, a nanoparticle or combinations thereof. In another embodiment, the target-binding moiety is an antibody, an antigen-binding fragment thereof, an antibody-like protein, an aptamer, a vitamin, an oligonucleotide, an affibody, a minibody, a lipid, a lipid carrier, a nanoparticle or combinations thereof. In another embodiment, the target-binding moiety is an antibody, an antigen-binding fragment thereof or an antibody-like protein. In another embodiment, the target-binding moiety is an antibody.

[0030] The present disclosure also includes a pharmaceutical composition comprising an amatoxin analog as described herein, or a conjugate as described herein and a pharmaceutically acceptable carrier.

[0031] The present disclosure also includes a use of an amatoxin analog as described herein, or a conjugate as described herein, for treatment of a disease associated with cells presenting a target in a subject in need thereof, wherein the target-binding moiety is specific for the target. In an embodiment, the disease associated with cells presenting a target is cancer, an autoimmune disease or a viral infection.

[0032] The present disclosure also includes a use of an amatoxin analog as described herein, or a conjugate as described herein, for treatment of cancer in a subject in need thereof. In an embodiment, the cancer is breast cancer.

[0033] The present disclosure also includes a method for preparing a sulfiliminium salt of Formula II, the method comprising S-imination of a thioether of Formula III in the presence of O-(diphenylphosphinyl)hydroxyl amine (DPPH):, wherein R9aand R9bare independently selected from C1-20alkyl, C2-20alkenyl, C2-20alkynyl, C3-20cycloalkyl, C6-30aryl, heterocycloalkyl, heteroaryl and a bioactive moiety, wherein the C1-20alkyl, C2-20alkenyl, C2-20alkynyl, C3-20cycloalkyl, C6-30aryl, heterocycloalkyl and heteroaryl is optionally substituted with one or more groups selected from C1-6alkyl, C1- 6alkoxy, aryl, NH2, halo, NO2, cyano, -C(O)C1-6alkyl, OH, =O and a bioactive moiety; or wherein R9aand R9b, together with the S to which they are attached, form heterocycloalkyl or a bioactive moiety, wherein the heterocycloalkyl is optionally substituted with one or more groups selected from C1-6alkyl, C1-6alkoxy, aryl, NH2, halo, NO2, cyano, acyl, OH, =O and a bioactive moiety; and wherein one or more available hydrogens is / are optionally replaced with deuterium; and / or one or more available hydrogens is / are optionally replaced with fluorine.

[0034] The present disclosure also includes a method for preparing a sulfoximine of Formula IV, the method comprising oxidizing a sulfiliminium salt of Formula II prepared by a method for preparing a sulfiliminium salt of Formula II of the present disclosure:, wherein R9aand R9bare independently selected from C1-20alkyl, C2-20alkenyl, C2-20alkynyl, C3-20cycloalkyl, C6-30aryl, heterocycloalkyl, heteroaryl and a bioactive moiety, wherein the C1-20alkyl, C2-20alkenyl, C2-20alkynyl, C3-20cycloalkyl, C6-30aryl, heterocycloalkyl and heteroaryl is optionally substituted with one or more groups selected from C1-6alkyl, C1- 6alkoxy, aryl, NH2, halo, NO2, cyano, -C(O)C1-6alkyl, OH, =O and a bioactive moiety; or wherein R9aand R9b, together with the S to which they are attached, form heterocycloalkyl or a bioactive moiety, wherein the heterocycloalkyl is optionally substituted with one or more groups selected from C1-6alkyl, C1-6alkoxy, aryl, NH2, halo, NO2, cyano, acyl, OH, =O and a bioactive moiety; and wherein one or more available hydrogens is / are optionally replaced with deuterium; and / or one or more available hydrogens is / are optionally replaced with fluorine.

[0035] In an embodiment, the method is a one-pot reaction.

[0036] In an embodiment, R9aand R9btogether form an amatoxin analog.

[0037] The present disclosure also includes a method for preparing a sulfoximine of Formula IV, the method comprising S-imination of a thioether of Formula V in the presence of O-(diphenylphosphinyl)hydroxyl amine (DPPH):, wherein R9aand R9bare independently selected from C1-20alkyl, C2-20alkenyl, C2-20alkynyl, C3-20cycloalkyl, C6-30aryl, heterocycloalkyl, heteroaryl and a bioactive moiety, wherein the C1-20alkyl, C2-20alkenyl, C2-20alkynyl, C3-20cycloalkyl, C6-30aryl, heterocycloalkyl and heteroaryl is optionally substituted with one or more groups selected from C1-6alkyl, C1- 6alkoxy, aryl, NH2, halo, NO2, cyano, -C(O)C1-6alkyl, OH, =O and a bioactive moiety; orwherein R9aand R9b, together with the S to which they are attached, form heterocycloalkyl or a bioactive moiety, wherein the heterocycloalkyl is optionally substituted with one or more groups selected from C1-6alkyl, C1-6alkoxy, aryl, NH2, halo, NO2, cyano, acyl, OH, =O and a bioactive moiety; and wherein one or more available hydrogens is / are optionally replaced with deuterium; and / or one or more available hydrogens is / are optionally replaced with fluorine.

[0038] Herein is described compositions and methods of synthesizing sulfilimine and sulfoximine-containing bioactive compounds, including amatoxin analogs, using diphenylphoshinylhydroxylamine (DPPH) to afford late-stage S-imination and access free-NH sulfilimines, sulfiliminium salts, and sulfoximines. Sulfilimine and sulfoximine analogs of bioactive small molecules and peptides (including such amatoxin analogs) are reported herein.

[0039] Accordingly, in an aspect there is provided a method for synthesizing a sulfiliminium- containing bioactive compound via S-imination using O-(diphenylphosphinyl)hydroxyl amine (DPPH) whereby electrophilic sulfilimination of a thioether-containing bioactive compound using DPPH generates a sulfiliminium-containing compound:where R9aand R9bare independently selected from C1-20alkyl, C2-20alkenyl, C2-20alkynyl, C3- 20cycloalkyl, C6-30aryl, heterocycloalkyl or heteroaryl. In another embodiment, R9aand R9bmay be selected from a 1-20 amino-acid peptide. In another embodiment, R9aand R9bare amino acid sequences in a protein.

[0040] In another aspect there is provided a method for synthesizing a sulfoximine- containing bioactive compound from a sulfiliminium salt whereby the sulfiliminium salt is oxidized to yield a sulfoximine- bioactive compound:where R9aand R9bare independently selected from C1-20alkyl, C2-20alkenyl, C2-20alkynyl, C3- 20cycloalkyl, C6-30aryl, heterocycloalkyl or heteroaryl. In another embodiment, R9aand R9amaybe selected from a 1-20 amino-acid peptide. In another embodiment, R9aand R9aare amino acid sequences in a protein. In another embodiment, the base is selected from the group consisting of Na2CO3, NH4OH, MgO, NaOH, NH3, DIPEA, DBU, lutidine, NaHCO3, K2CO3 and NaOMe.

[0041] In another aspect there is provided a method for synthesizing a sulfoximine- containing bioactive compound wherein S-imination of a thioether-containing compound using O-(diphenylphosphinyl)hydroxyl amine (DPPH) is followed by oxidation to yield a sulfoximine-containing bioactive compound:where R9aand R9bare independently selected from a C1-20alkyl, C2-20alkenyl, C2-20alkynyl, C3-20cycloalkyl, C6-30aryl, heterocycloalkyl or heteroaryl. In another embodiment, R9aand R9bmay be selected from a 1-20 amino-acid peptide. In another embodiment, R9aand R9bare amino acid sequences in a protein. In another embodiment, the base is selected from the group consisting of Na2CO3, NH4OH, MgO, NaOH, NH3, DIPEA, DBU, lutidine, NaHCO3, K2CO3and NaOMe.

[0042] In another aspect there is provided an amatoxin analog of Formula I(i):wherein: R10ais lone pair of electrons (l.p.) and R10bis NH2 or NH (or vice versa (R / S)), or R10ais NH and R10bis O (or vice versa (R / S));X1and X2are each independently (CH2)m, CHCH3, CHCH2CH3, C(CH3)2 or NRʹ; R1is CH(Z-CH3)2, wherein one or more available hydrogens is / are optionally substituted with SH; or R1is C3-10cycloalkyl, wherein one or more available hydrogens on the C3-10cycloalkyl is / are optionally substituted with C1-10alkyl and / or one or more available carbon atoms in the C3-10cycloalkyl is / are optionally replaced by O; and wherein one or more single bonds between two available carbon atoms in R1is / are optionally replaced by a double bond; R2aand R2bare each independently H or C1-10alkyl; or R2aand R2btogether with the carbon atom to which they are attached, together form C3-10cycloalkyl; R3is ORʹ, NH(ORʹ), NH-NHRʹ or N(Rʹ)2; R4is H or OH; R5and R6are each independently H, ORʹ, NHRʹ, or halo; each R7is independently ORʹ, N(Rʹ)2, NO2, CN, COORʹ, N3, NRʹNRʹ, ON(Rʹ)2, NRʹ- ORʹ, SeRʹ, SO3Rʹ, P(O)(ORʹ)2, C(O)N(Rʹ)2, CHO, B(ORʹ)2, CH3, CH2OH, or halo; each Z is independently (CH2)nO(CH2)p, (CH2)nSe(CH2)p or (CH2)q; each m is independently an integer from 1 to 5; each n is independently an integer from 0 to 4; each p is independently an integer from 0 to 4; n + p in each Z, is independently ≤ 4; each q is independently an integer from 0 to 4; r is an integer from 0 to 4; and each Rʹ is independently H, C1-20alkyl, C2-20alkenyl, C2-20alkynyl, C3-20cycloalkyl, C6-30aryl, heterocycloalkyl or heteroaryl, wherein one or more available carbon atoms in the C1-20alkyl, C2-20alkenyl and C2-20alkynyl is optionally replaced by a heteroatom, and wherein the C1-20alkyl, C2-20alkenyl, C2-20alkynyl, C3-20cycloalkyl, C6-30aryl, heterocycloalkyl and heteroaryl is optionally further substituted with one or more groups selected from ORʹʹ, halo, azide and nitrile, wherein Rʹʹ is independently H, C1-20alkyl, C2-20alkenyl, C2-20alkynyl, C3- 20cycloalkyl, C6-30aryl, heterocycloalkyl or heteroaryl, or a pharmaceutically acceptable salt thereof; optionally wherein the compound of Formula I or the pharmaceutically acceptable salt thereof has one or more(i) R1other than ;(ii) X1other than CH2; (iii) X2other than CH2; (iv) R2aother than H; and (v) R2bother than H, and wherein in the compound of Formula I or the pharmaceutically acceptable salt thereof, one or more available hydrogens is / are optionally replaced with deuterium and / or one or more available hydrogens is / are optionally replaced with fluorine and / or one or more available atoms is / are optionally replaced with its radioactive isotope. In another aspect, the amatoxin analog is selected from the following compounds:where S / R corresponds to the sulfur stereogenic center. In another aspect, the free-NH of the sulfilimine or sulfoximine group of such an amatoxin analog provides a handle for bioconjugation. In another aspect there is provided a pharmaceutical composition comprising such an amatoxin analog and a pharmaceutically acceptable carrier. In another aspect, there is provided a use of an effective amount of such a compound or conjugate for treatment ofcancer in a subject. Also provided herein is a method of treating cancer in a subject in need thereof, the method comprising administering an effective amount of such an amatoxin.

[0043] Other features and advantages of the present disclosure will become apparent from the following detailed description. It should be understood, however, that the detailed description and the specific examples, while indicating embodiments of the disclosure, are given by way of illustration only and the scope of the claims should not be limited by these embodiments, but should rather be given the broadest interpretation consistent with the description as a whole. BRIEF DESCRIPTION OF THE DRAWINGS

[0044] The embodiments of the disclosure will now be described in greater detail with reference to the attached drawings, in which:

[0045] FIG.1 shows an Oak Ridge Thermal-Ellipsoid Plot Program (ORTEP) diagram of the crystal structure of S,S-dibenzyl sulfiliminium diphenylphosphinate (2b).

[0046] FIG.2 shows an ORTEP diagram based of the crystal structure of Fmoc-Met-OH sulfiliminium diphenylphosphinate (2v[i]).

[0047] FIG.3 shows energy minimized models of (R)-sulfiliminium (upper) and (S)- sulfiliminium (lower) analogs of 5′-OH(Trp) Amanitin constructed using molecular operating environment (MOE) program. Highlighted in light grey lines are inter-hydrogen distances (10-10m) in the molecule for the assessment of observable NOE correlations.

[0048] FIG. 4 shows a schematic showing heteronuclear multiple bond correlation (HMBC) and nuclear Overhauser effect spectroscopy (NOESY) correlations observed (upper) in the1H-13C HMBC nuclear magnetic resonance (NMR) spectrum (600 MHz, DMSO) (lower left) and1H-1H NOESY NMR spectrum (600 MHz, DMSO) (lower right).

[0049] FIG.5 shows MTT assay results on HEK 293 cells for sulfiliminium analogues of S-deoxy-5′-OH(Trp) Ama 2za and 2zb shown as diastereomeric pairs in comparison to ^- amanitin and S-deoxy-5′-OH (Trp) Ama 1z.

[0050] FIG.6 shows MTT assay results on CHO cells for the sulfiliminium analogs of S- deoxy-5′-OH(Trp) Ama 2za and 2zb in comparison to ^-amanitin.

[0051] FIG.7 shows circular dichroism (CD) spectra of α-amanitin and sulfur derivatized 5′-OH(Trp) Amanitin analogs.

[0052] FIG.8 shows MTT assay results on HEK 293 cells for amanitin sulfoximine 3zb and sulfone 4z analogues in comparison to ^-amanitin and 1z.

[0053] FIG. 9 shows energy minimized models of (S)-sulfoximine (upper) and (R)- sulfoximine (lower) of 5′-OH(Trp) amanitin constructed using molecular operating environment (MOE) program. Highlighted in light grey lines are inter-hydrogen distances (10-10m) in the molecule for the assessment of observable NOE correlations.

[0054] FIG.10 shows a schematic showing HMBC and NOESY correlations observed (upper left); a1H-13C HMBC NMR spectrum (600 MHz, DMSO) (upper right); and a1H-1H 1D NOESY NMR spectrum (600 MHz, DMSO) generated by irradiation of the proton signal at δ 5.38 ppm overlapped with1H NMR spectrum (600 MHz, DMSO) (lower).

[0055] FIG.11 shows MTT assay IC50 curves for (S)-sulfoximine 5′-OH(Trp) Ama 3za against HEK293 cells in comparison to ^-amanitin. DETAILED DESCRIPTION I. Definitions

[0056] Unless otherwise indicated, the definitions and embodiments described in this and other sections are intended to be applicable to all embodiments and aspects of the disclosure herein described for which they would be understood to be suitable by a person skilled in the art.

[0057] As used herein, the words “comprising” (and any form thereof, such as “comprise” and “comprises”), “having” (and any form thereof, such as “have” and “has”), “including” (and any form thereof, such as “include” and “includes”) or “containing” (and any form thereof, such as “contain” and “contains”), are inclusive or open-ended and do not exclude additional, unrecited elements or process / method steps. As used herein, the word “consisting” and its derivatives are intended to be close-ended terms that specify the presence of the stated features, elements, components, groups, integers and / or steps, and also exclude the presence of other unstated features, elements, components, groups, integers and / or steps. The term “consisting essentially of”, as used herein, is intended to specify the presence of the stated features, elements, components, groups, integers, and / or steps as well as those that do not materially affect the basic and novel characteristic(s) of these features, elements, components, groups, integers and / or steps.

[0058] Terms of degree such as “substantially”, “about” and “approximately” as used herein mean a reasonable amount of deviation of the modified term such that the end result is notsignificantly changed. These terms of degree should be construed as including a deviation of at least ±5% of the modified term if this deviation would not negate the meaning of the term it modifies.

[0059] As used in this disclosure, the singular forms “a”, “an” and “the” include plural references unless the content clearly dictates otherwise.

[0060] The term “and / or” as used herein means that the listed items are present, or used, individually or in combination. In effect, this term means that “at least one of” or “one or more” of the listed items is present or used.

[0061] The term “alkyl” as used herein, whether it is used alone or as part of another group, means straight or branched chain, saturated alkyl groups. The number of carbon atoms that are possible in the referenced alkyl group are indicated by the numerical prefix “Cn1-n2”. For example, the term C1-6alkyl means an alkyl group having 1, 2, 3, 4, 5 or 6 carbon atoms.

[0062] The term “alkenyl” as used herein, whether it is used alone or as part of another group, means straight or branched chain, unsaturated alkenyl groups. The number of carbon atoms that are possible in the referenced alkenyl group are indicated by the numerical prefix “Cn1-n2”. For example, the term C2-20alkenyl means an alkenyl group having 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15, 16, 17, 18, 19 or 20 carbon atoms and at least one double bond, for example 1-3, 1-2 or 1 double bond.

[0063] The term “alkynyl” as used herein, whether it is used alone or as part of another group, means straight or branched chain, unsaturated alkynyl groups. The number of carbon atoms that are possible in the referenced alkynyl group are indicated by the numerical prefix “Cn1-n2”. For example, the term C2-20alkynyl means an alkenyl group having 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15, 16, 17, 18, 19 or 20 carbon atoms and at least one triple bond, for example 1-3, 1-2 or 1 triple bond.

[0064] The term “cycloalkyl” as used herein, whether it is used alone or as part of another group, means a saturated cycloalkyl group. The number of carbon atoms that are possible in the referenced cycloalkyl group are indicated by the numerical prefix “Cn1-n2”. For example, the term C3-20cycloalkyl means a cycloalkyl group having 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15, 16, 17, 18, 19 or 20 carbon atoms. Cycloalkyl groups may contain more than one ring.

[0065] The term “heterocycloalkyl” as used herein, whether it is used alone or as part of another group, refers to a non-aromatic, ring-containing group having one or more multivalent heteroatoms, independently selected from N, S and Se, as a part of the ring structure andincluding at least 3 and up to 20 atoms in the ring(s). Heterocycloalkyl groups are either saturated or unsaturated (i.e. contain one or more double bonds) and may contain more than one ring.

[0066] When a cycloalkyl or heterocycloalkyl group contains more than one cyclic structure or rings, the cyclic structures may be fused, bridged, spiro connected or linked by a single bond. The term “fused” as used herein in reference to a first cyclic structure being “fused” with a second cyclic structure means the first cyclic structure and the second cyclic structure share at least two adjacent atoms therebetween. The term “bridged” as used herein in reference to a first cyclic structure being “bridged” with a second cyclic structure means the first cyclic structure and the second cyclic structure share at least two non-adjacent atoms therebetween. The term “spiro-connected” in reference to a first cyclic structure being “spiro connected” with a second cyclic structure means the first cyclic structure and the second cyclic structure share one atom therebetween.

[0067] The term “aryl” as used herein, whether it is used alone or as part of another group, refers to cyclic groups that contain at least one aromatic ring. The number of carbon atoms that are possible in the referenced aryl group are optionally indicated by the numerical prefix “Cn1-n2”. For example, the term C6-30aryl means an aryl group having 6, 7, 8, 9, 10, 11, 12, 13, 14, 15, 16, 17, 18, 19, 20, 21, 22, 23, 24, 25, 26, 27, 28, 29 or 30 carbon atoms. In an embodiment, the aryl group contains from 6, 9, 10 or 14 carbon atoms, such as phenyl, naphthyl, indanyl or anthracenyl. In another embodiment, the aryl group is a phenyl.

[0068] The term “heteroaryl” as used herein, whether it is used alone or as part of another group, refers to an aromatic, ring-containing group having one or more multivalent heteroatoms, for example, independently selected from N, O, S and Se, as a part of the ring structure and including at least 5 and up to 20 atoms in the ring(s). Heteroaryl groups may contain more than one ring.

[0069] The term “halo” as used herein refers to a halogen atom and includes F, Cl and Br.

[0070] The term “counteranion” as used herein refers to a negatively charged species consisting of a single element, or a negatively charged species consisting of a group of elements connected by ionic and / or covalent bonds.

[0071] The term “available”, as used herein in reference to “available hydrogens”, “available carbon atoms”, “available atoms” and the like refers to atoms that would be known to a person skilled in the art to be capable of modification and / or replacement by another atom or substituent.

[0072] The term “replaced with its radioactive isotope” as used herein in reference to one or more available atoms in the amatoxin analogs of the present disclosure means that a non- radioactive isotope of the atom is replaced with the corresponding radioactive isotope. For example, in an embodiment, a non-radioactive isotope of hydrogen is replaced with3H (tritium). In another embodiment, a non-radioactive isotope of carbon is replaced with11C or14C. In a further embodiment, a non-radioactive isotope of iodine is replaced with123I,125I or131I. In another embodiment, a non-radioactive isotope of sulfur is replaced with35S. It will be appreciated by a person skilled in the art that depending, for example, on the radioactive isotope, such radiolabelled compounds may, for example, be useful as radiopharmaceuticals for treatment and / or diagnostic applications. The selection of a suitable radioactive isotope and methods for the preparation of radiolabelled compounds can be made by a person skilled in the art.

[0073] The term “subject” as used herein includes all members of the animal kingdom including mammals. In an embodiment, the subject is a human.

[0074] The term “pharmaceutically acceptable” as used herein means compatible with the treatment of subjects, for example, mammals such as humans.

[0075] The term “pharmaceutically acceptable salt” as used herein means either an acid addition salt or a base addition salt that is compatible with the treatment of subjects and includes salts wherein Q is a pharmaceutically acceptable counteranion.

[0076] An “acid addition salt that is compatible with the treatment of subjects” is any suitable non-toxic organic or inorganic salt of any basic compound. Basic compounds that form an acid addition salt include, for example, compounds comprising an amine group susceptible to protonation. Illustrative inorganic acids which form suitable salts include but are not limited to hydrochloric, hydrobromic, sulfuric and phosphoric acids, as well as metal salts such as but not limited to sodium monohydrogen orthophosphate and potassium hydrogen sulfate. Illustrative organic acids that may form suitable salts include but are not limited to mono-, di-, and tricarboxylic acids such as glycolic, lactic, pyruvic, malonic, succinic, glutaric, fumaric, malic, tartaric, citric, ascorbic, maleic, benzoic, phenylacetic, cinnamic and salicylic acids, as well as sulfonic acids such as but not limited to p-toluene sulfonic and methanesulfonic acids. The selection of a suitable salt can be made by a person skilled in the art. The formation of a desired acid addition salt is, for example, achieved using standard techniques. For example, in an embodiment, the neutral compound is treated withthe desired acid in a suitable solvent and the salt which is thereby formed then isolated by filtration, extraction and / or any other suitable method.

[0077] A “base addition salt that is compatible with the treatment of subjects” is any suitable nontoxic inorganic or organic salt of any acidic compound. Acidic compounds that form a base addition salt include, for example, compounds comprising a carboxylic, phosphonic or sulfonic acid group. Inorganic bases that may form suitable salts include, without limitation, lithium, sodium, potassium, calcium, magnesium or barium hydroxide. Organic bases that may form suitable salts include, without limitation, aliphatic, alicyclic or aromatic organic amines such as methylamine, trimethylamine and picoline or ammonia. The selection of a suitable salt can be made by a person skilled in the art. The formation of a desired base addition salt is, for example, achieved using standard techniques. For example, in an embodiment, the neutral compound is treated with the desired base in a suitable solvent and the salt which is thereby formed then isolated by filtration, extraction and / or any other suitable method.

[0078] The terms “to treat”, “treating” and “treatment” as used herein and as is well understood in the art, mean an approach for obtaining beneficial or desired results, including clinical results. Beneficial or desired clinical results include but are not limited to alleviation or amelioration of one or more symptoms of a disease (e.g. cancer), diminishment of the extent of the disease, stabilization (i.e. not worsening) of the disease, delay or slowing of the progression of the disease, amelioration or palliation of the state of the disease, diminishment of the recurrence of the disease and / or remission (whether partial or total) of the disease, whether detectable or undetectable. To “treat”, “treating” and “treatment” as used herein also include prophylactic treatment of the disease. For example, in an embodiment, a subject with early-stage disease is treated to prevent progression or alternatively a subject in remission is treated to prevent recurrence.

[0079] As used herein, the term “effective amount” means an amount effective, at dosages and for periods of time necessary to achieve a desired result. For example, in the context of treating cancer, an effective amount of an amatoxin analog or conjugate of the present disclosure is an amount that, for example, reduces the cancer compared to the cancer without administration or use of the amatoxin analog or conjugate, respectively. Effective amounts may vary according to factors such as the disease state, age, sex and / or weight of the subject. The amount of a given amatoxin analogue or conjugate, as the case may be, that will correspond to such an amount will vary depending upon various factors,such as the given amatoxin analog or conjugate, the pharmaceutical formulation, the type of disease being treated, the identity of the subject being treated, and the like, but can nevertheless be routinely determined by one skilled in the art. II. Amatoxin Analogs, Compound-Linker Constructs, and Conjugates

[0080] The present disclosure includes an amatoxin analog comprising a tryptathionine bridge of the Formula:, wherein A is S+(NH2)Q–, S=NH or S(O)=NH; Q is a counteranion; R2aand R2bare each independently H or C1-10alkyl; or R2aand R2btogether with the carbon atom to which they are attached, together form C3-10cycloalkyl; each R7is independently OR ^, N(R ^)2, NO2, CN, COOR ^, N3, NR ^NR ^, ON(R ^)2, NR ^-OR ^, SeR ^, SO3R ^, P(O)(OR ^)2, C(O)N(R ^)2, CHO, B(OR ^)2, CH3, CH2OH, or halo; r is an integer from 0 to 4; and each R ^ is independently H, C1-20alkyl, C2-20alkenyl, C2-20alkynyl, C3- 20cycloalkyl, C6-30aryl, heterocycloalkyl or heteroaryl, wherein one or more available carbon atoms in the C1-20alkyl, C2-20alkenyl and C2-20alkynyl is optionally replaced by a heteroatom, and wherein the C1-20alkyl, C2-20alkenyl, C2-20alkynyl, C3-20cycloalkyl, C6-30aryl, heterocycloalkyl and heteroaryl is optionally further substituted with one or more groups selected from OR ^ ^, halo, azide and nitrile, wherein R ^ ^ is independently H, C1-20alkyl, C2-20alkenyl, C2-20alkynyl, C3- 20cycloalkyl, C6-30aryl, heterocycloalkyl or heteroaryl, or a pharmaceutically acceptable salt thereof, wherein in the amatoxin analog or the pharmaceutically acceptable salt thereof, one or more available hydrogens is / are optionally replaced with deuterium and / or one or more available hydrogens is / are optionally replaced with fluorine and / or one or more available atoms is / are optionally replaced with its radioactive isotope.

[0081] The amatoxin can be any suitable amatoxin. The term “amatoxin” as used herein includes all cyclic peptides composed of 8 amino acids as isolated from the genus Amanita and described, for example, by Wieland, T. and Faulstich, H. in CRC Critical Reviews in Biochemistry 1978, 5 (3), 185-260 as well as all suitable chemical derivatives, semisynthetic analogs and synthetic analogs thereof built from building blocks according to the master structure of the natural compounds (cyclic, 8 amino acids). The term “amatoxin” as used herein also includes all suitable synthetic or semisynthetic analogs of amatoxins containing non- hydroxylated amino acids instead of the hydroxylated amino acids and / or amino acids comprising beta-alkyl groups such as beta-methyl groups and / or in which the sulfoxide moiety is replaced by a sulfone, or thioether, or by atoms different from sulfur, e.g., a carbon atom as in a carbanalog of amanitin. In an embodiment, the amatoxin has a functional group (e.g. a carboxylic group, an amino group, a hydroxy group, a thiol, a thiol-capturing group, an alkynyl group and / or an -N3 group) that can be reacted with a complementary functional group on a linker and / or a target-binding moiety as defined herein. In an embodiment of the present disclosure, the amatoxin is an ^-amanitin, ^-amanitin, ^-amanitin, ^-amanitin, amanullin, amanullinic acid, amanin, amaninamide, ^-amanin or ^-amaninamide or a derivative thereof.

[0082] In an embodiment, the amatoxin analog is a compound of Formula I:, wherein A is S+(NH2)Q–, S=NH or S(O)=NH; Q is a counteranion; X1and X2are each independently (CH2)m, CHCH3, CHCH2CH3, C(CH3)2or NR ^;R1is CH(Z-CH3)2, wherein one or more available hydrogens is / are optionally substituted with SH; or R1is C3-10cycloalkyl, wherein one or more available hydrogens on the C3-10cycloalkyl is / are optionally substituted with C1- 10alkyl and / or one or more available carbon atoms in the C3-10cycloalkyl is / are optionally replaced by O; and wherein one or more single bonds between two available carbon atoms in R1is / are optionally replaced by a double bond; R2aand R2bare each independently H or C1-10alkyl; or R2aand R2btogether with the carbon atom to which they are attached, together form C3-10cycloalkyl; R3is OR ^, NH(OR ^), NH-NHR ^ or N(R ^)2; R4is H or OH; R5and R6are each independently H, OR ^, NHR ^ or halo; each R7is independently OR ^, N(R ^)2, NO2, CN, COOR ^, N3, NR ^NR ^, ON(R ^)2, NR ^-OR ^, SeR ^, SO3R ^, P(O)(OR ^)2, C(O)N(R ^)2, CHO, B(OR ^)2, CH3, CH2OH, or halo; each Z is independently (CH2)nO(CH2)p, (CH2)nSe(CH2)p or (CH2)q; each m is independently an integer from 1 to 5; each n is independently an integer from 0 to 4; each p is independently an integer from 0 to 4; n + p in each Z, is independently ^ 4; each q is independently an integer from 0 to 4; r is an integer from 0 to 4; and each Rʹ is independently H, C1-20alkyl, C2-20alkenyl, C2-20alkynyl, C3-20cycloalkyl, C6-30aryl, heterocycloalkyl or heteroaryl, wherein one or more available carbon atoms in the C1-20alkyl, C2-20alkenyl and C2-20alkynyl is optionally replaced by a heteroatom, and wherein the C1-20alkyl, C2-20alkenyl, C2-20alkynyl, C3- 20cycloalkyl, C6-30aryl, heterocycloalkyl and heteroaryl is optionally further substituted with one or more groups selected from ORʹʹ, halo, azide and nitrile, wherein Rʹʹ is independently H, C1-20alkyl, C2-20alkenyl, C2-20alkynyl, C3-20cycloalkyl, C6-30aryl, heterocycloalkyl or heteroaryl, or a pharmaceutically acceptable salt thereof; wherein in the compound of Formula I or the pharmaceutically acceptable salt thereof, one or more available hydrogens is / are optionally replaced with deuterium and / or one or more available hydrogens is / are optionally replaced with fluorine and / or one or more available atoms is / are replaced with its radioactive isotope.

[0083] In some embodiments, the amatoxin analog has one or more of the following: R1other than X1other than CH2; X2other than CH2; R2aother than H; and R2bother than H.

[0084] In an embodiment, X1is(CH2)m, CH3 2 3 3 2. In an embodiment,CH , CHCH CH , or C(CH )X1is (CH2)m. In an embodiment, the m of X1is 1 or 2. In an embodiment, X1is CH2.

[0085] In an embodiment, X is2 (CH2)m, CHCH3,CHCH2CH3, or C(CH3)2. In an embodiment, X2is(CH2)m. In an embodiment, the mof X2is 1 or 2. In anembodiment, X2is CH2.

[0086] In an embodiment,R is H or C2a1-10alkyl. In an embodiment, R2ais H or C1-3alkyl. In an embodiment, R2ais H.

[0087] In an embodiment, R2bis H or C1-10alkyl. In an embodiment, R2bis H or C1-3alkyl. In an embodiment, R2bis H.

[0088] In another embodiment, the amatoxin analog is a compound of Formula I(a):whereinA is S+(NH) or S(O)=N2Q is a counteranion; R1is CH(Z-CH3)2, wherein one or mor a hydrogens is / are optionally substituted with SH; or R3is C3-10cycloalkyl,wherein each Z isindependently(CH2)nO(CH2)por(CH2)q;R3is OR ^, NH(OR ^), NH-NHR ^ or N(R ^)2; R4is H or OH; R5and R6are each independently H, OR ^, NHR ^ or halo; each R7is independently OR ^, N(R ^)2, NO2, CN, COOR ^, N3, NR ^NR ^, ON(R ^)2, NR ^-OR ^, SeR ^, SO3R ^, P(O)(OR ^)2, C(O)N(R ^)2, CHO, B(OR ^)2, CH3, CH2OH, or halo; each n is independently 0, 1, or 2;each p is independently 0, 1, or 2; each q is independently 0, 1, or 2; r is an integer from 0 to 4; and each Rʹ is independently H, C1-20alkyl, C2-20alkenyl, C2-20alkynyl, C3- 20cycloalkyl, C6-30aryl, heterocycloalkyl or heteroaryl, wherein one or more available carbon atoms in the C1-20alkyl, C2-20alkenyl and C2-20alkynyl is optionally replaced by a heteroatom, and wherein the C1-20alkyl, C2-20alkenyl, C2-20alkynyl, C3- 20cycloalkyl, C6-30aryl, heterocycloalkyl and heteroaryl is optionally further substituted with one or more groups selected from ORʹʹ, halo, azide and nitrile, wherein Rʹʹ is independently H, C1-20alkyl, C2-20alkenyl, C2-20alkynyl, C3- 20cycloalkyl, C6-30aryl, heterocycloalkyl or heteroaryl, or a pharmaceutically acceptable salt thereof; wherein in the compound of Formula I(a) or the pharmaceutically acceptable salt thereof, one or more available hydrogens is / are optionally replaced with deuterium and / or one or more available hydrogens is / are optionally replaced with fluorine and / or one or more available atoms is / are optionally replaced with its radioactive isotope.

