Synthesis of DLL3-binding peptides

Abstract

The present disclosure relates to processes for preparing peptides that can bind to DLL3.

Description

[0001] SYNTHESIS OF DLL3-BINDING PEPTIDES

[0002] RELATED APPLICATIONS

[0003] This application claims priority to U.S. Provisional Application No. 63 / 556,699 filed on February 22, 2024. The contents of each application are hereby incorporated by reference in their entireties.

[0004] BACKGROUND

[0005] Radiation therapy or radiotherapy is a cancer treatment that uses high doses of radiation to kill cancer cells and shrink tumors. In recent years, targeted radionuclide therapies for cancer utilizing radiolabeled peptides have been developed as an alternative to external radiation therapies. These peptides typically bind to receptors overexpressed by cancer cells. Despite these advancements, there remains a need for new targeted radionuclide therapies.

[0006] Delta-like ligand 3 (DLL3), a member of the Notch signaling system, is a potential target for radionuclide therapies. This evolutionarily conserved system regulates cell fate via cell-cell interactions. During embryonic development, DLL3 is highly expressed and transported to the cell membrane. Once development is complete, DLL3 expression is downregulated and confined to the inside of the cell, typically the Golgi apparatus. DLL3 expression, however, has been found to be highly expressed and localized to the cell membrane in many forms of cancer (Xiu et al., Onco. Targets Ther. (2020), 13:3881-3901 ).

[0007] In addition to being a biomarker, DLL3 plays a role in the regulation of cancer behavior. A study of small cell lung cancer (SCLC) showed that upregulation of DLL3 expression reduced the tumor’s sensitivity to chemotherapy. Additionally, by blocking DLL3, the proliferation and migration of SCLC cells was inhibited and the epithelial to mesenchymal transition (EMT) was reversed (Huang et al., Biochem. Biophys. Res. Commun. (2019) 514(3):853-860). The oncogenic behavior of DLL3 has also been documented in pancreatic cancer, melanoma, and gastric cancer (Mullendore, et al., Clin. Cancer. Res. (2009) 15(7):2291-301 ; Ding, et al., Life Sci. (2019) 226:149-155; Hu et al., Nan Fang Yi Ke Da Xue Xue Bao. (2018) 38(1 ): 14-19).

[0008] Taken together, these findings suggest that DLL3 plays a critical role in the regulation of oncogenic pathways and is specifically upregulated in cancer cells. Compositions that target DLL3, and, in particular, synthesis of those compositions, are therefore useful in the clinical treatment of cancer. SUMMARY

[0009] The present disclosure provides, inter alia, a process for preparing a cyclic peptide of Formula (I): or a pharmaceutically acceptable salt thereof, wherein said process comprises reacting a linear peptide of Formula II: or a pharmaceutically acceptable salt thereof, under conditions that produce a reaction between A1aand A1bto afford the compound of Formula I.

[0010] The present disclosure further provides a process for preparing a linear peptide of Formula (II):

[0011] or a pharmaceutically acceptable salt thereof, wherein said process comprises the step of deprotecting and cleaving a resin-bound peptide of Formula III:

[0012] (HI), or a pharmaceutically acceptable salt thereof, from a resin to provide the linear peptide of Formula (II).

[0013] The present disclosure further provides a process for preparing a resin-bound peptide of Formula III:

[0014] (HI), or a pharmaceutically acceptable salt thereof, wherein said process comprises the steps of

[0015] (A) providing a resin-bound peptide of Formula IV:

[0016] (IV), or a pharmaceutically acceptable salt thereof;

[0017] (B) deprotecting the resin-bound peptide of Formula IV, or a pharmaceutically acceptable salt thereof, to form a deprotected intermediate, wherein the deprotected intermediate is not substituted with a PGChelor PGChel-containing group; and

[0018] (C) reacting the deprotected intermediate with an optionally protected Chelator, ChelatorFree, to provide the resin-bound peptide of Formula III.

[0019] DETAILED DESCRIPTION

[0020] Provided here are processes for preparing compounds that target DLL3 according to the following general scheme:

[0021]

[0022] The compounds of Formula (I), as well as pharmaceutical compositions that comprise these compounds, are useful in the treatment of a variety of indications, including cancer.

[0023] I. Definitions

[0024] Listed below are definitions of various terms used to describe the compounds and compositions disclosed herein. These definitions apply to the terms as they are used throughout this specification and claims, unless otherwise limited in specific instances, either individually or as part of a larger group.

[0025] Unless defined otherwise, all technical and scientific terms used herein generally have the same meaning as commonly understood by one of ordinary skill in the art. Generally, the nomenclature used herein and the laboratory procedures in cell culture, molecular genetics, organic chemistry, and peptide chemistry are those well-known and commonly employed in the art.

[0026] As used in this specification and the appended claims, the singular forms “a,” “an” and “the” include plural referents unless the context clearly dictates otherwise. Thus, for example, reference to “a solvent” includes a combination of two or more such solvents, reference to “a base” includes one or more bases, or mixtures of bases, and the like. Unless specifically stated or obvious from context, as used herein, the term “or” is understood to be inclusive and covers both “or” and “and.”

[0027] As used herein, the term “comprise,” or variations thereof such as “comprises1or “comprising,” are to be read to indicate the inclusion of any recited integer (e.g. a feature, element, characteristic, property, method / process step or limitation) or group of integers (e.g. features, element, characteristics, properties, method / process steps or limitations) but not the exclusion of any other integer or group of integers. Thus, as used herein the term "comprising is inclusive or open-ended and does not exclude additional, unrecited integers or method / process steps.

[0028] The term “alkyl” employed alone or in combination with other terms, refers to a saturated hydrocarbon group that may be straight-chained or branched. The term “Cn-malkyl,” refers to an alkyl group having n to m carbon atoms. An alkyl group formally corresponds to an alkane with one C-H bond replaced by the point of attachment of the alkyl group to the remainder of the compound. In some embodiments, the alkyl group contains from 1 to 6 carbon atoms, from 1 to 4 carbon atoms, from 1 to 3 carbon atoms, or 1 to 2 carbon atoms. Examples of alkyl moieties include, but are not limited to, chemical groups such as methyl, ethyl, n-propyl, isopropyl, n-butyl, tert-butyl, isobutyl, sec-butyl; higher homologs such as 2-methyl-1 -butyl, n-pentyl, 3-pentyl, n-hexyl, 1 ,2,2-trimethylpropyl and the like.

[0029] The term “alkylene,” employed alone or in combination with other terms, refers to a divalent alkyl linking group. An alkylene group formally corresponds to an alkane with two C H bond replaced by points of attachment of the alkylene group to the remainder of the compound. The term “Cn-malkylene” refers to an alkylene group having n to m carbon atoms. Examples of alkylene groups include, but are not limited to, ethan-1 ,2-diyl, ethan-1 , 1 -diyl, propan-1 , 3-diyl, propan-1 ,2-diyl, propan-1 ,1 -diyl, butan-1 ,4-diyl, butan-1 ,3-diyl, butan-1 ,2- diyl, 2-methyl-propan-1 , 3-diyl and the like. As used herein, the term “peptide” refers to a polymer composed of 3 to 50 (or 4-50, 5-50, or 6-50, etc.) amino acid monomers typically linked via amide bond linkage. Peptides (including fragments and variants thereof) of and for use in the invention may be generated wholly or partly by chemical synthesis or by expression from nucleic acid.

[0030] As used herein, the term “carbonyl” refers to a divalent chemical moiety consisting of a carbon (C) atom and an oxygen (O) atom with the chemical formula C(=O). A carbonyl is the common moiety among aldehyde, amide, carboxylic acid, ester, ketone, acyl halide, and acid anhydride functional groups.

[0031] As used herein, the term “amide” refers to compounds that have a trivalent nitrogen attached to a carbonyl group -C(=O)-NH), Examples of amides include methylamide, ethylamide, propylamide, and the like.

[0032] As used herein, the term “optionally substituted” means that the referenced group may be unsubstituted (no substituents) or substituted, including with one or more additional groups individually and independently selected from groups described herein.

[0033] As used herein, the term “substituted” refers to substitution by independent replacement of one, two, or three or more of the hydrogen atoms with substituents described herein.

[0034] As used herein, the term “compound,” refers to a distinct chemical entity. Constructs, targeting constructs, targeting moieties, cargo, chelators, or other construct components, together with any fragments or variants of the foregoing, may be referred to independently or collectively as compounds.

[0035] Compounds may exist in one or more isomeric or isotopic forms (including, but not limited to stereoisomers, geometric isomers, tautomers, and isotopes). Compounds may be provided or utilized in singular form or as a mixture of two or more forms (including, but not limited to racemic mixtures of stereoisomers). Some compounds may exist in different forms, which may exhibit different properties and / or activities (including, but not limited to biological activities). For example, compounds containing asymmetrically substituted carbon atoms may be isolated in optically active or racemic forms. As used herein, the below structure indicates the presence of a double bond wherein substituents can be configured as an E or Z isomer:

[0036] Compounds containing at least two thiols (e.g., two cystine residues) may exist either in the form of a compound containing free thiol moieties, or in the form of a compound containing disulfide bond(s). This phenomenon is due to the spontaneous formation of disulfide bonds by molecular oxygen. For example, any peptide containing multiple cysteine residues, left exposed to air (specifically molecular oxygen, i.e., anerobic conditions) may be oxidized to form a disulfide bond.

[0037] As used herein, the term “amide bond” refers to the covalent linkage between the carbonyl carbon and nitrogen present in an amide group. In the context of peptide chemistry, amide bonds are also commonly referred to as peptide bonds where two consecutive alphaamino acids are linked from the amide carbonyl carbon of one alpha-amino acid to the amide nitrogen a subsequent alpha-amino acid, along a peptide or protein chain.

[0038] The terms “halo” or “halogen,” used alone or in combination with other terms, refers to fluoro, chloro, bromo and iodo. In some embodiments, “halo” refers to a halogen atom selected from F, Cl, or Br. In some embodiments, halo groups are F.