[0089] In an embodiment, the amatoxin analog of Formula I(a) has the following stereochemistry:.

[0090] In an embodiment, the amatoxin analog of Formula I(a) has the following stereochemistry:.

[0091] In an embodiment of Formula I or I(a), R1is CH(Z-CH3)2, wherein one or more available hydrogens is / are optionally substituted with SH; or R1is C3-10cycloalkyl. In an embodiment, R1is CH(Z-CH3)2. In an embodiment, each Z is independently (CH2)nO(CH2)por(CH2)q. In an embodiment, each Z is independently (CH2)q. In an embodiment, each q is independently 0, 1, or 2. In an embodiment, R1isCH(CH3)(CH2CH3). In an embodiment, R1in the stereochemistry shown for Formula I(a), has the following.

[0092] In another embodiment, the amatoxin analog is a compound of Formula I(a′):wherein A is S+(NH2)Q–, S=NH or S(O)=NH; Q is a counteranion; R3is OR ^, NH(OR ^), NH-NHR ^ or N(R ^)2; R4is H or OH; R5and R6are each independently H, OR ^, NHR ^ or halo; each R7is independently OR ^, N(R ^)2, NO2, CN, COOR ^, N3, NR ^NR ^, ON(R ^)2, NR ^-OR ^, SeR ^, SO3R ^, P(O)(OR ^)2, C N(R ^)2, CHO, B(OR ^)2, CH3, CH2OH, or halo;r is an integer from 0 to 4; and each Rʹ is independently H, C1-20alkyl, C2-20alkenyl, C2-20alkynyl, C3-20cycloalkyl, C6-30aryl, heterocycloalkyl or heteroaryl, wherein one or more available carbon atoms in the C1-20alkyl, C2-20alkenyl and C2-20alkynyl is optionally replaced by a heteroatom, and wherein the C1-20alkyl, C2-20alkenyl, C2-20alkynyl, C3-20cycloalkyl, C6-30aryl, heterocycloalkyl and heteroaryl is optionally further substituted with one or more groups selected from ORʹʹ, halo, azide and nitrile, wherein Rʹʹ is independently H, C1-20alkyl, C2-20alkenyl, C2-20alkynyl, C3- 20cycloalkyl, C6-30aryl, heterocycloalkyl or heteroaryl, or a pharmaceutically acceptable salt thereof; wherein in the compound of Formula I(a′) or the pharmaceutically acceptable salt thereof, one or more available hydrogens is / are optionally replaced with deuterium and / or one or more available hydrogens is / are optionally replaced with fluorine and / or one or more available atoms is / are optionally replaced with its radioactive isotope.

[0093] In an embodiment, the amatoxin analog of Formula I(a′) has the following stereochemistry:.

[0094] In an embodiment of Formula I, I(a), or I(a′), R3is OR ^ or N(R ^)2. In an embodiment, each Rʹ of R3is independently H or C1-3alkyl optionally substituted with one ormore halo group.In another embodiment, R3is OR ^ or N(R ^)2, wherein R ^ is H. In another embodiment, R3is OH or NH2. In a further embodiment, R3is NH2. In another embodiment, R3is -N(R ^)2, wherein one R ^ is H and the other R ^ is C1-20alkyl substituted with -N3. In a further embodiment, R3is -N(R ^)2, wherein one R ^ is H and the other R ^ is C1-6alkyl substituted with -N3. In another embodiment, R3is -N(H)CH2CH2N3.

[0095] In an embodiment of Formula I, , or I(a′), R4is H.

[0096] In an embodiment of Formula I, I(a), or I(a′), R4is OH.

[0097] In an embodiment of Formula I, I(a), or I(a′), R5and R6are each independently H or OR ^. In another embodiment, R5and R6are each independently H or OH. In an embodiment, R5is H and R6is OH. In another embodiment, R5is OH and R6is H. In an embodiment, R5and R6are each H. In another embodiment, R5and R6are each OH.

[0098] In an embodiment of Formula I, I(a), or I(a′), R5is H or ORʹ. In an embodiment, R5is H. In another embodiment of the present disclosure, R5is OR ^.In an embodiment, theRʹ of R5is H or C1-3alkyl optionally substituted with one or more halo group. In anembodiment, R5 is H or OH.In a further embodiment, R5is OH.

[0099] In an embodiment of Formula I, I(a), or I(a′), R6is Hor ORʹ.In an embodiment, R6is H. In another embodiment, R6is OR ^. In an embodiment, the Rʹ of R6is H or C1-3alkyl optionally substituted with one or more halo group. In an embodiment, R6is H or OH. In a further embodiment, R6is OH.

[0100] In an embodiment of Formula I, I(a), or I(a′), R4, R5and R6are each OH.

[0101] In an embodiment of Formula I, I(a), or I(a′), r is an integer from 0 to 3. In another embodiment, r is 0, 1 or 2. In another embodiment, r is 0 or 1. In an embodiment, r is 0. In another embodiment, r is 1.

[0102] In an embodiment of Formula I, I(a), or I(a′), each R7is independently OR ^, CN, or halo. In an embodiment, each R7is independently OR ^. In an embodiment, the Rʹ of each R7is independently H or C1-3alkyl optionally substituted with one or more halo group. Inanother embodiment, R7is OH. In a further embodiment, R7is 4-OH, 5-OH, 6-OH or 7-OH. In an embodiment, R7is 5-OH.

[0103] In an embodiment of Formula I, I(a), or I(a′), A is S+(NH2)Q–. It will be appreciated by a person skilled in the art that in embodiments wherein A is S+(NH2)Q–the corresponding sulfilimine free base may also or alternatively be present in samples comprising the amatoxin analog depending, for example, on the pKa of the particular sulfiliminium salt (which can be determined by the skilled person) and / or the pH of a solution or suspension comprising the amatoxin analog. In another embodiment, A is S=NH. It will similarly be appreciated by a person skilled in the art that in embodiments wherein A is S=NH the corresponding sulfilimine salt may also or alternatively be present in samples comprising the amatoxin analog depending,for example, on the pKa of the particular sulfiliminium salt (which can be determined by the skilled person) and / or the pH of a solution or suspension comprising the amatoxin analog.

[0104] In a further embodiment of Formula I, I(a), or I(a′), A is S(O)=NH.

[0105] In an embodiment of Formula I, I(a), or I(a′), A is (R)-A (i.e., the sulfur in A has an R configuration). In another embodiment, A is (S)-A. (i.e., the sulfur in A has an S configuration).

[0106] In an embodiment of Formula I, I(a), or I(a′), R ^ is H, C1-20alkyl, C2-20alkenyl, C2-20alkynyl, C3-20cycloalkyl, C6-30aryl, heterocycloalkyl or heteroaryl, wherein one or more available carbon atoms in the C1-20alkyl, C2-20alkenyl and C2-20alkynyl is optionally replaced by a heteroatom, and wherein the C1-20alkyl, C2-20alkenyl, C2-20alkynyl, C3-20cycloalkyl, C6-30aryl, heterocycloalkyl and heteroaryl is unsubstituted. In another embodiment, R ^ is H, C1- 20alkyl, C2-20alkenyl, C2-20alkynyl, C3-20cycloalkyl, C6-30aryl, heterocycloalkyl or heteroaryl, wherein the C1-20alkyl, C2-20alkenyl, C2-20alkynyl, C3-20cycloalkyl, C6-30aryl, heterocycloalkyl and heteroaryl is further substituted with one or more groups selected from OR ^ ^, halo, -N3 and nitrile, wherein R ^ ^ is independently H, C1-20alkyl, C2-20alkenyl, C2- 20alkynyl, C3-20cycloalkyl, C6-30aryl, heterocycloalkyl or heteroaryl. In a further embodiment, R′ is independently H or C1-20alkyl. In an embodiment, R′ is C1-6alkyl. In another embodiment, R′ is H. In a further embodiment, R″ is independently H or C1-20alkyl. In an embodiment, R″ is C1-6alkyl. In another embodiment, R″ is H.

[0107] In an embodiment, the amatoxin analog is:–; r , or a pharmaceutically acceptable salt thereof.

[0108] In an embodiment, the amatoxin analog is:

[0109] In an embodiment, the amatoxin analog is:

[0110] In an.

[0111] In an embodiment, the amatoxin analog is:.

[0112] The counteranion can be any suitable counteranion. In some embodiments, the counteranion is a pharmaceutically acceptable counteranion.

[0113] In some embodiments wherein A is S=NH or S(O)=NH, the amatoxin analog is not in the form of a salt. In alternative embodiments, the amatoxin analog is in the form of a pharmaceutically acceptable salt. It will be appreciated by a person skilled in the art that in embodiments wherein A is S+(NH2)Q–,the pharmaceutically acceptable salt thereof can include salts wherein an additional group is in the form of a pharmaceutically acceptable salt as well as pharmaceutically acceptable salts wherein Q is a pharmaceutically acceptable counteranion but no additional group(s) are in the form of a pharmaceutically acceptable salt.

[0114] The amatoxin analogs of the present disclosure such as the compounds of Formula I, I(a), I(a′), I(i) and salts thereof, as described herein may, for example, be coupled to a linker to provide an amatoxin-linker construct that may, for example, be used in the manufacture of conjugates which may, for example, be useful in the treatment of diseases such as cancer.

[0115] Accordingly, the present disclosure also includes an amatoxin-linker construct comprising an amatoxin analog as described herein (which may include pharmaceutically acceptable salts thereof) coupled to a linker, wherein the linker comprises a reactive group R8for conjugating the amatoxin-linker construct to a target-binding moiety.

[0116] The amatoxin analogs of the present disclosure are coupled to the linker in any suitable configuration, the selection of which can be made by a person skilled in the art. For example, the location of the coupling may depend, for example, on the identity of the amatoxin analog and / or the linker. In an embodiment, the linker is coupled to the amatoxin analog or the salt thereof at a site indicated by A, R3, R4, R5, R6and / or R7in an amatoxin analog as described herein. In another embodiment, the linker is coupled to the amatoxin analog or the salt thereof through a moiety obtained from the reaction of A, R3, R4, R5, R6and / or R7in an amatoxin analog as described herein with a complementary functional group on the linker.

[0117] The linker can be any suitable linker. For example, it will be appreciated by a person skilled in the art that amatoxins are relatively non-toxic when coupled to a biomolecule carrier such as a target-binding moiety, and advantageously only exert their cytotoxic activity after internalization in the target cells. Accordingly, a conjugate comprising the target-binding moiety conjugated to the compound coupled to the linker is advantageously substantially stable in the plasma after administration and a suitable linker may desirably allow, for example, for substantially releasing the compound subsequent to internalization in the target cells. Many linkers suitable for use in amatoxin-linker constructs are known in the art, for example, suitable linkers for some embodiments of the present disclosure are described in PCT Application Publication No. WO 2023 / 097407 entitled “Modified Amatoxins and Uses Thereof”.

[0118] In an embodiment, the linker is stable linker. The term “stable linker” as used herein refers to a linker that typically releases the compound after the target-binding moiety to which it is conjugated is degraded intracellularly, for example, in the lysosomes. In other words, the linker is substantially stable in an intracellular reducing environment and in the presence of enzymes such as lysosomal peptidases (e.g. Cathepsin B). In an embodiment, the stable linker is devoid of an enzyme- (e.g. a dipeptide sequence cleavableby Cathepsin B) and / or a disulfide group. In another embodiment, the stable linker comprises an –[CH2-X1-CH2]s–CH2– moiety, wherein X1is O, CH2or S, and s is an integer from 1 to 8.

[0119] In another embodiment of the present disclosure, the linker is a cleavable linker. The term “cleavable linker” as used herein refers to a linker that is cleavable by an enzyme and / or in a reducing environment. In an embodiment of the present disclosure, the cleavable linker is cleavable by an intracellular protease. In another embodiment of the present disclosure, the linker is cleavable by at least one agent selected from the group consisting of cysteine protease, metalloproteinase, serine protease, threonine protease, aspartic protease, glycosidase, phosphodiesterase, and reductase. Such linkers may, for example, comprise a peptide motif cleavable by such an enzyme. In another embodiment of the present disclosure, the linker comprises a motif selected from the group consisting of: Val-Ala, Val-Cit, Val- Lys, Val-Arg, Phe-Lys-Gly-Pro-Leu-Gly, Ala-Ala-Pro-Val, β-glucuronide and β-galactoside.

[0120] In an embodiment, the linker is a stable linker, but the linker is coupled to the amatoxin analog or the salt thereof through a moiety cleavable by an enzyme and / or in a reducing environment. In another embodiment, the linker is coupled to the amatoxin analog or the salt thereof through a moiety cleavable in a reducing environment. In another embodiment, the moiety cleavable in a reducing environment is a disulfide.

[0121] In an embodiment, the linker further comprises a self-immolating moiety. The term “self-immolating moiety” as used herein, refers to a moiety, which, after enzymatic cleavage of the linker, spontaneously cleaves from the remainder of the amatoxin-linker construct, thereby releasing the compound. In an embodiment, the self-immolating moiety is a p-aminobenzyl alcohol (PAB) moiety. In another embodiment, the PAB is conjugated to a peptide (e.g. a dipeptide) portion of the linker via the aromatic amine group of the PAB. In another embodiment, the PAB is conjugated to the amatoxin analog via a carbamate group coupled to a primary or secondary amine or in an alternative embodiment, the PAB is coupled directly to the amatoxin analogue. In another embodiment, the linker comprising the self- immolating moiety (e.g., PAB) is coupled to the amatoxin analog at a site indicated by A via an S-N-carbamoyl moiety. For example, in an embodiment, such amatoxin-linker constructs are prepared via reaction of an appropriate amatoxin analog with a suitable oxaziridine.

[0122] The reactive group R8is any reactive group suitable for conjugating the amatoxin- linker construct to a target-binding moiety and may depend, for example, on the identity of the target-binding moiety and / or a reactive group thereon.

[0123] In an embodiment of the present disclosure, R8is selected from: ; ;wherein represents the site of attachment of R8to the remainder of the linker; or R8comprises an azide, thiol, tetrazine, trans-cyclooctene or acrylamide functional group.

[0124] In an embodiment,

[0125] In an embodiment, R3comprises an N3 moiety, the complementary functional group on the linker is an alkyne, and the linker is coupled to the amatoxin analog or the salt thereof through a 1,2,3-triazole. In another embodiment, R3comprises -CH2CH2N3, the complementary functional group on the linker is an alkyne, and the linker is coupled to the amatoxin analog or the salt thereof through a 1,2,3-triazole.

[0126] In an embodiment, the linker is coupled to the amatoxin analog or the salt thereof through a moiety obtained from the reaction of A (e.g., the sulfilimine or sulfoximine of A) with a complementary functional group on the linker. In another embodiment, the moiety obtained from the reaction of A with the complementary functional group on the linker is an S-N-carbamoyl group.

[0127] The present disclosure also includes a conjugate comprising a target-binding moiety conjugated to an amatoxin analog as described herein or an amatoxin-linker construct as described herein. In an embodiment, the conjugate comprises the target-binding moietyconjugated to the amatoxin analog. In another embodiment, the conjugate comprises the target-binding moiety conjugated to the amatoxin-linker construct.

[0128] The term “target-binding moiety” as used herein refers to any suitable moiety that can specifically bind to a target molecule (e.g. protein) or epitope. In an embodiment, the target-binding moiety is a peptide, an oligonucleotide, a lipid, a lipid carrier, a nanoparticle or combinations thereof. In another embodiment, the target-binding moiety is an antibody, an antigen-binding fragment thereof, an antibody-like protein, an aptamer, a vitamin, an oligonucleotide, an affibody, a minibody, a lipid, a lipid carrier, a nanoparticle or combinations thereof. In another embodiment, the target-binding moiety is an antibody, an antigen-binding fragment thereof, an antibody-like protein, an aptamer, a vitamin, an oligonucleotide, an affibody, a minibody, a lipid, a lipid carrier or a nanoparticle. In a further embodiment, the target-binding moiety is an antibody, antigen-binding fragment thereof or an antibody-like protein. In a further embodiment, the target-binding moiety is an antibody. In an embodiment, the conjugate has a drug-to-target-binding moiety ratio e.g., a drug-to- antibody ratio (DAR) of about 0.1 to about 10, about 0.5 to about 5 or about 1 to about 3. In another embodiment, the conjugate has a drug-to-target-binding moiety ratio e.g., a drug-to- antibody ratio (DAR) of about 2. The term “antigen-binding fragment thereof” as used herein means that the fragment of the antibody comprises at least a functional antigen-binding domain. The term “antibody-like protein” as used herein refers to a protein that is not strictly an antibody but has the capability of binding to a target molecule (e.g. protein) or epitope. The “antibody-like protein” is a protein that has been engineered (e.g. by mutagenesis of Ig loops) to specifically bind to the target molecule. Typically, such an antibody-like protein comprises at least one variable peptide loop attached at both ends to a protein scaffold. This double structural constraint greatly increases the binding affinity of the antibody-like protein to levels comparable to that of an antibody. The length of the variable peptide loop typically consists of 10 to 20 amino acids. The scaffold protein may be any protein having good solubility properties. In an embodiment, the scaffold protein is a small globular protein. The scaffold of antibody-like proteins can be based on, for example, without limitation, affilin proteins, affibodies, anti-calins, lipocalins, ubiquitin, leucine-rich repeat proteins, and designed ankyrin repeat proteins (see, for example: Binz et al., “Engineering novel binding proteins from nonimmunoglobulin domains” Nat Biotechnol. 2005, 23:10, 1257-68). The antibody or antigen-binding fragment thereof can be from any suitable immunoglobulin type (e.g. IgG, IgE, IgM, IgD, IgA and / or IgY), (e.g., IgG1, IgG2, IgG3, IgG4, IgA1 and / orIgA2) or subclass. Suitable antibodies and / or antigen-binding fragments thereof may include but are not limited to polyclonal, monoclonal, monovalent, bispecific, heteroconjugate, multispecific, human, humanized (e.g. CDR-grafted), deimmunized, and / or chimeric antibodies, single chain antibodies (e.g. scFv), Fab fragments, F(ab')2 fragments, fragments produced by a Fab expression library, diabodies or tetrabodies, nanobodies, anti-idiotypic (anti-Id) antibodies (including, but not limited to anti-Id antibodies to antibodies of the present disclosure), and epitope-binding fragments of any of the above.

[0129] In an embodiment, the antigen-binding fragments are human antigen-binding antibody fragments and include, but are not limited to, Fab, Fab' and F(ab')2, Fd, single- chain Fvs (scFv), single-chain antibodies, disulfide-linked Fvs (dsFv) and fragments comprising either a VL or VH domain. Antigen-binding antibody fragments, including single-chain antibodies, may comprise the variable domain(s) alone or in combination with the entirety or a portion of the following: hinge region, CL, CH1, CH2, and CH3 domains. Also included are antigen-binding fragments also comprising any combination of variable domain(s) with a hinge region, CL, CH1, CH2, and CH3 domains. The antibody, antigen- binding fragment thereof or antibody-like protein may be from any animal origin including birds and mammals. For example, in an embodiment, the antibody, antigen-binding fragment thereof or antibody-like protein is from human, rodent (e.g. mouse, rat, guinea pig, or rabbit), chicken, pig, sheep, goat, camel, cow, horse, donkey, cat, or dog origin. In another embodiment, the antibody, antigen-binding fragment thereof or antibody-like protein is of human or murine origin. The term “human” as used herein in reference to antibodies includes antibodies having the amino acid sequence of a human immunoglobulin and also includes antibodies isolated from human immunoglobulin libraries or from animals transgenic for one or more human immunoglobulin and that do not express endogenous immunoglobulins, as described for example in U.S. Patent No.5,939,598.

[0130] The term “specifically bind” as used herein in reference to a target-binding moiety specifically binding to a target molecule or epitope means, for example, that it has a dissociation constant KDto the target molecule or epitope of at most about 100 ^M. In an embodiment, KD is about 100 ^M or lower, about 50 ^M or lower, about 30 ^M or lower, about 20 ^M or lower, about 10 ^M or lower, about 5 ^M or lower, about 1 ^M or lower, about 900 nM or lower, about 800 nM or lower, about 700 nM or lower, about 600 nM or lower, about 500 nM or lower, about 400 nM or lower, about 300 nM or lower, about 200nM or lower, about 100 nM or lower, about 90 nM or lower, about 80 nM or lower, about 70 nM or lower, about 60 nM or lower, about 50 nM or lower, about 40 nM or lower, about 30 nM or lower, about 20 nM or lower or about 10 nM or lower, about 1 nM or lower, about 900 pM or lower, about 800 pM or lower, about 700 pM or lower, about 600 pM or lower, about 500 pM or lower, about 400 pM or lower, about 300 pM or lower, about 200 pM or lower, about 100 pM or lower, about 90 pM or lower, about 80 pM or lower, about 70 pM or lower, about 60 pM or lower, about 50 pM or lower, about 40 pM or lower, about 30 pM or lower, about 20 pM or lower or about 10 pM or lower.

[0131] The terms “target molecule” and “target epitope” as used herein may refer to an antigen and an epitope of an antigen, respectively, that is specifically bound by a target- binding moiety such as an antibody, antigen-binding fragment thereof or antibody-like protein. The term “epitope” as used herein, also sometimes referred to in the art as an “antigenic determinant”, refers to a molecular structure to which, in the context of an adaptive immune response, antibodies or T cell receptors are directed and / or generated, and / or which can elicit a specific immune response. In the context of antibodies or antigen-binding fragments thereof, the term “epitope” as used herein relates to the specific molecular structure on the antigen to which the antigen-recognition site or paratop of the antibody or antigen- binding fragment thereof, binds. In an embodiment, the target molecule or target epitope is associated with cancer, non-cancerous neoplasms, an autoimmune disease, an inflammatory disease or a viral infection. In an embodiment, the target molecule or target epitope is associated with cancer, an autoimmune disease, or a viral infection. In an embodiment, the target molecule or epitope is associated with cancer. In another embodiment, the target molecule or epitope associated with cancer or non-cancerous neoplasms is present on the surface of one or more tumor cell types or tumor-associated cells in an increased concentration and / or in a different steric configuration as compared to the surface of non- tumor cells. In an embodiment, the target molecule or epitope associated with cancer is an epitope of human epidermal growth receptor 2 (HER2), prostate-specific membrane antigen (PSMA), CD20, CD269, sialyl LewisX, HER-2 / neu or epithelial cell adhesion molecule (EpCAM). In a further embodiment, the target molecule or epitope associated with cancer is an epitope of human epidermal growth receptor 2 (HER2). In another embodiment, the target- binding moiety is an anti-HER2 antibody. In another embodiment, the anti-HER2 antibody is trastuzumab. In an embodiment, the target molecule or target epitope is associated with autoimmune disease. In another target molecule or epitope associated withautoimmune disease is preferentially expressed on cells involved in an autoimmune disease. In an embodiment, the target molecule or target epitope is associated with a viral infection. In another embodiment, the target molecule or epitope associated with a viral infection is preferentially expressed on cells involved in a viral infection.

[0132] In an embodiment, the conjugate comprises the amatoxin-linker construct, the target-binding moiety comprises an engineered acceptor residue, R8is a reactive group to a moiety comprised in the engineered acceptor residue, and the amatoxin-linker construct is conjugated to the target-binding moiety via a moiety resulting from the reaction of the moiety comprised in the engineered acceptor residue with R8. The term “engineered acceptor residue” as used herein refers to a residue that is introduced into a peptide sequence of a suitable target-binding moiety that is generally not present in the native peptide sequence of the target-binding moiety. Such residues are available for reaction with R8but desirably do not substantially affect, for example, immunoglobulin folding, antibody assembly, antigen binding and / or Fc domain effector functions. In an embodiment, the engineered acceptor residue is an engineered cystine residue and R8is a thiol-reactive group. The term “engineered cysteine residue” as used herein refers to a cysteine residue that is introduced into the peptide sequence of a suitable target-binding moiety that is generally not present in the native peptide sequence of the target-binding moiety. Such cysteine residues are available for conjugation but desirably do not substantially affect, for example, immunoglobulin folding, antibody assembly, antigen binding and / or Fc domain effector functions. For example, the engineered cysteine residue can take the place of the amino acid that naturally occurs at a given position in the peptide sequence; i.e. in an embodiment of the present disclosure, the engineered cysteine residue is a cysteine substitution. Engineered cysteine residues can be introduced into the peptide sequence of the target-binding moiety through suitable techniques such as site-directed mutagenesis, the selection of which can be made by a person skilled in the art. In an embodiment, the target-binding moiety comprises one engineered cysteine residue. In another embodiment, the target-binding moiety comprises greater than one engineered cysteine residue, for example, two engineered cysteine residues. For example, antibodies wherein the amino acid aspartic acid at position 265 has been exchanged to cysteine (D265) contain two introduced cysteines at each chain of the Fc region, which can serve as conjugation sites for the amatoxin-linker construct to produce a conjugate with DAR=2.

[0133] In an embodiment, the engineered cysteine residue is selected from the group consisting of heavy chain 118Cys, heavy chain 239Cys, and heavy chain 265Cys. In another embodiment, the engineered cysteine residue is heavy chain 265Cys.

[0134] In an embodiment, the target-binding moiety comprises a biorthogonal functional group, R8is a complementary biorthogonal functional group, and the amatoxin-linker construct is conjugated to the target-binding moiety via a moiety resulting from the reaction of the biorthogonal functional group on the target-binding moiety with R8. The term “biorthogonal” as used herein refers to a chemical reaction capable of occurring inside of a living system without interfering with native biochemical processes. Biorthogonal reactions are well known in the art and include but are not limited to reaction between an azide and a soft nucleophile such as a phosphine; reaction between an azide and a suitable acetylene, and 1,3-dipolar cycloaddition between an azide and a suitable cyclooctyne or azacyclooctyne (copper-free click chemistry).

[0135] In an embodiment, the target-binding moiety comprises a primary amino group, R8is a reactive group to the primary amino group, and the amatoxin-linker construct is conjugated to the target-binding moiety via a moiety resulting from the reaction of the primary amino group with R8. In another embodiment, the primary amino group is a lysine side chain. III. Uses

[0136] The present disclosure also includes a composition comprising an amatoxin analog or conjugate of the present disclosure and a carrier. In an embodiment, the composition comprises the amatoxin analog of the present disclosure and the carrier. In another embodiment, the composition comprises the conjugate of the present disclosure and the carrier. The amatoxin analogs and / or conjugates of the present disclosure are optionally formulated into pharmaceutical compositions for administration or use in a biologically compatible form, for example, a form suitable for administration to or for use in subjects in vivo. Accordingly, the present disclosure also includes a pharmaceutical composition comprising an amatoxin analog or conjugate of the present disclosure and a pharmaceutically acceptable carrier. In an embodiment, the pharmaceutical composition comprises the amatoxin analog of the present disclosure and the pharmaceutically acceptable carrier. In another embodiment, the pharmaceutical composition comprises the conjugate of the present disclosure and the pharmaceutically acceptable carrier.

[0137] The amatoxin analog or conjugate of the present disclosure can be administered to a subject or used in a variety of forms depending on the selected route of administration or use, as will be understood by a person skilled in the art. For example, the amatoxin analog or conjugate of the present disclosure is suitably administered to the subject or for use parenterally; i.e. taken into the body or administered or used in a manner other than through the gastrointestinal tract. In an embodiment, the amatoxin analog or conjugate of the present disclosure is administered or for use as an injectable or infusion. Injectables can be formulated in the form of ampules and / or as a ready-for-use injectable such as a ready-to-use syringe, a single-use syringe and / or in a puncturable flask for multiple withdrawal. In another embodiment, the injectable is administered or for use in the form of a subcutaneous (s.c.), intramuscular (i.m.), intravenous (i.v.) or intracutaneous (i.c.) injection. In an embodiment, the infusion is in the form of an isotonic solution, fatty emulsion, liposomal formulation or micro-emulsion. A person skilled in the art would know how to prepare suitable formulations. In some embodiments, the injectable or infusion formulation is in the form of a concentrate which can be dissolved or dispersed with aqueous isotonic diluents. Injectable formulations can also be administered or for use in the form of a permanent infusion e.g. via a mini-pump.

[0138] In some embodiments, the parenteral formulation further comprises albumin, plasma, expander, surface-active substances, organic diluents, pH-influencing substances, complexing substances, polymeric substances or combinations thereof, for example to influence the adsorption of the amatoxin analog or conjugate of the present disclosure to proteins or polymers and / or to reduce the adsorption of the amatoxin analog or conjugate of the present disclosure to materials like injection instruments or packaging-materials, for example, plastic or glass.

[0139] In some embodiments, adjuvants and carriers in the pharmaceutical compositions formulated as parenterals are one or more of aqua sterilisata (sterilized water), pH value influencing substances (for example, suitable organic or inorganic acids or bases and salts thereof or suitable combinations thereof), buffering substances for adjusting pH values, substances for isotonization (for example, sodium chloride, sodium hydrogen carbonate, glucose, fructose or combinations thereof), surfactants (for example, partial esters of fatty acids of polyoxyethylene sorbitans such as a TweenTMsurfactant or fatty acid esters of polyoxyethylenes such as a CremophorTMsurfactant or combinations thereof), fatty oils (for example, soybean oil, castor oil or combinations thereof), synthetic esters of fatty acids (for example, ethyl oleate, isopropyl myristate or combinations thereof), polymeric adjuvants (forexample, gelatine, dextran, polyvinylpyrrolidone or combinations thereof), additives which increase the solubility of organic solvents (for example, propylene glycol, ethanol, N,N- dimethylacetamide or combinations thereof), complex forming substances (for example, citrate, urea or combinations thereof), preservatives (for example, benzoic acid hydroxypropyl ester, benzoic acid methyl ester, benzyl alcohol or combinations thereof), antioxidants (for example, sodium sulfite) and stabilizers (for example, ethylenediaminetetraacetic acid, EDTA).

[0140] In another embodiment, the amatoxin analog or conjugate is orally administered or used, for example, with an inert diluent or with an assimilable edible carrier, or enclosed in hard- or soft-shell gelatin capsules, or compressed into tablets, or incorporated directly with the food of the diet. In an embodiment, for oral therapeutic administration or use, the amatoxin analog or conjugate is incorporated with excipient and administered or used in the form of ingestible tablets, buccal tablets, troches, capsules, elixirs, suspensions, syrups, wafers, and the like. Oral dosage forms also include modified release, for example immediate release and timed-release, formulations. Examples of modified-release formulations include, for example, sustained-release (SR), extended-release (ER, XR, or XL), time-release or timed-release, controlled-release (CR), or continuous-release (CR or Contin), employed, for example, in the form of a coated tablet, an osmotic delivery device, a coated capsule, a microencapsulated microsphere, an agglomerated particle, e.g., as molecular sieving type particles, or, a fine hollow permeable fiber bundle, or chopped hollow permeable fibers, agglomerated or held in a fibrous packet. Timed-release compositions can be formulated, e.g. liposomes or those wherein the amatoxin analog or conjugate is protected with differentially degradable coatings, such as by microencapsulation, multiple coatings, etc.

[0141] The present disclosure also includes all uses for the amatoxin analogs, amatoxin- linker constructs and conjugates of the present disclosure, including, for example, use in therapeutic methods, diagnostic assays and as research tools whether alone or in combination with another active pharmaceutical ingredient.

[0142] The synthesis and biochemical evaluation of new amatoxin analogs comprising modifications of the sulfur atom of the tryptathionine bridge are disclosed herein. Such amatoxin analogs and conjugates of the present disclosure may be useful as medicaments. Accordingly, the present disclosure also includes an amatoxin analog or conjugate of the present disclosure for use as a medicament. In an embodiment, the amatoxin analog of thepresent disclosure is for use as a medicament. In another embodiment, the conjugate of the present disclosure is for use as a medicament.

[0143] The present disclosure also includes a method of treating a disease associated with cells presenting a target in a subject in need thereof, the method comprising administering an effective amount of an amatoxin analog or a conjugate of the present disclosure to the subject, wherein the target-binding moiety is specific for the target. The present disclosure also includes a method of treating a disease associated with cells presenting a target in a subject in need thereof, the method comprising administering an effective amount of an amatoxin analog of the present disclosure to the subject. The present disclosure also includes a method of treating a disease associated with cells presenting a target in a subject in need thereof, the method comprising administering an effective amount of a conjugate of the present disclosure to the subject, wherein the target-binding moiety is specific for the target.

[0144] The present disclosure also includes a use of an amatoxin analog or a conjugate of the present disclosure for treatment of a disease associated with cells presenting a target in a subject in need thereof, wherein the target-binding moiety is specific for the target. The present disclosure also includes a use of an amatoxin analog of the present disclosure for treatment of a disease associated with cells presenting a target in a subject in need thereof. The present disclosure also includes a use of a conjugate of the present disclosure for treatment of a disease associated with cells presenting a target in a subject in need thereof, wherein the target-binding moiety is specific for the target.