[0039] As used herein, the term “chelator” refers to any class of compound or moiety of a compound that can form a stable complex between itself and a metal ion. Chelators may also be commonly referred to as chelating agents. Examples of chelators include ethylenediamine (en), ethylenediaminetetraacetate (EDTA), dimercaptosuccinic acid (DMSA), nitrilotriacetic acid (NTA), citric acid (CA), cyclic polyethers, 1 ,4,7,10- Tetraazacyclododecane-1 ,4,7,10-tetraacetic acid (DOT A), and the like.

[0040] As used herein, the term “peptide backbone” consists of repeat units of an amino group, an a-carbon, and a carbonyl group (e.g., -NH-C(R)H-C(O)-).

[0041] As used herein, the term “linker” refers to any chemical species with bifunctionality that aids in the tethering of two chemically relevant moieties through covalent bond formation. As used herein, the term “amino acid” includes the residues of the natural amino acids as well as unnatural amino acids. The 20 natural proteinogenic amino acids are identified and referred to herein by either the one-letter or three-letter designations as follows: aspartic acid (Asp:D), isoleucine (He: I), threonine (Thr:T), leucine (Leu:L), serine (Ser:S), tyrosine (Tyr:Y), glutamic acid (Glu:E), phenylalanine (Phe:F), proline (Pro:P), histidine (His:H), glycine (Gly:G), lysine (Lys:K), alanine (Ala:A), arginine (Arg:R), cysteine (Cys:C), tryptophan (Trp:W), valine (Val:V), glutamine (Gln:Q) methionine (Met:M), asparagine (Asn:N). Naturally occurring amino acids exist in their levorotary (L) stereoisomeric forms. Amino acids referred to herein are L-stereoisomers except where otherwise indicated. The term “amino acid” also includes amino acids bearing a conventional amino protecting group (e.g., acetyl or benzyloxycarbonyl), as well as natural and unnatural amino acids protected at the carboxy terminus (e.g., as a (C1-C6) alkyl, phenyl or benzyl ester or amide; or as an alpha-methylbenzyl amide). Other suitable amino and carboxy protecting groups are known to those skilled in the art (See for example, Greene, T. W.; Wutz, P. G. M., Protecting Groups in Organic Synthesis; second edition, 1991 , New York, John Wiley & sons, Inc., and documents cited therein, the contents of each of which are herein incorporated by reference in their entirety). Peptides and / or peptide compositions of the present disclosure may also include modified amino acids.

[0042] “Unnatural” amino acids have side chains or other features not present in the 20 naturally-occurring amino acids listed above and include, but are not limited to: N-methyl amino acids, N-alkyl amino acids, alpha, alpha substituted amino acids, beta-amino acids, alpha-hydroxy amino acids, D-amino acids, and other unnatural amino acids known in the art (See, e.g., Josephson et al., (2005) J. Am. Chem. Soc. 127: 11727-11735; Forster, A.C. et al. (2003) Proc. Natl. Acad. Sci. USA 100: 6353-6357; Subtelny et al., (2008) J. Am. Chem. Soc. 130: 6131-6136; Hartman, M.C.T. et al. (2007) PLoS ONE 2:e972; and Hartman et al., (2006) Proc. Natl. Acad. Sci. USA 103:4356-4361 ). Further unnatural amino acids useful for the optimization of peptides and / or peptide compositions of the present disclosure include, but are not limited to 1 ,2,3, 4-tetrahydroisoquinoline-1 -carboxylic acid, 1-amino-2,3-hydro-1 H- indene-1 -carboxylic acid, homolysine, homoarginine, homoserine, 2-aminoadipic acid, 3- aminoadipic acid, beta-alanine, aminopropionic acid, 2-aminobutyric acid, 4-aminobutyric acid, 5-aminopentanoic acid, 5-afminohexanoic acid, 6-aminocaproic acid, 2-aminoheptanoic acid, 2-aminoisobutyric acid, 3-aminoisobutyric acid, 2-aminopimelic acid, desmosine, 2,3- diaminopropionic acid, N-ethylglycine, N-ethylasparagine, homoproline, hydroxy lysine, allohydroxylysine, 3-hydroxyproline, 4-hydroxyproline, isodesmosine, allo-isoleucine, N- methylpentylglycine, naphthylalanine, ornithine, pentylglycine, thioproline, norvaline, tertbutylglycine (also known as tert-leucine), phenylglycine, azatryptophan, 5-azatryptophan, 7- azatryptophan, 4-fluorophenylalanine, penicillamine, sarcosine, homocysteine, 1- aminocyclopropanecarboxylic acid, 1 -aminocyclobutanecarboxylic acid, 1- aminocyclopentanecarboxylic acid, 1 -aminocyclohexanecarboxylic acid, 4-aminotetrahydro- 2H-pyran-4-carboxylic acid, (S)-2-amino-3-(1H-tetrazol-5-yl)propanoic acid, cyclopentylglycine, cyclohexylglycine, cyclopropylglycine, q-co-methyl-arginine, 4- chlorophenylalanine, 3-chlorotyrosine, 3-fluorotyrosine, 5-fluorotryptophan, 5- chlorotryptophan, citrulline, 4-chloro-homophenylalanine, homophenylalanine, 4- aminomethyl-phenylalanine, 3-aminomethyl-phenylalanine, octylglycine, norleucine, tranexamic acid, 2-amino pentanoic acid, 2-amino hexanoic acid, 2-amino heptanoic acid, 2- amino octanoic acid, 2-amino nonanoic acid, 2-amino decanoic acid, 2-amino undecanoic acid, 2-amino dodecanoic acid, aminovaleric acid, and 2-(2-aminoethoxy)acetic acid, pipecolic acid, 2-carboxy azetidine, hexafluoroleucine, 3-Fluorovaline, 2-amino-4,4-difluoro- 3-methylbutanoic acid, 3-fluoro-isoleucine, 4-fluoroisoleucine, 5-fluoroisoleucine, 4-methyl- phenylglycine, 4-ethyl-phenylglycine, 4-isopropyl-phenylglycine, (S)-2-amino-5- azidopentanoic acid (also referred to herein as “X02”), (S)-2-aminohept-6-enoic acid (also referred to herein as “X30”), (S)-2-aminopent-4-ynoic acid (also referred to herein as “X31”), (S)-2-aminopent-4-enoic acid (also referred to herein as “X12”), (S)-2-amino-5-(3- methylguanidino) pentanoic acid, (S)-2-amino-3-(4-(aminomethyl)phenyl)propanoic acid, (S)- 2-amino-3-(3-(aminomethyl)phenyl)propanoic acid, (S)-2-amino-4-(2-aminobenzo[d]oxazol- 5-yl)butanoic acid, (S)-leucinol, (S)-valinol, (S)-tert-leucinol, (R)-3-methylbutan-2-amine, (S)- 2-methyl-1-phenylpropan-1-amine, and (S)-N,2-dimethyl-1-(pyridin-2-yl)propan-1-amine, (S)-

[0043] 2-amino-3-(oxazol-2-yl)propanoic acid, (S)-2-amino-3-(oxazol-5-yl)propanoic acid, (S)-2- amino-3-(1 ,3,4-oxadiazol-2-yl)propanoic acid, (S)-2-amino-3-(1 ,2,4-oxadiazol-3-yl)propanoic acid, (S)-2-amino-3-(5-fluoro-1 H-indazol-3-yl)propanoic acid, and (S)-2-amino-3-(1 H-indazol-

[0044] 3-yl)propanoic acid, (S)-2-amino-3-(oxazol-2-yl)butanoic acid, (S)-2-amino-3-(oxazol-5-yl) butanoic acid, (S)-2-amino-3-(1 ,3,4-oxadiazol-2-yl) butanoic acid, (S)-2-amino-3-(1 ,2,4- oxadiazol-3-yl) butanoic acid, (S)-2-amino-3-(5-fluoro-1 H-indazol-3-yl) butanoic acid, and (S)-2-amino-3-(1 H-indazol-3-yl) butanoic acid, 2-(2’MeOphenyl)-2-amino acetic acid, tetrahydro 3-isoquinolinecarboxylic acid and stereoisomers thereof (including, but not limited, to D and L isomers).

[0045] As used herein, the term “resin” refers to polymer support composed of polystyrene, polystyrene-PEG composites, PEG, poly-e-Lysine (e-PL), or the like, and a linker to which a peptide is anchored by its N- or C-terminus and therefore bound to the insoluble polymer. Examples of resins are Merrifield, 4-methylbenzhydryl amine (MBHA), Wang, 4- (Hydroxymethyl)phenoxyaceamidomethyl polystyrene (HMPA), 2-chlorotrityl chloride, and the like.

[0046] Certain abbreviations are used throughout the present disclosure and are defined in the following table:

[0047]

[0048] As used herein, the term “SPPS” (solid-phase peptide synthesis) refers to the use of an insoluble resin-based solid support for peptide synthesis where a peptide and / or peptides are assembled stepwise from the C to N terminus using Na-protected (blocked) amino acids (See, e.g. Merrifield, R. B., J. Am. Chem. Soc., 1963, 85, 2149-2154; Merrifield, R. B., Recent Prog. Horm. Res., 1967, 23, 451-82; Merrifield, R. B., Science, 1986, 232, 341-347; Carpino, L. A., Han, G. Y., J. Am. Chem. Soc., 1970, 92, 5748-5749.)

[0049] As used herein, “resin-bound peptide” refers to a synthetic peptide scaffold that is covalently bound to the linker of the insoluble polymer / resin. As used herein, “protecting group” refers to a molecular framework that is temporarily introduced onto a specific functional group in a poly-functional molecule to decrease reactivity so that the protected functional group does not react under synthetic conditions to which the molecule is subjected in one or more subsequent steps, to make modifications elsewhere in the molecule. Examples of protecting groups are disclosed in Greene's Protective Groups in Organic Synthesis, 4thEd., pp. 1-16, John Wiley & Sons: New York, 2014, which is incorporated by reference herein. Examples of common protecting groups are benzyloxycarbonyl (Cbz), 2,2,2-trichloroethoxycarbonyl (Troc), 2- (trimethylsilyl)ethoxycarbonyl (Teoc), 2-(4-trifluoromethylphenylsulfonyl)ethoxycarbonyl (Tsc), t-butoxycarbonyl (Boc), 1-adamantyloxycarbonyl (Adoc), 2-adamantylcarbonyl (2- Adoc), 2,4-dimethylpent-3-yloxycarbonyl (Doc), cyclohexyloxycarbonyl (Hoc), 1 ,1-dimethyl- 2,2,2-trichloroethoxycarbonyl (TcBoc), vinyl, 2-chloroethyl, 2-phenylsulfonylethyl, allyl, benzyl, 2-nitro benzyl, 4-nitrobenzyl, diphenyl-4-pyridylmethyl, N’,N’-dimethylhydrazinyl, methoxymethyl (MOM), 2-methoxyethoxymethyl (MEM), t-butoxymethyl (Bum), benzyloxymethyl (BOM), or 2-tetrahydropyranyl (THP), methoxymethyl (MOM), 2- methoxyethoxymethyl (MEM), allyl, t-butyldimethylsilyl (TBDMS), or pivoyl (Piv), 2- (trimethylsilyl)ethoxymethyl (SEM), t-butyl carbamate (Boc), or tosyl (Ts), and the like.

[0050] As used herein, “amino protecting group” refers to a protecting group designed to block the reactivity of nitrogen as a nucleophile in amino functional groups (-NH2). Examples of common amino protecting groups are 9-fluorenylmethyl carbamate (Fmoc), t-butyl carbamate (Boc), benzyl carbamate (Z or Cbz), acetamide (Ac), trifluoroacetamide, phthalimide, benzylamine (Bn), triphenylmethylamine (Tr), benzylideneamine, p- Toluenesulfonamide (Ts), and the like.

[0051] As used herein, “carboxylic acid protecting group” refers to a protecting group designed to block the reactivity of carboxylic acid functional groups (-CO2H). Examples of common carboxylic acid protecting groups are methyl, t-Butyl, benzyl, S-t-butyl, 2-alkyl-1 ,3- oxazoline, and the like.

[0052] As used herein, “hydroxyl protecting group” refers to a protecting group designed to block the reactivity of alcohol functional groups (-OH). Examples of common alcohol or hydroxyl protecting groups are methoxymethyl ether (MOM), tetrahydropyranyl ether (THP), t-butyl ether (t-Bu), allyl ether (Allo), benzyl ether (Bn), t-butyldimethylsilyl ether (TBDMS), t- butyldiphenylsilyl ether (TBDPS), t-butylisopropylsilyl ether (TIPS), trimethylsilyl ether (TMS), acetic acid ester (Ac), pivalic acid ester (Piv), benzoic acid ester (Bz), and the like.

[0053] As used herein, “thiol protecting group” refers to a protecting group designed to block the reactivity of sulfur as a nucleophile in thiol functional groups (-SH). Examples of common thiol protecting groups are benzyl (Bn), trityl (Trt), tert-butyl (t-Bu), 1-adamantyl (Ad), 9- fluorenylmethyl (Fm), 9-fluorenylmethyl-oxycarbonyl (Fmoc), thiazolidine (Thz), 2-Nitrobenzyl (o-NB), tert-butylsulphenyl (S-t-Bu), and the like.

[0054] As used herein, “deprotecting” refers to the process in which a protecting group is intentionally removed furnishing the original unprotected functional group as it was before protection.

[0055] As used herein, “deblocking” refers to the method of orthogonally removing Na- protecting (blocking) groups (e.g. Fmoc) while maintaining protecting groups on other moieties within the molecule (e.g. Boc-, t-Bu-, Trt-, Mtt-protected sidechains)

[0056] As used herein, “leaving group” refers to a chemical moiety that detaches from the main or residual part of a substrate during a reaction or elementary step of a reaction. Commonly, a leaving group is a fragment that departs with a pair of electrons in a heterolytic bond cleavage generally as an anionic or neutral species (Lewis base), departing from a neutral or cationic substrate, respectively. Examples of leaving groups are halides, sulfonate esters, water, ammonia, and the like.

[0057] As used herein, the term “base” refers to any species that contains a filled orbital containing an electron pair which is not involved in bonding. In some embodiments, bases include sodium hydroxide, potassium hydroxide, sodium bicarbonate, potassium bicarbonate, cesium bicarbonate, sodium carbonate, potassium carbonate, cesium carbonate, sodium acetate, potassium acetate, cesium acetate, pyridine, imidazole, triethylamine, triethylamine, N,N-diisopropylethylamine (DIPEA), sodium ethoxide, potassium ethoxide, and the like. In other embodiments, bases include lithium hydroxide, sodium hydroxide, potassium hydroxide, lithium carbonate, sodium carbonate, and potassium carbonate. Some example strong bases include, but are not limited to, hydroxide, alkoxides, metal amides, metal hydrides, metal dialkylamides, and arylamines, wherein; alkoxides include lithium, sodium, and potassium salts of methyl, ethyl, and t-butyl oxides; metal amides include sodium amide, potassium amide, and lithium amide; metal hydrides include sodium hydride, potassium hydride, and lithium hydride; and metal dialkylamides include sodium, lithium, and potassium salts of methyl, ethyl, n-propyl, i-propyl, n-butyl, t-butyl, trimethylsilyl, and cyclohexyl substituted amides.

[0058] Upon carrying out preparation of compounds according to the processes described herein, isolation, and purification operations such as concentration, filtration, extraction, solid-phase extraction, recrystallization, chromatography, and the like may be used, to isolate the desired products.

[0059] The compounds disclosed herein may exist as tautomers and optical isomers (e.g., enantiomers, diastereomers, diastereomeric mixtures, racemic or non-racemic mixtures, and the like). The absolute stereochemistry is specified according to the Cahn-lngold-Prelog R-S system.

[0060] Compounds provided herein can also include all isotopes of atoms occurring in the intermediates or final compounds. Isotopes include those atoms having the same atomic number but different mass numbers. For example, isotopes of hydrogen include tritium and deuterium. One or more constituent atoms of the compounds of the invention can be replaced or substituted with isotopes of the atoms in natural or non-natural abundance. In some embodiments, the compound includes at least one deuterium atom. For example, one or more hydrogen atoms in a compound of the present disclosure can be replaced or substituted by deuterium. In some embodiments, the compound includes two or more deuterium atoms. In some embodiments, the compound includes 1 , 2, 3, 4, 5, 6, 7, 8, 9, 10, 11 , or 12 deuterium atoms. Synthetic methods for including isotopes into organic compounds are known in the art (Deuterium Labeling in Organic Chemistry by Alan F. Thomas (New York, N.Y., Appleton-Century-Crofts, 1971 ; The Renaissance of H / D Exchange by Jens Atzrodt, Volker Derdau, Thorsten Fey and Jochen Zimmermann, Angew. Chem. Int. Ed. 2007, 7744-7765; The Organic Chemistry of Isotopic Labelling by James R. Hanson, Royal Society of Chemistry, 2011 ). Isotopically labeled compounds can used in various studies such as NMR spectroscopy, metabolism experiments, and / or assays.

[0061] In the compounds provided herein, any atom not specifically designated as a particular isotope is meant to represent any stable isotope of that atom. Unless otherwise stated, when a position is designated specifically as “H” or “hydrogen,” the position is understood to have hydrogen at its natural abundance isotopic composition. Also, unless otherwise stated, when a position is designated specifically as “D” or “deuterium”, the position is understood to have deuterium at an abundance that is at least 3000 times greater than the natural abundance of deuterium, which is 0.015% (i.e., at least 45% incorporation of deuterium).

[0062] As used herein, the term “pharmaceutically acceptable salt” refers to derivatives of the disclosed cyclic peptides wherein the parent compound is modified by converting an existing acid or base moiety to its salt form. In some embodiments, the side-chain amino acid groups of the cyclic peptide (e.g., R0, R1, R2, R3, R4...etc) can be modified. Examples of pharmaceutically acceptable salts include, but are not limited to, mineral or organic acid salts of basic residues such as amines; alkali or organic salts of acidic residues such as carboxylic acids; and the like. The pharmaceutically acceptable salts of the present disclosure include the conventional non-toxic salts of the parent compound formed, for example, from non-toxic inorganic or organic acids. The pharmaceutically acceptable salts of the present disclosure can be synthesized from the parent compound which contains a basic or acidic moiety by conventional chemical methods. Generally, such salts can be prepared by reacting the free acid or base forms of these compounds with a stoichiometric amount of the appropriate base or acid in water or in an organic solvent, or in a mixture of the two; generally, non-aqueous media like ether, ethyl acetate, ethanol, isopropanol, or acetonitrile are preferred. In some embodiments, the pharmaceutically acceptable salt comprises the corresponding pharmaceutically acceptable cation or anion. The phrase “pharmaceutically acceptable salt” is not limited to a mono, or 1 :1 , salt. For example, “pharmaceutically acceptable salt” also includes bis-salts, such as a bis-hydrochloride salt. Lists of suitable salts are found in Remington’s Pharmaceutical Sciences, 17th ed., Mack Publishing Company, Easton, Pa., 1985, p. 1418 and Journal of Pharmaceutical Science, 66, 2 (1977), each of which is incorporated herein by reference in its entirety. II. Synthetic Processes

[0063] The present disclosure provides, inter alia, processes for preparing peptides that can bind to delta like canonical Notch ligand 3 (DLL3). Cyclization

[0064] In an aspect, provided herein is a process for preparing a cyclic peptide of Formula I: or a pharmaceutically acceptable salt thereof, wherein:

[0065] P1is selected from: H, -L1-Chelator, D1is selected from H, CH3, C(O)OH, and -NR”-Chelator;

[0066] L1is absent or selected from wherein the amino group of L1connects to the carbonyl group of P1or Chelator to form an amide bond;

[0067] P2is selected from C(O)NH2, C(O)OH,

[0068] L2is absent or selected from: wherein the amino group of L2connects to the carbonyl group of P2or Chelator to form an amide bond;

[0069] P3is selected from H, Ac, -L3-Chelator,

[0070]

[0071] L3is absent or independently selected from wherein the carbonyl group of L3connects to an amine group of P2to form an amide bond;

[0072] D3is independently selected from: CH3, C(O)OH, -NR”-Chelator, and

[0073] X is halogen;

[0074] R° is an amino acid side chain of a natural amino acid or an amino acid side chain of an unnatural amino acid;

[0075] R1is an amino acid side chain of a natural amino acid or an amino acid side chain of an unnatural amino acid;

[0076] R2is an amino acid side chain of a natural amino acid or an amino acid side chain of an unnatural amino acid;