[0145] The present disclosure also includes a use of an amatoxin analog or a conjugate of the present disclosure for preparation of a medicament for treatment of a disease associated with cells presenting a target in a subject in need thereof, wherein the target- binding moiety is specific for the target. The present disclosure also includes a use of an amatoxin analog of the present disclosure for preparation of a medicament for treatment of a disease associated with cells presenting a target in a subject in need thereof. The present disclosure also includes a use of a conjugate of the present disclosure for preparation of a medicament for treatment of a disease associated with cells presenting a target in a subject in need thereof, wherein the target-binding moiety is specific for the target.

[0146] The present disclosure also includes an amatoxin analog or a conjugate of the present disclosure for use to treat a disease associated with cells presenting a target in a subject, wherein the target-binding moiety for the target. The present disclosurealso includes an amatoxin analog of the present disclosure for use to treat a disease associated with cells presenting a target in a subject. The present disclosure also includes a conjugate of the present disclosure for use to treat a disease associated with cells presenting a target in a subject, wherein the target-binding moiety is specific for the target.

[0147] The term “disease associated with cells presenting a target” as used herein refers, for example, to a pathological state characterized by a cellular marker such as but not limited to a receptor and / or enzyme which can be used in a targeted fashion. In an embodiment, the disease associated with cells presenting a target is cancer, a disease associated with non- cancerous neoplasms, an autoimmune disease, an inflammatory disease or a viral infection. In another embodiment, the disease associated with cells presenting a target is cancer, an autoimmune disease or a viral infection. The term “cancer” as used herein refers to diseases caused by uncontrolled cell division and / or the ability of cells to metastasize, or to establish new growth in additional sites. In an embodiment, the cancer is a skin cancer (e.g., melanoma), a connective tissue cancer (e.g., sarcomas), an adipose cancer, a breast cancer, a head and neck cancer, a lung cancer (e.g., mesothelioma), a stomach cancer, a pancreatic cancer, an ovarian cancer, a cervical cancer, a uterine cancer, an anogenital cancer (e.g., testicular cancer), a kidney cancer, a bladder cancer, a colon cancer, a prostate cancer, a central nervous system (CNS) cancer, retinal cancer, a blood cancer, a neuroblastoma, multiple myeloma, or a lymphoid cancer (e.g., Hodgkin’s and non-Hodgkin’s lymphomas). In an embodiment, the cancer is breast cancer. In a further embodiment, the cancer is HER2- positive breast cancer. The term “autoimmune disease” can be used interchangeably with the term “autoimmune disorder” and refers to a condition in a subject characterized by cellular, tissue and / or organ injury caused by an immunologic reaction of the subject to its own cells, tissues and / or organs. The term “inflammatory disease” can be used interchangeably with the term “inflammatory disorder” and refers to a condition in a subject characterized by inflammation, such as chronic inflammation. Autoimmune disorders may or may not be associated with inflammation. Moreover, inflammation may or may not be caused by an autoimmune disorder. Thus, the skilled person would appreciate that certain disorders may e.g. be characterized as both autoimmune and inflammatory disorders. In an embodiment, the inflammatory disease is systemic Lupus Erythematosus (SLE), Rheumatoid Arthritis (RA), Autoimmune Hemolytic Anaemia (AIHA), or Sjögren’s syndrome. In an embodiment wherein the disease associated with cells presenting a target is a viral infection, the cellspresenting a target are virally infected cells. In another embodiment, the viral infection is human immunodeficiency virus (HIV).

[0148] The present disclosure also includes a method of treating cancer in a subject in need thereof, the method comprising administering an effective amount of an amatoxin analog or a conjugate of the present disclosure to the subject. The present disclosure also includes a method of treating cancer in a subject in need thereof, the method comprising administering an effective amount of an amatoxin analog of the present disclosure to the subject. The present disclosure also includes a method of treating cancer in a subject in need thereof, the method comprising administering an effective amount of a conjugate of the present disclosure to the subject.

[0149] The present disclosure also includes a use of an amatoxin analog or a conjugate of the present disclosure for treatment of cancer in a subject in need thereof. The present disclosure also includes a use of an amatoxin analog of the present disclosure for treatment of cancer in a subject in need thereof. The present disclosure also includes a use of a conjugate of the present disclosure for treatment of cancer in a subject in need thereof. The present disclosure also includes a use of an amatoxin analog or a conjugate of the present disclosure for preparation of a medicament for treatment of cancer in a subject in need thereof. The present disclosure also includes a use of an amatoxin analog of the present disclosure for preparation of a medicament for treatment of cancer in a subject in need thereof. The present disclosure also includes a use of a conjugate of the present disclosure for preparation of a medicament for treatment of cancer in a subject in need thereof. The present disclosure also includes an amatoxin analog or a conjugate of the present disclosure for use to treat cancer in a subject. The present disclosure also includes an amatoxin analog of the present disclosure for use to treat cancer in a subject. The present disclosure also includes a conjugate of the present disclosure for use to treat cancer in a subject.

[0150] Treatment methods or uses comprise administering to a subject or use of an effective amount of an amatoxin analog or conjugate of the present disclosure, optionally consisting of a single administration or use, or alternatively comprising a series of administrations or uses. For example, the amatoxin analogs or conjugates of the present disclosure are administered or used at least once a week. However, in another embodiment, the amatoxin analog or conjugate is administered to the subject or for use from one time per three weeks, or one time per week to once daily for a given treatment or use. The length of the treatment period or use depends on a variety of factors, such as the severity of the the age of the subject, the activity of theamatoxin analog or conjugate of the present disclosure and / or a combination thereof. It will also be appreciated by the person skilled in the art that the effective amount of an amatoxin analog or conjugate used for the treatment or use may increase or decrease over the course of a particular treatment regime or use. Changes in dosage may result and become apparent by standard diagnostic assays known in the art. In some instances, chronic administration or use is required. For example, the amatoxin analog or conjugate of the present disclosure is administered or for use in an amount and for a duration suitable to treat the subject.

[0151] The amatoxin analog or conjugate of the present disclosure may be administered or used alone or in combination with other therapeutic agents useful for treating a disease (e.g. cancer). When administered or for use in combination with other known therapeutic agents, it is an embodiment that the amatoxin analog or conjugate of the present disclosure is administered or for use contemporaneously with those therapeutic agents. As used herein, the term “contemporaneous” in reference to administration of two substances to a subject or use means providing each of the two substances so that they are both biologically active in the individual at the same time. The exact details of the administration or use will depend on the pharmacokinetics of the two substances in the presence of each other, and can include administration or use of the two substances within a few hours of each other, or even administration or use of one substance within 24 hours of administration or use of the other, if the pharmacokinetics are suitable. Design of suitable dosing regimens is routine for a person skilled in the art. In some embodiments of the present disclosure, two substances will be administered or for use substantially simultaneously, i.e. within minutes of each other, or in a single composition that includes both substances. It is a further embodiment of the present disclosure that a combination of the two substances is administered to a subject or for use in a non-contemporaneous fashion.

[0152] The dosage of the amatoxin analog or conjugate of the disclosure can vary depending on many factors such as the pharmacodynamic properties of the amatoxin analog or conjugate, the age, health and / or weight of the subject, the nature and / or extent of the symptoms of the disease, the frequency of the treatment or use and the type of concurrent treatment or use, if any, and the clearance rate of the amatoxin analog or conjugate in the subject. A person skilled in the art can determine the appropriate dosage based on the above factors. In an embodiment, the amatoxin analog or conjugate of thepresent disclosure is administered or for use initially in a suitable dosage that is optionally adjusted as required, depending on the clinical response.

[0153] The present disclosure also includes a kit comprising an amatoxin analog as described herein, a linker as described herein and optionally instructions for preparing a amatoxin-linker construct as described herein from the amatoxin analog and the linker. The present disclosure also includes a kit comprising an amatoxin analog as described herein, a linker as described herein, a target-binding moiety as described herein and optionally instructions for preparing a conjugate as described herein from the amatoxin analog, the linker and the target-binding moiety. The present disclosure also includes a kit comprising an amatoxin-linker construct as described herein, a target-binding moiety and optionally instructions for preparing a conjugate as described herein from the amatoxin-linker construct and the target-binding moiety. IV. Methods for Preparation

[0154] Herein is reported a safe, metal-free, efficient, and high-yielding sulfide imination using O-(diphenylphosphinyl)hydroxyl amine (DPPH) as a versatile electrophilic NH- transfer reagent accommodating sulfilimine salts on a myriad of substrates including peptides of biological importance and a notorious amatoxin substrate. Using DPPH, a metal-free sulfoximination strategy was developed employing an imination-oxidation route with appreciable yields for a broad substrate scope along with a Rh catalyzed sulfoxide imination strategy to also access free-NH sulfoximines with high yields.

[0155] Accordingly, the present disclosure also includes a method for preparing a sulfiliminium salt of Formula II, the method comprising S-imination of a thioether of Formula III in the presence of O-(diphenylphosphinyl)hydroxyl amine (DPPH):, wherein R9aand R9bare independently selected from C1-20alkyl, C2-20alkenyl, C2-20alkynyl, C3-20cycloalkyl, C6-30aryl, heterocycloalkyl, heteroaryl and a bioactive moiety, wherein the C1-20alkyl, C2-20alkenyl, C2-20alkynyl, C3-20cycloalkyl, C6-30aryl, heterocycloalkyl andheteroaryl is optionally substituted with one or more groups selected from C1-6alkyl, C1-6alkoxy, aryl, NH2, halo, NO2, cyano, -C(O)C1-6alkyl, OH, =O and a bioactive moiety; or wherein R9aand R9b, together with the S to which they are attached, form heterocycloalkyl or a bioactive moiety, wherein the heterocycloalkyl is optionally substituted with one or more groups selected from C1-6alkyl, C1-6alkoxy, aryl, NH2, halo, NO2, cyano, acyl, OH, =O and a bioactive moiety; and wherein one or more available hydrogens is / are optionally replaced with deuterium; and / or one or more available hydrogens is / are optionally replaced with fluorine.

[0156] The bioactive moiety can be any suitable bioactive moiety. In an embodiment, the bioactive moiety comprises a natural or unnatural amino acid, peptide or protein. In an embodiment, R9aand R9bare as defined for any of compounds 2a-2z. In another embodiment, the compound of Formula II is a sulfiliminium salt analog of a drug. In another embodiment, the compound of Formula II is a sulfiliminium salt analog of an agrochemical.

[0157] In an embodiment, R9aand R9btogether form an amatoxin analog. For example, in an embodiment, R1, R2a, R2b, R3, R4, R5, R6, R7, R′, R″, X1, X2, Z, m, n, p and / or r can be varied as described herein for the amatoxin analogs of Formula I, I(i), I(a) and / or I(a′).

[0158] The conditions for S-imination of the thioether of Formula III in the presence of the O-(diphenylphosphinyl)hydroxyl amine (DPPH) can be any suitable conditions. In an embodiment, the conditions comprise reacting the thioether of Formula III with the DPPH in a suitable solvent or mixture thereof for example, a solution or suspension comprising a suitable alcohol (such as methanol), dichloromethane, tetrahydrofuran, dimethyl formamide, acetonitrile, water or mixtures thereof, at a suitable temperature, for example, ambient temperature (e.g., a temperature of from about 4 ^C to about 40 ^C or about 25 ^C).

[0159] The present disclosure also includes method for preparing a sulfoximine of Formula IV, the method comprising oxidizing a sulfiliminium salt of Formula II prepared by a method for a sulfiliminium salt of Formula II of the disclosure:, whereinR9aand R9bare independently selected from C1-20alkyl, C2-20alkenyl, C2-20alkynyl, C3-20cycloalkyl, C6-30aryl, heterocycloalkyl, heteroaryl and a bioactive moiety, wherein the C1-20alkyl, C2-20alkenyl, C2-20alkynyl, C3-20cycloalkyl, C6-30aryl, heterocycloalkyl and heteroaryl is optionally substituted with one or more groups selected from C1-6alkyl, C1-6alkoxy, aryl, NH2, halo, NO2, cyano, -C(O)C1-6alkyl, OH, =O and a bioactive moiety; or wherein R9aand R9b, together with the S to which they are attached, form heterocycloalkyl or a bioactive moiety, wherein the heterocycloalkyl is optionally substituted with one or more groups selected from C1-6alkyl, C1-6alkoxy, aryl, NH2, halo, NO2, cyano, acyl, OH, =O and a bioactive moiety; and wherein one or more available hydrogens is / are optionally replaced with deuterium; and / or one or more available hydrogens is / are optionally replaced with fluorine.

[0160] The conditions for oxidizing the sulfiliminium salt of Formula II to prepare the sulfoximine of Formula IV can be any suitable conditions. In an embodiment, the conditions comprise reacting the sulfiliminium salt of Formula II in the presence of a suitable base (e.g., Na2CO3, NH4OH, MgO, NH3, DBU, NaHCO3, K2CO3or NaOMe) and a suitable oxidant (e.g., a suitable peroxycarboxylic acid such as meta-chloroperoxybenzoic acid) in a suitable solvent or mixture thereof, for example, a suitable alcohol (such as methanol, ethanol, isopropanol, tert-butanol 2,2,2-trifluoroethanol or mixtures thereof), at a suitable temperature, for example, a temperature of from about 0 ^C to about 10 ^C or about 4 ^C.

[0161] In an embodiment, the method is a one-pot reaction.

[0162] The bioactive moiety can be any suitable bioactive moiety. In an embodiment, the bioactive moiety comprises a natural or unnatural amino acid, peptide or protein. In an embodiment, R9aand R9bare as defined for any of compounds 3a-3z. In another embodiment, the compound of Formula IV is a sulfoximine analog of a drug. In another embodiment, the compound of Formula IV is a sulfoximine analog of an agrochemical.

[0163] In an embodiment, R9aand R9btogether form an amatoxin analog. For example, in an embodiment, R1, R2a, R2b, R3, R4, R5, R6, R7, R′, R″, X1, X2, Z, m, n, p and / or r can be varied as described herein for the amatoxin analogs of Formula I, I(i), I(a) and / or I(a′).

[0164] The present disclosure also includes a method for preparing a sulfoximine of Formula IV, the method comprising S-imination of a thioether of Formula V in the presence of O-(diphenylphosphinyl)hydroxyl amine (DPPH):, wherein R9aand R9bare independently selected from C1-20alkyl, C2-20alkenyl, C2-20alkynyl, C3-20cycloalkyl, C6-30aryl, heterocycloalkyl, heteroaryl and a bioactive moiety, wherein the C1-20alkyl, C2-20alkenyl, C2-20alkynyl, C3-20cycloalkyl, C6-30aryl, heterocycloalkyl and heteroaryl is optionally substituted with one or more groups selected from C1-6alkyl, C1-6alkoxy, aryl, NH2, halo, NO2, cyano, -C(O)C1-6alkyl, OH, =O and a bioactive moiety; or wherein R9aand R9b, together with the S to which they are attached, form heterocycloalkyl or a bioactive moiety, wherein the heterocycloalkyl is optionally substituted with one or more groups selected from C1-6alkyl, C1-6alkoxy, aryl, NH2, halo, NO2, cyano, acyl, OH, =O and a bioactive moiety; and wherein one or more available hydrogens is / are optionally replaced with deuterium; and / or one or more available hydrogens is / are optionally replaced with fluorine.

[0165] The conditions for S-imination of the thioether of Formula V in the presence of O-(diphenylphosphinyl)hydroxyl amine (DPPH) can be any suitable conditions. In an embodiment, the conditions comprise reacting the thioether of Formula V with the DPPH and optionally a metal catalyst in a suitable solvent or mixture thereof at a suitable temperature. A person skilled in the art having regard to the present disclosure, for example, Table 4 and its discussion would readily be able to select suitable conditions. In an embodiment, the conditions comprise reaction in the presence of the metal catalyst. The metal catalyst can be any suitable metal catalyst, the selection of which can be made by the skilled person. In an embodiment, the metal catalyst is a rhodium catalyst. In another embodiment, the rhodium catalyst comprises Rh2(esp)2. In another embodiment, the metal catalyst is not present.

[0166] The bioactive moiety can be any suitable bioactive moiety. In an embodiment, the bioactive moiety comprises a natural or unnatural amino acid, peptide or protein. In an embodiment, R9aand R9bare as defined for any of compounds 3a-3v[ii]. In another embodiment, the compound of Formula IV is a sulfoximine analog of a drug. In another embodiment, the compound of Formula IV is a sulfoximine analog of an agrochemical.

[0167] The following non-limiting examples are illustrative of the present disclosure: EXAMPLES Example 1: Diphenylphoshinylhydroxylamine (DPPH) Affords Late-Stage S-imination to access free-NH Sulfilimines and Sulfoximines

[0168] Sulfilimines, as potential aza-isosteres of sulfoxides, are valued as building blocks, auxiliaries, ligands, bioconjugation handles, and as precursors to versatile S(VI) scaffolds including sulfoximines and sulfondiimines. Here, is reported a new thioether imination methodology that exploits O-(diphenylphosphinyl)hydroxyl amine (DPPH). Under mild, metal-free, and biomolecule-compatible conditions, DPPH enables late-stage S- imination on peptides and natural products and shows excellent chemoselectivity and broad functional group tolerance. This methodological study is extended to a one-pot reaction for accessing free-NH sulfoximines with diverse substrates including ones of clinical importance. In the presence of a rhodium catalyst, sulfoxides undergo DPPH-mediated S-imination yielding free-NH sulfoximines. Most importantly, DPPH enables late-stage S-imination, that is validated on the complex peptide substrate of an amatoxin to give sulfilimine and sulfoximine congeners. Notably, these new sulfilimine-amatoxins show cytotoxicity, thereby supporting the notion that a S=NH is a competent isostere for a S=O. I. General Experimental Procedures (a) General Information

[0169] Reactions requiring the exclusion of air and / or moisture were conducted in flame- dried glassware under an argon atmosphere. Reagent or high-performance liquid chromatography (HPLC) grade solvents were used without any further purification or drying. When in need of dry solvents, HPLC grade solvents dried over flame dried 3 Å or 4 Å sieves, stored under argon or freshly distilled solvents were used. Reagents and solvents were purchased from Sigma-Aldrich, AmBeed, Alfa Aesar, Acros Organics, AK Scientific Inc., Oakwood Chemical, TCI America, and Enamine and used without further purification unless noted otherwise. Reactions requiring a set temperature were performed using a mineral oil bath and a temperature controlled hot plate (IKA Ceramig Midi equipped with an IKA ETS-D4 fuzzy thermometer). Reactions conducted below room temperature were performed in an ice / water bath (0 °C) or in a cold room (4 °C). Reaction progress was monitored by analytical thin layer chromatography (TLC) performed using pre-coated Merck aluminum backed silica gel plates (Silica gel 60 F254). Visualization was achieved using ultraviolet light (254 nm) andchemical staining with silica gel impregnated with iodine, potassium permanganate, bromocresol green, and ninhydrin as appropriate. Reaction progress was monitored by analytical reverse phase (RP)-HPLC using an AgilentTM1100 HPLC (HPLC 1) or an Agilent 1260 Infinity II (HPLC 2), equipped with a photodiode array detector, using an Agilent Eclipse reverse phase XDB-C18250 ^ 9.4 mm (Column 1) or an Agilent 5 Prep C1850 ^ 21.2 mm (Column 2) columns. Flash column chromatography purification was performed using silica gel 60 (230-400 mesh, SilicycleTM, Quebec, Canada and 230-400 mesh, high purity 9385, Sigma Aldrich, Germany) as the stationary phase and eluent mixtures (hexane / EtOAc or methylene chloride / MeOH) as mobile phase. Sep-PakTMC18 cartridges were purchased from Waters (Sep-Pak C1835 cc Vac Cartridge, 10 g, 55-105 μm) and used for RP-purification using an eluent mixture of H2O (MilliporeTMfiltered) / acetonitrile (MeCN; HPLC grade) with 0.1% formic acid (FA) or 0.1% trifluoroacetic acid (TFA) as the mobile phase. All HPLC purifications were performed using HPLC 1 and HPLC 2 with Column 1 and Column 2 respectively. A linear gradient was achieved by combining eluent A and B as the mobile phase (solvent A: 0.1% FA H2O or 0.1% TFA H2O. Solvent B: 0.1% FA MeCN or 0.1% TFA MeCN). Absorbance was monitored simultaneously at 230 nm, 260 nm, 280 nm, and 290 nm. For reinjections, all analytical HPLC chromatograms were acquired on HPLC 1 using Column 1 applying a linear solvent gradient by combining eluent A and B as the mobile phase (solvent A: 0.1% FA H2O or 0.1% TFA H2O, solvent B: 0.1% FA MeCN or 0.1% TFA MeCN). Absorbance was monitored simultaneously at 230 nm, 260 nm, 280 nm, and 290 nm. Solvents were evaporated under reduced pressure using a BüchiTMrotary evaporator. Lyophilization of water or water / MeCN mixtures, with or without FA or TFA, proceeded by sublimation below 200 mTorr after freezing the solution in a dry ice / acetone bath. All peptides were quantified by UV spectrophotometry on a CaryTM5000 UV-Vis-NIR Spectrophotometer. Tryptathionine containing peptides were quantified using tryptathionine as a chromophore with extinction coefficient of 10,000 M-1cm-1(for compounds with sulfur atom in thioether oxidation state) and 12,600 M-1cm-1(for compounds with sulfur atom in sulfoxide, sulfone, sulfoximine oxidation states) at λmax (in MeOH). Lyophilized peptides were dissolved in a known volume of MeOH, transferred to a quartz cuvette and absorbance was measured at the λmax. (b) List of HPLC gradients

[0170] HPLC gradient A: HPLC 2, Column 2, Flow rate: 12 mL / min; Solv. A: 0.1% FA H2O and Solv. B: 0.1% FA MeCN 0-5 min 5-50% B, 5-10 min 50- B, 10-11 min 100% B

[0171] HPLC gradient B: HPLC 2, Column 2, Flow rate: 12 mL / min; Solv. A: 0.1% FA H2O and Solv. B: 0.1% FA MeCN 0-6 min 10-60% B, 6-8 min 60-100% B, 8-9 min 100% B

[0172] HPLC gradient C: HPLC 2, Column 2, Flow rate: 12 mL / min; Solv. A: 0.1% TFA H2O and Solv. B: 0.1% TFA MeCN 0-7 min 20-50% B, 7-9 min 50-100% B, 9-10 min 100% B

[0173] HPLC gradient D: HPLC 2, Column 2, Flow rate: 12 mL / min; Solv. A: 0.1% TFA H2O and Solv. B: 0.1% TFA MeCN 0-8 min 10-50% B, 8-9 min 50-100% B, 9-10 min 100 % B

[0174] HPLC gradient E: HPLC 1, Column 1, Flow rate: 2 mL / min; Solv. A: 0.1% TFA H2O and Solv. B: 0.1% TFA MeCN 0-20 min 10-38% B, 20-25 min 38-100% B, 25-28 min 100% B, 28-31 min 100- 10% B, 31-34 min 10% B

[0175] HPLC gradient F: HPLC 2, Column 2, Flow rate: 12 mL / min; Solv. A: 0.1% TFA H2O and Solv. B: 0.1% TFA MeCN 0-5 min 10-35% B, 5-12 min 35-70% B, 12-14 min 70-100% B, 14-16 min 100% B

[0176] HPLC gradient G: HPLC 2, Column 2, Flow rate: 10 mL / min; Solv. A 0.1% TFA H2O and Solv. B: 0.1% TFA MeCN 0-10 min 82-89% B, 10-11 min 89-95% B, 11-12 min 95-100% B, 12-14 min 100% B

[0177] HPLC gradient H: HPLC 2, Column 2, Flow rate: 12 mL / min; Solv. A: 0.1% TFA H2O and Solv. B: 0.1% TFA MeCN 0-10 min 5-50% B, 10-12 min 50-100% B, 12-13 min 100% B

[0178] HPLC gradient I: HPLC 2, Column 2, Flow rate: 12 mL / min; Solv. A: 0.1% TFA H2O and Solv. B: 0.1% TFA MeCN 0-12 min 20-40% B, 12-14 min 40-100% B, 14-15 min 100% B

[0179] HPLC gradient J: HPLC 1, Column 1, Flow rate: 2 mL / min; Solv A: 0.1% TFA H2O and Solv. B: 0.1% TFA MeCN 0-19 min 5-50% B, 19-25 min 50-100% B, 25-28 min 100% B, 28-31 min 100- 10% B, 31-34 min 10% B

[0180] HPLC gradient K: HPLC 1, Column 1, Flow rate: 2 mL / min; Solv A: 0.1% TFA H2O and Solv. B: 0.1% TFA MeCN 0-19 min 5-40% B, 19-25 min 40-100% B, 25-28 min 100% B, 28-31 min 100- 5% B, 31-34 min 10% B

[0181] HPLC gradient L: HPLC 2, Column 2, Flow rate: 12 mL / min; Solv. A: 0.1% TFA H2O and Solv. B: 0.1% TFA MeCN 0-4 min 5-50% B, 4-10 min 50-100% B, 10-11 min 100% B

[0182] HPLC gradient M: HPLC 2, Column 2, Flow rate: 12 mL / min; Solv A: 0.1% TFA H2O and Solv. B: 0.1% TFA MeCN 0-4 min 20-50% B, 4-10 min 50-100% B, 10-12 min 100% B

[0183] HPLC gradient N: HPLC 2, Column 2, Flow rate: 12 mL / min; Solv. A: 0.1% TFA H2O and Solv. B: 0.1% TFA MeCN 0-8 min 10-50% B, 8-10 min 50-100% B, 10-11 min 100 % B

[0184] HPLC gradient O: HPLC 2, Column 2, Flow rate: 12 mL / min; Solv. A: 0.1% TFA H2O and Solv. B: 0.1% TFA MeCN 0-10 min 40-85% B, 10-14 min 85-100% B, 14-16 min 100 % B (c) Instrumentation

[0185] 1H,31P,19F,13C, and 2D NMR spectra were recorded on BrukerTMAvanceTM300 (300 MHz), Bruker Avance 400dir (400 MHz), Bruker Avance 400inv (400 MHz), and Bruker Avance 600-CRP (600 MHz) spectrometers. Chemical shifts (δ) are reported in ppm and referenced to the appropriate residual solvent peaks (acetone-d6, CD3CN, CD2Cl2, CDCl3, or DMSO-d6). Low-resolution mass spectrometry (LRMS) in Electrospray Ionization (ESI) mode was obtained using WatersTMZQ mass spectrometer equipped with an ESCi ion source and Waters 2695 HPLC. High-resolution mass spectrometry (HRMS) in ESI mode was obtained using Water / MicromassTMLCT-TOF mass spectrometer equipped with ESI ion source. Circular dichroism (CD) spectra were obtained using a JASCOTMJ-815 CD Spectrometer. Ultraviolet-visible (UV-Vis) spectroscopy was performed using Cary 5000 Spectrophotometer. For all HPLC purifications and analytical HPLC reinjections, an AgilentTM1100 HPLC (HPLC 1) or an Agilent 1260 Infinity II (HPLC 2), equipped with an autoinjector and a photodiode array detector was used. HPLC 1 was outfitted with the following modules: G1379A Degasser, G1311A Quat Pump, G1313A Autosampler, G1316ACOLCOM, G1315B DAD, G1364C Analytical Fraction Collector. HPLC 2 was outfitted with the following modules: G7161A Prep Pump, G7157A Prep Autosampler, G7115A DAD, G1364E Fraction Collector. X-ray crystal data was acquired using a Bruker APEX-II CCD diffractometer operating at T = 173(2) K. Automated solid-phase peptide synthesis was performed using a Gyros PurePep Chorus GT outfitted with induction heating. (d) Cell Viability Assays Against CHO and HEK 293 Cells

[0186] Cells were cultured in alpha Minimum Essential Medium ( ^-MEM) or high-sucrose Dulbecco’s Modified Eagle Medium (DMEM), purchased from GibcoTM. Fetal bovine serum (FBS), 0.25 % trypsin (with 1.3 mM ethylenediaminetetraacetic acid, EDTA), 0.85 % Trypan blue, and the antibiotic mixture Pen / Strep (10K U / mL penicillin, 10K mg / mL streptomycin) were also purchased from Gibco. All cell culture plasticware was obtained from CorningTMor Falcon. Cells were cultured at 37 °C in a humidified chamber with 5 % CO2. When used in cell culture, DMSO was purified by filtration through a 0.2 mm filter. All experiments are carried out in a laminar flow culture cabinet, unless otherwise noted. Absorbance measurements of the 96-well plates were obtained using a FilterMax F5 muti-mode microplate reader, equipped with an excitation filter of 570 nm. Immortalized cells had been stored in liquid nitrogen. To revive cells, a 1 mL tube of the frozen cells in medium containing 10 % DMSO was warmed in a 30 °C water bath and diluted with 9 mL of fresh media. Media contained 10 % FBS and 100 U / mL penicillin and 100 mg / mL streptomycin, unless otherwise indicated. The cells were incubated in a T-25 flask at 37 °C at 5% CO2. After 24 hours, the medium was aspirated and replaced with fresh medium. When cells reached a level of 90 - 100 % confluence, they were sub- cultured. The medium was removed, and the cells were treated with 0.25 % trypsin containing 1.3 mM EDTA in the incubator. Once the cells were detached from the tissue culture flask, 3- 5 mL media was added to quench the trypsin, and transferred to a 10 mL centrifuge tube. The mixture was centrifuged for 5 min at 8000 rpm, and the supernatant was discarded. The cells were suspended in fresh medium, diluted as required, and transferred to a new culture flask. To assay cell viability, a nearly confluent tissue culture flask was trypsinized, and the cells were counted following treatment with Trypan blue, using a CountessTMII FL Automated Cell Counter. The cells were then diluted to the appropriate stock concentrations in fresh medium and transferred in 100 μL to a 96-well plate using a multi-channel pipette. The number of cells plated varied from experiment-to-experiment. These were incubated a 37 °C and 5% CO2 for a 24-hour period to allow for adherence. The medium was aspirated, and fresh medium was added, which contained the desired additives DMSO. The cells were then re-incubated for72 h. At the completion of the experiment, a 100 μL aliquot of 25 mg / mL 3-(4,5- dimethylthiazol-2-yl)-2,5-diphenyl-2H-tetrazolium bromide (MTT) in phosphate-buffered saline (PBS) was added to each well. The plate was incubated three hours further, to allow for the formation of the formazan product in viable cells. The media was carefully aspirated, and the purple product was solubilized in DMSO. The absorbance of each well was recorded at 570 nm, and an image of the plate was generated using a scanner. Data was processed in MicrosoftTMExcel and GraphPadTMPrism. Experiments were performed either in triplicate, unless otherwise noted, and the error bars were calculated as the standard error of the mean. Trypsinized cells were diluted to a concentration of 3.3 ^ 104cells / mL for cells. Each cell line was plated in a 96-well plate, with 100 μL of the stock solution per well (5000 cells per well) and incubated for 24 hours. Stocks of α-amanitin or analogs were prepared at various concentrations, and added to various wells, according to the desired final concentration, often 25, 8.333, 2.778, 0.926, 0.309, 0.103, 0.034, 0.011, or 0.004 μM. The cells were incubated for 72 hours, at which point viability was assessed. (e) Circular Dichroism (CD) Spectra for sulfur derivatized amatoxins

[0187] Sample preparation for CD: α-amanitin and sulfur derivatized 5′-OH(Trp) amanitin analogs (25 nmol) were each dissolved in 80 µL of MeOH. All CD spectra were acquired on a JASCO J-815 CD spectrometer. Three scans were accumulated for each peptide and a smoothing algorithm was applied. (f) X-ray crystallographic studies

[0188] S,S-dibenzyl sulfiliminium diphenylphosphinate (2b): Experimental. Single colourless needle-shaped crystals of 2b recrystallised from DCM by slow evaporation. A suitable crystal with dimensions 0.37 × 0.11 × 0.08 mm3was selected and mounted on a Bruker APEX-II CCD diffractometer. The crystal was kept at a steady T = 173(2) K during data collection. The structure was solved with the ShelXT 2018 / 2 (Sheldrick, 2015) solution program using Intrinsic Phasing methods and by using Olex21.5 (Dolomanov et al., 2009) as the graphical interface. The model was refined with XL (Sheldrick, 2015) using full matrix least squares minimisation on F2. Crystal Data. C26H26NO2PS, Mr = 447.51, orthorhombic, Pbca (No.61), a = 18.0512(18) Å, b = 10.4700(10) Å, c = 24.559(2) Å, α = β = γ = 90°, V = 4641.6(8) Å3, T = 173(2) K, Z = 8, Z' = 1, µ(MoKα) = 0.231, 68607 reflections measured, 4286 unique (Rint = 0.0572) which were used in all calculations. The final wR2 was 0.0950 (all data) and R1 was 0.0372 (I≥2 σ(I)). properties and parameters. Compound:S,S-dibenzyl sulfiliminium diphenylphosphinate (2b), Formula: C26H26NO2PS, Dcalc. / g cm-3: 1.281, µ / mm-1: 0.231, Formula Weight: 447.51, Colour: colourless, Shape: needle-shaped, Size / mm3: 0.37×0.11×0.08, T / K: 173(2), Crystal System: orthorhombic, Space Group: Pbca, a / Å: 18.0512(18), b / Å: 10.4700(10), c / Å 24.559(2), α / °: 90, β / °: 90, γ / °: 90, V / Å3: 4641.6(8), Z: 8, Z': 1, Wavelength / Å: 0.71073, Radiation type: MoKα, θmin / °: 2.256, θmax / °: 25.488, Measured Refl's.: 68607, Indep't Refl's: 4286, Refl's I≥2 σ(I): 3402, Rint:0.0572, Parameters: 288, Restraints: 0, Largest Peak: 0.465, Deepest Hole: -0.276, GooF: 1.044, wR2 (all data): 0.0950, wR2: 0.0861, R1 (all data): 0.0540, R1: 0.0372.