[0077] R3is an amino acid side chain of a natural amino acid or an amino acid side chain of an unnatural amino acid;

[0078] B1is C1-6 alkylene;

[0079] C1is C1-6 alkylene; A1is selected from: wherein w is selected from 1 , 2, or 3;

[0080] R4is an amino acid side chain of a natural amino acid or an amino acid side chain of an unnatural amino acid, both of which are optionally substituted with Chelator, CH2C(O)OH, or C(O)(CH2CH2O)P(CH2)2N(CH3)3+, wherein the Chelator is optionally substituted to the amino acid side chain through a Linker;

[0081] R5is an amino acid side chain of a natural amino acid or an amino acid side chain of an unnatural amino acid, both of which are optionally substituted with Chelator, wherein the Chelator is optionally substituted to the amino acid side chain through a Linker;

[0082] R6is an amino acid side chain of a natural amino acid or an amino acid side chain of an unnatural amino acid;

[0083] R7is selected from:

[0084] (i) an amino acid side chain of a natural amino acid,

[0085] (ii) an amino acid side chain of an unnatural amino acid, and

[0086] (iii) selected from the group consisting of wherein L4is absent or independently selected from: wherein the carbonyl group of L4connects to an amine group of R7to form an amide bond;

[0087] R8is an amino acid side chain of a natural amino acid or an amino acid side chain of an unnatural amino acid;

[0088] R9is an amino acid side chain of a natural amino acid or an amino acid side chain of an unnatural amino acid;

[0089] R10is an amino acid side chain of a natural amino acid or an amino acid side chain of an unnatural amino acid; m is 0 or 1 ; each n, q, and u are independently an integer from 0 to 16; each p is independently an integer from 0 to 24; each s is independently an integer from 0 to 16; each t is independently 1 , 2, 3, 4, 5, or 6; each R’ is independently selected from H, C(O)OH, (CH2)OH, and NHAc; and each R” is independently selected from H and CH3; wherein each backbone nitrogen atom or alpha carbon is optionally substituted with a methyl group. wherein either the cyclic peptide of Formula I does not comprise a Chelator, or at least one of R4, R5, or R7is substituted with a Chelator or Chelator-containing group, wherein said process comprises reacting a linear peptide of Formula II: or a pharmaceutically acceptable salt thereof, under conditions that produce a reaction between A1aand A1bto afford the compound of Formula I, wherein:

[0090] A1aand A1bare each selected from: wherein either the linear peptide of Formula II does not comprise a Chelator, or at least one of R4, R5, or R7is substituted with a Chelator or Chelator-containing group, wherein each backbone nitrogen atom or alpha carbon is optionally substituted with a methyl group. In an embodiment, the peptide of Formula I is a peptide of Formula la: or a pharmaceutically acceptable salt thereof, and the peptide of Formula II is a peptide of Formula Ila: or a pharmaceutically acceptable salt thereof.

[0091] In another embodiment, the peptide of Formula I is a peptide of Formula lb:

[0092] or a pharmaceutically acceptable salt thereof, and the peptide of Formula II is a peptide of

[0093] Formula lib: or a pharmaceutically acceptable salt thereof.

[0094] In an embodiment, P1is selected from: H, wherein:

[0095] D1is selected from H, CH3, C(O)OH, and -NR”-Chelator; and

[0096] L1is absent or selected from:

[0097] wherein the amino group of L1connects to the carbonyl group of P1to form an amide bond;

[0098] In another embodiment, P1is selected from: -L1-Chelator, wherein:

[0099] L1is absent or selected from wherein the amino group of L1connects to the carbonyl group of P1or Chelator to form an amide bond.

[0100] In another embodiment, P2is selected from C(O)NH2, C(O)OH. In yet another embodiment, P2is selected from: wherein:

[0101] D2is OH or NH2;

[0102] L2is absent or selected from:

[0103] In an embodiment, P3is selected from H, Ac,

[0104] D3is independently selected from: CH3, C(O)OH, -NR”-Chelator, and

[0105] X is halogen; each n, q, and u are independently an integer from 0 to 16; each p is independently an integer from 0 to 24; each s is independently an integer from 0 to 16; each t is independently 1 , 2, 3, 4, 5, or 6; each R’ is independently selected from H, C(O)OH, (CH2)OH, and NHAc; and each R” is independently selected from H and CH3;

[0106] In another embodiment, P3is selected from: -L3-Chelator, and Chelator

[0107] L3is absent or independently selected from wherein: the carbonyl group of L3connects to an amine group of P2to form an amide bond; each t is independently 1 , 2, 3, 4, 5, or 6; each R’ is independently selected from H, C(O)OH, (CH2)OH, and NHAc; and each R” is independently selected from H and CH3.

[0108] In yet another embodiment, R° is an amino acid side chain of a natural amino acid.

[0109] In an embodiment, R° is an amino acid side chain of an unnatural amino acid.

[0110] In another embodiment, R1is an amino acid side chain of a natural amino acid or an amino acid side chain of an unnatural amino acid.

[0111] In still another embodiment, R1is an amino acid side chain of an unnatural amino acid.

[0112] In an embodiment, R2is an amino acid side chain of a natural amino acid.

[0113] In another embodiment, R2is an amino acid side chain of an unnatural amino acid.

[0114] In yet another embodiment, R3is an amino acid side chain of a natural amino acid.

[0115] In still another embodiment, R3is an amino acid side chain of an unnatural amino acid.

[0116] In an embodiment, R4is an amino acid side chain of a natural amino acid.

[0117] In another embodiment, R4is an amino acid side chain of an unnatural amino acid.

[0118] In still another embodiment, R4is optionally substituted with Chelator, CH2C(O)OH, or C(O)(CH2CH2O)P(CH2)2N(CH3)3+, wherein the Chelator is optionally substituted to the amino acid side chain through a Linker.

[0119] In an embodiment, R5is an amino acid side chain of a natural amino acid.

[0120] In another embodiment, R5is an amino acid side chain of an unnatural amino acid. In yet another embodiment, R5is optionally substituted with Chelator, CH2C(O)OH, or C(O)(CH2CH2O)P(CH2)2N(CH3)3+, wherein the Chelator is optionally substituted to the amino acid side chain through a Linker.

[0121] In an embodiment, R6is an amino acid side chain of a natural amino acid.

[0122] In another embodiment, R6is an amino acid side chain of an unnatural amino acid.

[0123] In an embodiment, R7is an amino acid side chain of a natural amino acid.

[0124] In another embodiment, R7an amino acid side chain of an unnatural amino acid.

[0125] In yet another embodiment, R7selected from the group consisting of wherein L4is absent or independently selected from: wherein the carbonyl group of L4connects to an amine group of R7to form an amide bond; wherein: each n, q, and u are independently an integer from 0 to 16; each p is independently an integer from 0 to 24; each s is independently an integer from 0 to 16; each t is independently 1 , 2, 3, 4, 5, or 6; each R’ is independently selected from H, C(O)OH, (CH2)OH, and NHAc; and each R” is independently selected from H and CH3.

[0126] In an embodiment, R8is an amino acid side chain of a natural amino acid.

[0127] In another embodiment, R8is an amino acid side chain of an unnatural amino acid.

[0128] In an embodiment, R9is an amino acid side chain of a natural amino acid.

[0129] In another embodiment, R9is an amino acid side chain of an unnatural amino acid. In an embodiment, R10is an amino acid side chain of a natural amino acid.

[0130] In another embodiment, R10is an amino acid side chain of an unnatural amino acid.

[0131] In an embodiment, each backbone nitrogen atom is optionally substituted with a methyl group.

[0132] In another embodiment, each backbone alpha carbon is optionally substituted with a methyl group.

[0133] In an embodiment:

[0134] P1is selected from H, Ac, , wherein n and s are each independently 9,

[0135] 10, 11 , 12, or 13;

[0136] D1is CH3or C(O)OH;

[0137] X is halogen;

[0138] R1is selected from the group consisting of an amino acid side chain of Trp, 2Nal, 1 Nal, 4CF3-Phe, 7Aza-Trp, 1Me-Trp, 5OH-Trp, BIP, 5OMe-Trp, 4F-Phe, 3Pya, 4Pya, PAF, MAF, OAF, 5Qui, 7MeO-Trp, 7Me-Trp, 5F-Trp, 7CI-Trp, D-Ala, and Ala;

[0139] R2is selected from the group consisting of an amino acid side chain of Thr, D-Ala, Ala, and Lys;

[0140] R3is selected from the group consisting of an amino acid side chain of He, Env, CHA, CBA, Nle, Tbg, THPG, Chg, 2Nal, 1 Nal, 2CF3-Phe, D-Ala, Ala, Leu, t-Bu-Ala, a-tert-amylGly, Allo-lle, Lys(C12), Lys(C14), and Lys(C16);

[0141] B1is C1-6 alkylene;

[0142] C1is C1-6 alkylene;

[0143] A1is selected from the group consisting of

[0144] R4is selected from the group consisting of an amino acid side chain of Asn, D-Ala, Ala, DAB-4-NHCOC5HH , DAB-4-NHCOC7H15, Asp, Ser, Lys(DOTA), Lys, 3-(4-piperidinyl)- Ala, 3-(1-morpholinyl)-Ala, 3Pya, 4Pya, Glu, Pip(CH2CO2H)Ala, Pip(PegNMe3)Ala, and Pip(GAE-DOTA)Ala;

[0145] R5is selected from the group consisting of an amino acid side chain of Asn, Ala, D- Ala, Trp, Asp, Lys, Lys(DOTA), 3Pya, 4Pya, 3-(4-piperidinyl)-Ala, 3-(1-morpholinyl)-Ala, Glu, and Ser;

[0146] R6is selected from the group consisting of an amino acid side chain of Trp, 4CF3- Phe, 1Me-Trp, 7Aza-Trp, BIP, 2Nal, 1 Nal, D-Ala, Ala, 4F-Phe, 5F-Trp, 5MeO-Trp, Asn, 5OH- Trp, 7Me-Trp, 7MeO-Trp, and 7CI-Trp;

[0147] R7is:

[0148] (i) selected from the group consisting of an amino acid side chain of 3Pya, 4Pya,

[0149] Lys(Me)3, His, Ala, D-Ala, Gin, Lys, Glu, Arg, Orn, and Ser; or

[0150] (ii) selected from the group consisting of , wherein each s is independently 3, 5,10,

[0151] 12, or 14;

[0152] R8is selected from the group consisting of an amino acid side chain of Asp, D-Ala,

[0153] Ala, Asn, and Thr; R9is selected from the group consisting of an amino acid side chain of Trp, 7Aza- Trp, 1 Me-Trp, D-Ala, Ala, 4F-Phe, 1 Nal, 2Nal, 5F-Trp, 5MeO-Trp, 7CI-Trp, 5OH-Trp, 7Me- Trp, and 7MeO-Trp;

[0154] R10is selected from the group consisting of an amino acid side chain of Pro, D-Ala, Ala, trans4Fluoro-Pro, cis4Fluoro-Pro, trans4OH-Pro, cis4OH-Pro, Pip, 5,5-diMe-Pro, trans4NH2-Pro, cis4NH2-Pro, Aze, R-3Me-Aze, ACI, and 3Me2-Aze; m is 0.