[0189] Fmoc-Met-OH sulfiliminium diphenylphosphinate (2v[i]): Experimental. Single colourless blade-shaped crystals of 2v[i] recrystallised from a mixture of methanol and water by slow evaporation. A suitable crystal with dimensions 0.14 × 0.08 × 0.02 mm3was selected and mounted on a mylar loop in oil on a Bruker APEX II area detector diffractometer. The crystal was kept at a steady T = 90(2) K during data collection. The structure was solved with the ShelXT 2018 / 2 (Sheldrick, 2015) solution program using Intrinsic Phasing methods and by using Olex21.5 (Dolomanov et al., 2009) as the graphical interface. The model was refined with XL (Sheldrick, 2015) using full matrix least squares minimisation on F2. Crystal Data. C33H37N2O7PS, Mr = 636.67, monoclinic, P21 (No.4), a = 10.1852(8) Å, b = 8.7155(6) Å, c = 18.5220(14) Å, β = 103.698(3)°, α = γ = 90°, V = 1597.4(2) Å3, T = 90(2) K, Z = 2, Z' = 1, µ(MoKα) = 0.202, 35253 reflections measured, 5895 unique (Rint= 0.0550) which were used in all calculations. The final wR2 was 0.0950 (all data) and R1 was 0.0470 (I≥2 σ(I)). Crystal properties and parameters: Compound: Fmoc-Met-OH sulfiliminium diphenylphosphinate (2v[i]), Formula: C33H37N2O7PS, Dcalc. / g cm-3: 1.324, µ / mm-1: 0.202, Formula Weight: 636.67, Colour: colourless, Shape: blade-shaped, Size / mm3: 0.14×0.08×0.02, T / K: 90(2), Crystal System: monoclinic, Flack Parameter: -0.04(4), Hooft Parameter : -0.04(3), Space Group: P21, a / Å: 10.1852(8), b / Å: 8.7155(6), c / Å: 18.5220(14), α / °: 90, β / °: 103.698(3), γ / °: 90, V / Å3: 1597.4(2), Z: 2, Z': 1, Wavelength / Å: 0.71073, Radiation type: MoKα, θmin / °: 1.132, θmax / °: 25.486, Measured Refl's.: 35253, Indep't Refl's: 5895, Refl's I≥2 σ(I): 5143, Rint: 0.0550, Parameters: 419, Restraints: 1, Largest Peak: 0.467, Deepest Hole: -0.376, GooF: 1.119, wR2 (all data): 0.0950, wR2: 0.0914, R1 (all data): 0.0589, R1: 0.0470.II. Synthetic Procedures and Analytical Data of Starting Material (a) Synthesis of N-(((9H-fluoren-9-yl)methoxy)carbonyl)-S-butyl-L-homocysteine (1v[ii])

[0190] A was eq., g, 1 mmol) in 10% NaHCO3(aq) / tetrahydrofuran (THF; 6 mL / 2 mL). The solution was cooled to 0 °C in an ice bath and fluorenylmethyloxycarbonyl chloride (Fmoc-Cl; 1 eq., 0.2640 g, 1 mmol) dissolved in 2 mL of THF was added dropwise over 15 minutes. The reaction mixture was stirred at 0 °C for 30 minutes and then warmed to 21 °C and stirred for 6 hours. The reaction mixture was concentrated under reduced pressure to remove THF. The clear reaction mixture was acidified to pH 2 with 1 M HCl (aq) and extracted with EtOAc (4 ^ 15 mL). The organic layer was dried with anhydrous MgSO4, filtered, and concentrated under reduced pressure. The crude solid was immediately purified using silica gel flash column chromatography. (Isocratic elution, 2% MeOH / dichloromethane, DCM) to obtain NαFmoc-L-Buthionine-OH 1v[ii] (0.2762 g, 0.67 mmol) as a yellow oil in 67% yield.1H NMR (300 MHz, CD2Cl2) δ = 7.78 (d, J=7.5 Hz, 2H), 7.61 (dd, J=7.7 Hz, 2.9, 2H), 7.40 (t, J=1.3 Hz, 2H), 7.31 (t, J=1.3 Hz, 2H), 5.52 (d, J=8.2 Hz, 1H), 4.44 (dd, J=15.1, 6.6 Hz, 3H), 4.23 (t, J=6.8 Hz, 1H), 2.67 – 2.38 (m, 4H), 2.17 (dq, J=13.5, 6.9 Hz, 1H), 1.97 (dq, J=13.9, 7.2 Hz, 1H), 1.69 – 1.48 (m, 2H), 1.46 – 1.31 (m, 2H), 0.90 (t, J=7.3 Hz, 3H) ppm.13C NMR (75 MHz, CD2Cl2) δ = 176.58, 156.56, 144.31, 144.18, 141.69, 128.11, 127.47, 125.44, 120.35, 67.43, 47.56, 32.32, 32.03, 32.00, 28.22, 22.35, 13.85 ppm. TLC (DCM:MeOH:acetic acid 94:5:1 v / v / v): Rf= 0.34 (UV, I2). (b) Synthesis of methyl (S)-2-((tert-butoxycarbonyl)amino)-3-(2-(dodecylthio)-1H- indol-3-yl)propanoate (1t)

[0191] Following a literature procedure (Pryyma et al., 2019), the model tryptathionine substrate (1t) was synthesized as a white solid (0.5937 g, 1.1 mmol) in 76% yield.1H NMR (300 MHz, CD2Cl2) δ = 8.36 (s, 1H), 7.52 (d, J=7.9 Hz, 1H), 7.31 (d, J=8.1 Hz, 1H), 7.21 – 7.13 (m, 1H), 7.13 – 6.97 (m, 1H), 5.15 (d, J=8.2 Hz, 1H), 4.67 – 4.47 (m, 1H), 3.67 (s, 3H), 3.31 (qd, J=14.1, 6.2 Hz, 2H), 2.77 (t, J=7.4 2H), 1.66 – 1.45 (m, 3H), 1.38 (s, 9H), 1.25(s, 17H), 0.87 (t, J=6.9 Hz, 3H). LRMS (ESI-TOF, m / z): [M+H]+found 519.2; calc.519.3 for C29H47N2O4S. TLC (Hexane:EtOAc 40:60 v / v): Rf= 0.8 (UV, I2). (c) Synthesis of Cholecystokinin fragment 30-33 amide / CCK-4 tetragastrin (1x[i])

[0192] The linear tetrapeptide was synthesized by extending the amino acid sequence on rink-amide resin using Fmoc-solid phase peptide synthesis (SPPS). The synthesis was carried out using an automated peptide synthesizer (Gyros Protein Technologies PureprepTMChorus instrument). Fmoc-amino acids were coupled in the following sequential order: Fmoc-Phe- OH, Fmoc-Asp(OtBu)-OH, Fmoc-Met-OH, and Fmoc-Trp(Boc)-OH. All coupling and deprotection reactions were carried out under nitrogen at 50 °C. The dried rink-amide resin (100 mg) was swelled with DCM for 20 minutes. The solvent was drained followed by dimethylformamide DMF washes (2 ^ 5 min). The resin beads were subjected to Fmoc- deprotection in 20% piperidine / DMF (2 ^ 5 min) followed by DMF washes (2 ^ 5 min). The proceeding coupling step draws the respective Fmoc-Xaa-OH in DMF (7.5 eq., 100 mM), O- (1H-6-chlorobenzotriazole-1-yl)-1,1,3,3-tetramethyluronium hexafluorophosphate (HCTU) in DMF (7.5 eq., 100mM) and N-methylmorpholine in DMF (15 eq., 200 mM) to the reaction vessel and the coupling reaction left to proceed with agitation for 10 min at 50 °C. This was followed by DMF washes (2 ^ 5 min). Upon sequential coupling of Fmoc-amino acids the resin beads were subjected to a final Fmoc deprotection step and DMF and DCM washes. Resin-cleavage was afforded by the treatment of peptide bound resin with a cleavage cocktail solution: TFA:triisopropyl silane:H2O (95:2.5:2.5 v / v / v) for 1 hr with agitation and nitrogen bubbling. Finally, the TFA solution was collected, and the mixture was dried under reduced pressure. The resulting solution was diluted with ice-cold Et2O, vortexed and then spun down on a centrifuge. The supernatant was discarded, and the resulting white pellet was allowed to dry. The pellet was dissolved in a minimal volume of 0.1% FA H2O / MeCN and subjected to HPLC purification using gradient A with the CCK-4 peptide 1x[i] (tR: 4.0 min at 280 nm) isolated as a white powder after lyophilization with 52% yield (with respect to 0.7 mmol / gloading capacity). HRMS (ESI-TOF, m / z): [M+H]+found 597.2492; calc.597.2495 for C29H36N6O6S. HPLC Re-injection (gradient K): tR= 20.5 min (280 nm). (d) Synthesis of N-acetyl cholecystokinin fragment 30-33 amide / CCK-4 tetragastrin (1x[iii])

[0193] The linear tetrapeptide was synthesized by extending the amino acid sequence on rink-amide resin using Fmoc-solid phase peptide synthesis (SPPS) identical to the procedure followed in the synthesis of 1x[i]. Upon sequential coupling of Fmoc-amino acids the resin beads were subjected to a final Fmoc deprotection step then DMF and DCM washes followed by an acetylation cocktail treatment for 20 min with agitation and nitrogen bubbling. Resin- cleavage was afforded by the treatment of peptide bound resin with a cleavage cocktail solution: TFA:triisopropyl silane:H2O (95:2.5:2.5 v / v / v) for 1 hr with agitation and nitrogen bubbling. Finally, the TFA solution was collected, and themixture was dried under reduced pressure. The resulting solution was dilutedwith ice-cold Et2O, vortexed andthen spun down in a centrifuge. The supernatant was discarded, and the resultingwhite pellet was allowed to dry. The pellet was dissolved in a minimal volume of 0.1%TFA H2O / MeCN and subjected to HPLC purification using gradient M with the N-acetyl CCK-4peptide 1x[iii] (tR: 4.0 min at 280 nm) isolatedasa white powder after lyophilization with 56% yield (with respect to 0.7 mmol / g loading capacity). HPLC Re-injection (gradient M)Rt =4.04 min (280 nm). HRMS (ESI-TOF, m / z): [M-H] - found 637.2449; calc.637.2450 for C31H37N6O7S- (e) Synthesis of Bombesin (1y)

[0194] The lie mr e de w sn by extendingthe amino acid sequence on rink-amide resin using Fmoc-solid pha eptide synt( . The synthesis wascarried out using an automated peptide synthesizer (Gyros Protein Technologies Pureprep Chorus instrument). Fmoc-amino acids were coupled in the following sequential order: Fmoc-Met-OH, Fmoc-Leu-OH, Fmoc-His-OH, Fmoc-Gly-OH, Fmoc-Val-OH, Fmoc-Ala- OH, Fmoc-Trp(Boc)-OH, Fmoc-Gln(Trt)-OH, Fmoc-Asn(Trt)-OH, Fmoc-Gly-OH, Fmoc- Leu-OH, Fmoc-Arg-OH, Fmoc-Gln(Trt)-OH, and Boc-Pyr-OH. All coupling and deprotection reactions were carried out under nitrogen at 50 °C. The dried rink-amide resin (100 mg) was swelled with DCM for 20 minutes. The solvent was drained followed by DMF washes (2 ^ 5 min). The resin beads were subjected to Fmoc-deprotection in 20% piperidine / DMF (2 ^ 5 min) followed by DMF washes (2 ^ 5 min). The proceeding coupling step draws the respective Fmoc-Xaa-OH in DMF (7.5 eq., 100 mM), HCTU in DMF (7.5 eq., 100mM) and N-methylmorpholine in DMF (15 eq., 200 mM) to the reaction vessel and the coupling reaction left to proceed with agitation for 10 min at 50 °C. This was followed by DMF washes (2 ^ 5 min). Upon sequential coupling of Fmoc-amino acids the resin beads were subjected to DMF and DCM washes. Resin-cleavage was afforded by the treatment of peptide bound resin with a cleavage cocktail solution: TFA:triisopropyl silane:H2O (95:2.5:2.5 v / v / v) for 1 hr with agitation and nitrogen bubbling. Finally, the TFA solution was collected and concentrated under reduced pressure. The resulting solution was diluted with ice-cold Et2O, vortexed and then spun down on a centrifuge. The supernatant was discarded, and the resulting white pellet was allowed to dry. The pellet was dissolved in a minimal volume of 0.1% FA H2O / MeCN and subjected to HPLC purification using gradient B with the Bombesin peptide (tR: 3.5 min at 280 nm) isolated as a white powder after lyophilization with 57% yield (with respect to 0.7 mmol / g loading capacity). HRMS (ESI-TOF, m / z): [M+H]+found 1619.8221; calc.1619.8229 for C71H111N24O18S. HPLC Re-injection (gradient D): tR= 4.9 min (280 nm). (f) Synthesis of S-deoxy-5′-OH-6′-deoxy-amanitin (1z)

[0195] Following a literature procedure (Pryyma et al., 2020), the S-deoxy-5′-OH-6′- deoxy-amanitin (1z) was synthesized as a white powder (2.9 µmol) in 48% HPLC purified yield. LRMS (ESI-TOF, m / z): [M+Na]+found 925.6; calc. 925.3 for C39H54N10NaO13S. HPLC Re-injection (gradient J, 0.1% FA H2O / MeCN): tR = 13.5 min (290 nm). III. Synthesis of Sulfoxides General procedure for the synthesis of sulfoxides

[0196] An oven-dried flask equipped with a magnetic stir bar, was charged with the corresponding sulfide (1.0 eq., 2.5 mmol) followed by MeOH (7 mL) and cooled to 0 °C in an ice-bath. Next a solution of NaIO4(1.2 eq., 0.6547 g, 3 mmol) in H2O (13 mL) cooled in an ice bath, was added dropwise over several minutes. The reaction mixture was stirred at 0- 4 °C for 16 h. The crude reaction mixture was filtered, and the filtrate was extracted using CHCl3(3 ^ 20 mL). The organic extracts were combined, washed with brine, dried over anhydrous MgSO4, filtered, and concentrated under reduced pressure. The crude product was purified by silica gel column chromatography when necessary. (a) S-Methyl-S-phenyl sulfoxide (1a′)

[0197] 1a′ was synthesized following the general procedure for the preparation of sulfoxides starting from thioanisole (1 eq., 5 mmol, 596 µL) to afford 0.6497 g (93% yield) of the desired product as a yellow oil.1H NMR (300 MHz, CDCl3) δ = 7.73 – 7.58 (m, 1H), 7.55 – 7.42 (m, 1H), 2.71 (s, 1H) ppm.13C NMR (75 MHz, CDCl3) δ = 145.66, 131.13, 129.44, 123.58, 43.98 ppm. LRMS (ESI, m / z): [M+Na]+found 163.2; calc.163.0 for C7H8NaOS+. (b) S-(4-methylphenyl)-S-methyl sulfoxide (1e′)

[0198] 1e′ was synthesized following the general procedure for the preparation of sulfoxides starting from 4-methylthioanisole (1 eq., 5 mmol, 673 µL) to afford 0.6715 g (87% yield) of the desired product as a white solid upon silica gel flash column chromatography (Isocratic elution, 1% .1H NMR (300 MHz, CDCl3) δ =7.53 (d, J=8.2 Hz, 2H), 7.32 (d, J=7.9 Hz, 2H), 2.69 (s, 3H), 2.40 (s, 3H) ppm.13C NMR (75 MHz, CDCl3) δ = 142.54, 141.63, 130.13, 123.66, 44.06, 21.49 ppm. LRMS (ESI, m / z): [M+K]+found 193.1; calc.193.0 for C8H10KOS+. (c) S-(4-methoxylphenyl)-S-methyl sulfoxide (1f′)

[0199] 1f′ was synthesized procedure for the preparation of sulfoxides starting from 4-methoxythioanisole (1 eq., 2.5 mmol, 0.3935 g) to afford 0.3471 g (82% yield) of the desired product as a white solid upon silica gel flash column chromatography (Isocratic elution, 1% MeOH / DCM).1H NMR (300 MHz, DMSO) δ = 7.62 (d, J=8.8 Hz, 1H), 7.12 (d, J=8.8 Hz, 1H), 3.81 (s, 3H), 2.69 (s, 3H) ppm.13C NMR (75 MHz, DMSO) δ = 161.23, 137.26, 125.53, 114.74, 55.50, 43.34 ppm. LRMS (ESI, m / z): [M+Na]+found 193.2; calc.193.0 for C8H10NaO2S+. (d) S-(4-fluorophenyl)-S-methyl sulfoxide (1i′)

[0200] 1i′ was synthesized following the general procedure for the preparation of sulfoxides starting from 4-fluorothioanisole (1 eq., 5 mmol, 627 µL) to afford 0.7232 g (91% yield) of the desired product as a white solid.1H NMR (300 MHz, CDCl3) δ = 7.87 – 7.49 (m, 2H), 7.33 – 6.87 (m, 2H), 2.70 (s, 3H) ppm.13C NMR (75 MHz, CDCl3) δ = 164.40 (d, J=251.4 Hz), 141.26 (d, J=3.1 Hz), 125.93 (d, J=8.8 Hz), 116.77 (d, J=22.5 Hz), 44.25 ppm.19F NMR (282 MHz, CDCl3) δ = -108.56 ppm. LRMS (ESI, m / z): [M+Na]+found 181.2; calc.181.0 for C7H7FNaOS+. (e) S-phenyl-S-cyclopropyl sulfoxide

[0201] 1o′ was synthesized following the general procedure for the preparation of sulfoxides starting from phenyl-cyclopropyl sulfide (1 eq., 2.5 mmol, 394 µL) to afford 0.3433 g (82% yield) of the desired product as a yellow oil.1H NMR (300 MHz, CDCl3) δ = 7.70 – 7.55 (m, 2H), 7.51 – 7.34 (m, 3H), 2.19 (dddd, J=10.9, 7.9, 4.9, 1.2 Hz, 1H), 1.35 – 1.08 (m, 1H), 1.05 – 0.90 (m, 1H), 0.91 – 0.77 (m, 2H) ppm.13C NMR (75 MHz, CDCl3) δ = 144.78, 130.85, 129.08, 123.91, 33.68, 3.34, 2.65 ppm. LRMS (ESI, m / z): [M+H]+found 167.2; calc.167.1 for C9H11OS+. IV. Optimization of Reaction Conditions (a) DPPH mediated thioether imination of thioanisole (1a)

[0202] The test reactions for the solvent screen were run as follows: In an oven-dried flask, thioanisole 1a (1 eq., 0.1 mmol, 0.0125 g) was dissolved in solvent (0.2 mL, MeCN-d3 solvent used for entry 4 and DMSO-d6 solvent used for entry 6) followed by the addition of diphenyl- phoshinylhydroxylamine (DPPH; 1.1 eq., 0.11 mmol, 0.027 g) and the reaction mixture was left stirring for 3 hours at room temperature. The clear solution was then dried under reduced pressure (except for crude reaction of entry 4 and 6). The dried crude reaction mixture was redissolved in DMSO-d6 and subjected to1H NMR analysis. The % conversion was calculated using the integral ratio of the peak of 2a (δ 3.33 ppm) and 1a (δ 2.46 ppm) in the1H NMR spectrum. Table 1. Optimization of reaction conditions: Solvent screen for DPPH mediated imination of thioanisole (1a). Entry Solvent Conversion [%] of 2a[a]1 MeOH Quantitative 2 CH2Cl2 Quantitative 3 THF Quantitative 4 MeCN-d389 5 DMF Quantitative 6 DMSO 20 [a] % Conversion determined using1H NMR spectral analysis of crude reaction mixtures.(b) Oxidation of NH-free sulfilimine salts

[0203] The test flask methyl phenyl sulfiliminium diphenylphosphinate (2a) (0.1 mmol[a], 0.5 mmol[b]) was dissolved in solvent (2 mL) and the solution was cooled to 0 °C in an ice-bath. Next, meta-chloroperoxybenzoic acid (mCPBA) was added and left stirring at 0 °C for 5 minutes. Afterwards, the base was added (precooled for bases(l) and base solutions at 0 °C). The reaction mixture was left stirring at 4 °C for 16 hrs. For entries 1-12[a]the crude reaction mixture was dried under reduced pressure and redissolved in DMSO-d6 and subjected to NMR spectral analysis. The % conversion was calculated using the integral ratio of the peak of 3a (δ 3.06 ppm) and 4a (δ 3.21 ppm) in1H NMR spectrum. For entries 1, 8, 13-15[b], the crude reaction mixture was filtered and the filtrate was concentrated under reduced pressure. The product was purified by flash column chromatography using hexane:EtOAc 1:4 to 100% EtOAC gradient elution. Table 2. Optimization of reaction conditions: Oxidation of methyl phenyl sulfiliminium diphenylphosphinate (2a) with different solvents, bases. Entry Base (equiv.) Oxidant (equiv.) Solvent%Conv.[a] / Isolated Yield[b]1 NH4OH (100) mCPBA (5) MeOH 92[a] / 78[b]2 NH4OH (100) mCPBA (5) EtOH 88[a]3 NH4OH (100) mCPBA (5) iPrOH 91[a]4 NH4OH (100) mCPBA (5) TFE 85[a]5 MgO (20) mCPBA (5) MeOH 55[a]6 NaOH (20) mCPBA (5) MeOH trace[a]7 NaOH (20)[c]mCPBA (5) MeOH trace[a]8 Na2CO3(20) mCPBA (5) MeOH 96[a] / 87[b]9 7 M NH3 (20)[d]mCPBA (5) MeOH 84[a]10 DIPEA (20) mCPBA (5) MeOH trace[a]11 DBU (20) mCPBA (5) MeOH trace[a]12 NaOMe (20) mCPBA (5) MeOH 95[a]13 Na2CO3 (1) mCPBA (1) MeOH 45[b]14 Na2CO3 (2) mCPBA (2) MeOH 67[b]15 Na2CO3 (10) mCPBA (5) MeOH 55[b][a] % conversion determined using NMR spectroscopy. [b] Isolated yields from column chromatography. [c] use of freshly ground NaOH, [d] methanolic solution. (c) Oxidation of model tryptathionine substrate

[0204] The test reactions were run as follows. In an oven dried flask the model tryptathionine (Ttn) sulfiliminium diphenylphosphinate (2t) (1 µmol) was dissolved in solvent (30 µL) and the solution was cooled to 0 °C in an ice-bath. Next, an mCPBA solution (20 µL) pre-cooled at 0 °C was added and left stirring at 0 °C for 5 minutes. Afterwards, the base was added (precooled for bases(l)and base solutions at 0 °C). The reaction mixture was left stirring at 4 °C for 16 hrs. The crude reaction mixture was dried under reduced pressure and redissolved in 40% ACN / H2O (0.1% TFA) and analyzed by reverse-phase HPLC using gradient G. The % conversion was determined by taking the ratio of A(sulfoximine diastereomer peakstR: 3.5 and 4.1) / ΣA (All peaks that display Ttn UV absorption profile), where A = integral area of the peak of interest determined using standard Agilent data analysis software. Table 3. Optimization of reaction conditions: Oxidation of model tryptathionine substrate (2t) with different solvents, bases. Entry Base (equiv.) Oxidant (equiv.) Solvent %Conv.[a]1 NH4OH (50) mCPBA (5) MeOH 48 2 NH4OH (100) mCPBA (5) MeOH 55 3 NH4OH (100) mCPBA (5) EtOH 56 4 NH4OH (100) mCPBA (5) iPrOH 58 5 NH4OH (100) mCPBA (5) tBuOH 34 6 2 M NH3(100) mCPBA (5) MeOH 40 10 DIPEA (20) mCPBA (5) MeOH trace 11 DBU (20) mCPBA (5) MeOH 50 12 Lutidine (20) mCPBA (5) MeOH trace 13 NaHCO3 (20) mCPBA (5) MeOH 28 14 K2CO3(20) mCPBA (5) MeOH 4915 Na2CO3 (20) mCPBA (5) MeOH 56 16 Na2CO3 (10) mCPBA (5) MeOH 54 17 Na2CO3 (20) mCPBA (2.5) MeOH 63 18 Na2CO3(10) mCPBA (2.5) MeOH 58 19 Na2CO3 (2) mCPBA (5) MeOH 38 20 Na2CO3 (2) mCPBA (2) MeOH 38 [a] % conversion determined from reverse-phase HPLC. Integrations were performed with a standard Agilent data analysis software (d) Imination of sulfoxides

[0205] The test reactions were run as follows: In an oven dried flask, methyl phenyl sulfoxide 1a′ (0.1 mmol) was dissolved in solvent (0.2 / 1 mL). Next, DPPH (3 eq., 0.3 mmol, 0.073 g) was added and kept stirring at the required temperature. Afterwards, the catalyst (2.5 mol% if present) was added and the reaction was left stirring at the required temperature for 16 hrs. The crude reaction mixture was dried under reduced pressure and redissolved in DMSO-d6and subjected to NMR spectral analysis. The % conversion was calculated using the integral ratio of the peak of 3a (δ 3.06 ppm) and thioanisole sulfoxide (δ 2.73 ppm) in1H NMR spectrum. Table 4. Optimization of reaction conditions: Oxidation of methyl phenyl sulfoxide (1a′) with different solvents, catalysts at different temperatures. Entry Solvent (conc. M) Temperature (°C) Catalyst (mol %) %Conv.[a]1 CH2Cl2 (0.1) 21 N / A <10 2 CH2Cl2 (0.5) 21 N / A 20 2 MeCN (0.5) 21 N / A 15 3 Toluene (0.1) 21 N / A <10 4 Toluene (0.5) 21 N / A 40 5 MeOH (0.5) 21 N / A 29 6 EtOH (0.5) 21 N / A 16 7 TFE (0.5) 21 N / A 36 8 MeOH (0.5) 45 N / A 49 9 TFE (0.5) 50 N / A 29 10 iPrOH (0.5) 50 N / A 3111 tBuOH (0.5) 50 N / A 36 12 ACN (0.5) 70 N / A 44 13 DCE (0.5) 70 N / A 37 14 Toluene (0.5) 50 N / A 46 15 ACN (0.1) 21(20FemSoOl4%)1316 TFE (0.1) 21 Rh2(OAc)4 (2.5 mol%)4117 TFE (0.1) 21(2R.h52m(eospl%)2)9718 MeOH (0.1) 21(2R.h52m(eospl%)2)90[a] % conversion determined using NMR spectroscopy. V. Procedures and Characterization Data General Procedure for DPPH mediated thioether imination to access sulfiliminium salts 2a-2v[ii]

[0206] An oven-dried flask equipped with a magnetic stir bar, was charged with DPPH (1.1 eq., 0.1350 g, 0.55 mmol) followed by MeOH (0.5 mL). Next, the corresponding sulfide 1a-1v[ii] (1 eq.0.5 mmol) was added and the reaction mixture was left stirring at room temperature until the reaction was completed, confirmed using thin layer chromatography (TLC). The crude reaction mixture was dried under reduced pressure and redissolved in CH2Cl2(2 mL). The sulfiliminium salt was extracted with water (3 ^ 1.5 mL). All aqueous extracts were pooled together and subjected to lyophilization after freezing. (a) S-Methyl-S-phenyl sulfiliminium diphenylphosphinate (2a)

[0207] 2a was synthesized following the general procedure for the preparation of sulfiliminium salts starting from thioanisole (1 eq., 0.5 mmol, 61 µL) to afford 0.1661 g (93% yield) of the desired product as a colourless gelatinous solid.1H NMR (300 MHz, CD2Cl2) δ = 9.09 (s, 2H), 7.91 (d, J=8.0 Hz, 2H), 7.83 – 7.66 (m, 4H), 7.45 (t, J=7.3 Hz, 1H), 7.37 – 7.11 (m, 8H), 3.10 (s, 3H) ppm.13C NMR (75 MHz, CD2Cl2) δ = 141.89 (d, J=128.0 Hz),135.63, 132.90, 131.59 (d, J=9.1 Hz), 130.14, 129.54 (d, J=2.5 Hz), 127.99 (d, J=11.5 Hz), 127.69, 35.58 ppm.31P NMR (122 MHz, CD2Cl2) δ = 15.59 ppm. HRMS (ESI-TOF, m / z): [M]+found 140.0531; calc.140.0528 for C7H10NS+. (b) S,S-Dibenzyl sulfiliminium diphenylphosphinate (2b)

[0208] 2b was synthesized following the general procedure for the preparation of sulfiliminium salts starting from dibenzylsulfide (1 eq., 1.2 mmol, 0.2572 g) to afford 0.3883 g (72% yield) of the desired product as a white solid upon trituration with diethyl ether.1H NMR (300 MHz, CD2Cl2) δ = 8.20 (s, 2H), 7.88 – 7.71 (m, 4H), 7.44 – 7.02 (m, 16H), 4.89 (d, J=12.8 Hz, 2H), 4.47 (d, J=12.7 Hz, 2H) ppm.13C NMR (75 MHz, CD2Cl2) δ = 141.40 (d, J=128.6 Hz), 131.70 (d, J=9.2 Hz), 131.13, 129.91 (d, J=2.6 Hz), 129.42, 129.16, 128.22 (d, J=11.7 Hz), 51.94 ppm.31P NMR (122 MHz, CD2Cl2) δ = 16.68 ppm. HRMS (ESI-TOF, m / z): [M]+found 230.0097; calc.230.0098 for C14H16NS+. (c) S-(2-Methylphenyl)-S-methyl sulfiliminium diphenylphosphinate (2c)

[0209] 2c was synthesized following the general procedure for the preparation of sulfiliminium salts starting from 2-methylthioanisole (1 eq., 0.5 mmol, 0.069 g) to afford 0.1861g (quantitative yield) of the desired product as a colourless gelatinous oil.1H NMR (300 MHz, CD2Cl2) δ = 9.00 (s, 2H), 8.45 (d, J=8.0 Hz, 1H), 7.93 – 7.76 (m, 4H), 7.42 – 7.26 (m, 7H), 7.17 (d, J=7.7 Hz, 2H), 3.08 (s, 3H), 2.29 (s, 3H) ppm.13C NMR (75 MHz, CD2Cl2) δ = 141.47 (d, J=128.5 Hz), 136.71, 134.26, 132.75, 131.53 (d, J=9.1 Hz), 131.21, 129.59 (d, J=2.7 Hz), 128.39, 127.95 (d, J=11.8 Hz), 34.87, 18.87 ppm.31P NMR (122 MHz, CD2Cl2) δ = 16.07 ppm. HRMS (ESI-TOF, m / z): [M]+found 154.0695; calc.154.0685 for C8H12NS+(d) S-(3-Methylphenyl)-S-methyl sulfiliminium diphenylphosphinate (2d)

[0210] 2d was synthesized following the general procedure for the preparation of sulfiliminium salts starting from 3-methylthioanisole (1 eq., 0.5 mmol, 69 µL) to afford 0.1881 g (Quantitative yield) of the desired product as a colourless gelatinous solid.1H NMR (300 MHz, CD2Cl2) δ = 9.08 (s, 2H), 7.85 – 7.68 (m, 6H), 7.39 – 7.18 (m, 8H), 3.11 (s, 3H), 2.25 (s, 3H) ppm.13C NMR (75 MHz, CD2Cl2) δ = 142.00 (d, J=127.7 Hz), 140.63, 135.43, 133.68, 131.54 (d, J=8.9 Hz), 129.91, 129.43 (d, J=2.8 Hz), 127.92 (d, J=11.5 Hz), 127.79, 124.66, 35.44, 21.25 ppm.31P NMR (122 MHz, CD2Cl2) δ = 15.31 ppm. HRMS (ESI-TOF, m / z): [M]+found 154.0686; calc.154.0685 for C8H12NS+. (e) S-(4-Methylphenyl)-S-methyl sulfiliminium diphenylphosphinate (2e)

[0211] 2e was synthesized following the general procedure for the preparation of sulfiliminium salts starting from 4-methylthioanisole (1 eq., 0.5 mmol, 68 µL) to afford 0.1887 g (quantitative yield) of the desired product as a colourless gelatinous solid.1H NMR (300 MHz, CD2Cl2) δ = 9.03 (s, 2H), 7.93 – 7.64 (m, 6H), 7.46 – 7.22 (m, 6H), 7.10 (d, J=8.1 Hz, 2H), 3.11 (s, 3H), 2.33 (s, 3H) ppm.13C NMR (75 MHz, CD2Cl2) δ = 143.81, 142.05 (d, J=127.6 Hz), 132.28, 131.57 (d, J=9.0 Hz), 130.69, 129.40 (d, J=2.6 Hz), 127.98, 127.78 (d, J=7.2 Hz), 35.41, 21.51 ppm.31P NMR (122 MHz, CD2Cl2) δ = 15.29 ppm. HRMS (ESI- TOF, m / z): [M]+found 154.0686; calc.154.0685 for C8H12NS+. (f) S-(4-Methoxyphenyl)-S-methyl sulfiliminium (2f)