[0155] In an embodiment, P1is either H or Ac.

[0156] In another embodiment, P1is selected from: , , wherein n and s are each independently 9,

[0157] 10, 11 , 12, or 13;

[0158] D1is CH3or C(O)OH.

[0159] In an embodiment, P2is selected from

[0160] X is halogen.

[0161] In an embodiment, R1is selected from the group consisting of an amino acid side chain of Trp and Ala.

[0162] In another embodiment, R1is an amino acid side chain of D-Ala

[0163] In yet another embodiment, R1is selected from the group consisting of an amino acid side chain of 2Nal, 1 Nal, 4CF3-Phe, 7Aza-Trp, 1 Me-Trp, 5OH-Trp, BIP, 5OMe-Trp, 4F-Phe, 3Pya, 4Pya, PAF, MAF, OAF, 5Qui, 7MeO-Trp, 7Me-Trp, 5F-Trp, and 7CI-Trp.

[0164] In an embodiment, R2is selected from the group consisting of an amino acid side chain of Thr, Ala, and Lys.

[0165] In another embodiment, R2is an amino acid side chain of D-Ala. In an embodiment, R3is selected from the group consisting of an amino acid side chain of lie, Ala, and Leu.

[0166] In another embodiment, R3is selected from the group consisting of an amino acid side chain of Env, CHA, CBA, Nle, Tbg, THPG, Chg, 2Nal, 1 Nal, 2CF3-Phe, D-Ala, t-Bu-Ala, a-tert-amylGly, and Allo-lle.

[0167] In yet another embodiment, R3is selected from the group consisting of an amino acid side chain of Lys(C12), Lys(C14), and Lys(C16).

[0168] In an embodiment, A1is selected from the group consisting of

[0169] In another embodiment, A1is selected from the group consisting of

[0170] In yet another embodiment, A1is selected from the group consisting of

[0171] In an embodiment, R4is selected from the group consisting of an amino acid side chain of Asn, Ala, Asp, Ser, Lys, and Glu.

[0172] In another embodiment, R4is selected from the group consisting of an amino acid side chain of DAB-4-NHCOC5Hn, DAB-4-NHCOC7H15, Lys(DOTA), 3-(4-piperidinyl)-Ala, 3- (l-morpholinyl)-Ala, 3Pya, 4Pya, Pip(CH2CO2H)Ala, Pip(PegNMe3)Ala, and Pip(GAE- DOTA)Ala.

[0173] In yet another embodiment, R4is an amino acid side chain of D-Ala.

[0174] In another embodiment, R4is an amino acid side chain of Pip(CH2CO2H)Ala.

[0175] In still another embodiment, R4is an amino acid side chain of Pip(CH2CO2X)Ala, wherein X is a pharmaceutically acceptable cation.

[0176] In an embodiment, R5is selected from the group consisting of an amino acid side chain of Asn, Ala, Trp, Asp, Lys, Glu, and Ser.

[0177] In another embodiment, R5is selected from the group consisting of an amino acid side chain of Lys(DOTA), 3Pya, 4Pya, 3-(4-piperidinyl)-Ala, and 3-(1-morpholinyl)-Ala.

[0178] In yet another embodiment, R5is an amino acid side chain of D-Ala.

[0179] In an embodiment, R6is selected from the group consisting of an amino acid side chain of Trp, Ala, and Asn. In another embodiment, R6is selected from the group consisting of an amino acid side chain of 4CF3-Phe, 1Me-Trp, 7Aza-Trp, BIP, 2Nal, 1 Nal, 4F-Phe, 5F-Trp, 5MeO-Trp, 5OH-Trp, 7Me-Trp, 7MeO-Trp, and 7CI-Trp.

[0180] In yet another embodiment, R6is an amino acid side of D-Ala.

[0181] In an embodiment, R7is selected from the group consisting of an amino acid side chain of His, Ala, D-Ala, Gin, Lys, Glu, Arg, Orn, and Ser.

[0182] In another embodiment, R7is selected from the group consisting of an amino acid side chain of 3Pya, 4Pya, and Lys(Me)3.

[0183] In yet another embodiment, R7is selected from the group consisting of wherein each s is independently 3, 5,10,

[0184] 12, or 14;

[0185] In an embodiment, R8is selected from the group consisting of an amino acid side chain of Asp, Ala, Asn, and Thr.

[0186] In another embodiment, R8is an amino acid side chain of D-Ala.

[0187] In an embodiment, R9is selected from the group consisting of an amino acid side chain of Trp and Ala.

[0188] In another embodiment, R9is selected from the group consisting of an amino acid side chain of 7Aza-Trp, 1Me-Trp, 4F-Phe, 1Nal, 2Nal, 5F-Trp, 5MeO-Trp, 7CI-Trp, 5OH-Trp, 7Me-Trp, and 7MeO-Trp.

[0189] In yet another embodiment, R9is an amino acid side chain of D-Ala.

[0190] In an embodiment, R10is selected from the group consisting of an amino acid side chain of Pro and Ala.

[0191] In another embodiment, R10is selected from the group consisting of an amino acid side chain of trans4Fluoro-Pro, cis4Fluoro-Pro, trans4OH-Pro, cis4OH-Pro, Pip, 5,5-diMe- Pro, trans4NH2-Pro, cis4NH2-Pro, Aze, R-3Me-Aze, ACI, and 3Me2-Aze; In yet another embodiment, R10is an amino acid side chain of D-Ala.

[0192] In an embodiment, the process for preparing a cyclic peptide of Formula I further encompasses:

[0193] P1is Ac;

[0194] P2is C(O)NH2or C(O)OH;

[0195] R1is an amino acid side chain of Trp;

[0196] R2is an amino acid side chain of Thr;

[0197] R3is an amino acid side chain of t-Bu-Ala;

[0198] B1is Ci alkylene;

[0199] C1is Ci alkylene;

[0200] R4is an amino acid side chain of 3-(4-piperidinyl)-Ala or 3-[cHex(4-Aza-4- CH2COOH)]-Ala;

[0201] R5is an amino acid side chain of Asn;

[0202] R6is an amino acid side chain of 2Nal;

[0203] R7is selected from the group consisting of

[0204] R8is an amino acid side chain of Asp;

[0205] R9is an amino acid side chain of Trp;

[0206] R10is an amino acid side chain of Pro; m is 0; and

[0207] VSH

[0208] A1aand A1bare each ; wherein each backbone nitrogen atom or alpha carbon is optionally substituted with a methyl group. In an embodiment:

[0209] P1is Ac;

[0210] P2is C(O)H2or C(O)OH;

[0211] R1is an amino acid side chain of Trp;

[0212] R2is an amino acid side chain of Thr;

[0213] R3is an amino acid side chain of t-Bu-Ala;

[0214] B1is Ci alkylene;

[0215] C1is Ci alkylene;

[0216] R4is an amino acid side chain of 3-(4-piperidinyl)-Ala or 3-(cHex(4-Aza-4- CH2COOH)]-Ala;

[0217] R5is an amino acid side chain of Asn;

[0218] R6is an amino acid side chain of 2Nal;

[0219] R7is selected from the group consisting of

[0220] R8is an amino acid side chain of Asp;

[0221] R9is an amino acid side chain of Trp;

[0222] R10is an amino acid side chain of Pro; m is 0; and

[0223] A1aand A1bare each wherein each backbone nitrogen atom or alpha carbon is optionally substituted with a methyl group.

[0224] In another embodiment,

[0225] R1is an amino acid side chain of Trp; R2is an amino acid side chain of Thr;

[0226] R3is an amino acid side chain of NMe-tBuAla;

[0227] R4is an amino acid side chain of PipA(acetic);

[0228] R5is an amino acid side chain of Asn;

[0229] R6is an amino acid side chain of 2Nal;

[0230] R7is an amino acid side chain of Lys substituted with the chelator DOTA;

[0231] R8is an amino acid side chain of Asp;

[0232] R9is an amino acid side chain of Trp; and

[0233] R10is an amino acid side chain of Pro.