[0212] 2f was synthesized following the general procedure for the preparation of sulfiliminium salts starting from 4-methoxylthioanisole (1 eq., 0.5 mmol, 88 µL) to afford 0.2052 g (quantitative yield) of the desired product as a colourless gelatinous solid.1H NMR (300 MHz, CD2Cl2) δ = 8.82 (s, 2H), 7.88 (d, J=8.9 Hz, 2H), 7.82 – 7.72 (m, 4H), 7.36 – 7.24 (m, 6H), 6.72 (d, J=9.0 Hz, 2H), 3.73 (s, 3H), 3.10 (s, 3H) ppm.13C NMR (75 MHz, CD2Cl2) δ = 163.37, 141.90 (d, J=127.9 Hz), 131.61 (d, J=8.9 Hz), 130.23, 129.49 (d, J=2.5 Hz), 127.96 (d, J=11.5 Hz), 126.12, 115.41, 55.90, 35.45 ppm.31P NMR (122 MHz, CD2Cl2) δ = 15.59 ppm. HRMS (ESI-TOF, m / z): [M]+found 170.0634; calc.170.0634 for C8H12NOS+. (g) S-(2-Aminophenyl)-S-methyl sulfiliminium diphenylphosphinate (2g)

[0213] 2g was synthesized following the general procedure for the preparation of sulfiliminium salts starting from 2-(methylthio)aniline (1 eq., 0.5 mmol, 64 µL) to afford 0.2017 g (quantitative yield) of the desired product as a colourless gelatinous solid.1H NMR (300 MHz, CD2Cl2) δ = 8.38 (s, 2H), 7.87 – 7.68 (m, 3H), 7.57 (dd, J=8.2, 1.5 Hz, 1H), 7.39 – 7.17 (m, 7H), 6.98 (ddd, J=8.4, 7.1, 1.4 Hz, 1H), 6.62 (dd, J=8.3, 1.2 Hz, 1H), 6.40 (ddd, J=8.2, 7.1, 1.2 Hz, 1H), 6.12 (s, 2H), 2.81 (s, 3H) ppm.13C NMR (75 MHz, CD2Cl2) δ = 148.28, 141.27 (d, J=128.7 Hz), 134.47, 131.60 (d, J=9.2 Hz), 129.83 (d, J=2.7 Hz), 128.94, 128.17 (d, J=11.6 Hz), 118.24, 117.82, 115.30, 32.00 ppm.31P NMR (122 MHz, CD2Cl2) δ = 17.16 ppm. HRMS (ESI-TOF, m / z): [M]+found 155.0639; calc.155.0637 for C7H11N2S+. (h) S-(4-Bromophenyl)-S-methyl sulfiliminium diphenylphosphinate (2h)

[0214] 2h was synthesized following the general procedure for the preparation of sulfiliminium salts starting from 4-bromothioanisole(1 eq., 0.5 mmol, 0.1047 g) to afford 0.2101 g (96% yield) of the desired product as a colourless gelatinous solid.1H NMR (300 MHz, CD2Cl2) δ = 9.14 (s, 2H), 8.00 – 7.54 (m, 6H), 7.48 – 7.05 (m, 7H), 3.14 (s, 3H) ppm.13C NMR (75 MHz, CD2Cl2) δ = 141.55 (d, J=128.1 Hz) 133.15, 131.44 (d, J=9.1 Hz), 129.62 (d,J=2.5 Hz), 129.25, 128.02 (d, J=11.5 Hz), 127.61, 35.25 ppm.31P NMR (122 MHz, CD2Cl2) δ = 15.83 ppm. HRMS (ESI-TOF, m / z): [M]+found 217.9633; calc.217.9634 for C7H9BrNS+. (i) S-(4-Fluorophenyl)-S-methyl sulfiliminium diphenylphosphinate (2i)

[0215] 2i was synthesized procedure for the preparation of sulfiliminium salts starting from 4-fluorothioanisole(1 eq., 0.5 mmol, 63 µL) to afford 0.1866 g (quantitative yield) of the desired product as a colourless gelatinous solid.1H NMR (300 MHz, CD2Cl2) δ = 9.06 (s, 2H), 8.06 – 7.84 (m, 2H), 7.83 – 7.55 (m, 4H), 7.53 – 7.16 (m, 6H), 6.92 (t, J=8.6 Hz, 2H), 3.13 (s, 3H) ppm.13C NMR (75 MHz, CD2Cl2) δ = 165.30 (d, J=254.3 Hz), 141.60 (d, J=128.1 Hz), 131.52 (d, J=8.9 Hz), 131.30 (d, J=3.2 Hz), 130.70 (d, J=9.4 Hz), 129.69 (d, J=2.6 Hz), 128.06 (d, J=11.7 Hz), 117.34 (d, J=22.7 Hz), 35.57 ppm.31P NMR (122 MHz, CD2Cl2) δ = 15.94 ppm.19F NMR (282 MHz, CD2Cl2) δ = -105.71 ppm. HRMS (ESI-TOF, m / z): [M]+found 158.0435; calc.158.0434 for C7H9FNS+. (j) S-(4-Nitrophenyl)-S-methyl sulfiliminium diphenylphosphinate (2j)

[0216] 2j was synthesized following the general procedure for the preparation of sulfiliminium salts starting from 4-nitrothioanisole (1 eq., 0.5 mmol, 0.08633 g) to afford 0.1978 g (94% yield) of the desired product as a colourless gelatinous solid.1H NMR (300 MHz, CD2Cl2) δ = 9.25 (s, 2H), 8.15 – 7.80 (m, 4H), 7.74 – 7.48 (m, 4H), 7.33 – 7.11 (m, 6H), 3.27 (s, 3H) ppm.13C NMR (75 MHz, CD2Cl2) δ = 150.06, 141.95 (d, J=39.7 Hz), 139.97, 131.42 (d, J=9.2 Hz), 129.97 (d, J=2.6 Hz), 128.70, 128.16 (d, J=11.7 Hz), 124.85, 35.40 ppm.31P NMR (122 MHz, CD2Cl2) δ = 16.92 ppm. HRMS (ESI-TOF, m / z): [M]+found 185.0379; calc.185.0379 for C7H9N2O2S+.(k) S-(4-Cyanophenyl)-S-methyl sulfiliminium diphenylphosphinate (2k)

[0217] 2k was synthesized follo ngthe ge procedure for the preparation ofsulfiliminium salts starting from 4-(methyl nzonitrile (1 eq., 0.5 mmol, 0.0757 g) to afford 0.1906 g (98% yield) of the desired product as a colourless gelatinous solid.1H NMR (300 MHz, CD2Cl2) δ = 9.17 (s, 2H), 7.94 (d, J=8.6 Hz, 2H), 7.65 (ddd, J=11.2, 8.0, 1.6 Hz, 4H), 7.43 (d, J=8.5 Hz, 2H), 7.34 – 7.18 (m, 6H), 3.22 (s, 3H) ppm.13C NMR (75 MHz, CD2Cl2) δ = 141.13 (d, J=128.5Hz), 140.58, 133.46, 131.36 (d, J=9.0 Hz), 129.86 (d, J=2.6 Hz), 128.17, 128.04 (d, J=3.6 Hz), 117.54, 116.19, 35.22 ppm.31P NMR (122 MHz, CD2Cl2) δ = 16.47 ppm. HRMS (ESI-TOF, m / z): [M]+ found 165.0480; calc.165.0481 for C8H9N2S+. (l) S-(4-Acetylphenyl)-S-methyl sulfiliminium diphenylphosphinate (2l)

[0218] 2l was synthesized following the general procedure for the preparation of sulfiliminium salts starting from 4-(methylthio)thioacetophenone (1 eq., 0.5 mmol, 0.0848 g) to afford 0.1928 g (98% yield) of the desired product as a colourless gelatinous solid.1H NMR (300 MHz, CD2Cl2) δ = 9.29 (s, 2H), 7.98 (d, J=8.5 Hz, 2H), 7.81 – 7.59 (m, 6H), 7.43 – 7.14 (m, 6H), 3.22 (s, 3H), 2.51 (s, 3H) ppm.13C NMR (75 MHz, CD2Cl2) δ = 196.84, 141.54 (d, J=128.2 Hz), 139.97, 139.90, 131.47 (d, J=9.1 Hz), 129.60 (d, J=2.6 Hz), 129.48, 128.00 (d, J=11.5 Hz), 127.69, 35.32, 26.97 ppm.31P NMR (122 MHz, CD2Cl2) δ = 15.88 ppm. HRMS (ESI-TOF, m / z): [M]+ found 182.0636; calc.182.0634 for C9H12NOS+.(m) S,S-Diphenyl sulfiliminium diphenylphosphinate (2m)

[0219] 2m was synthesized following the general procedure for the preparation of sulfiliminium salts starting from diphenyl sulfide (1 eq., 0.5 mmol, 0.0931 g) to afford 0.2285 g (quantitative yield) of the desired product as a white solid.1H NMR (300 MHz, CD2Cl2) δ = 9.60 (s, 2H), 7.80 (dd, J=8.5 Hz, 1.3, 4H), 7.67 (ddd, J=9.6, 7.1, 1.6 Hz, 4H), 7.54 – 7.43 (m, 2H), 7.34 (dd, J=8.5, 7.1 Hz, 4H), 7.29 – 7.18 (m, 6H) ppm.13C NMR (75 MHz, Acetone) δ = 141.15 (d, J=129.7 Hz), 135.35, 132.84, 131.65 (d, J=9.1 Hz), 130.26, 129.70 (d, J=2.5 Hz), 128.58, 128.01 (d, J=11.8 Hz) ppm.31P NMR (122 MHz, CD2Cl2) δ = 16.29 ppm. HRMS (ESI-TOF, m / z): [M]+found 202.0690; calc.202.0685 for C12H12NS+. (n) S-Phenyl-S-(2-hydroxyethyl) sulfiliminium diphenylphosphinate (2n)

[0220] 2n was synthesized following the general procedure for the preparation of sulfiliminium salts starting from 2-(phenylthiol)ethanol (1 eq., 0.5 mmol,70 µL) to afford 0.2019 g (99% yield) of the desired product as a colourless gelatinous solid.1H NMR (300 MHz, CD2Cl2) δ = 8.42 (s, 2H), 7.84 (d, J=7.2 Hz, 2H), 7.75 (ddd, J=11.3, 7.8, 1.7 Hz, 4H), 7.56 – 7.45 (m, 1H), 7.30 (dddd, J=16.2, 11.2, 6.5, 2.0 Hz, 9H), 4.00 (ddd, J=12.3, 8.8, 3.0 Hz, 1H), 3.86 – 3.73 (m, 1H), 3.56 (dt, J=12.8, 4.3 Hz, 1H), 3.29 (ddd, J=12.8, 8.8, 4.1 Hz, 1H) ppm.13C NMR (75 MHz, CD2Cl2) δ = 140.51 (d, J=129.7 Hz), 133.36, 132.99, 131.46 (d, J=9.3 Hz), 130.25, 130.02 (d, J=2.8 Hz), 128.17 (d, J=11.7 Hz), 127.91, 55.50, 54.84 ppm.31P NMR (122 MHz, CD2Cl2) δ = 17.71 ppm. HRMS (ESI-TOF, m / z): [M]+found 170.0633; calc.170.0634 for C8H12NOS+.(o) S-Phenyl-S-cyclopropyl sulfiliminium diphenylphosphinate (2o)

[0221] 2o was synthesized following the general procedure for the preparation of sulfiliminium salts starting from phenyl-cyclopropyl sulfide (1 eq., 0.5 mmol,73 µL) to afford 0.1898 g (99% yield) of the desired product as a colourless gelatinous solid.1H NMR (300 MHz, CD2Cl2) δ = 9.10 (s, 2H), 8.11 – 7.90 (m, 2H), 7.85 – 7.65 (m, 4H), 7.59 – 7.46 (m, 1H), 7.38 (dd, J=8.3, 6.9 Hz, 2H), 7.34 – 7.23 (m, 6H), 3.13 (dtd, J=7.9, 6.3, 4.4 Hz, 1H), 1.49 – 1.25 (m, 1H), 1.09 – 0.79 (m, 3H) ppm.13C NMR (75 MHz, CD2Cl2) δ = 141.16 (d, J=129.2 Hz), 134.87, 132.81, 131.56 (d, J=9.1 Hz), 130.13, 129.71 (d, J=2.8 Hz), 128.07, 127.87 (d, J=7.1 Hz), 29.35, 6.77, 6.66 ppm.31P NMR (122 MHz, CD2Cl2) δ = 16.09 ppm. HRMS (ESI-TOF, m / z): [M]+found 166.0685; calc.166.0685 for C9H12NS+. (p) Tetrahydrothiophene sulfiliminium diphenylphosphinate (2p)

[0222] 2p was synthesized following the general procedure for the preparation of sulfiliminium salts but the reaction was carried out at 0 °C, starting from tetrahydrothiophene (1 eq., 0.5 mmol, 46.8 µL) to afford 0.1326 g (82% yield) of the desired product as a colourless gelatinous solid.1H NMR (300 MHz, CD2Cl2) δ = 8.29 – 8.13 (m, 2H), 7.86 – 7.65 (m, 4H), 7.43 – 7.19 (m, 6H), 3.32 – 2.94 (m, 4H), 2.50 – 2.17 (m, 2H), 1.81 – 1.45 (m, 2H) ppm.13C NMR (75 MHz, CD2Cl2) δ = 141.84 (d, J=128.0 Hz), 131.59 (d, J=9.0 Hz), 129.63 (d, J=2.6 Hz), 128.05 (d, J=11.6 Hz), 50.29, 27.07 ppm.31P NMR (122 MHz, CD2Cl2) δ = 15.64 ppm. HRMS (ESI-TOF, m / z): [M]+found 104.0527; calc.104.0528 for C4H10NS+. (q) 2-(Methylthio)thiophene (2q)

[0223] 2q was synthesized following the general procedure for the preparation of sulfiliminium salts starting from 2-(methylthio)thiophene (1 eq., 0.5 mmol, 54 µL) to afford 0.1418 g (78% yield) of the desired product as a colourless gelatinous solid.1H NMR (300 MHz, CD2Cl2) δ = 8.99 (s, 2H), 7.86 – 7.69 (m, 5H), 7.61 (dd, J=5.1, 1.3 Hz, 1H), 7.39 – 7.21 (m, 6H), 6.97 (dd, J=5.1, 3.8 Hz, 1H), 3.24 (s, 3H) ppm.13C NMR (75 MHz, CD2Cl2) δ = 141.45 (d, J=128.6 Hz), 135.18, 134.36, 134.06, 131.62 (d, J=9.2 Hz), 129.74 (d, J=2.6 Hz), 128.50, 128.07 (d, J=11.6 Hz), 36.51 ppm.31P NMR (122 MHz, CD2Cl2) δ = 15.93 ppm. HRMS (ESI-TOF, m / z): [M]+found 140.0092; calc.140.0093 for C5H8NS2+. (r) 2-(Methylthio)pyridine sulfiliminium diphenylphosphinate (2r)

[0224] 2r was synthesized following the general procedure for the preparation of sulfiliminium salts starting from 2-(methylthio)pyridine (1 eq., 0.5 mmol, 57 µL) to afford 0.1890 g (Quantitative yield) of the desired product as a colourless gelatinous solid.1H NMR (300 MHz, CD2Cl2) δ = 9.41 – 9.07 (m, 2H), 8.47 (ddd, J=4.7, 1.8, 0.9 Hz, 1H), 8.12 (dt, J=8.1, 1.0 Hz, 1H), 7.81 – 7.41 (m, 5H), 7.36 – 6.97 (m, 8H), 3.23 (s, 3H) ppm.13C NMR (75 MHz, CD2Cl2) δ = 155.53, 150.03, 141.38 (d, J=128.6 Hz), 139.11, 131.46 (d, J=9.2 Hz Hz), 129.58 (d, J=2.6), 127.95 (d, J=11.7 Hz), 125.98, 122.93, 33.28 ppm.31P NMR (122 MHz, CD2Cl2) δ = 16.18 ppm. HRMS (ESI-TOF, m / z): [M]+found 141.0479; calc.141.0481 for C6H9N2S+. (s) 2-(Ethylthio)benzothiazole sulfiliminium diphenylphosphinate (2s)

[0225] 2s was synthesized following the general procedure for the preparation of sulfiliminium salts starting from 2-(ethylthio)benzothiazole (1 eq., 0.5 mmol, 81 µL). The crude reaction mixture was dried under pressure and purified using a Sep-pak (10 g) with gradient elution 5 - 50% MeCN / H2O (0.1% TFA) to afford 0.090 (42 % yield) of the desired product as a white powder.1H NMR (300 MHz, MeOD) δ = 8.25 – 8.19 (m, 2H), 7.78 – 7.61 (m, 2H), 4.11 – 3.80 (m, 2H), 1.59 (t, J=7.4 Hz, 3H) ppm.13C NMR (75 MHz, MeOD)δ = 162.43, 153.94, 138.51, 129.20, 125.70, 46.02, 7.97. HRMS (ESI-TOF, m / z): [M]+found 211.0360; calc.211.0358 for C9H11N2S2+. (t) Model tryptathionine sulfiliminium diphenylphosphinate (2t)

[0226] An oven-dried round bottom flask was charged with methyl (S)-2-((tert- butoxycarbonyl)amino)-3-(2-(dodecylthio)-1H-indol-3-yl)propanoate 1t (1 eq., 0.13 mmol, 0.0688 g) in CH2Cl2(20 mL). Next, DPPH (3 eq., 0.39 mmol, 0.0968 g) was added and the reaction mixture was left stirring for 3 hours. The crude reaction was concentrated under reduced pressure to remove all CH2Cl2. The crude solid was immediately purified using silica gel flash column chromatography (gradient elution, 1% MeOH / CH2Cl2 to 8% MeOH / CH2Cl2to afford 0.0822 g (84%) of the sulfiliminium diphenylphosphinate salt, a diastereomeric mixture (1.3:1 based on integral ratio of the peaks at δ 3.60, 3.57 ppm in1H NMR spectrum) as a colourless oil.1H NMR (600 MHz, DMSO), two diasteromers, δ = 7.88 – 7.73 (m, 5H), 7.72 – 7.58 (m, 1H), 7.50 (d, J=8.4 Hz, 1H), 7.43 (dd, J=8.4, 5.9 Hz, 1H), 7.45 – 7.25 (m, 5H), 7.30 (t, J=7.8 Hz, 1H), 7.12 (q, J=7.9 Hz, 1H), 4.37 (td, J=8.2, 6.3 Hz) and 3.73 (ddd, J=12.4, 10.0, 5.7 Hz) [1H], 4.31 – 4.24 (m, 1H), 4.20 (s, 2H), 3.50 – 3.42 (m, 1H), 3.60 (s) and 3.57 (s) [3H], 3.50 – 3.42 (m, 1H), 3.40 – 3.36 (m, 1H), 3.31 – 3.19 (m, 1H), 1.72 – 1.59 (m, 1H), 1.58 – 1.47 (m, 1H), 1.29 (s, 4H), 1.27 – 1.18 (m, 15H), 1.18 – 1.06 (m, 7H), 1.01 (s, 1H), 0.90 – 0.79 (m, 3H) ppm.13C NMR (151 MHz, DMSO), two diastereomers, δ = 171.90, 171.88, 155.23, 155.20, 141.23 (d, J=127.6), 130.94 (d, J=8.9), 129.38 (d, J=2.5), 127.69 (d, J=11.4), 125.89, 125.73, 125.64, 125.51, 123.08, 122.75, 120.72, 120.41, 120.28, 120.21, 120.10, 112.87, 112.77, 78.51, 78.43, 54.41, 54.30, 52.07, 52.00, 48.64, 46.90, 46.54, 31.37, 29.05, 28.90, 28.87, 28.78, 28.41, 28.33, 28.03, 27.95, 27.43, 27.37, 26.24, 25.84, 23.53, 23.49, 22.17, 13.99 ppm.31P NMR (122 MHz, DMSO) δ = 16.48 ppm. HRMS (ESI-TOF, m / z): [M]+found 534.3362; calc.534.3360 for C29H48N3O4S+. HPLC Re-injection (gradient G) tR = 2.39 min, 2.46 min. UV λmax: 289 nm. NMR data for HPLC purified sulfiliminium salt (Major Diastereomer).1HNMR (400 MHz, CD2Cl2) δ = 7.54 (t, J=9.5 Hz, 2H), 7.44 – 7.27 (m, 1H), 7.18 (ddd, J=8.1, 6.9, 1.0 Hz, 1H), 6.50 (s, 2H), 5.49 (s, 1H), 4.73 (s, 1H), 4.24 (s, 1H), 4.06 (s, 1H), 3.63 (s, 3H), 3.56 – 3.30 (m, 2H), 1.75 – 1.59 (m, 2H), 1.49 – 1.44 (m, 2H), 1.41 (s, 9H), 1.32 – 1.21 (m, 16H), 0.88 (t, J=6.8 Hz, 3H) ppm.13C NMR (101 MHz, CD2Cl2) δ = 171.49, 155.05, 139.73, 127.41, 126.25, 122.17, 121.54, 120.54, 113.71, 81.46, 53.02, 49.59, 32.30, 30.09, 29.96, 29.82, 29.72, 29.61, 29.28, 28.38, 27.32, 24.38, 23.08, 14.27, 1.16 ppm. (u) Biotin sulfiliminium diphenylphosphinate (2u)

[0227] 2u was synthesized following the general procedure for the preparation of sulfiliminium salts starting from Biotin (1 eq.,1.5 mmol, 0.3720 g) to afford 0.6828 g (94% yield) of the desired product as a yellow amorphous solid. It was not possible to comment on the diastereomeric ratio given that1H NMR spectral peaks were identical.1H NMR (300 MHz, DMSO) two diastereomers, δ = 7.86 – 7.58 (m, 4H), 7.46 – 7.11 (m, 6H), 7.24 (s, 1H), 7.07 (s, 1H), 4.53 – 4.40 (m, 1H), 4.39 – 4.26 (m, 1H), 4.03 (td, J=7.5, 4.3 Hz, 1H), 3.85 (dd, J=12.7, 6.5 Hz, 1H), 3.75 – 3.55 (m, 1H), 2.33 – 2.06 (m, 2H), 1.74 (q, J=8.1 Hz, 2H), 1.49 (p, J=7.2 Hz, 2H), 1.43 – 1.17 (m, 2H) ppm.13C NMR (75 MHz, DMSO) two diastereomers, δ = 174.63, 161.39, 142.12 (d, J=126.7), 131.00 (d, J=8.8), 129.00 (d, J=2.6), 127.52 (d, J=11.2), 65.73, 55.72, 53.08, 52.50, 33.98, 25.90, 24.36 ppm.31P NMR (122 MHz, DMSO) δ = 13.04 ppm. HRMS (ESI-TOF, m / z): [M]+found 260.1060; calc.260.1063 for C10H18N3O3S+. (v) Fmoc-Met-OH sulfiliminium diphenylphosphinate (2v[i])

[0228] 2v[i] was synthesized following the general procedure for the preparation of sulfiliminium salts starting from Fmoc-Met-OH (1 eq.,1.5 mmol, 0.1857 g) to afford 0.8063 g (89% yield) of the desired product as a white solid. The product was isolated as a diastereomeric mixture (d.r. 4:1 based on the integral ratio of signals in the13C NMRspectrum). The diastereomeric mixture was recrystallized in 14% H2O / MeOH to afford the stereochemically pure (R)-sulfiliminium salt, 0.0597 g (31% yield).1H NMR (300 MHz, DMSO) two diastereomer, δ = 7.96 (d, J=7.9 Hz, 1H), 7.89 (d, J=7.5 Hz, 2H), 7.81 – 7.59 (m, 6H), 7.41 (t, J=7.4 Hz, 2H), 7.37 – 7.19 (m, 8H), 6.67 (s, 2H), 4.38 – 4.05 (m, 4H), 3.53 – 3.20 (m, 2H), 2.94 (s, 3H), 2.30 – 2.00 (m, 2H) ppm.13C NMR two diastereomers, (75 MHz, DMSO) δ = 172.76, 156.28, 142.28 (d, J=232.7), 140.19, 138.46, 131.04 (d, J=9.4), 129.85 (d, J=2.7), 127.79 (d, J=12.1), 127.14, 125.36, 120.14, 65.83, 53.10, 52.64, 48.63, 46.66, 45.07, 32.14, 31.74, 24.71 ppm.31P NMR (122 MHz, DMSO) δ = 16.50 ppm. HRMS (ESI-TOF, m / z): [M]+found 387.1374; calc.387.1373 for C20H23N2O4S+. (w) Fmoc-Buthionine-OH sulfiliminium trifluoroacetate (2v[ii])

[0229] 2v[ii] was synthesized following the general procedure for the preparation of sulfiliminium salts starting from Fmoc-buthionine-OH, 1v[ii] (1 eq., 0.1 mmol, 0.0414 g). The crude reaction mixture was dried under pressure and purified using a Sep-pak (10 g) with gradient elution 10 - 70% MeCN / H2O (0.1% TFA) to afford 0.06824 g (quantitative conversion by HPLC, 84 % yield) of the desired product as a white powder. The product was isolated as a diastereomeric mixture (d.r.1:1 based on the integral ratio of signals in the13C NMR spectrum).1H NMR (600 MHz, DMSO) two diastereomers, δ = 7.88 (d, J=7.6 Hz, 2H), 7.85 (dd, J=8.4, 4.2 Hz, 1H), 7.41 (t, J=7.5 Hz, 2H), 7.33 (td, J=7.4, 1.2 Hz, 2H), 6.11 (s, 2H), 4.36 (ddd, J=10.6, 7.1, 2.1 Hz, 1H), 4.30 (ddd, J=10.2, 6.9, 2.5 Hz, 1H), 4.23 (t, J=7.0 Hz, 1H), 4.18 – 4.12 (m, 1H), 3.36 – 3.15 (m, 4H), 2.34 – 2.19 (m, 1H), 2.16 – 1.98 (m, 1H), 1.77 – 1.58 (m, 2H), 1.48 – 1.30 (m, 2H), 0.89 (t, J=7.4 Hz, 3H) ppm.13C NMR (151 MHz, DMSO) two diastereomers, δ = 172.72, 172.70, 156.41, 156.36, 143.90, 143.89, 140.90, 127.28, 125.40, 125.38, 120.31, 120.29, 65.96, 52.83, 52.40, 46.76, 46.00, 45.76, 43.71, 43.56, 24.86, 24.56, 24.49, 20.84, 20.83, 13.45 Hz. HRMS (ESI-TOF, m / z): [M]+found 429.1846; calc.429.1843 for C23H29N2O4S+.(x) Fulvestrant sulfiliminium diphenylphosphinate (2w′)

[0230] To a 15 ml-falcon tube equipped with a magnetic stir bar was added S-deoxy- Fulvestrant 1w (1 eq., 0.017 mmol, 0.010 g) followed by CH2Cl2(0.14 mL). Next, DPPH (1.1 eq., 0.019 mmol, 0.005 g) was added and the reaction mixture was left stirring at room temperature for 12 hrs. The crude reaction mixture was diluted with CH2Cl2 (2 mL). The sulfiliminium salt was extracted with water (3 ^ 2 mL). All aqueous extracts were pooled together and lyophilized after freezing to afford 0.0122 g (87% yield) of the product 2w′, as a white powder. The product was isolated as a diastereomeric mixture (d.r.1:1 based on the integral ratio of signals in the13C NMR spectrum).1H NMR (600 MHz, DMSO) two diastereomers, δ = 7.73 – 7.54 (m, 4H), 7.34 – 7.11 (m, 6H), 7.03 (d, J=8.5 Hz, 1H), 6.66 (s, 2H), 6.52 (dt, J=8.4, 2.6 Hz, 1H), 6.45 (dd, J=5.4, 2.6 Hz, 1H), 5.75 (s, 1H), 4.52 – 4.51 (m, 1H), 4.13-4.11 (m, 1H), 3.52 (qd, J=8.8, 5.3 Hz, 2H), 3.42 – 3.33 (m, 1H), 3.27-3.22 (m, 1H), 3.15 – 3.10 (m, 1H), 2.75-2.73 (d, J=14.6 Hz, 1H), 2.64 – 2.52 (m, 1H), 2.41 – 2.28 (m, 2H), 2.27 – 2.20 (m, 1H), 2.21 – 2.10 (m, 1H), 2.05 – 1.95 (m, 1H), 1.95 – 1.83 (m, 2H), 1.79 (dt, J=12.4, 3.2 Hz, 1H), 1.69 – 1.56 (m, 3H), 1.54 – 1.43 (m, 2H), 1.36 (dtt, J=11.6, 8.6, 4.5 Hz, 2H), 1.33 – 1.04 (m, 16H), 0.96 – 0.85 (m, 1H), 0.66 (s, 3H) ppm.13C NMR (151 MHz, DMSO) two diastereomers, δ = 155.46, 135.87, 131.05 (d, J=8.9 Hz), 129.23, 127.54 (d, J=11.4 Hz), 126.58, 115.90, 113.01, 80.16, 54.97, 46.07, 45.76, 44.63, 43.01, 41.82, 37.90, 36.84, 34.22, 32.88, 32.85, 29.91, 29.25, 29.21, 28.88, 28.80, 28.62, 28.57, 28.41, 27.91, 27.40 (t, J=4.2 Hz), 27.11, 25.00, 22.45, 22.33, 14.51, 11.36 ppm.31P NMR (122 MHz, DMSO) δ = 11.42 ppm.19F NMR (282 MHz, DMSO) δ = -84.56, -117.19 ppm. HRMS (ESI- TOF, m / z): [M]+ found 606.3399; calc.606.3399 for C32H49F5NO2S+. (y) Fulvestrant sulfiliminium trifluoroacetate (2w)

[0231] To a 15 ml-falcon tube equipped with a magnetic stir bar was added S-deoxy- Fulvestrant 1w (1 eq., 0.034 mmol, 0.020 g) by CH2Cl2 (0.28 mL). Next, DPPH (1.1eq., 0.038 mmol, 0.009 g) was added and the reaction mixture was left stirring at room temperature for 12 hrs. The crude reaction mixture was dried under reduced pressure and diluted in the HPLC buffer and methanol and directly purified on HPLC-2 using gradient O to afford the desired sulfiliminium trifluoroacetate salt (quantitative conversion, HPLC). It was not possible to comment on the diastereomeric ratio given that1H NMR and13C NMR spectral peaks were identical. HPLC crude-reaction after 12 h (gradient O), tR = 4.1 min [Product] (280 nm). HPLC Re-injection (gradient O) tR = 4.4 min (280 nm). (z) Cholecystokinin-4 sulfiliminium trifluoroacetate (2x[i])

[0232] To a 15 mL-falcon tube equipped with a stir bar was added cholecystokinin-4, 1x[i] (1 eq., 4.5 µmol, 0.0027 g). Next, DPPH (2 eq., 9 µmol, 2.2 mg, 90 µL of a solution of 0.0225 g DPPH in 900 µL MeOH) was added. The reaction was left stirring at room temperature for 3 h. The crude reaction mixture was diluted in the HPLC buffer and directly purified on HPLC- 2 using gradient A to afford the desired sulfiliminium trifluoroacetate salt (78% conversion, HPLC) as a diastereomeric mixture (d.r.1.5:1, based on integral ratio of the peaks at δ 2.93, 2.95 ppm in1H NMR spectrum). HPLC crude-reaction after 3h (gradient K), tR = 16.6 min [Product, 78%], 20.5 min [Starting material, 22%] (280 nm). HPLC Re-injection (gradient K) tR = 16.9 min (280). HRMS (ESI-TOF, m / z): [M]+found 612.2603; calc. 612.2599 for C29H38N7O6S+.19F NMR (282 MHz, DMSO, ref. CFCl3 = 0 ppm) δ = -73.73 ppm. Table 5.1H-NMR assignments for compound 2x[i] (600 MHz, DMSO-d6). Residue Proton Shift (ppm) Coupling constant (J, Hz) Carbon Shift (ppm) Trp-1 NH2n / d – – – HCα 4.07 ddd, J = 5.35, 8.45, 17.82 Cα 52.35 HCβ 3.05 m (overlapping peaks) Cβ 27.21 HCβ 3.21 m (overlapping peaks) C-3 106.79 H-2 7.19 m (overlapping peaks) C-2 125.25 H-4 7.66 t, J = 8.35 C-4 118.10 H-5 7.02 t, J = 7.99 C-5 118.10 H-6 7.09 t, J = 7.52 C-6 120.91H-7 7.37 d, J = 8.12 C-7 111.40 HN-Indole 11.00 s C-7a 136.53 – – – C-3a 127.10 – – – Carbonyl (amide) 168.94 Met-2 NH 9.03 d, J = 8.13 – – HCα 4.53 m (overlapping peaks) Cα 50.42 HCβ 1.94 m (overlapping peaks) Cβ 25.98 HCβ 2.08 m (overlapping peaks) – – HCγ 3.21 m (overlapping peaks) Cγ 44.27 H(CH3) 2.93, 2.95 (2 diastereomers) s C(CH3) 31.78 NH2 6.00, 5.99 (sulfiliminium) (2 diastereomers) s Carbonyl (amide) n / d Asp-3 NH 8.53, 8.56 (2 diastereomers) d, J = 7.46 – – HCα 4.53 m (overlapping peaks) Cα 49.89 HCβ 2.52 n / d (overlapping with solvent peak) Cβ 35.83 HCβ 2.69 ddd, J = 16.4, 10.7, 5.2 Carbonyl (amide) 169.55 Tyr-4 NH 7.96 d, J = 8.12 – – HCα 4.42 m (overlapping peaks) Cα 53.76 HCβ 2.83 ddd, J = 2.35, 8.88, 13.93 Cβ 37.23 HCβ 3.03 m (overlapping peaks) – – 7.26 (2H 129.35, H(C6H5) ), m 7.19-7.23 (3H) m (overlapping peaks) C(C6H5) 137.97 (3 peaks n / d) 7.20, NH27.44, 7.48 m (overlapping peaks) Carbonyl d, J = 2.15 (amide) 172.83 (2 diastereomers) (aa) N-Boc cholecystokinin-4 sulfiliminium trifluoroacetate (2x[ii])

[0233] To a 15 mL-falcon tube equipped with a stir bar was added N-Boc cholecystokinin-4, (1 eq., 10 µmol, 0.0070 g) dissolved in DMF (1.25 mL). Next, DPPH (3 eq., 30 µmol, 0.0074 g) was added followed by CH2Cl2 (1.25 mL). The reaction was left stirring at room temperature for 3 h. The crude reaction mixture was diluted in the HPLC buffer and directly purified on HPLC-2 using gradient C to afford the desired sulfiliminiumtrifluoroacetate salt (quantitative conversion, HPLC) as a diastereomeric mixture (d.r.1.4:1, based on integral ratio of the peaks at tR: 4.9 and 4.6 min in the HPLC Chromatogram). HPLC crude-reaction after 3h (gradient C), tR =4.6 min [Diastereomer 1], 4.9 min [Diastereomer 2], No starting material (290 nm). HPLC Re-injection (gradient K) tR = 20.5 min (290 nm). HPLC Re-injection (gradient K) tR= 21.0 min (290 nm). HRMS (ESI-TOF, m / z for diastereomer 1): [M]+found 712.3120; calc.712.3123 for C34H46N7O8S+. HRMS (ESI-TOF, m / z for diastereomer 2): [M]+found 712.3120; calc.712.3123 for C34H46N7O8S+. (bb) N-Acetyl cholecystokinin-4 sulfiliminium trifluoroacetate (2x[iii])

[0234] To a 15 mL-falcon tube equipped with a stir bar was added N-acetyl cholecystokinin-41x[iii] (1 eq., 4 µmol, 0.0025 g) dissolved in DMF (0.5 mL). Next DPPH (3 eq., 12 µmol, 0.0030 g) was added followed by CH2Cl2 (0.5 mL). The reaction was left stirring at room temperature for 3 h. The crude reaction mixture was diluted in the HPLC buffer and directly purified on HPLC-2 using gradient M to afford the desired sulfiliminium trifluoroacetate salt (quantitative conversion, HPLC) as a diastereomeric mixture (d.r.1.2:1, based on integral ratio of the peaks at δ 1.78, 1.77 ppm in1H NMR spectrum). HPLC crude- reaction after 3 h (gradient M), tR=2.8 min, No starting material (280 nm).1H NMR (600 MHz, DMSO) two diastereomers, δ = 10.81, 10.80 (d, J=2.4 Hz, 1H), 8.44, 8.41 (d, J=8.3 Hz, 1H), 8.30, 8.27 (d, J=7.6 Hz, 1H), 8.12, 8.10 (d, J=7.2 Hz, 1H), 7.94, 7.89 (d, J=8.1 Hz, 1H), 7.61, 7.60 (d, J=3.5 Hz, 1H), 7.42, 7.39 (d, J=2.1 Hz, 1H), 7.33 (d, J=8.1 Hz, 1H), 7.26 (t, J=7.6 Hz, 2H), 7.24 – 7.18 (m, 4H), 7.16, 7.15 (d, J=2.4 Hz, 1H), 7.05 (t, J=7.6 Hz, 1H), 6.97 (t, J=7.4 Hz, 1H), 5.92, 5.89 (s, 1H), 4.59 – 4.50 (m, 1H), 4.50 – 4.45 (m, 1H), 4.45 – 4.42 (m, 1H), 4.41 – 4.35 (m, 1H), 3.24 – 3.13 (m, 2H), 3.14 – 3.05 (m, 1H), 3.05 – 2.99 (m, 1H), 2.94, 2.91 (s, 3H), 2.86 – 2.78 (m, 1H), 2.71 – 2.63 (m, 1H), 2.56 – 2.51 (m, 1H), 2.21 – 2.03 (m, 1H), 2.01 – 1.85 (m, 1H), 1.78, 1.77 (s, 3H) ppm. HRMS (ESI-TOF, m / z): [M]+ found 654.2708; calc.654.2704 for C31H40N7O7S+.(cc) N-Acetyl cholecystokinin-4 sulfiliminium trifluoroacetate (2x[iii])-Reaction in water

[0235] To a15 mL-falcon tube equipped with a stir bar was added N-acetyl cholecystokinin-41x[iii] (1 eq., 0.5 µmol, UV quantified). Next,DPPH (3eq., 1.5 µmol, 0.0004 g, 125 µL of a suspension of 8 mg of DPPH in 2.5 mL of water) was added. The reaction was left stirring at roomtemperature for 16 h.The crude reaction mixture was diluted in the HPLC buffer and directly purified on HPLC-2 using gradient M to afford the desired sulfiliminium trifluoroacetate salt (99% conversion, HPLC). HPLC crude-reaction after 16 h (gradient M), tR =2.6 min [Product, 99%], 3.9 min [Starting material, 1%] (280 nm). LRMS (ESI-TOF, m / z): [M]+found 654.2; calc.654.3 for C31H40N7O7S+. (dd) Bombesin sulfiliminium trifluoroacetate (2y)

[0236] To a m faltu eq p wi a s ba was adde NB b e 1y, (1eq., 10 62 g) dissolved in DMF (1.25 mL). Next, DPPH (3 e 30 µ 0.0074 g)was added followed by CH2Cl2 (1.25 mL). The reaction was left stirring at temperature for 3 h. The crude reaction mixture was diluted in the HPLC buffer and directly purified on HPLC-2 using gradient D to afford the desired sulfiliminium trifluoroacetate salt (quantitative conversion, HPLC) as a diastereomeric mixture (d.r.1:1, based on integral ratio of the peaks at δ 2.97, 2.96 ppm in1H NMR spectrum). HPLC crude-reaction after 3h (gradient D), tR =4.0 min, No starting material (290 nm). HRMS (ESI-TOF, m / z for diastereomer 1): [M]+found 817.9201; calc.817.9203 for C71H113N25O18S+2.1H NMR (600 MHz, DMSO) δ = 14.47 (s, 1H), 10.81 (s, 1H), 8.96 (s, 1H), 8.42 – 8.08 (m, 9H), 7.99 (d, J=7.6 Hz, 1H), 7.89 (d, J=7.1 Hz, 1H), 7.83 (s, 1H), 7.74 (d, J=5.7 Hz, 1H), 7.67 – 7.60 (m, 1H), 7.59 – 7.53 (m, 2H), 7.46 (d, J=3.7 Hz, 1H), 7.40 – 7.31 (m, 2H), 7.31 (s, , 7.22 – 7.14 (m, 2H), 7.08 (s, 1H), 7.04 (t,J=7.5 Hz, 1H), 6.96 (t, J=7.4 Hz, 1H), 6.81 (s, 2H), 6.03 (d, J=8.1 Hz, 2H), 4.76 – 4.54 (m, 3H), 4.58 – 4.16 (m, 11H), 4.15 – 3.97 (m, 4H), 3.82 – 3.62 (m, 4H), 3.23 (dq, J=11.6, 6.0 Hz, 2H), 3.20 – 3.11 (m, 2H), 3.08 (q, J=6.8 Hz, 2H), 2.97 (s, 3H), 2.59 (dd, J=15.7, 6.9 Hz, 1H), 2.47 (d, J=7.2 Hz, 1H), 2.23 (ddd, J=10.9, 7.5, 3.9 Hz, 1H), 2.13 (qdd, J=14.5, 12.0, 6.7 Hz, 4H), 2.04 (q, J=6.0 Hz, 3H), 1.96 (dq, J=11.1, 5.9 Hz, 1H), 1.88 (ddt, J=13.0, 9.6, 4.6 Hz, 2H), 1.84 – 1.74 (m, 2H), 1.68 (p, J=5.9 Hz, 2H), 1.60 (q, J=6.7 Hz, 2H), 1.56 – 1.51 (m, 2H), 1.50 – 1.44 (m, 5H), 1.22 (d, J=7.0 Hz, 3H), 1.06 – 0.68 (m, 20H) ppm. (ee) 5′-OH(Trp) Ama sulfiliminium trifluoroacetate (2z)

[0237] To a 15 mL-falcon tube containing S-deoxy-5′-OH(Trp) Ama, 1z (1 eq., 1 µmol, UV quantified) was added anhydrous DCM (200 µL) followed by anhydrous DMF (250 µL). This solution was treated with DPPH (3 eq., 3 µmol, 0.74 mg; 50 µL of a solution of 73.8 mg of DPPH dissolved in 5 mL of anhydrous DCM). The reaction contents were stirred for 3 hours at 21oC. The solvent was removed under reduced pressure and the crude mixture was diluted in HPLC buffer and directly purified on HPLC-1 using gradient E to afford the sulfiliminium diastereomers with 98% conversion (HPLC) and 75% isolated yield (d.r.96:2, based on integral ratio of the peaks at tR: 12.6 and 12.9 min in the HPLC Chromatogram). HPLC crude-reaction after 3h (gradient E), tR =12.6 min [Diastereomer 1], 13.0 min [Diastereomer 2] (290 nm). HPLC Re- injection (gradient E) tR = 12.8 min (290). HPLC Re-injection (gradient E) tR = 13.1 min (290). UV λmax: 288 nm (Diastereomer 1,2). HRMS (ESI-TOF, m / z for diastereomer 2): [M-H+Na]+found 940.3597; calc.940.3594 for C39H55N11O13SNa+. Table 6.1H-NMR assignments for compound 2zb (600 MHz, DMSO-d6). Residue Proton C (Soupling Constant (J, Shift phpimft)Hz)Carbon(ppm) Asn-1 NH 8.55 d, J = 3.2C(aamrbiodney)l166.21HCα 4.76 m (overlapping peaks) Cα 50.24 HCβ 2.65 dd, J = 16.6, 9.6 Cβ 33.54 HCβ 2.78 m – – H2N 7.21 s Carbonyl 7.50 s(1oamide)170.48Hyp-2 – – –C(aamrbiodney)l171.83 HCα 4.17 dd, J = 11.2, 6.8 Cα 61.85 H′Cβ 1.92 td, J = 12.4, 4.0 Cβ 37.23 H″Cβ 2.15 m (overlapping peaks) – – HCγ 4.46 m (overlapping peaks) Cγ 68.35 H′Cδ 3.61 m (overlapping peaks) Cδ 55.34 H″Cδ 3.83 dd, J = 10.9, 3.8 – – OH 5.37 s – – DHIle-3 NH 8.19 d, J = 6.2C(aamrbiodney)l169.58 HCα 4.29 dd, J = 6.2, 2.9 Cα 55.17 HCβ 2.15 m (overlapping peaks) Cβ 36.53 HCγ 3.65 m (overlapping peaks) Cγ 72.22 H′Cδ 3.39 masked by water peak Cδ 63.43 H″Cδ 3.46 m (overlapping peaks) – – CH30.92 d, J = 7.0 CH313.50 HOγ n / d – – – HOδ n / d – – – Trp-4 NH 7.92 d, J = 9.5C(aamrbiodney)l169.36 HCα 4.49 m (overlapping peaks) Cα 53.41 H′Cβ 2.81 m (overlapping peaks Cβ 27.04 H″Cβ 3.77 m C-3 117.24 H-4 6.96 d, J = 2.2 C-4 102.10 HO-5 9.26 s C-5 152.29 H-6 6.94 dd, J = 8.7, 2.3 C-6 117.05 H-7 7.49 d, J = 8.9 C-7 113.53 HN-Indole 11.20 s C-7a 132.97 – – – C-3a 126.45 – – – C-2 119.49 Gly-5 NH 7.77 d, J = 8.3C(aamrbiodney)l169.36 H′Cα 3.45 m (overlapping peaks) Cα 40.93 H″Cα 4.23 m – – Ile-6 NH 8.52 d, J = 3.9C(aamrbiodney)l175.42 HCα 3.89 dd, J = 8.0, 3.9 Cα 58.86 HCβ 1.61 m (overlapping peaks) Cβ 34.60 H′γ 1.19 m Cγ 24.93 H″γ 1.60 m (overlapping peaks) – – CH3β 0.85 d, J = 6.7 CH3β 14.73CH3γ 0.87 t, J = 7.3 CH3γ 10.51 Gly-7 NH 9.60 t, J = 6.1C(aamrbiodney)l169.13 H′Cα 3.66 m (overlapping peaks) Cα 42.68 H″Cα 3.96 dd, J = 17.2, 6.4 – – Cys-8 NH 7.87 d, J = 6.1C(aamrbiodney)l166.89 HCα 5.06 m Cα 49.36 H′Cβ 4.38 d, J = 14.6 Cβ 53.76 H″Cβ 4.46 m (overlapping peaks) – – (SulfiNlimHi2nium)5.90 s – –General Procedure for one-pot DPPH mediated thioether imination followed by oxidation to access sulfoximines 3a-3r

[0238] An oven-dried flask equipped with a magnetic stir bar, was charged with DPPH (1.1 eq., 0.1350 g, 0.55 mmol) followed by MeOH (2 mL). Next, the corresponding sulfide (1a-1r, 1 eq.0.5 mmol) was added and the reaction mixture was left stirring at room temperature for 0.25-5 hrs depending on the substrate. Next, the reaction mixture was cooled to 0 °C in an ice- water bath and mCPBA (5 eq., 2.5 mmol, 0.56 g) dissolved in MeOH (18 mL) pre-cooled to 0 °C was added. This was allowed to stir for 5 min in the ice-water bath followed by the addition of Na2CO3 (20 eq., 10 mmol, 1.06 g). The resulting suspension was stirred at 0-4 °C for 16 h. The crude reaction mixture was filtered, and the filtrate was concentrated under reduced pressure. The crude solid was immediately purified using silica gel flash column chromatography (gradient elution, 20-100% EtOAc / Hexane) to afford the sulfoximine product. General Procedure for oxidation of sulfiliminium salts to access sulfoximines 3t-3z

[0239] An oven-dried flask equipped with a magnetic stir bar, was charged with the corresponding sulfiliminium salt 2t-2z (1 eq.) in MeOH and was cooled to 0 °C in an ice- water bath. Then, mCPBA (5 eq.) in MeOH solution pre-cooled to 0 °C was added. This was allowed to stir for 5 min in the ice-water bath followed by the addition of NH4OH (100 eq.). The resulting suspension (C[sulfiliminium salt]= 0.025 M / 0.0125 M) was stirred at 0-4 °C for 16 h. The crude reaction mixture was concentrated under reduced pressure. The crude solid was immediately purified to afford the sulfoximine product.(a) S-Methyl-S-phenyl sulfoximine (3a)

[0240] 3a was synthesized procedure for the preparation of sulfoximines starting from thioanisole (1 eq., 0.5 mmol, 61 µL) to afford 0.0629 g (81% yield) of the desired product as a colourless oil.1H NMR (300 MHz, CD2Cl2) δ = 8.06 – 7.90 (m, 2H), 7.72 – 7.43 (m, 3H), 3.49 (s, 1H), 3.09 (s, 3H) ppm.13C NMR (75 MHz, CD2Cl2) δ = 143.68, 133.36, 129.55, 128.01, 46.39 ppm. HRMS (ESI-TOF, m / z): [M+H]+found 156.0481; calc.156.0478 for C7H10NOS+. (b) S,S-Dibenzyl sulfoximine (3b)

[0241] 3b was synthesized following the general procedure for the preparation of sulfoximines starting from dibenzylsulfide (1 eq., 0.5 mmol, 0.1094 g) to afford 0.0911 g (74% yield) of the desired product as a white solid.1H NMR (300 MHz, DMSO) δ = 7.50 – 7.28 (m, 10H), 4.68 – 4.11 (m, 4H), 3.46 (s, 1H) ppm.13C NMR (75 MHz, DMSO) δ = 131.20, 129.46, 128.25, 128.07, 59.62 ppm. HRMS (ESI-TOF, m / z): [M+H]+found 246.0951; calc.246.0947 for C14H16NOS+. (c) S-(2-Methylphenyl)-S-methyl sulfoximine (3c)

[0242] 3c was synthesized following the general procedure for the preparation of sulfoximines starting from 2-methylthioanisole (1 eq., 0.5 mmol, 0.0723 g) to afford 0.0423 g (50% yield) of the desired product as a colourless oil.1H NMR (300 MHz, CD2Cl2) δ = 8.06 (dd, J=7.9, 1.5 Hz, 1H), 7.48 (td, J=7.5, 1.5 Hz, 1H), 7.35 (t, J=7.9 Hz, 2H), 3.08 (s, 3H), 2.73 (s, 3H), 2.66 (s, 1H) ppm.13C NMR (75 MHz, CD2Cl2) δ = 142.29,137.94, 133.17, 133.13, 129.53, 126.84, 44.91, 20.81 ppm. HRMS (ESI-TOF, m / z): [M+H]+found 170.0635; calc.170.0634 for C8H12NOS+. (d) S-(3-Methylphenyl)-S-methyl sulfoximine (3d)

[0243] 3d was synthesized procedure for the preparation of sulfoximines starting from 3-methylthioanisole (1 eq., 0.5 mmol, 69.4 µL) to afford 0.0679 g (80% yield) of the desired product as a yellow oil.1H NMR (300 MHz, CD2Cl2) δ = 7.88 – 7.69 (m, 2H), 7.54 – 7.35 (m, 2H), 3.04 (s, 3H), 2.70 (s, 1H), 2.44 (s, 3H) ppm.13C NMR (75 MHz, CD2Cl2) δ = 143.94, 139.91, 133.95, 129.32, 128.35, 125.02, 46.56, 21.42. HRMS (ESI-TOF, m / z): [M+H]+found 170.0637; calc.170.0634 for C8H12NOS+. (e) S-(4-Methylphenyl)-S-methyl sulfoximine (3e)

[0244] 3e was synthesized following the general procedure for the preparation of sulfoximines starting from 4-methylthioanisole (1 eq., 0.5 mmol, 68.7 µL) to afford 0.0616 g (73% yield) of the desired product as a colourless oil.1H NMR (300 MHz, CD2Cl2) δ = 7.86 (d, J=8.3 Hz, 1H), 7.37 – 7.30 (m, 2H), 3.03 (s, 3H), 2.45 (s, 1H), 2.43 (s, 3H) ppm.13C NMR (75 MHz, CD2Cl2) δ = 144.23, 141.23, 130.11, 128.01, 46.71, 21.59 ppm. HRMS (ESI-TOF, m / z): [M+H]+found 170.0634; calc.170.064 for C8H12NOS+. (f) S-(4-Methoxylphenyl)-S-methyl sulfoximine (3f)

[0245] 3f was synthesized following the general procedure for the preparation of sulfoximines starting from 4-methoxylthioanisole (1 eq., 0.5 mmol, 69.5 µL) to afford 0.0616 g (92% yield) of the desired product as a colourless oil.1H NMR (300 MHz, CD2Cl2) δ = 7.90 (d, J=8.9 Hz, 1H), 7.01 (d, J=8.9 Hz, 1H), 3.87 (s, 3H), 3.03 (s, 3H), 2.56 (s, 1H) ppm.13C NMR (75 MHz, CD2Cl2) δ = 163.63, 135.70, 130.16, 114.60, 56.07, 46.96 ppm. HRMS (ESI-TOF, m / z): [M+H]+found 186.0580; calc.186.0583 for C8H12NO2S+. (g) S-(3-Aminophenyl)-S-methyl sulfoximine (3g)

[0246] 3g was synthesized procedure for the preparation of sulfoximines starting from 3-(methylthio)aniline (1 eq., 0.5 mmol, 63.5 µL) to afford 0.0415 g (49% yield) of the desired product as a colourless oil.1H NMR (300 MHz, CD2Cl2) δ = 7.45 – 7.21 (m, 3H), 6.98 – 6.80 (m, 1H), 3.02 (s, 3H), 1.26 (s, 1H) ppm.13C NMR (75 MHz, CD2Cl2) δ = 148.14, 145.00, 130.37, 119.13, 117.04, 113.50, 46.45 ppm. HRMS (ESI-TOF, m / z): [M+H]+found 171.0585; calc.171.0587 for C7H11N2OS+. (h) S-(4-Bromophenyl)-S-methyl sulfoximine (3h)

[0247] 3h was synthesized following the general procedure for the preparation of sulfoximines starting from 4-bromothioanisole (1 eq., 0.5 mmol,0.1015 g) to afford 0.0833 g (71% yield) of the desired product as a colourless oil.1H NMR (300 MHz, CD2Cl2) δ = 8.00 – 7.79 (m, 2H), 7.79 – 7.59 (m, 2H), 3.05 (s, 3H), 2.62 (s, 1H) ppm.13C NMR (75 MHz, CD2Cl2) δ = 143.38, 132.77, 129.78, 128.24, 46.59 ppm. HRMS (ESI-TOF, m / z): [M+H]+found 233.9582; calc.233.9583 for C7H9BrNOS+. (i) S-(4-Fluorophenyl)-S-methyl sulfoximine (3i)

[0248] 3i was synthesized following the general procedure for the preparation of sulfoximines starting from 4-bromothioanisole (1 eq., 0.5 mmol, 62.8 µL) to afford 0.0688 g (77% yield) of the desired product as a white solid.1H NMR (300 MHz, CD2Cl2) δ = 8.16 – 7.86 (m, 2H), 7.38 – 7.07 (m, 2H), 3.06 (s, 3H), 2.50 (s, 1H) ppm.13C NMR (75 MHz, CD2Cl2) δ =165.80 (d, J=253.7 Hz), 140.24 (d, J=3.2 Hz), 130.92 (d, J=9.5 Hz), 116.60 (d, J=22.5 Hz), 46.77 ppm. HRMS (ESI-TOF, m / z): [M+H]+found 174.0381; calc.174.0383 for C7H9BrNOS+. (j) S-(4-Nitrophenyl)-S-methyl sulfoximine (3j)

[0249] 3j was synthesized procedure for the preparation of sulfoximines starting from 4-nitrothioanisole (1 eq., 0.5 mmol,0.0863 g) to afford 0.0719 g (76% yield) of the desired product as a yellow oil.1H NMR (300 MHz, CD2Cl2) δ = 8.52 – 8.33 (m, 2H), 8.31 – 8.09 (m, 2H), 3.14 (s, 3H), 2.83 (s, 1H) ppm.13C NMR (75 MHz, CD2Cl2) δ = 150.86, 149.82, 129.59, 124.78, 46.28 ppm. HRMS (ESI-TOF, m / z): [M+H]+found 201.0325; calc.201.0328 or C7H9N2O3S+. (k) S-(4-Cyanophenyl)-S-methyl sulfoximine (3k)

[0250] 3k was synthesized following the general procedure for the preparation of sulfoximines starting from 4-(methylthio)benzonitrile (1 eq., 0.5 mmol, 0.0761 g) to afford 0.0391g (43% yield) of the desired product as a yellow solid. Low yield, while not wishing to be limited by theory, possibly due to decomposition of product during silica gel column chromatography owing to acidity in silica.1H NMR (300 MHz, CD2Cl2) δ = 8.12 (d, J=8.7 Hz, 1H), 7.89 – 7.84 (m, 1H), 3.10 (s, 3H), 3.04 (s, 1H) ppm.13C NMR (75 MHz, CD2Cl2) δ = 148.34, 133.47, 128.80, 117.83, 117.07, 46.24 ppm. HRMS (ESI-TOF, m / z): [M+H]+found 181.0431; calc.181.0430 for C8H9N2OS+. (l) S-(4-Acetylphenyl)-S-methyl sulfoximine (3l)

[0251] 3l was synthesized following the general procedure for the preparation of sulfoximines starting from 4-(methylthio)thioacetophenone (1 eq., 0.5 mmol, 0.0848 g)to afford 0.0695 g (75% yield) of the desired product as a white solid.1H NMR (300 MHz, CD2Cl2) δ = 8.08 (s, 4H), 3.08 (s, 3H), 2.63 (s, 3H) ppm.13C NMR (75 MHz, CD2Cl2) δ = 197.23, 148.00, 140.76, 129.28, 128.36, 46.37, 27.17 ppm. HRMS (ESI-TOF, m / z): [M+H]+found 198.0585; calc.198.0583 for C9H12NO2S+. (m) S,S-Diphenyl sulfoximine (3m)

[0252] 3m was synthesized following the general procedure for the preparation of sulfoximines starting from diphenylsulfide (1 eq., 0.5 mmol, 85.1 µL) to afford 0.0915 g (84% yield) of the desired product as a white solid.1H NMR (300 MHz, CD2Cl2) δ = 8.03 (dd, J=7.6, 1.9 Hz, 4H), 7.79 – 7.06 (m, 6H), 3.00 (s, 1H) ppm.13C NMR (75 MHz, CD2Cl2) δ = 144.06, 132.87, 129.48, 128.23 ppm. HRMS (ESI-TOF, m / z): [M+H]+found 218.0636; calc.218.0634 for C12H12NOS+. (n) S-Phenyl-S-(2-hydroxyethyl) sulfoximine (3n)

[0253] 3n was synthesized following the general procedure for the preparation of sulfoximines starting from 2-(phenylthio)ethanol(1 eq., 0.5 mmol, 69.1 µL) to afford 0.0682 g (74% yield) of the desired product as a yellow oil.1H NMR (300 MHz, CD2Cl2) δ = 8.03 – 7.90 (m, 2H), 7.75 – 7.64 (m, 1H), 7.63 – 7.54 (m, 2H), 4.14 – 3.88 (m, 1H), 3.85 – 3.69 (m, 1H), 3.60 (s, 2H), 3.28 (dd, J=5.7, 4.5 Hz, 2H) ppm.13C NMR (75 MHz, CD2Cl2) δ = 142.34, 133.80, 129.71, 128.69, 58.67, 56.75 ppm. HRMS (ESI-TOF, m / z): [M+H]+found 186.0581; calc.186.0583 for C8H12NO2S+. (o) S-Phenyl-S-cyclopropyl

[0254] 3o was synthesized following the general procedure for the preparation of sulfoximines starting from phenyl-cyclopropyl sulfide (1 eq., 0.5 mmol, 72.3 µL) to afford 0.0766 g (85% yield) of the desired product as a colourless oil.1H NMR (300 MHz, CD2Cl2) δ = 8.08 – 7.80 (m, 2H), 7.72 – 7.46 (m, 3H), 2.73 (s, 1H), 2.51 (tt, J=7.9, 4.8 Hz, 1H), 1.33 – 1.22 (m, 1H), 1.21 – 1.08 (m, 1H), 1.06 – 0.84 (m, 2H) ppm.13C NMR (75 MHz, CD2Cl2) δ = 143.73, 132.98, 129.40, 128.17, 34.53, 6.18, 5.72 ppm. HRMS (ESI-TOF, m / z): [M+H]+found 182.0632; calc.182.0634 for C9H12NOS+. (p) Tetrahydrothiophene sulfoximine (3p)

[0255] 3p was synthesized following the general procedure for the preparation of sulfoximines starting from tetrahydrothiophene (1 eq., 0.5 mmol, 45.1 µL) to afford 0.0596 g (75% yield) of the desired product as a colourless oil.1H NMR (300 MHz, CD2Cl2) δ = 3.25 – 2.95 (m, 4H), 2.41 (s, 2H), 2.19 (m, 4H) ppm.13C NMR (75 MHz, CD2Cl2) δ = 55.77, 24.34 ppm. HRMS (ESI-TOF, m / z): [M+H]+found 120.0479; calc.120.0478 for C4H10NOS+. (q) 2-(Methylthio)thiophene sulfiliminium diphenylphosphinate (3q)

[0256] 3q was synthesized following the general procedure for the preparation of sulfoximines starting from 2-(methylthio)thiophene (1 eq., 0.5 mmol, 54.3 µL) to afford 0.0568 g (70% yield) of the desired product as a colourless oil.1H NMR (300 MHz, CD2Cl2) δ = 7.66 (ddd, J=10.2, 4.4, 1.4 Hz, 2H), 7.13 (dd, J=5.0, 3.7 Hz, 1H), 3.19 (s, 3H).13C NMR (75 MHz, CD2Cl2) δ = 146.56, 133.78, 133.42, 128.26, 47.93 ppm. HRMS (ESI-TOF, m / z): [M+H]+found 162.0041; calc.162.0042 for C5H8NOS2+(r) 2-(Methylthio)pyridine sulfoximine (3r)

[0257] 3r was synthesized following the general procedure for the preparation of sulfoximines starting from 2-(methylthio)pyridine (1 eq., 0.5 mmol, 57.0 µL) to afford0.0667 g (85% yield) of the desired product as a colourless oil.1H NMR (300 MHz, CD2Cl2) δ = 8.76 – 8.62 (m, 1H), 8.09 (dt, J=7.9, 1.1 Hz, 1H), 7.95 (td, J=7.7, 1.7 Hz, 1H), 7.51 (ddd, J=7.6, 4.7, 1.2 Hz, 1H), 3.20 (s, 3H), 2.53 (s, 2H) ppm.13C NMR (75 MHz, CD2Cl2) δ = 161.17, 150.29, 138.62, 127.03, 121.26, 42.60 ppm. HRMS (ESI-TOF, m / z): [M+H]+found 157.0431; calc.157.0430 for C6H9N2OS+. (s) Model tryptathionine sulfoximine (3t)

[0258] An oven-dried flask equipped with a magnetic stir bar, was charged with the corresponding sulfiliminium salt of the model tryptathionine substrate, 2t (1 eq.0.05 mmol, 0.0376 g) in MeOH and was cooled to 0 °C in an ice-water bath. Then, an mCPBA (2.5 eq. 0.125 mmol, 0.028 g) in MeOH (5 mL) solution pre-cooled to 0 °C was added. This was allowed to stir for 5 min in the ice-water bath followed by the addition of Na2CO3(20 eq., 1 mmol, 0.106 g). The resulting suspension was stirred at 0-4 °C for 16 h. The crude reaction mixture was centrifuged, and the supernatant was concentrated under reduced pressure. The crude solid was redissolved in 40% ACN / H2O (0.1% TFA) and purified by reverse-phase HPLC using gradient G to isolate the desired product with 68% conversion (HPLC) as a diastereomeric mixture (d.r. 1.1:1). HPLC crude-reaction (gradient G), tR =3.5 min [Diastereomer 1], 4.1 min [Diastereomer 2], 8.6 min [sulfone byproduct] (290 nm). HPLC Re-injection (gradient G) tR= 3.6 min (290 nm). HPLC Re-injection (gradient G) tR= 4.2 min (290 nm). HRMS (ESI-TOF, m / z for diastereomer 1): [M+Na]+found 572.3127; calc. 572.3129 for C29H47NaO5S+. HRMS (ESI-TOF, m / z for diastereomer 2): [M+Na]+found572.3126; calc.572.3129 for C29H47NaO5S+.1H NMR (Sulfoximine diastereomer 1, 600 MHz, DMSO) δ = 11.76 (s, 1H), 7.64 (d, J=8.1 Hz, 1H), 7.48 (d, J=7.4 Hz, 1H), 7.44 (d, J=8.3 Hz, 1H), 7.26 (t, J=7.6 Hz, 1H), 7.10 (t, J=7.5 Hz, 1H), 4.28 (ddd, J=9.9, 7.3, 5.4 Hz, 1H), 3.55 (s, 2H), 3.46 – 3.33 (m, 2H), 3.31 – 3.24 (m, 2H), 1.67 – 1.49 (m, 2H), 1.28 – 1.24 (m, 3H), 1.23 (s, 9H), 1.21 – 1.09 (m, 15H), 0.84 (t, J=7.0 Hz, 3H).13C NMR (Sulfoximine diastereomer 1, Assigned from HSQC, HMBC phase edited 150 MHz,DMSO) δ = 172.74,155.55, 135.78, 130.62, 127.19, 124.43, 120.04, 119.88, 115.58, 112.48, 57.98, 54.64, 51.65, 31.36, 26.69, 25.35, 23.35, 23.19, 22.33, 13.50 ppm (20 / 29 Cs assigned). (t) Fmoc-Met-OH sulfoximine (3v[i])

[0259] An oven-dried flask equipped with a magnetic stir bar, was charged with the Fmoc-Met-OH sulfiliminium salt, 2v[i] (1 eq.0.025 mmol, 0.0151 g) in MeOH and was cooled to 0 °C in an ice-water bath. Then, an mCPBA (5 eq.0.125 mmol, 0.028 g) in MeOH (1.5 mL) solution pre-cooled to 0 °C was added. This was allowed to stir for 5 min in the ice- water bath followed by the addition of NH4OH (100 eq., 0.5 mmol, 500 µL) pre-cooled to 0 °C. The resulting suspension was stirred at 0-4 °C for 16 h. The crude reaction mixture was concentrated under reduced pressure. The crude solid was resuspended in H2O (5 mL) followed by CH2Cl2 washes (3 ^ 5 mL). The aqueous phase was diluted with 10% ACN / H2O (0.1% TFA) and purified by reverse-phase HPLC using gradient L to isolate the desired product with 91% conversion (HPLC) and 45% HPLC-purified yield. The product was isolated as a diastereomeric mixture (d.r.1:1, based on the integral ratio of signals at 3.37 and 3.38 in the1H NMR spectrum). HPLC crude-reaction (gradient A), tR = 4.6 min [Sulfoximine diastereomers], 5.7 min [sulfone by-product] (280 nm). HRMS (ESI-TOF, m / z): [M+H]+found 403.1324; calc. 403.1322 for C20H23N2O5S+.1H NMR (600 MHz, DMSO) two diastereomers, δ = 7.90 (d, J=7.6 Hz, 2H), 7.83 (dd, J=10.0 Hz, 8.4, 1H), 7.72 (d, J=7.4 Hz, 2H), 7.48 – 7.38 (m, 2H), 7.36 – 7.29 (m, 2H), 4.38 – 4.27 (m, 2H), 4.24 (t, J=7.0 Hz, 1H), 4.16 (td, J=9.1, 4.5 Hz, 1H), 3.87 – 3.71 (m, 1H, overlapping with H2O peak), 3.71 – 3.58 (m, 1H, overlapping with H2O peak), 3.53 (s, 3H, diastereomer 1), 3.52 (s, 3H, diastereomer 2), 2.36 – 2.26 (m, 1H), 2.19 – 1.98 (m, 1H).13C NMR (151 MHz, DMSO) two diastereomers, δ = 172.44, 156.17, 156.14, 143.74, 143.72, 140.73, 127.70, 127.12, 125.21, 120.17, 65.78, 52.07, 50.86, 46.58, 38.93, 23.74, 23.62 ppm. (u) Fmoc-Buthionine-OH sulfoximine