[0234] In an embodiment, m is 0;

[0235] P1is:

[0236] P2is C(O)NH2;

[0237] R1is an amino acid side chain of Trp;

[0238] R2is an amino acid side chain of Thr;

[0239] R3an amino acid side chain of NMe-tBuAla;

[0240] A1is

[0241] VSH

[0242] A1aand A1bare each * ;

[0243] B1is CH2;

[0244] C1is CH2;

[0245] R4is an amino acid side chain of PipA(acetic);

[0246] R5is an amino acid side chain of Asn;

[0247] R6is an amino acid side chain of 2Nal;

[0248] R7is y^^N^OTA H

[0249] R8is an amino acid side chain of Asp;

[0250] R9is an amino acid side chain of Trp; and

[0251] R10is an amino acid side chain of Pro. In an embodiment:

[0252] V

[0253] (i) A1aisSHV and A1bisSH

[0254] V

[0255] In an embodiment, (i) A1aand A1bare bothSH

[0256] In another embodiment,

[0257] O V

[0258] In yet another embodiment, A1ais andA1bis \NH2

[0259] In still another embodiment, A1a

[0260] In some embodiments,

[0261] In other embodiments, In an embodiment:

[0262] V

[0263] A1aisSHV and A1bisSH; and the process comprises combining the linear peptide of Formula II with a compound selected from: to form a group having a structure selected from: wherein Lv, independently for each occurrence, is a leaving group. As used herein, the term “Chelator” refers to a metal chelating agents that associate with metal cargo (e.g., metallic nuclide cargo). Chelators may include macromolecular compounds. Exemplary Chelators are shown in the following table:

[0264] Non-limiting examples of Chelators include 1 ,4,7,10-tetraazacyclododecane-1 ,4,7, 10- tetraacetic acid (DOTA); DOTA derivative: DO3A; diethylenetriamine-N,N,N',N",N"- pentaacetic acid (DTPA); DTPA derivatives: 2-(p-SCN-Bz)-6-methyl-DTPA, CHX-A"-DTPA, and the cyclic anhydride of DTPA (CA-DTPA); 1 ,4,7-triazacyclononane-1 ,4-7-triacetic acid (NOTA); NOTA derivatives (e.g., BCNOTA, p-NCS-Bz-NOTA, BCNOT); 6- hydrazinonicotinamide (HYNIC); ethylenediamine tetraacetic acid (EDTA); N,N'-ethylene-di- L-cysteine; N,N'-bis(2,2-dimethyl-2-mercaptoethyl)ethylenediamine-N,N'-diacetic acid (6SS); 1-(4-carboxymethoxybenzyl)-N-N'-bis[(2-mercapto-2,2-dimethyl)ethyl]-1 ,2-ethylenediamine- N,N'-diacetic acid (B6SS); Deferoxamine (DFO); 1 ,1 ,1-tris(aminomethyl)ethane (TAME); tris(aminomethyl)ethane-N,N,N’,N’,N”,N”-hexaacetic acid (TAME Hex); O-hydroxybenzyl iminodiacetic acid; 1 ,4,7-triazacyclononane (TACN); 1 ,4,7,10-tretraazacyclododecane (cyclen); 1 ,4, 7-triazacyclononane-1 -succinic acid-4, 7-diacetic acid (NODASA); 1-(1-carboxy- 3-carboxypropyl)-4,7-bis-(carboxymethyl)-1 ,4,7-triazacyclononane (NODAGA); 1 ,4,7-tris(2- mercaptoethyl)-1 ,4,7-triazacylclonane (triazacyclononane-TM); 1 ,4,7-triazacyclononane- N,N',N"-tris(methylenephosphonic)acid (NOTP); 1 , 4, 8, 1 1-tetraazacyclo’et”de”’e- N,N',N",N '"-tetraacetic acid (TETA); 1 ,4,7, 10,13-pentaazacyclopentadecane-N,N',N",N"',N""- pentaacetic acid (PEPA), 1 ,4,7, 10,13,16-hexaazacyclohexadecane-N,N',N",N"',N"",N - hexaacetic acid (HEHA); 1 ,4,7,10-tetrakis(carbamoylmethyl)-1 ,4,7, 10- tetraazacyclododecane (TCMC); and derivatives or analogs thereof.

[0265] In an embodiment, the Chelator is independently selected from the group consisting of ethylenediamine tetraacetic acid (EDTA), diethylenetriamine pentaacetic acid (DTPA), 1 ,4,7,10-tetra-azacylcododecane-N,N',N",N"-tetraacetic acid (DOTA), 6-((16-((6- Carboxypyridin-2-yl)methyl)-1 ,4, 10,13-tetraoxa-7, 16-diazacyclooctadecan-7-yl)methyl)-4- isothiocyanatopicolinic acid (Macropa), Macrodipa, 2,2',2",2"'-(1 , 10-dioxa-4,7,13,16- tetraazacyclooctadecane-4,7,13,16-tetrayl)tetraacetic acid) (Crown), 1 ,4,7,10- Tetraazacyclododecane-1 ,4,7,10-tetraacetic acid, a-(2-carboxyethyl) (DOTAGA), 1 ,4,7- Triazacyclononane-N,N',N"-triacetic acid (NOTA), 1 ,4,7,10-tetraazacyclododecane- N,N',N",N"'-tetraacetic acid (TETA), 1 ,4,7,10,13-pentaazacyclopentadecane-N,N',N",N"',N""- pentaacetic acid (PEPA), and 1 ,4,7, 10,13, 16- hexaazacyclohexadecane-N,N',N",N"',N"",N - hexaacetic acid (HEHA).

[0266] In some embodiments, a Chelator of the present disclosure include DOTA, DOTAGA, or any derivative / analog thereof. Any Chelator disclosed in Eisenwiener et al., Bioorg Med Chem Lett., vol.10(18):2133 (2000), the contents of which are incorporated herein by reference in their entirety, may be used as a Chelator.

[0267] Chelators such as DOTA can be attached to any place of the cyclic peptide (i.e., one of skill in the art would be able to discern how placement of the chelator affects the binding by performing the studies described herein). In some embodiments, chelators such as DOTA can be attached directly to the N-terminal amine or to a short linker attached to that same residue. Alternatively, chelators such as DOTA can be attached via a short linker to the C- terminus or to a side chain that can tolerate its presence. In some embodiments, a crosslinker, such as dibromoxilene, that has previously prefunctionlaized with a chelator moiety can be attached to the cyclic peptide.

[0268] It is to be understood that when a variable group R°, R1, R2, R3, R4, R5, R6, R7, R8, R9, or R10of the compound of Formula I, la, lb, II, Ila, or lib is the side chain of an amino acid that forms a cycle with the peptide backbone (e.g., Pro), the corresponding amino acid nitrogen of the peptide backbone forms part of the cyclic group.

[0269] For example, in the formulae provided herein, a variable, e.g., an R°, R1, R2, R3, R4, R5, R6, R7, R8, R9, or R10group (or, alternately, a Rop, R1P, R2P, R3P, R4P, R5P, R6P, R7P, R8P, R9P, or R10Pgroup), can be defined as the side chain of a cyclic amino acid, e.g., proline. In that instance, the corresponding amino acid nitrogen of the peptide backbone of the generic formula forms part of the cyclic group. For example, “R10is an amino acid side chain of Pro” is defined as follows: In another embodiment, the compound of Formula I is selected from the group consisting of a compound from Table A.

[0270] Table A.

[0271]

[0272]

[0273]

[0274]

[0275]

[0276]

[0277]

[0278]

[0279]

[0280]

[0281]

[0282]

[0283]

[0284]

[0285]

[0286]

[0287]

[0288]

[0289]

[0290]

[0291]

[0292]

[0293]

[0294]

[0295]

[0296]

[0297]

[0298]

[0299]

[0300]

[0301]

[0302]

[0303]

[0304]

[0305]

[0306]

[0307]

[0308] In yet another embodiment, the cyclic polypeptide of Formula I is selected from a polypeptide in Table B.

[0309] Table B. or a pharmaceutically acceptable salt thereof. Deprotection and Cleavage from Resin

[0310] The present disclosure further provides a process for deprotecting and cleaving a resin-bound peptide of Formula III:

[0311] (HI), or a pharmaceutically acceptable salt thereof, from a resin; wherein:

[0312] P1pis selected from H, -L1p-Chelatorp,

[0313] D1Pis selected from H, CH3, C(O)O-PG1, and -NR”-Chelatorp;

[0314] L1Pis absent or selected from wherein the amino group of L1Pconnects to the carbonyl group of P1Por Chelatorpto form an amide bond;

[0315] P2pis selected from C(O)-D2P,

[0316] D2Pis the resin;

[0317] L2Pis absent or selected from

[0318] P3pis selected from H, an amino protecting group, Ac, -L3p-Chelatorp,

[0319] wherein the carbonyl group of L3Pconnects to an amine group of P2pto form an amide bond;

[0320] D3Pis independently selected from: CH3, C(O)O-PG1, -NR”-Chelatorp, and

[0321] X is halogen;

[0322] Ropis an optionally protected amino acid side chain of a natural amino acid or an optionally protected amino acid side chain of an unnatural amino acid;

[0323] R1Pis an optionally protected amino acid side chain of a natural amino acid or an optionally protected amino acid side chain of an unnatural amino acid;

[0324] R2Pis an optionally protected amino acid side chain of a natural amino acid or an optionally protected amino acid side chain of an unnatural amino acid;

[0325] R3Pis an optionally protected amino acid side chain of a natural amino acid or an optionally protected amino acid side chain of an unnatural amino acid;

[0326] B1is C1-6 alkylene; C1is C1-6 alkylene;

[0327] A1aPand A1bPare each selected from:

[0328] R4Pis an optionally protected amino acid side chain of a natural amino acid or an optionally protected amino acid side chain of an unnatural amino acid, both of which are further optionally substituted with Chelatorp, CH2C(O)O-PG1, or C(O)(CH2CH2O)p(CH2)2N(CH3)3+, wherein the Chelatorpis optionally substituted to the amino acid side chain through a Linker;

[0329] R5Pis an optionally protected amino acid side chain of a natural amino acid or an optionally protected amino acid side chain of an unnatural amino acid, both of which are optionally further substituted with Chelatorp, wherein the Chelatorpis optionally substituted to the amino acid side chain through a Linker;

[0330] R6Pis an optionally protected amino acid side chain of a natural amino acid or an optionally protected amino acid side chain of an unnatural amino acid;

[0331] R7Pis selected from:

[0332] (i) an optionally protected amino acid side chain of a natural amino acid,

[0333] (ii) an optionally protected amino acid side chain of an unnatural amino acid, or

[0334] (iii) the group consisting of wherein L4is absent or independently selected from wherein the carbonyl group of L4connects to an amine group of R7Pto form an amide bond; R8Pis an optionally protected amino acid side chain of a natural amino acid or an optionally protected amino acid side chain of an unnatural amino acid;

[0335] R9Pis an optionally protected amino acid side chain of a natural amino acid or an optionally protected amino acid side chain of an unnatural amino acid;

[0336] R10Pis an optionally protected amino acid side chain of a natural amino acid or an optionally protected amino acid side chain of an unnatural amino acid; m is 0 or 1 ; each n, q, and u are independently an integer from 0 to 16; each p is independently an integer from 0 to 24; each s is independently an integer from 0 to 16; each t is independently 1 , 2, 3, 4, 5, or 6; each R’” is independently selected from H, C(O)O-PG1, (CH2)O-PG4and NHAc; and each R” is independently selected from H and CH3;

[0337] PG1is H or a carboxylic acid protecting group;

[0338] PG2is H or a thiol protecting group;

[0339] PG3is H or an amino protecting group;

[0340] PG4is H or a hydroxyl protecting group;

[0341] Chelatorpis an optionally protected Chelator; wherein each backbone nitrogen atom or alpha carbon is optionally substituted with a methyl group. wherein either the resin-bound peptide of Formula III does not comprise a Chelatorp, or at least one of R4P, R5P, or R7Pis substituted with a Chelatorpor Chelatorp-containing group; to provide a linear peptide of Formula II.