[0260] An oven-dried flask equipped with a magnetic stir bar, was charged with the Fmoc-Buthionine-OH sulfiliminium salt, 2v[ii] (1 eq.0.025 mmol, 0.0162 g) in MeOH and was cooled to 0 °C in an ice-water bath. Then, an mCPBA (5 eq.0.125 mmol, 0.028 g) in MeOH (1.5 mL) solution pre-cooled to 0 °C was added. This was allowed to stir for 5 min in the ice-water bath followed by the addition of NH4OH (100 eq., 0.5 mmol, 500 µL) pre- cooled to 0 °C. The resulting suspension was stirred at 0-4 °C for 16 h. The crude reaction mixture was concentrated under reduced pressure. The crude solid was resuspended in H2O (5 mL) followed by CH2Cl2washes (3 ^ 5 mL). The aqueous phase was diluted with 10% ACN / H2O (0.1% TFA) and purified by reverse-phase HPLC using gradient L to isolate the desired product with 92% conversion (HPLC). The product was isolated as a diastereomeric mixture (d.r.1:1, based on the integral ratio of signals in the13C NMR spectrum). HPLC crude-reaction (gradient L), tR =5.1 min [Sulfoximine diastereomers], 7.30 min [sulfone byproduct] (290 nm). HRMS (ESI-TOF, m / z): [M+H]+found 445.1790; calc.445.1792 for C23H29N2O5S+.1H NMR (600 MHz, DMSO) two diastereomers, δ = 7.89 (d, J=7.4 Hz, 2H), 7.82 (dd, J=8.4, 2.5 Hz, 1H), 7.71 (dt, J=8.5 Hz, 4.3, 2H), 7.42 (t, J=7.5 Hz, 2H), 7.33 (tt, J=7.4, 1.5 Hz, 2H), 4.36 – 4.28 (m, 2H), 4.23 (t, J=7.0, 1H), 4.20 – 4.13 (m, 1H), 3.64 – 3.58 (m, 2H, overlapping with H2O peak), 3.55 – 3.45 (m, 2H, overlapping with H2O peak), 2.38 – 2.22 (m, 1H), 2.14 – 2.01 (m, 1H), 1.83 – 1.60 (m, 2H), 1.41 (hd, J=7.4, 1.7 Hz, 2H), 0.90 (t, J=7.4, 3H) ppm.13C NMR (151 MHz, DMSO) two diastereomers, δ = 172.68, 166.23, 143.85, 140.86, 127.83, 127.25, 125.34, 120.29, 65.89, 52.28, 51.68, 51.44, 49.39, 49.35, 23.65, 23.49, 23.45, 23.38, 20.88, 13.49 ppm. (v) Fulvestrant sulfoxime (3w)

[0261] A 15 mL-falcon tube equipped with a magnetic stir bar, was charged with S-deoxy- Fulvestrant 1w (1 eq., 0.085 mmol, 0.052 g) followed by CH2Cl2 (0.34 mL). Next, DPPH (1.1 eq., 0.094 mmol, 0.023 g) was added and the reaction mixture was left stirring at room temperature for 12 hrs. The crude reaction mixture was concentrated under reduced pressure followed by the addition of MeOH (1.7 mL). Next the reaction mixture was cooled to 0 °C in an ice-water bath and mCPBA (5 eq., 0.42 mmol, 0.0975 g) was added. This was allowed to stir for 5 min in the ice-water bath followed addition of NH4OH (100 eq., 1.7 mL) pre-cooled to 0 °C. The resulting suspension was stirred at 0-4 °C for 16 h. The crude reaction mixture was filtered, and the filtrate was concentrated under reduced pressure. The reaction mixture was acidified to pH 6 with 1M HCl(aq) and extracted with CH2Cl2 (3 ^ 10 mL). The organic layer was dried with anhydrous MgSO4, filtered, and concentrated under reduced pressure. The crude solid was immediately purified using silica gel flash column chromatography. (Gradient elution, 0.5%-4% MeOH / DCM) to obtain Fulvestrant sulfoximine 3w (0.0431 g) in 82% yield as a white solid. The product was isolated as a diastereomeric mixture (d.r.1:1 based on the integral ratio of signals in the13C NMR spectrum).1H NMR (600 MHz, CD2Cl2) two diastereomers, δ = 7.11 (d, J=8.4 Hz, 1H), 6.59 (ddd, J=8.4, 5.5, 2.7 Hz, 1H), 6.54 (dd, J=9.9, 2.7 Hz, 1H), 3.72 (t, J=8.5 Hz, 1H), 3.10 (td, J=7.6, 3.4 Hz, 2H), 3.03 (dt, J=11.7, 5.0 Hz, 2H), 2.85-2.82 (d, J=5.3 Hz, 1H), 2.72-2.69 (d, J=1.8 Hz, 1H), 2.46 – 2.22 (m, 4H), 2.21 – 2.13 (m, 2H), 2.08 (dtd, J=13.2, 9.0, 4.9 Hz, 1H), 1.88 (dt, J=12.5, 3.1 Hz, 1H), 1.86 – 1.76 (m, 2H), 1.75 – 1.70 (m, 1H), 1.67 – 1.54 (m, 2H), 1.50 – 1.14 (m, 25H), 1.27 (br. s, grease impurity), 1.06 – 0.95 (m, 1H), 0.77 (s, 3H) ppm.13C NMR (151 MHz, CD2Cl2) δ = 154.53, 154.42, 137.51, 137.47, 133.37, 131.94, 131.83, 130.21, 127.35, 116.48, 116.42, 113.25, 82.30, 55.47, 53.74, 46.91, 43.78, 42.55, 38.73, 38.71, 37.39, 35.11, 35.07, 33.77, 33.73, 30.88, 30.10, 29.95, 29.84, 29.80, 29.69, 29.55, 29.51, 29.44, 29.39, 29.31, 29.12, 28.82, 28.81, 28.05, 27.80, 27.78, 25.62, 25.52, 23.00, 22.67, 22.59, 14.68 (q, J=4.5 Hz), 11.35 ppm.19F NMR (282 MHz, CD2Cl2) δ = -85.78, -118.51 ppm. HRMS (ESI-TOF, m / z): [M+H]+found 622.3346; calc.622.3353 for C32H49F5NO3S+. (w) Cholecystokinin-4 sulfoximine (3x[i])

[0262] An oven-dried flask equipped with a magnetic stir bar, was charged with CCK-4 sulfiliminium salt, 2x[i] (1 eq.5 µmol, 9 mg) in MeOH and was cooled to 0 °C in an ice- water bath. Then, an mCPBA (5 eq.25 µmol, 6 mg) in MeOH (2 mL) solution pre-cooled to 0 °C was added. This was allowed to stir for 5 min in the ice-water bath followed by the addition of NH4OH (100 eq., 0.5 mmol, 500 µL) pre-cooled to 0 °C. The resulting solution was stirred at 0-4 °C for 16 h. The crude reaction mixture was concentrated under reducedpressure and was diluted with 5% ACN / H2O (0.1% TFA) and purified by reverse-phase HPLC using gradient K to isolate the desired sulfoximine (85% conversion,HPLC) as a diastereomeric mixture (d.r.1.1:1, based on the integral ratio of the peaks at tR 17.6 and tR: 18.0 in the HPLC chromatogram). HPLC crude-reaction (gradient I), tR = 17.6 min [Diastereomer 1, 41%], 18.0 min [Diastereomer 2, 44%], 19.5 min [Sulfone, 5%] (290 nm). HRMS (ESI-TOF, m / z): [M+H]+found 628.7; calc.628.2548 for C34H46N7O9S+. (x) Bombesin sulfoximine (3y)

[0263] An oven-flas epewamstibarwar with Bombesin inium salt, 2y (1 eq.5 µmol, 4 mg) in MeOH and was cooled to 0 °C in an ice-water bath. Then, an mCPBA (5 eq.25 µmol, 6 mg) in MeOH (2 mL) solution pre-cooled to 0 °C was added. This was allowed to stir for 5 min in the ice-water bath followed by the addition of NH4OH (100 eq., 0.5 mmol, 500 µL) pre-cooled to 0 °C. The resulting solution was stirred at 0-4 °C for 16 h. The crude reaction mixture was concentrated under reduced pressure and was diluted with 5% ACN / H2O (0.1% TFA) and purified by reverse-phase HPLC using gradient I isolate the desired sulfoximine (85% conversion, HPLC) as a diastereomeric mixture (3:1, based on the integral ratio of the peaks at tR 4.7 min and tR: 4.8 min in the HPLC chromatogram). HPLC crude-reaction (gradient I), tR = 4.7 min [Diastereomer 1, 18%], 4.8 min [Diastereomer 2, 62%], 5.2 min [Sulfone, 10%] (290 nm). HRMS (ESI-TOF, m / z): [M+H]+found1650.8284; calc.1650.8282 for C71H112N25O19S+. (y) N-Acetyl cholecystokinin-4 sulfoximine (3x[iii]) - One-pot reaction

[0264] To a 15 mL-falcon tube equipped with a stir bar was added N-acetyl cholecystokinin-41x[iii] (1 eq., 0.5 µmol, quantified). Next, DPPH (3 eq., 1.5 µmol,0.0004 g, 125 µL of a suspension of 8 mg of DPPH in 2.5 mL of DMF / DCM 1:1) was added. The reaction was left stirring at room temperature for 3 h. The crude reaction mixture was dried under reduced pressure and diluted with water, frozen, and lyophilized. The dried crude reaction mixture equipped with a magnetic stir bar, was charged with MeOH (50 µL) and was cooled to 0 °C in an ice-water bath. Then, mCPBA (10 eq.5 µmol, 1.12 mg, 50 µL of a solution of 11.2 mg of mCPBA in 500 µL of MeOH precooled to 0 °C) was added. This was allowed to stir for 5 min in the ice-water bath followed by the addition of Na2CO3 (20 eq.,1.1 mg). The resulting suspension was stirred at 0-4 °C for 16 h. The crude reaction mixture was diluted with 5% ACN / H2O (0.1% TFA) and purified by reverse-phase HPLC using gradient H to isolate the desired sulfoximine (84% conversion, HPLC). HPLC crude-reaction (gradient H), tR = 6.5 min [Product, 84%], 7.2 min [Sulfone byproduct, 16%] (280 nm). Table 7.1H-NMR assignments for compound 3x[iii] (600 MHz, DMSO-d6). Residue Proton Shift (ppm) Coupling constant (J, Hz) Carbon Shift (ppm) Trp-1 NH 8.10 dd, J = 7.4, 2.9C(aarcbeotynly)l169.61 HCα 4.48 m Cα 53.60 HCβ 2.92 dd, J = 14.9, 9.8 Cβ 27.08 HCβ 3.10 dd, J = 14.9, 9.8 C-3 110.01 H-2 7.14 d, J = 2.4, 1H C-2 123.47 H-4 7.60 d, J = 7.9 C-4 118.28 H-5 6.97 t, J = 7.4 C-5 118.00 H-6 7.05 t, J = 7.5 C-6 120.60 H-7 7.32 d, J = 8.1 C-7 111.03 HN-indole 10.80 s C-7a 136.03 CH3-acetyl 1.77 s C-3a 127.07 – – –C(aamrbiodney)l172.07 Met-2 NH 8.35 dd, J = 8.0, 5.7 – – HCα 4.43 m Cα 50.60 HCβ 2.05 m Cβ 25.44 HCβ 2.15 m – – HCγ 3.26, 3.30 (overlapping with water peak) Cγ 51.28 H(CH3) 3.17 s C(CH3) 40.48 (sulfoNxHimine)– –Carbonyl (amide)170.14Asp-3 NH 8.27 d, J = 7.5C(CarObOonHy)l171.72 HCα 4.53 m Cα 49.50 HCβ 2.53 d, J = 1.9 Cβ 35.83 HCβ 2.68 ddd, =16.8, 5.6, 2.1C(aamrbiodney)l169.96Tyr-4 NH 7.94 dd, J = 8.2, 2.7 – – HCα 4.36 m Cα 53.88 HCβ 2.83 dd, J = 13.8, 8.8, 1H Cβ 37.20 HCβ 3.02 dd, J = 13.9, 5.0 – – H(C6H5)-H-2 7.18 d, J = 7.2 C(C6H5)-C-2 128.94 H-3 7.20 m C-3 127.85 H-4 7.26 t, J = 7.5 C-4 126.07 C-1 137.79 NH27.17, 7.35 d, J = 2.2 Carbonyl (amide)172.42(z) Bombesin sulfoximine (3y) - One-pot reaction

[0265] To a 15 mL-falcon tube equipped with a stir bar was added Bombesin 1y (1 eq., 0.5 µmol, UV quantified). Next, DPPH (3 eq., 1.5 µmol, 0.0004 g, 125 µL of a suspension of 8 mg of DPPH in 2.5 mL of DMF / DCM 1:1) was added. The reaction was left stirring at room temperature for 3 h. The crude reaction mixture was dried under reduced pressure and diluted with water, frozen, and lyophilized. The dried crude reaction mixture equipped with a magnetic stir bar, was charged with MeOH (50 µL) and was cooled to 0 °C in an ice-water bath. Then, mCPBA (10 eq.5 µmol, 1.12 mg, 50 µL of a solution of 11.2 mg of mCPBA in 500 µL of MeOH pre-cooled to 0 °C) was added. This was allowed to stir for 5 min in the ice-water bath followed by the addition of Na2CO3 (20 eq.,1.1 mg). The resulting suspension was stirred at 0-4 °C for 16 h. The crude reaction mixture was diluted with 10% ACN / H2O (0.1% TFA) and purified by reverse-phase HPLC using gradient N to isolate the desired sulfoximine 3y (83% conversion, HPLC). HPLC crude-reaction (gradient N), tR = 4.1 min [Product, 83%], 4.5 min [Sulfone byproduct] (280 nm).1H NMR (600 MHz, DMSO) two diastereomers, δ = 10.78 (s, 1H), 8.35 – 8.11 (m, 8H), 8.08 (t, J=9.7 Hz, 2H), 7.97 (d, J=7.8 Hz, 1H), 7.89 (t, J=7.3 Hz, 1H), 7.81 (s, 1H), 7.61 (dd, J=8.2, 4.4 Hz, 1H), 7.55 (s, 2H), 7.42 (d, J=11.6 Hz, 1H), 7.31 (d, J=8.9 Hz, 3H), 7.27 (s, 1H), 7.24 (s, 1H), 7.18 (s, 1H), 7.15 (s, 1H), 7.10 (s, 1H), 7.07 (s, 1H), 7.04 (t, J=7.5 Hz, 1H), 6.96 (td, J=7.4, 2.3 Hz, 1H), 6.80 (s, 2H), 6.46 (s, 1H), 5.97 (d, J=2.6 Hz, 1H), 4.66-4.64 (m, 1H), 4.61-4.54 (m, 2H), 4.44 (s, 1H), 4.37 – 4.16 (m, 6H), 4.06 (ddd, J=17.6, 7.6, 3.6 Hz, 4H), 3.06 (q, J=6.6 Hz, 2H), 3.03 – 2.91(m, 3H), 2.86 (dd, J=15.3, 8.9 Hz, 1H), 2.55 (td, J=14.6, 5.4 Hz, 1H), 2.45 (dd, J=15.7, 6.4 Hz, 1H), 2.32 – 2.15 (m, 2H), 2.17 – 2.04 (m, 5H), 2.02 (t, J=7.8 Hz, 3H), 1.99-1.94 (m, 1H), 1.90-1.82 (m, 1H), 1.82-1.78 (m, 1H), 1.76- 1.70 (m, 1H), 1.69-1.63 (m, 2H), 1.62-1.55 (m, 2H), 1.55 – 1.38 (m, 7H), 1.21 (d, J=7.1 Hz, 3H), 0.91 – 0.74 (m, 19H) ppm. LRMS (ESI- TOF, m / z): [M+H]+found 1650.8; calc.1650.8 for C71H112N25O19S+. (aa) 5′-OH(Trp) Ama sulfoximine (3z)

[0266] To a 15 mL-falcon tub co i ing Sd x -OH(Trp) Ama sulfiliminium salt, 2zb (1 eq., 0.6 µmol, UV quantified) was added MeOH (200 µL). This solution was treated with mCPBA (5 eq., 3 µmol, 0.67 mg; 50 µL of a solution of 67 mg of mCPBA dissolved in 5 mL of MeOH pre-cooled at 0 °C). The reaction contents were stirred for 5 min at 0 °C followed by the addition of NH4OH (100 eq., 60 µmol, 60 µL) also pre-cooled to 0 °C. The resulting solution was stirred at 0-4 °C for 16 h. The crude mixture was diluted in HPLC buffer and directly purified on HPLC-1 using gradient J to afford the sulfoximine diastereomers 3za, 3zb with 65% conversion (HPLC) with the diastereomers separable by HPLC (d.r.4:1, based on integral ratio of the peaks at tR: 13.1 and 13.2 min in the HPLC Chromatogram). HPLC crude-reaction after 3h (gradient J), tR =13.1 min [Sulfoximine diastereomer 1, 3za], 13.2 min [Sulfoximine diastereomer 2, 3zb], 13.7 [Sulfone by- product, 4z], 14.4 [Sulfoximine of OH2(Trp) Ama, 3zc] (290 nm). HPLC Re-injection (gradient J at 0.5 mL / min) tR =14.9 min (290 nm). HPLC Re-injection (gradient J at 0.5 mL / min) tR= 16.6 min (290 nm). HPLC Re-injection (gradient J at 0.5 mL / min) tR= 17.1 min (290 nm). HPLC Re-injection (gradient J at 0,5 mL / min) tR = 17.7 min (290 nm). HRMS (ESI-TOF, m / z for diastereomer 13za): [M+Na]+found 956.3542; calc.956.4543 for C39H55N11O14SNa+. HRMS (ESI-TOF, m / z for diastereomer 23zb): [M+H]+found 934.3724; calc. 940.3594 for C39H56N11O14S+. HRMS (ESI-TOF, m / z for 4z): [M+H]+found 935.3560; calc.935.3564 for C39H55N10O15SNa+. HRMS (ESI-TOF, m / z for 3zc): [M+H]+found 950.3673; calc.950.3673Table 8.1H-NMR assignments for compound 3zb (600 MHz, DMSO-d6). Residue Proton(SphShift pimft) Coupling constant (J, Hz) Carbon (ppm) Asn-1 NH 10.49 d, J = 6.2C(aamrbiodney)l169.76 HCα 4.81 m Cα 50.42 HCβ 2.60 dd, J = 15.0, 7.8 Cβ 35.30 HCβ 2.78 dd, J = 15.3, 4.7 – – H2N 7.28 s(C1oarabmoindyel) 171.19 7.74 s – – Hyp-2 – – –C(aamrbiodney)l171.60 HCα 4.17 m Cα 61.67 H′Cβ 1.87 td, J = 12.2, 4.0 Cβ 37.76 H″Cβ 2.15 m (overlapping peaks) – – HCγ 4.42 br s Cγ 68.35 H′Cδ 3.67(ovdedr,laJp=pi7n.g8,p4e.a1ks)Cδ 55.87 H″Cδ 3.84 dd, J = 10.9, 3.8 – – OH 5.32 d, J = 2.7 – – DHIle-3 NH 8.08 dd, J = 15.9, 8.3C(aamrbiodney)l170.17 HCα 4.33(ovdedr,laJp=pi6n.g7,p3e.a3ks)Cα 55.52 HCβ 2.13 m (overlapping peaks) Cβ 37.06 HCγ 3.59 d, J = 6.0 Cγ 72.34 H′Cδ 3.34 Masked by H2O peak Cδ 63.52 H″Cδ 3.42 Masked by H2O peak – – CH3 0.86 d, J = 7.0 CH3 13.47 HOγ 4.87 d, J = 5.5 – – HOδ 4.61 t, J = 5.3 – – Trp-4 NH 7.97 d, J = 9.9C(aamrbiodney)l169.55 HCα 5.21 dt, J = 12.8, 9.5 Cα 51.83 H′Cβ 2.95 dd, J = 15.4, 6.9 Cβ 28.75 H″Cβ 3.65(ovdedr,laJp=pi7n.g8,p4e.a1ks)C-3 112.74 H-4 7.07 d, J = 2.3 C-4 104.74 HO-5 9.09 s C-5 151.09 H-6 6.79 dd, J = 8.8, 2.3 C-6 115.99 H-7 7.23 d, J = 8.8 C-7 113.35 HN-indole 11.41 s C-7a 130.38 – – – C-3a 128.33 – – – C-2 131.61Gly-5 NH 7.58 d, J = 9.2C(aamrbiodney)l169.35 H′Cα 3.16d (iomvperulraiptypipnegakw)ithCα 40.75H″Cα 4.29 d, J = 12 – – Ile-6 NH 8.17 d, J = 4.3C(aamrbiodney)ln / d HCα 3.67(ovdedr,laJp=pi7n.g8,p4e.a1ks)Cα 58.80 HCβ 1.52 m (overlapping peaks) Cβ 34.60 H′γ 1.09 m (overlapping peaks) Cγ 25.16 H″γ 1.50 m (overlapping peaks) – – CH3β 0.78 d, J = 6.7 CH3β 14.73 CH3γ 0.80 t, J = 7.3 CH3γ 10.51 Gly-7 NH 8.98 t, J = 6.1C(aamrbiodney)l172.83 H′Cα 3.44 Masked by H2O peak Cα 42.86 H″Cα 3.77 dd, J = 17.1, 6.7 – – Cys-8 NH 8.08 dd, J = 15.9, 8.3C(aamrbiodney)l169.55 HCα 5.15 t, J = 9.5 Cα 44.09 H′Cβ 2.47 dd, J = 14.4, 5.1 Cβ 61.67 H″Cβ 4.38 m – – (sulfoNxHimine)5.37 d, J = 5.0 – –General Procedure for DPPH mediated imination of sulfoxides to access sulfoximines

[0267] An oven-dried flask equipped with a magnetic stir bar, was charged with the corresponding sulfoxide (1 eq., 0.25 mmol) followed by MeOH (1.5 mL, HPLC grade solvent dried over molecular sieves). Next DPPH (2 eq., 0.1227 g, 0.5 mmol) was added followed by the Rh2(esp)2 catalyst (1.25 mol%, 2.5 mg). Finally, MeOH (1 mL, HPLC grade solvent dried over molecular sieves) was added, and the reaction mixture was left stirring at room temperature until reaction completion, confirmed using mass-spectrometry and TLC. The crude reaction mixture was filtered through a CeliteTMsandwich, and the filtrate was concentrated under reduced pressure. The crude product mixture was redissolved in CH2Cl2 (20 mL) and extracted with 1 M HCl (4 ^ 15 mL). The aqueous extracts were combined, and the pH was adjusted to about 10. This was followed by CH2Cl2extractions (4 ^ 25 mL), and the organic extracts were combined, dried over anhydrous MgSO4, filtered and the filtrate was dried under reduced pressure. When required, silica gel flash column chromatography (gradient elution, 20-100% EtOAc / Hexane) was used to afford the sulfoximine product.(a) S-Methyl-S-phenyl sulfoximine (3a)

[0268] 3a was synthesized procedure for the preparation of sulfoximines starting from thioanisole sulfoxide 1a′ (1 eq., 0.25 mmol, 30 µL) to afford 0.0374 g (86% yield) of the desired product as a colorless oil.1H NMR (300 MHz, CD2Cl2) δ = 8.08 – 7.89 (m, 2H), 7.70 – 7.47 (m, 3H), 3.05 (s, 3H), 2.64 (s, 1H) ppm.13C NMR (75 MHz, CD2Cl2) δ = 144.17, 133.19, 129.50, 127.96, 46.55 ppm. HRMS (ESI-TOF, m / z): [M+H]+found 156.0481; calc.156.0478 for C7H10NOS+. (b) S-(4-Methylphenyl)-S-methyl sulfoximine (3e)

[0269] 3e was synthesized following the general procedure for the preparation of sulfoximines starting from 4-methylthioanisole sulfoxide 1e′ (1 eq., 0.5 mmol, 0.772 g) to afford 0.0753 g (89% yield) of the desired product as a colorless oil.1H NMR (300 MHz, CD2Cl2) δ = 8.58 – 7.69 (m, 2H), 7.52 – 7.17 (m, 2H), 3.03 (s, 3H), 2.51 (s, 1H), 2.43 (s, 3H) ppm.13C NMR (75 MHz, CD2Cl2) δ = 144.22, 141.22, 130.10, 128.01, 46.69, 21.58 ppm. HRMS (ESI-TOF, m / z): [M+H]+found 170.0634; calc.170.064 for C8H12NOS+. (c) S-(4-Methoxylphenyl)-S-methyl sulfoximine (3f)

[0270] 3f was synthesized following the general procedure for the preparation of sulfoximines starting from 4-methoxylthioanisole sulfoxide 1f′ (1 eq., 0.5 mmol, 0.0856) to afford 0.0848 g (91% yield) of the desired product as a colorless oil.1H NMR (300 MHz, CD2Cl2) δ = 8.02 – 7.72 (m, 2H), 7.22 – 6.79 (m, 2H), 3.86 (s, 3H), 3.03 (s, 3H), 2.57 (s, 1H) ppm.13C NMR (75 MHz, CD2Cl2) δ = 163.57, 135.60, 130.13, 114.55, 56.04, 46.90 ppm. HRMS (ESI-TOF, m / z): [M+H]+found 186.0582; calc.186.0583 for C8H12NO2S+.(d) S-(4-Fluorophenyl)-S-methyl sulfoximine (3i)

[0271] 3i was synthesized procedure for the preparation of sulfoximines starting from 4-fluorothioanisole sulfoxide 1i′ (1 eq., 0.25 mmol, 0.0395 g) to afford 0.0359 g (83% yield) of the desired product as a white solid.1H NMR (300 MHz, CD2Cl2) δ = 8.35 – 7.78 (m, 2H), 7.54 – 6.85 (m, 2H), 3.06 (s, 3H), 2.63 (s, 1H) ppm.13C NMR (75 MHz, CD2Cl2) δ = 165.79 (d, J=253.8 Hz), 140.23 (d, J=3.2 Hz), 130.92 (d, J=9.5 Hz), 116.60 (d, J=22.6 Hz), 46.75 ppm.19F NMR (282 MHz, CD2Cl2) δ = -106.64 ppm. HRMS (ESI-TOF, m / z): [M+H]+found 174.0381; calc.174.0389 for C7H9FNOS+. (e) S-Phenyl-S-cyclopropyl sulfoximine (3o)

[0272] 3o was synthesized following the general procedure for the preparation of sulfoximines starting from phenyl-cyclopropyl sulfoxide 1o′ (1 eq., 0.25 mmol, 37.0 µL) to afford 0.0373 g (82% yield) of the desired product as a colorless oil.1H NMR (300 MHz, CD2Cl2) δ = 8.10 – 7.84 (m, 2H), 7.72 – 7.43 (m, 3H), 2.68 – 2.46 (m, 1H), 1.42 – 1.22 (m, 1H), 1.21 – 1.08 (m, 1H), 1.08 – 0.79 (m, 2H) ppm.13C NMR (75 MHz, CD2Cl2) δ = 143.75, 132.98, 129.40, 128.17, 34.53, 6.17, 5.72 ppm. HRMS (ESI-TOF, m / z): [M+H]+found 182.0635; calc.182.0634 for C9H12NOS+. VI. Results & Discussion

[0273] Standard S-iminating conditions e.g. PhI(OAc)2 / NH4H2NCO2, MSH or Rh / DPH either proved problematic to handle or gave no reaction with thioether and sulfoxide-bearing amatoxins. However, the versatile reactivity of diphenyl-phoshinylhydroxylamine (DPPH) with respect to a large number of thioether building blocks, along with other complex peptides, and methodological extension to accessing sulfoximines is reported herein.

[0274] This report on the reactivity of DPPH starts with a description of its action on thioanisole (1a) to which 1.1 equivalents of DPPH was added; in under 15 minutes at 21 °C,the formation of the sulfiliminium diphenylphosphinate salt was complete (Scheme 5). Simple aqueous extraction gave the desired sulfilimine salt in high purity.Scheme 5. Initial reactivity screening with thioanisole (Ra= Ph, Rb= CH3).

[0275] Solvent screening revealed that the reaction proceeded cleanly in THF, CH2Cl2, MeOH, and DMF, with quantitative conversion observed by (NMR) thus exemplifying the broad applicability in various common solvents (Table 1).

[0276] With these conditions in hand, the generality of this method was investigated on a broad substrate scope to test electronic and steric effects and functional group tolerance (Table 9). X-ray diffraction of crystalline compounds 2b (FIG. 1) and 2v[i] (FIG. 2) unambiguously confirmed the identity of the sulfilimine salt. Substrates bearing electron donating aryl substituents (1c-g) reacted in under 15 minutes in excellent yields whereas substrates with electron withdrawing substituents (1h-l) required 3-5 hours for complete conversion. Substrates featuring ortho- and meta-aryl substituents (1c, 1d, 1g) reacted rapidly suggesting that ortho and meta-steric effects are negligible. Aryl alkyl thioethers (1n, 1o) including phenyl cyclopropyl sulfide (1o), a structural motif found in sulfoximine-bearing clinical candidates (Lücking, 2022), afforded quantitative yield. This imination strategy was extended to diaryl and dialkyl sulfide substrates (1b, 1m, 1p) with high yields. S- and N- heterocyclic substrates (1q-t) also afforded high yields. This broad substrate scope further demonstrated the chemoselectivity and functional group tolerance in the presence of amine (1g), hydroxyl (1n), nitro (1j), halide (1h, 1i), nitrile (1k), ketone (1l), and carboxyl (1u- v[ii]) functionalities. Generally, these sulfiliminium salts can be stably stored at -20 °C for several weeks (Passia et al., 2023) which can be transformed to the corresponding free-NH sulfilimines, either via basic work-up or by means of passing an ethanolic solution of the salt through an amberlite (OH- form) ion exchange resin (Bizet et al., 2015).

[0277] More biologically relevant substrates e.g. biotin (1u), L-methionine (1v[i]), L- buthionine (1v[ii]), and S-deoxy-Fulvestrant (1w) were also investigated and were transformed to the corresponding sulfilimines in appreciable yields. Notably, this methodafforded the sulfiliminium salts of Fmoc-methionine (2v[i]) and Fmoc-buthionine (2v[ii]) in high yields; compound 2v[i] was produced as a diastereomeric mixture (d.r.4:1), from which the (R)-isomer crystallized as a single diastereomer, the oxidation of which would ultimately yield the biologically active L-methionine-(S)-sulfoximine (Manning et al., 1969; Richman et al., 1973). Sulfimination of methionine and buthionine is of great interest, as these are precursors in the synthesis of methionine sulfoximine (MSO) and buthionine sulfoximine (BSO), known inhibitors of γ-glutamylcysteine synthetase, that are used clinically in the combination treatment of tumors that overexpress glutathione (GSH) (Lücking, 2019; Tagde et al., 2014). The sulfiliminium salt analogue of Fulvestrant (2w) was synthesized in high yield notably without use of protecting groups. Table 9. Substrate scope for DPPH-mediated thioether imination. Compound Structure Yield (%) 2a 93 2b 72 2c98 2d 99 2e 99 2f 99 2g992h 961092i 99 2j 942k 98 2l 98 2m 992n992o 99 2p 82 2q 78 2r 99 2s 422t 84 2u 94 v[i] 89 d.r.4:1 (NMR) v[ii] 84 / Quant Conv.ad.r.1:1 (NMR) 87 2w d.r.1:1 (NMR) 78ax[i] from CCK fragment d.r.1.5:1 (NMR) WMDF (SEQ ID NO:1) Quant. Conv.ax[ii] from CCK fragment d.r.1.4:1 (HPLC) WMDF (SEQ ID NO:2) Quant. Conv.ax[iii] from CCK fragment d.r.1.2:1 (NMR) WMDF (SEQ ID NO:3)Quant. Conv.a2y from Bombesin d.r.1.8:1 (NMR) XQRLGNQWAVGHLM (SEQ ID NO:6)2za2+2a22zb 96aIsolated yields given for compounds 2a–2w. [a] % Conversion determined from reverse-phase HPLC for peptide substrates 2x–2z—isolated yields have been lower owing to loss on HPLC; integration is less than 100% owing to the appearance of another small peak integrating for 2% that represents an uncharacterized impurity for 2z; Reaction run in CH2Cl2for 16 h for substrate 2w. Reactions run in CH2Cl2: DMF 1:1 for substrates 2x[ii]–2z.

[0278] To address chemoselectivity on more complex substrates, sulfimination of methionine residues in the context of two well-known, functionally diverse peptides was pursued: cholecystokinin (CCK-4) and bombesin (14-mer) giving corresponding sulfilimine salts of peptides with free and protected N-termini (2x[i–iii] and 2y) in near quantitative conversion (HPLC), albeit with low diastereoselectivity, similar to that observed with oxaziridines (Lin et al., 2017). The synthesis of sulfiliminium salts of 5- OH(Trp) amanitin (2za,b) employing DPPH resulted in quantitative conversion (HPLC) with surprisingly high diastereoselectivity; two sulfiliminium diastereomers were separable by HPLC (d.r.48:1). Interestingly, DPPH did not react with indoles, imidazoles phenols or the very electron-rich hydroxy indoles. Taken together, these results exemplify the utility of DPPH for a late-stage sulfimination of complex and functionality-dense molecules with excellent chemoselectivity. DPPH was also shown to S-iminate CCK-4(2x[iii]) with near quantitative conversion in water demonstrating a potential for S- imination of proteins or other molecules that are obligately soluble in water.

[0279] Whereas the oxidation of N-substituted sulfilimines to access sulfoximines is well-established, the oxidation of free-NH sulfilimines to sulfoximines has met with limited success. Previous attempts using oxidants such as KMnO4, H2O2, and p-methylperbenzoic acid afforded variable yields (Yoshimura et al., 1976) whereas attempts to oxidize the corresponding sulfiliminium salts did not show any conversion. There is but a single report on the oxidation of a free-NH sulfiliminium salt by simultaneous NH3 / mCPBA treatment resulting in 36-65% yield (Furukawa et al., 1983). The inventors attribute these low yields to competitive sulfoxide / sulfone by-product formation as the sulfiliminium-nitrogen is susceptible to nucleophilic displacement (Nakayama et al., 2001). A screen of various bases found that Na2CO3afforded the best conversion (Table 2). Attempts to decrease the number of equivalents of base and oxidant did not result in uniformly high yields (Table 2). Due to the heterogenous nature of the reaction, a higher number of base equivalences appeared necessary. Hence, the inventors sought to suppress sulfoxide / sulfone formation in accessing the corresponding sulfoximines. Inspired by past reports (Johnson & Kirchhoff, 1979; Huang & Swern, 1979), the inventors appreciated that a Bronsted base plays a critical role in i) accessing the free-NH sulfilimine from the salt and ii) generating m- chloroperbenzoate anion, which serves as a nucleophilic oxidant. Previous reports for sulfiliminium salt oxidation specify saturating the reaction with dry NH3 gas (Furukawa et al., 1983). We conveniently used an excess of reagent-grade concentrated NH4OH(aq) and ran the reaction at 0-4oC to suppresses sulfoxide / sulfone by-product formation (although the lower temperature increased the reaction time to ca. 18 h). Under these conditions, appreciable conversion was observed with alcoholic solvents (Table 2).

[0280] To streamline this method further, we also developed a one-pot imination-then- oxidation strategy that converts free-NH sulfiliminium salts to free-NH sulfoximines with minimal sulfoxide / sulfone by-products (Scheme 6, Table 10). A number of thioether substrates, including peptides and amatoxins, were converted to the free-NH sulfoximines in yields exceeding 70%. Arylmethyl thioether substrates bearing electron donating and withdrawing groups para to the sulfoximine scaffold gave appreciable yields (3a-3l). A lower yield was associated with an ortho-substituted substrate (3c), which can be attributed to steric effects. A diaryl thioether (1m) and aryl alkyl thioethers (1n, 1o) affordedsulfoximines in appreciable yields, including the phenyl cyclopropyl sulfoximine substrate (1o), a structural unit present in the clinical drug candidate: AZD6738 (Lücking, 2022).Scheme 6. Sulfoximine substrate one-pot scope-imination and then oxidation route. Table 10. Sulfoximine substrate scope-imination and then oxidation route. Compound Structure Yield (%) 3a 81 3b 74 3c 50 3d 80 3e 73 3f 92 3g 49 3h 713i 77 3j 76 3k 43 3l 75 3m 84 3n 74 3o 85 3p 75 3q 70 3r 85 3s –3t 63a3u – v[i] 91ad.r.1:1 v[ii] 92ad.r.1:1 3w 82bd.r.1:1 (NMR) x[i] 85ad.r.1:1 (HPLC) WMDF (SEQ ID NO:4) x[iii] 84bWMDF (SEQ ID NO:5) 75a3y d.r.3:1 83bXQRLGNQWAVGHLM (SEQ ID NO:7)3za 13a3zb 52aIsolated yields given for compounds 3a–3r and 3w, % conversion determined from reverse-phase HPLC for substrates 3t–3 z—isolated yields have been lower owing to loss on HPLC; [a] sulfiliminium product is isolated followed by oxidation in the presence of NH4OH; [b] one-pot imination and then oxidation method in which the imination solvent was removed by evaporation or lyophilization followed by oxidation in the presence of Na2CO3.

[0281] The reaction scope also extended to aromatic heterocycles in appreciable yields (1q-t). The broad reaction scope was further evidenced by high yielding sulfoximination of dialkyl thioethers (1b, 1p) including biologically relevant substrates L-methionine (1v[i]), L-buthionine (1v[ii]) and S-deoxy-Fulvestrant (1w). This method renders facile access to MSO and BSO which are of clinical importance (Lücking, 2019; Tagde et al., 2014). The sulfoximine analog of Fulvestrant (3w) is an equipotent analogue of Fulvestrant while the sulfilimine is lacking precedent (Sirvent & Lücking, 2017). This one-pot imination-then-oxidation strategy afforded the known sulfoximine analogue of Fulvestrant (3w) in 82% yield. The transformation reported here does not require protecting group manipulations which was necessary for standard sulfoxide imination strategies used in previously reported synthesis of the same (Sirvent & Lücking, 2017).

[0282] Next, we examined late-stage sulfoximination on complex substrates (2x-z) for which the sulfiliminium salt was first isolated and subsequently oxidized to the sulfoximine. Sulfoximination was effected on methionine residues of two polypeptides: CCK and bombesin, with appreciable conversion (HPLC) via the two-step method as well as the one- pot method. Whereas a one-pot NH- and O- transfer strategy involving PIDA / NH2COONH4had been employed for methionine in polypeptide substrates, in our handsthis methodology did not afford the desired sulfoximine on tryptathionine bearing substrates. With the goal of accessing the sulfoximine scaffold on the Ttn staple of amanitin, conditions were screened on a model substrate (Table 3). Despite not being able to completely supress sulfone formation on amatoxin-thioether substrates, the sulfoximine was installed stepwise on an amatoxin: using the isolated sulfilimine salt bearing 5′-OH(Trp) amanitin substrate (2zb), two novel sulfoximine diastereomers (d.r.4:1) were isolated by HPLC.

[0283] The synthesis of NH-sulfoximines by direct imination of sulfoxides is also a widely sought-after approach (Bull et al., 2017; Andresini et al., 2021), especially in terms of asymmetric sulfoxidation given the vast precedence of enantioselective methods (Wojaczyńska & Wojaczyński, 2020; Wojaczyńska & Wojaczyński, 2010). Previously, this transformation was effected under metal-free conditions by MSH (Tamura et al., 1972) or via PhI(OAc)2 / NH4H2NCO2(Zenzola et al., 2016). Additionally, transition- metal catalyzed imination methods e.g. Rh / DPH (Miao et al., 2014) and Fe / 4- nitroarylhydroxylammonium triflate enable high-yielding free-NH sulfoximination.

[0284] In seeking similar reactivity with DPPH, we found that under metal-free conditions at high temperature, DPPH iminates a sulfoxide with about 50% conversion by NMR (3a). In comparison to the work of Miao et al. (2014) who reported on Rh-catalyzed synthesis of NH-sulfoximines using DPH as the electrophilic iminating agent, the inventors found similar conditions to iminate sulfoxides with much higher yields using lower catalyst loading, while also replacing trifluoroethanol with methanol as the solvent (Table 4). The scope of this methodology was extended to aryl-alkyl sulfide substrates in reasonable to high yields (Scheme 7, Table 11). Whereas imination of sulfoxides is a well-established strategy, this foray further exemplifies the utility of DPPH which can be employed for asymmetric sulfoximination by means of Rh-catalyzed electrophilic imination starting with chiral sulfoxides. Scheme 7. Sulfoximine oxidation then imination.Table 11. Sulfoximine substrate scope-oxidation then imination. Compound Structure Yield (%) 3a 86 3e 89 3f 91 3i 83 3o 82

[0285] This Rh / DPPH-mediated sulfoximination strategy failed to S-iminate the natural product α-amanitin presenting an (R)-sulfoxide, likely owing to steric encumbrance near the tryptathionine bridgehead. Nevertheless, the integration of the sulfoximine scaffold on the tryptathionine staple of amanitin was accomplished late-stage via the imination-then- oxidation route, which exemplifies the versatility of this late-stage strategy in accessing the sulfoximine scaffold in sterically hindered spaces of complex molecules.

[0286] Turning to the question of addressing bioisosterism with S-modified amatoxins (Scheme 8) and intrigued by the differential cytotoxicity governed by the stereochemical configuration of the sulfoxide, we used DPPH to study the aza-analogs in greater detail. The major sulfiliminium diastereomer (2zb), produced by direct imination was ultimately assigned as the (R)-sulfilimine salt (FIG.3 and FIG.4). The assignment of the sulfiliminium- NH2protons was1by H-13C HMBC correlations observed with Trp4-C2 (FIG.4, lower left). The1H-1H NOESY NMR spectrum showed three distinct NOE correlations between sulfiliminium-NH2 protons and HN-indole Trp-4, 1Hβ Cys8, and Hα Cys8 (FIG.4, lower right). These correlations are consistent with the (R)-sulfiliminium configuration at the sulfur center (FIG.3, upper). Additionally, it is reported (Wieland et al., 1983) in sulfur oxygenated amatoxins the oxygen of (S)-sulfoxide participates in forming anintramolecular hydrogen bond with the peptide bond of Asn1. Hence, one would expect to observe NOE correlations between sulfiliminium-NH2protons and amide HN protons of Asn1 for (S)-sulfiliminium diastereomer, which is not observable in this case. The major sulfiliminium diastereomer (2zb) displayed appreciable cytotoxicity, albeit about 2.5-fold reduced relative to the corresponding amatoxin bearing an (R)-sulfoxide (FIG.5). By contrast, the minor diastereomer (2za), presumed to be the (S)-sulfilimine, showed reduced about 6- fold reduced potency) (FIG.5). This relative cytotoxicity difference is fully consistent with that reported for amanitins bearing (R) / (S)-sulfoxides (Pryyma et al., 2020). Similar cytotoxicity was observed when the same were evaluated against CHO cells (FIG.6)Scheme 8. S-modified amatoxins.

[0287] The sulfilimine toxin (2zb) was isolated as a sulfiliminium salt (HPLC in 0.1% TFA) with two N-associated protons observed in1H NMR displaying correlations in NOESY, TROESY and HMBC spectra. The sulfiliminium-NH2protons display characteristic HMBC correlations that evidence its chemoselective incorporation on the tryptathionine bridge. The NOE correlations observed by sulfiliminium-NH2 protons supported by NOESY, TROESY, 1D-NOESY, and 1D-ROESY NMR spectra (FIGs.3 and 4) provide comprehensive evidence for an (R) stereoassignment at the sulfur centre. This is further supported by circular dichroism data (FIG.7) and the cytotoxicity data (FIG.6).

[0288] The (R)-NH2-sulfilimine, following diastereomeric separation by HPLC, was then directly converted to the corresponding sulfoximine amatoxins; (3za, 3zb), which was accompanied by a sulfone by-product (4z) (FIG.8). The major sulfoximine diastereomer (3za) was assigned as the (R)-sulfoximine (FIG. 9 and FIG. 10). The assignment of the sulfoximine-NH protons was supported by1H-13C HMBC correlations observed with Cys8- βC (FIG.10, upper right). The1H-1H NOESY NMR spectrum shows seven sets of distinct NOE correlations with sulfoximine-NH protons which includes correlations to 1) 2Hβ Trp-4, 2) HN-indole Trp-4, 3) 2Hβ Cys-8, 4) Hα Cys8, 5) HN-amide Asn-1, 6) 2Hβ Asn-1, 7) 1oH2N-amide Asn-1 (FIG. 10, lower). correlations are consistent with the (R)-sulfoximine configuration at the sulfur centre (FIG.9, lower). Energy minimized models show that in the (R)-diastereomer, the sulfoximine NH proton is oriented towards the interior of the peptide molecule which is in agreement with the higher NOE correlations observed. Furthermore, the (R)-sulfoximine NH proton and the oxygen of the (S)-sulfoxide would be in the same phase about the chiral sulfur centre. Given that the oxygen of (S) sulfoxide forms an intramolecular hydrogen bond with peptide bond NH of Asn-4 (Wieland et al., 1983), it is reasonable to postulate that the (R)-sulfoximine NH proton would be in spatial proximity to the peptide bond NH of Asn-4 which is observable in terms of characteristic NOE correlations. Interestingly, the major sulfoximine diastereomer (3zb) was about 19-fold less cytotoxic relative to the sulfone (4z). On the contrary, the minor diastereomer (3za) was only 8-fold less cytotoxic (FIG. 11) thus exemplifying stereochemically distinct cytotoxicity values (IC50s) for sulfoximine diastereomers of these novel amatoxins (FIG.8 and FIG.11). Surprisingly, both amatoxin-sulfoximines are significantly less cytotoxic than the corresponding sulfone, with significant differences seen in terms of both diastereomers.

[0289] Historically, sulfur-modified amatoxins are characterized using circular dichroism (CD) spectra, which we acquired as part of standard characterization (FIG.7). It is worth noting that the (R)-sulfoxide and (R)-sulfilimininium (2zb) analogs of amanitin show similar CD spectral profiles as do the predominant sulfoximine diastereomer (3zb) and the sulfone (4z). Despite such conformational similarities between the sulfoximine and sulfone amanitin analogs, reasons for this diminished cytotoxicity are not readily intuited. While not wishing to be limited by theory, differences in cytotoxicity might also be attributed to variability in cell uptake or other unforeseen effects. Importantly, the integration of S-N bonds on amanitin may find potential applications in bioconjugation for ADC applications. Applications of DPPH for generating amino-handles along with the use of oxaziridines for the purpose of bioconjugation become clear next steps. For example, these results should enable bioconjugation through the sulfilimine-NH via recently reported Chan–Lam coupling strategies (Meng et al., 2022), while portending the use of oxaziridines in the development of immolative pro-drugs.

[0290] To the best of the inventors’ knowledge, the direct comparison of a bioactive sulfoxide and its sulfilimine congener has never been reported for any natural product, despite a number of reports comparing sulfoximine- and sulfone-bearing bioactives. We have now demonstrated this using sulfilimine analogues of an example of a peptide-toxin.

[0291] A distinct difference between a sulfilimine and a sulfoxide is the presence of a positive charge. As the pKaof sulfiliminium salts range from 7.5–8.5, (Furukawa et al., 1974) both the sulfiliminium salt and sulfilimine free base are likely present at physiological pH and such may affect a number of pharmacokinetic parameters. Yet irrespective of which species is ultimately responsible for bioactivity, it is significant that the substitution of a sulfoxide for a sulfilimine / sulfiliminium motif results in reasonable potency in the case of an exemplary amatoxin, and suggests potential for bio-isosterism and new applications, for example, in respect to other amatoxins and / or in medicinal chemistry generally.

[0292] While amatoxins present a level of oxidative delicacy not typically seen in simple building blocks, it was important to demonstrate the generality of using DPPH on simpler substrates. Not surprisingly, DPPH robustly iminated a large number of other thioethers. Interestingly, in the case of a bicyclic peptide amatoxin, high diastereoselectivity was observed. Remarkably, Fmoc-protected methionine and buthionine are also iminated in high yields and subsequent oxidation affords convenient access to clinically useful MSO and BSO in high yields as well. Not surprisingly, S-imination of methionines in common peptides did not proceed with high diastereoselectivity, consistent with other methods that show little-to- no diastereoselectivity. Nevertheless, assessing sulfilimine and sulfoximine on methionine- bearing polypeptides further enables eventual bioconjugation via Chen-Lam coupling.

[0293] Imination of a sulfoxide to give a free-NH sulfoximine proved more challenging. Whilst metal-free use of DPPH afforded reasonable yields, addition of bis[rhodium(α,α,α',α'-tetramethyl-1,3-benzenedipropionic acid)] (Rh(esp)2) provided greatly improved yields. While not wishing to be limited by theory, we surmise that DPPH is converted to a rhodium-nitrene which serves as the electrophilic-N source in the same manner as DPH (Miao et al., 2014). It is noteworthy that use of Rh catalysis opens the possibility for stereoselective imination provided a suitable chiral ligand system is used.

[0294] In terms of delivering greater diastereoselectivity as well as potential for enantioselectivity, it is intriguing to contemplate use of chiral P(V) reagents and the eventual extension of this work to aminoxyphosphodiesters (Boche & Schrott, 1982). III. Additional Discussion

[0295] Sulfilimines are mono-aza analogs of sulfoxides which serve as auxiliaries, ligands, bioconjugation handles, and precursors to medicinally relevant S(VI) scaffolds including sulfoximines and sulfondiimines. Despite to access N-substituted sulfilimines,synthetic access to free-NH sulfoximines via electrophilic N transfer onto sulfides is rather limiting due to safety concerns with the conventionally used reagents and methods.

[0296] Herein we report the use of O-(diphenylphosphinyl)hydroxyl amine (DPPH) for sulfide imination under safe, mild, metal-free, and bio-molecule-compatible conditions with excellent chemoselectivity and broad functional group tolerance with applicability in late-stage derivatization of complex molecules (Scheme 10).Scheme 10. O-(diphenylphosphinyl)hydroxyl amine (DPPH) for sulfide imination.

[0297] Metal-free access to free-NH sulfoximines was rendered via oxidation of sulfilimium salts with yields more than 70% suppressing sulfoxide and sulfone by-product formation. This methodology afforded successful integration of the sulfoximine scaffold on clinically relevant Methionine and Buthionine substrates and also on complex peptides and a natural-product bearing a sterically encumbered thioether scaffold, late-stage. For stereoselective access to free-NH sulfoximines a Rh catalyzed DPPH mediated sulfoxide imination method was developed with high yields (more than 80%). Amanitin is a notorious sulfoxide bearing toxin which has found clinical applications in the context of antibody-drug conjugate therapy. Bioisosterism between sulfoxide and sulfilimine scaffolds and sulfoximine and sulfone scaffolds was studied by integrating these functionalities to access sulfur- derivatized amatoxin analogs and evaluating their cytotoxicity.

[0298] In sum, DPPH has been identified as a relatively safe, bench-stable, highly efficient S-iminating agent for facile metal-free, and biomolecule compatible sulfimination. This reagent afforded excellent chemoselectivity, broad functional group tolerance, and applicability in thecontext of late-stage derivatization under bio-molecule compatible conditions. For amatoxins, it was demonstrated that a R2S=NH appears to be a competent isostere for a R2S=O.

[0299] While the disclosure has been described with reference to what are presently considered to be the preferred examples, it is to be understood that the disclosure is not limited to the disclosed examples. To the contrary, the present disclosure is intended to cover various modifications and equivalent arrangements included within the spirit and scope of the appended claims.

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Claims

What is claimed is:

1. An amatoxin analog comprising a tryptathionine bridge of the Formula:whereinA is S'(NH2)Q., S=NH or S(O)=NH;Q is a counteranion;R” and R” are each independently H or Ci-10alkyl; or R™ and R” togetherwith the carbon atom to which they are attached, together form C3-10cycloalky1;each R’ is independently OR’, N(R’)2, NOz, CN, COOR’, N3, NR’NR’, ON(R’),NR’-OR’, SeR’, SO3R’, P(O)OR’)2, C(O)N(R’), CHO, B(OR’)2, CHa, CH20H, or halo;ris an integer from 0 to 4; andeach R’ is independently H, C1-20alkyl, C2-20alkenyl, C2-20alkynyl, Cs20cycloalkyl, Ce-soaryl, heterocycloalkyl or heteroaryl, wherein one or more availablecarbon atoms in the C1-20alkyl, C2-20alkenyl and C2-20alkynyl is optionally replacedby a heteroatom, and wherein the Cj-20alkyl, C2-20alkenyl, C2-20alkynyl, Cs.20cycloalkyl, Ce-soaryl, heterocycloalkyl and heteroary! is optionally furthersubstituted with one or more groups selected from OR”, halo, azide and nitrile,wherein R” is independently H, C1-20alkyl, C2-20alkenyl, C2-20alkynyl, Cs20cycloalkyl, Ce-soaryl, heterocycloalkyl or heteroaryl,or a pharmaceutically acceptable salt thereof,wherein in the amatoxin analog or the pharmaceutically acceptable saltthereof, one or more available hydrogens is / are optionally replaced with deuteriumand / or one or more available hydrogens is / are optionally replaced with fluorine and / orone or more available atoms is / are optionally replaced with its radioactive isotope.1292. The amatoxin analog of claim 1, that is a compound of Formula I:whereinA is S'(NH2)Q., S=NH or S(O)=NH;Q is a counteranion;X! and X? are each independently (CH2)m, CHCHs, CHCH2CHs3, C(CH3)2 or NR’:R! is CH(Z-CH3)2, wherein one or more available hydrogens is / areoptionally substituted with SH; or R! is C3-10cycloalkyl, wherein one or moreavailable hydrogens on the C3-10cycloalkyl is / are optionally substituted with C1.1oalkyl and / or one or more available carbon atoms in the C3-10cycloalkyl is / areoptionally replaced by O; and wherein one or more single bonds between twoavailable carbon atoms in R! is / are optionally replaced by a double bond;R” and R” are each independently H or Ci-10alkyl; or R™ and R” togetherwith the carbon atom to which they are attached, together form C3-10cycloalky1;R? is OR’, NH(OR’), NH-NHR’ or N(R’);R* is H or OH:R° and R° are each independently H, OR’, NHR’ or halo:each R’ is independently OR’, N(R’)2, NOz, CN, COOR’, N3, NR’NR’, ON(R’),NR’-OR’, SeR’, SO3R’, P(O)OR’)2, C(O)N(R’), CHO, B(OR’)2, CHa, CH20H, or halo;each Z is independently (CH2)nO(CH2)p, (CH2)nSe(CH2)p or (CH2)q:each m is independently an integer from 1 to 5;each n is independently an integer from 0 to 4;each p is independently an integer from 0 to 4;n+ pin each Z, is independently < 4;each q is independently an integer from 0 to 4;ris an integer from 0 to 4; andeach R’ is independently H, Ci-20alkyl, C2-20alkenyl, C2-20alkyny1, Cs20cycloalkyl, Cs-soaryl, heterocycloalkyl or heteroaryl, wherein one or more availablecarbon atoms in the Cy-20alkyl, C2-20alkenyl and C2-20alkynyl is optionally replacedby a heteroatom, and wherein the Cj-20alkyl, C2-20alkenyl, C2-20alkynyl, Cs.20cycloalkyl, Ce-soaryl, heterocycloalkyl and heteroary! is optionally furthersubstituted with one or more groups selected from OR”, halo, azide and nitrile,wherein R” is independently H, C1-20alkyl, C2-20alkenyl, C2-20alkynyl, Cs20cycloalkyl, Ce-soaryl, heterocycloalkyl or heteroaryl,or a pharmaceutically acceptable salt thereof;wherein in the compound of Formula I or the pharmaceutically acceptable saltthereof, one or more available hydrogens is / are optionally replaced with deutert'umand / or one or more available hydrogens is / are optionally replaced with fluorine and / orone or more available atoms is / are optionally replaced with its radioactive isotope.

3. The amatoxin analog of claim 2, wherein the amatoxin analog has one or more ofthe following:(i) R! other than KO(ii) | X! other than CH>:(iii) |X? other than CH2:(iv) R** other than H; and(v) R* other than H.4, The amatoxin analog of claim 2 or 3, that is a compound of Formula I(a):whereinA is S'(NH2)Q., S=NH or S(O)=NH;Q is a counteranion;R! is CH(Z-CH3)2, wherein one or more available hydrogens is / areoptionally substituted with SH; or R? is C3-10cycloalkyl, wherein each Z isindependently (CH2),O(CH2)p or (CH2)q;R? is OR’, NH(OR’), NH-NHR’ or N(R’);R* is H or OH:R° and R° are each independently H, OR’, NHR’ or halo:each R’ is independently OR’, N(R’)2, NOz, CN, COOR’, N3, NR’NR’, ON(R’),NR’-OR’, SeR’, SO3R’, P(O)OR’)2, C(O)N(R')p, CHO, B(OR’)2, CHa, CH20H, or halo;each n is independently 0, 1, or 2;each p is independently 0, 1, or 2;each q is independently 0, 1, or 2;ris an integer from 0 to 4; andeach R’ is independently H, Ci-20alkyl, C2-20alkenyl, C2-20alkyny1, Cs20cycloalkyl, Ce-soaryl, heterocycloalkyl or heteroaryl, wherein one or more availablecarbon atoms in the Cy-20alkyl, C2-20alkenyl and C2-20alkynyl is optionally replacedby a heteroatom, and wherein the Cj-20alkyl, C2-20alkenyl, C2-20alkynyl, Cs.20cycloalkyl, Ces-soaryl, heterocycloalkyl and heteroary! is optionally furthersubstituted with one or more groups selected from OR”, halo, azide and nitrile,wherein R” is independently H, C1-20alkyl, C2-20alkenyl, C2-20alkyny1, Cs20cycloalkyl, Ce-soaryl, heterocycloalkyl or heteroaryl,or a pharmaceutically acceptable salt thereof;wherein in the compound of Formula I(a) or the pharmaceutically acceptablesalt thereof, one or more available hydrogens is / are optionally replaced with deuteriumand / or one or more available hydrogens is / are optionally replaced with fluorine and / orone or more available atoms is / are optionally replaced with its radioactive isotope.1325. The amatoxin analog of claim 4, having the following stereochemistry:

6. The amatoxin analog of claim 4 or 5, having the following stereochemistry:

7. The amatoxin analog of any one of claims 2 to 6, wherein R! is CH(CH3)(CH2CHs).

8. The amatoxin analog of any one of claims 2 to 7, wherein R* is OH or NHo.

9. The amatoxin analog of any one of claims 2 to 7, wherein R° is -N(R’)2, wherein oneR’ is H and the other R’ is Ci-20alkyl substituted with -N3.

10. The amatoxin analog of any one of claims 2 to 9, wherein R*, R° and R° are each OH.

11. The amatoxin analog of any one of claims 2 to 10, wherein ris 1.

12. The amatoxin analog of claim 11, wherein R’ is 5-OH.

13. The amatoxin analog of any one of claims 1 to 12, wherein A is S'(NH2)Q.

14. The amatoxin analog of any one of claims 1 to 12, wherein A is S=NH.

15. The amatoxin analog of any one of claims 1 to 12, wherein A is S(O)=NH.

16. The amatoxin analog of any one of claims | to 15, wherein A is (R)-A.

17. The amatoxin analog of any one of claims 1 to 15, wherein A is (S)-A.

18. The amatoxin analog of claim 1, wherein the amatoxin analog is:or a pharmaceutically acceptable salt thereof.

19. The amatoxin analog of any one of claims | to 12 and 14 to 18 that is not in the formof a salt.

20. The amatoxin analog of any one of claims 1 to 19 that is in the form of apharmaceutically acceptable salt of the amatoxin analog.

21. An amatoxin-linker construct comprising the amatoxin analog of any one of claims 1to 19 coupled to a linker, wherein the linker comprises a reactive group R® forconjugating the amatoxin-linker construct to a target-binding moiety.

22. The amatoxin-linker construct of claim 21, wherein the linker is coupled to theamatoxin analog or the salt thereof at a site indicated by A, R°, R*, R°, R° and / or R’in an amatoxin analog as defined in any one of claims 2 to 20.

23. The amatoxin-linker construct of claim 21 or 22, wherein the linker is coupled to theamatoxin analog or the salt thereof through a moiety obtained from the reaction of A,R?, R*, R°, R° and / or R’ as defined in claim 2 with a complementary functional groupon the linker.

24. The amatoxin-linker construct of claim 23, wherein R? comprises an N3 moiety, thecomplementary functional group on the linker is an alkyne, and the linker is coupledto the amatoxin analog or the salt thereof through a 1,2,3-triazole.

25. The amatoxin-linker construct of claim 23, wherein the linker is coupled to theamatoxin analog or the salt thereof through a moiety obtained from the reaction of Awith a complementary functional group on the linker.

26. The amatoxin-linker construct of claim 25, wherein the moiety obtained from thereaction of the nitrogen of A with the complementary functional group on the linkeris an S-N-carbamoyl group.

27. A conjugate comprising a target-binding moiety conjugated to an amatoxin analog ofany one of claims | to 20 or an amatoxin-linker construct of any one of claims 21 to 26.

28. The conjugate of claim 27, wherein the target-binding moiety is a peptide, anoligonucleotide, a lipid, a lipid carrier, a nanoparticle or combinations thereof.

29. The conjugate of claim 27, wherein the target-binding moiety is an antibody, anantigen-binding fragment thereof, an antibody-like protein, an aptamer, a vitamin, anoligonucleotide, an affibody, a minibody, a lipid, a lipid carrier, a nanoparticle orcombinations thereof.

30. The conjugate of claim 27, wherein the target-binding moiety is an antibody, anantigen-binding fragment thereof or an antibody-like protein.

31. The conjugate of claim 30, wherein the target-binding moiety is an antibody.

32. A pharmaceutical composition comprising the amatoxin analog of any one of claims 1 to17, or the conjugate of any one of claims 27 to 31 and a pharmaceutically acceptable carrier.

33. A use of an amatoxin analog of any one of claims | to 20, or a conjugate of any oneof claims 27 to 31, for treatment of a disease associated with cells presenting a targetin asubject in need thereof, wherein the target-binding moiety is specific for the target.34, The use of claim 33, wherein the disease associated with cells presenting a target iscancer, an autoimmune disease or a viral infection.35, A use of an amatoxin analog of any one of claims | to 20, or a conjugate of any oneof claims 27 to 31, for treatment of cancer in a subject in need thereof.

36. The use of claim 35, wherein the cancer is breast cancer.

37. A method for preparing a sulfiliminium salt of Formula II, the method comprising Simination of a thioether of Formula III in the presence of O-(diphenylphosphiny])hydroxylamine (DPPH):whereinR™ and R® are independently selected from C1-20alkyl, C2-20alkenyl, C2-20alkyny],C3-20cycloalkyl, Ce-soaryl, heterocycloalkyl, heteroaryl and a bioactive moiety, wherein theCi-20alky1, C2-20alkeny1, C2-20alkynyl, C3-20cycloalky1, Co-soaryl, heterocycloalkyl andheteroaryl is optionally substituted with one or more groups selected from C1-salkyl, C1-ealkoxy, aryl, NH2, halo, NOz, cyano, -C(O)C1-calkyl, OH, =O and a bioactive moiety; orwherein R™ and R®, together with the S to which they are attached, formheterocycloalkyl or a bioactive moiety, wherein the heterocycloalky] is optionallysubstituted with one or more groups selected from C1-6alkyl, Ci-calkoxy, aryl, NHb, halo,NOd2, cyano, acyl, OH, =O and a bioactive moiety; andwherein one or more available hydrogens is / are optionally replaced with deuterium;and / or one or more available hydrogens is / are optionally replaced with fluorine.

38. A method for preparing a sulfoximine of Formula IV, the method comprisingoxidizing a sulfiliminium salt of Formula II prepared by a method as defined in claim 34:wherein R™ and R® are as defined in claim 37.39, The method of claim 38, wherein the method is a one-pot reaction.40, The method of any one of claims 37 to 39, wherein R® and R” together form anamatoxin analog.Al. A method for preparing a sulfoximine of Formula IV, the method comprising Simination of a thioether of Formula V in the presence of O-(diphenylphosphiny])hydroxylamine (DPPH):HaN~9 Iq)U8 (DPPH) aR° R%® Rid Rab(V) (IV) ;whereinR™ and R” are independently selected from C1-20alkyl, C2-2alkenyl, C2-20alkynyl,C3-20cycloalkyl, Ce-soaryl, heterocycloalkyl, heteroaryl and a bioactive moiety, wherein theCi-20alky1, C2-20alkeny1, C2-20alkynyl, C3-20cycloalky1, Co-soaryl, heterocycloalkyl andheteroaryl is optionally substituted with one or more groups selected from C1-salkyl, C1-ealkoxy, aryl, NH2, halo, NOz, cyano, -C(O)C1-calkyl, OH, =O and a bioactive moiety; orwherein R™ and R®, together with the S to which they are attached, formheterocycloalkyl or a bioactive moiety, wherein the heterocycloalky] is optionallysubstituted with one or more groups selected from C1-salkyl, Ci-calkoxy, aryl, NH2, halo,NOd2, cyano, acyl, OH, =O and a bioactive moiety; andwherein one or more available hydrogens is / are optionally replaced with deuterium;and / or one or more available hydrogens is / are optionally replaced with fluorine.

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