[0342] In an embodiment, P1pis selected from: -L1 p-Chelatorp,

[0343] In still another embodiment, P1Pis H. In some embodiments, D1Pis selected from H, CH3, and C(O)O-PG1.

[0344] In an embodiment, D1Pis -NR”-Chelatorp.

[0345] In yet another embodiment, L1 Pis absent or selected from wherein the amino group of L1Pconnects to the carbonyl group of P1Por Chelatorpto form an amide bond.

[0346] In still another embodiment, L1Pis absent or selected from: wherein the amino group of L1Pconnects to the carbonyl group of P1Por Chelatorpto form an amide bond.

[0347] In some embodiments, D3Pis independently selected from: CH3, C(O)O-PG1, and - NR”-Chelatorp.

[0348] In yet another embodiment, D3Pis R" ; wherein X is a halogen.

[0349] In an embodiment, Ropis an optionally protected amino acid side chain of a natural amino acid.

[0350] In another embodiment, Ropis an optionally protected amino acid side chain of an unnatural amino acid.

[0351] In yet another embodiment, Ropis optionally protected with a carboxylic acid protecting group.

[0352] In yet another embodiment, Ropis optionally protected with a thiol protecting group.

[0353] In yet another embodiment, Ropis optionally protected with an amino protecting group.

[0354] In yet another embodiment, Ropis optionally a hydroxyl protecting group.

[0355] In an embodiment, R1Pis an optionally protected amino acid side chain of a natural amino acid. In another embodiment, R1Pis an optionally protected amino acid side chain of an unnatural amino acid.

[0356] In yet another embodiment, R1Pis optionally protected with amino protecting group Boc.

[0357] In still another embodiment, R1Pis optionally protected with amino protecting group Trt.

[0358] In an embodiment, R2Pis an optionally protected amino acid side chain of a natural amino acid.

[0359] In another embodiment, R2Pis an optionally protected amino acid side chain of an unnatural amino acid.

[0360] In yet another embodiment, R2Pis optionally protected with a hydroxyl protecting group.

[0361] In still another embodiment, R2Pis optionally protected with a tert-butyl alkyl group.

[0362] In an embodiment, R3Pis an optionally protected amino acid side chain of a natural amino acid.

[0363] In another embodiment, R3Pis an optionally protected amino acid side chain of an unnatural amino acid.

[0364] In yet another embodiment, R3Pis optionally protected with a thiol protecting group.

[0365] In still another embodiment, R3Pis optionally protected with the protecting group Trt.

[0366] In some embodiments, B1is C1.3 alkylene.

[0367] In another embodiment, B1is C4.6alkylene.

[0368] In still another embodiment, C1is C1.3 alkylene.

[0369] In another embodiment, C1is C4.6alkylene.

[0370] In yet another embodiment, A1aPand A1bPare each selected from:

[0371] In another embodiment, A1aPand A1 bPare each selected from:

[0372] In an embodiment, the process to provide a linear peptide of Formula II comprises the step of deprotecting and cleaving a resin-bound peptide of Formula III:

[0373]

[0374] (HI), or a pharmaceutically acceptable salt thereof, from a resin; wherein:

[0375] P1pis selected from: H, Ac, , wherein n and s are each independently 9, 10, 1 1 , 12, or 13;

[0376] D1Pis selected from CH3and C(O)O-PG1;

[0377] X is halogen;

[0378] R1Pis an amino acid side chain of 2Nal, 1 Nal, 4CF3-Phe, 1 Me-Trp, 4F-Phe, 5Qui, D-

[0379] Ala, or Ala, or R1Pis a protected amino acid side chain of Trp, 7Aza-Trp, 5OH-Trp, BIP,

[0380] 5OMe-Trp, 3Pya, 4Pya, PAF, MAF, OAF, 7MeO-Trp, 7Me-Trp, 5F-Trp, or 7CI-Trp;

[0381] R2Pis an amino acid side chain of D-Ala or Ala, or R2Pis a protected amino acid side chain of Thr or Lys;

[0382] R3Pis an amino acid side chain of He, Env, CHA, CBA, Nle, Tbg, THPG, Chg, 2Nal, 1 Nal, 2CF3-Phe, 2PhEt-Ala, D-Ala, Ala, Leu, t-Bu-Ala, a-tert-amylGly, Allo-lle, Lys(C12),

[0383] Lys(C14), or Lys(C16); B1is C1-6 alkylene;

[0384] C1is C1-6 alkylene;

[0385] A1aPand A1bPare each selected from: , , COC5Hn , DAB-4- NHCOC7H15, 3-(1-morpholinyl)-Ala, 3Pya, 4Pya, or Pip(PegNMe3)Ala, or R4Pis a protected amino acid side chain of Asn, Asp, Ser, Lys(DOTA), Lys, 3-(4-piperidinyl)-Ala, Glu, Pip(CH2CO2H)Ala, or Pip(GAE-DOTA)Ala;

[0386] R5Pis an amino acid side chain of Ala, D-Ala, 3Pya, 4Pya, or 3-(1-morpholinyl)-Ala, or R5Pis a protected amino acid side chain of Asn, Trp, Asp, Lys, Lys(DOTA), 3-(4- piperidiny l)-Ala, Glu, or Ser;

[0387] R6Pis an amino acid side chain of 4CF3-Phe, 1 Me-Trp, BIP, 2Nal, 1 Nal, D-Ala, Ala, or 4F-Phe, or R6Pis a protected amino acid side chain of Trp, 7Aza-Trp, 5F-Trp, 5MeO-Trp, Asn, 5OH-Trp, 7Me-Trp, 7MeO-Trp, or 7CI-Trp;

[0388] R7Pis

[0389] (i) an amino acid side chain of 3Pya, 4Pya, Lys(Me)3, Ala, or D-Ala,

[0390] (ii) a protected amino acid side chain of His, Gin, Lys, Glu, Arg, Orn, or Ser, or

[0391] (iii) selected from the group consisting of , pendently 3, 5,10, 12, or 14, and wherein DOTA is optionally protected with three PG1groups or one LG1group;

[0392] R8Pis an amino acid side chain of D-Ala or Ala, or R8Pis a protected amino acid side chain of Asp, Asn, or Thr;

[0393] R9Pis an amino acid side chain of 1 Me-T rp, D-Ala, Ala, 4F-Phe, 1 Nal, or 2Nal, or R9Pis a protected amino acid side chain of Trp, 7Aza-Trp, 5F-Trp, 5MeO-Trp, 7CI-Trp, 5OH-Trp, 7Me-Trp, or 7MeO-Trp;

[0394] R10Pis an amino acid side chain of Pro, D-Ala, Ala, trans4Fluoro-Pro, cis4Fluoro-Pro, Pip, 5,5-diMe-Pro, Aze, R-3Me-Aze, ACI, or 3Me2-Aze, or R10Pis a protected amino acid side chain of trans4OH-Pro, cis4OH-Pro, trans4NH2-Pro, or cis4NH2-Pro; m is 0;

[0395] PG1is H or a carboxylic acid protecting group;

[0396] PG2is H or a thiol protecting group;

[0397] PG3is H or an amino protecting group;

[0398] PG4is H or a hydroxyl protecting group;

[0399] LG1is an amine reactive leaving group; wherein each backbone nitrogen atom or alpha carbon is optionally substituted with a methyl group; wherein either the resin-bound peptide of Formula III does not comprise DOTA, or at least one of R4P, R5P, or R7Pis substituted with DOTA or a DOTA-containing group;

[0400] In an embodiment, the process to provide a linear peptide of Formula II comprises the step of deprotecting and cleaving a resin-bound peptide of Formula III:

[0401] (HI), or a pharmaceutically acceptable salt thereof, from a resin; wherein:

[0402] P1Pis Ac;

[0403] P2Pis C(O)-D2P;

[0404] D2Pis the resin; R1Pis a protected amino acid side chain of Trp;

[0405] R2Pis a protected amino acid side chain of Thr;

[0406] R3Pis an amino acid side chain of t-Bu-Ala;

[0407] B1is Ci alkylene;

[0408] C1is Ci alkylene;

[0409] A1aPand A1bPare each

[0410] R4Pis a protected amino acid side chain of 3-(4-piperidinyl)-Ala or 3-(cHex(4-Aza-4- CH2COOH)]-Ala;

[0411] R5Pis a protected amino acid side chain of Asn;

[0412] R6Pis an amino acid side chain of 2Nal;

[0413] R7Pis selected from the group consisting of three PG1groups or one LG1group;

[0414] R8Pis a protected amino acid side chain of Asp;

[0415] R9Pis a protected amino acid side chain of Trp;

[0416] R10Pis an amino acid side chain of Pro; m is 0;

[0417] PG1is H or a carboxylic acid protecting group;

[0418] PG2is H or a thiol protecting group;

[0419] PG4is H or a hydroxyl protecting group;

[0420] LG1is an amine reactive leaving group; wherein each backbone nitrogen atom or alpha carbon is optionally substituted with a methyl group; wherein either the resin-bound peptide of Formula III does not comprise DOTA, or at least one of R4P, R5P, or R7Pis substituted with DOTA or a DOTA-containing group. In an embodiment,

[0421] R1is an amino acid side chain of Trp;

[0422] R2is an amino acid side chain of Thr;

[0423] R3is an amino acid side chain of NMe-tBuAla;

[0424] R4is an amino acid side chain of PipA(acetic);

[0425] R5is an amino acid side chain of Asn;

[0426] R6is an amino acid side chain of 2Nal;

[0427] R7is an amino acid side chain of Lys substituted with the chelator DOTA;

[0428] R8is an amino acid side chain of Asp;

[0429] R9is an amino acid side chain of Trp;

[0430] R10is an amino acid side chain of Pro;

[0431] R1Pis an amino acid side chain of Trp that is protected with a Boc group;

[0432] R2Pis an amino acid side chain of Thr that is protected with a t-Bu group;

[0433] R3Pis an amino acid side chain of NMe-tBuAla;

[0434] R4Pis an amino acid side chain of PipA(acetic);

[0435] R5Pis an amino acid side chain of Asn that is protected with a trityl group;

[0436] R6Pis an amino acid side chain of 2Nal;

[0437] R7Pis an amino acid side chain of Lys substituted with the chelator DOTA;

[0438] R8Pis an amino acid side chain of Asp that is protected with a t-Bu group;

[0439] R9Pis an amino acid side chain of Trp that is protected with a Boc group; and R10Pis an amino acid side chain of Pro.

[0440] In an embodiment, m is 0;

[0441] P1is:

[0442] P2is C(O)NH2;

[0443] R1is an amino acid side chain of Trp;

[0444] R2is an amino acid side chain of Thr;

[0445] R3an amino acid side chain of NMe-tBuAla;

[0446] A1is vSH

[0447] A1aand A1bare each ;

[0448] B1is CH2;

[0449] C1is CH2;

[0450] R4is an amino acid side chain of PipA(acetic);

[0451] R5is an amino acid side chain of Asn;

[0452] R6is an amino acid side chain of 2Nal;

[0453] R7is

[0454] R8is an amino acid side chain of Asp;

[0455] R9is an amino acid side chain of Trp;

[0456] R10is an amino acid side chain of Pro;

[0457] P1pis:

[0458] P2pis C(O)NH2;

[0459] R1Pis an amino acid side chain of Trp that is protected with a Boc group;

[0460] R2Pis an amino acid side chain of Thr that is protected with a t-Bu group;

[0461] R3Pan amino acid side chain of NMe-tBuAla;

[0462] A1aPand A1bPare each

[0463] R4Pis an amino acid side chain of PipA(acetic);

[0464] R5Pis an amino acid side chain of Asn that is protected with a trityl group;

[0465] R6Pis an amino acid side chain of 2Nal;

[0466] R7Pis y^^N^OTA H ;

[0467] R8Pis an amino acid side chain of Asp that is protected with a t-Bu group;

[0468] R9Pis an amino acid side chain of Trp that is protected with a Boc group; and

[0469] R10Pis an amino acid side chain of Pro.

[0470] In an embodiment, the resin is Rink amide MBHA resin.

[0471] In another embodiment, the deprotection and cleavage of the resin-bound peptide of

[0472] Formula III is performed under acidic conditions. In some embodiments, each protecting group is an acid-labile protecting group.

[0473] In yet another embodiment, the deprotection and cleavage of the resin-bound peptide of Formula III is performed in the presence of a reducing agent.

[0474] In still another embodiment, the deprotection and cleavage of the resin-bound peptide of Formula III is performed in the presence of a nucleophilic scavenger.

[0475] In an embodiment, the deprotection and cleavage of the resin-bound peptide of Formula III is performed in the presence of trifluoroacetic acid (TFA), thioanisole, and dithiothreitol (DTT).

[0476] As described previously, it is to be understood that when a variable group Rop, R1P, R2P, R3P, R4P, R5P, R6P, R7P, R8P, R9P, or R10Pof the compound of Formula III is the side chain of an amino acid that forms a cycle with the peptide backbone (e.g., Pro), the corresponding amino acid nitrogen of the peptide backbone forms part of the cyclic group.

[0477] Preparation of Resin-Bound Peptide

[0478] The present disclosure further provides a process for preparing a resin-bound peptide of Formula (III), as defined herein, comprising the steps of

[0479] (A) providing a resin-bound peptide of Formula IV:

[0480] (IV), or a pharmaceutically acceptable salt thereof, wherein:

[0481] P1Pis selected from: H, -|_1p-PGChel,

[0482]

[0483] D1Pis selected from H, CH3, C(O)O-PG1, and -NR”-PGChel;

[0484] L1Pis absent or selected from wherein the amino group of L1Pconnects to the carbonyl group of P1Pto form an amide bond or the amino group of L1Pforms a covalent bond with PGChel; P2pis selected from C(O)-D2P,

[0485] D2Pis a resin;

[0486] L2Pis absent or selected from

[0487] P3pis selected from H, an amino protecting group, Ac, -|_3P-PGChel,

[0488] L3Pis absent or independently selected from wherein the carbonyl group of L3Pconnects to an amine group of P2Pto form an amide bond;

[0489] D3Pis independently selected from: CH3, C(O)O-PG1, -NR”-PGChel, and

[0490] X is halogen;

[0491] Ropis an optionally protected amino acid side chain of a natural amino acid or an optionally protected amino acid side chain of an unnatural amino acid;

[0492] R1Pis an optionally protected amino acid side chain of a natural amino acid or an optionally protected amino acid side chain of an unnatural amino acid;

[0493] R2Pis an optionally protected amino acid side chain of a natural amino acid or an optionally protected amino acid side chain of an unnatural amino acid;

[0494] R3Pis an optionally protected amino acid side chain of a natural amino acid or an optionally protected amino acid side chain of an unnatural amino acid;

[0495] B1is C1-6 alkylene;

[0496] C1is C1-6 alkylene;

[0497] A1aPand A1bPare each selected from:

[0498] R4Pis an optionally protected amino acid side chain of a natural amino acid or an optionally protected amino acid side chain of an unnatural amino acid, both of which are further optionally substituted with PGChel, CH2C(O)O-PG1, or C(O)(CH2CH2O)p(CH2)2N(CH3)3+, wherein the PGChelis optionally substituted to the amino acid side chain through a Linker;

[0499] R5Pis an optionally protected amino acid side chain of a natural amino acid or an optionally protected amino acid side chain of an unnatural amino acid, both of which are optionally further substituted with PGChel, wherein the PGChelis optionally substituted to the amino acid side chain through a Linker;

[0500] R6Pis an optionally protected amino acid side chain of a natural amino acid or an optionally protected amino acid side chain of an unnatural amino acid;

[0501] R7Pis selected from:

[0502] (i) an optionally protected amino acid side chain of a natural amino acid,

[0503] (ii) an optionally protected amino acid side chain of an unnatural amino acid, or

[0504] (iii) the group consisting of

[0505] wherein L4is absent or independently selected from: wherein the carbonyl group of L4connects to an amine group of R7Pto form an amide bond;

[0506] R8Pis an optionally protected amino acid side chain of a natural amino acid or an optionally protected amino acid side chain of an unnatural amino acid;

[0507] R9Pis an optionally protected amino acid side chain of a natural amino acid or an optionally protected amino acid side chain of an unnatural amino acid;

[0508] R10Pis an optionally protected amino acid side chain of a natural amino acid or an optionally protected amino acid side chain of an unnatural amino acid; m is 0 or 1 ; each n, q, and u are independently an integer from 0 to 16; each p is independently an integer from 0 to 24; each s is independently an integer from 0 to 16; each t is independently 1 , 2, 3, 4, 5, or 6; each R’” is independently selected from H, C(O)O-PG1, (CH2)O-PG4and NHAc; and each R” is independently selected from H and CH3;

[0509] PG1is H or a carboxylic acid protecting group;

[0510] PG2is H or a thiol protecting group;

[0511] PG3is H or an amino protecting group;

[0512] PG4is H or a hydroxyl protecting group;

[0513] PGChelis a protecting group; wherein at least one of R4P, R5P, or R7Pis substituted with a PGChelor PGChel- containing group; wherein each backbone nitrogen atom or alpha carbon is optionally substituted with a methyl group;

[0514] (B) deprotecting the resin-bound peptide of Formula IV, or a pharmaceutically acceptable salt thereof, to form a deprotected intermediate, wherein the deprotected intermediate is not substituted with a PGChelor PGChel-containing group; and

[0515] (C) reacting the deprotected intermediate with an optionally protected Chelator, ChelatorFree, to provide the resin-bound peptide of Formula III.

[0516] In an embodiment, the process comprises the steps of

[0517] (A) providing a resin-bound peptide of Formula IV:

[0518] (IV), or a pharmaceutically acceptable salt thereof, wherein:

[0519] P1pis selected from: H, Ac, independently 9, 10, 1 1 , 12, or 13;

[0520] D1Pis selected from CH3and C(O)O-PG1;

[0521] X is halogen; R1Pis an amino acid side chain of 2Nal, 1Nal, 4CF3-Phe, 1Me-Trp, 4F-Phe, 5Qui, D- Ala, or Ala, or R1Pis a protected amino acid side chain of Trp, 7Aza-Trp, 5OH-Trp, BIP, 5OMe-Trp, 3Pya, 4Pya, PAF, MAF, OAF, 7MeO-Trp, 7Me-Trp, 5F-Trp, or 7CI-Trp;

[0522] R2Pis an amino acid side chain of D-Ala or Ala, or R2Pis a protected amino acid side chain of Thr or Lys;

[0523] R3Pis an amino acid side chain of He, Env, CHA, CBA, Nle, Tbg, THPG, Chg, 2Nal, 1 Nal, 2CF3-Phe, 2PhEt-Ala, D-Ala, Ala, Leu, t-Bu-Ala, a-tert-amylGly, Allo-lle, Lys(C12), Lys(C14), or Lys(C16);

[0524] B1is C1-6 alkylene;

[0525] C1is C1-6 alkylene;

[0526] A1aPand A1bPare each selected from:

[0527] R4Pis an amino acid side chain of D-Ala, Ala, DAB-4-NHCOC5Hn, DAB-4- NHCOC7H15, 3-(1-morpholinyl)-Ala, 3Pya, 4Pya, or Pip(PegNMe3)Ala, or R4Pis a protected amino acid side chain of Asn, Asp, Ser, Lys(DOTA), Lys, 3-(4-piperidinyl)-Ala, Glu, Pip(CH2CO2H)Ala, or R4Pis Pip(GAE-PGChel)Ala;

[0528] R5Pis an amino acid side chain of Ala, D-Ala, 3Pya, 4Pya, or 3-(1-morpholinyl)-Ala, or R5Pis a protected amino acid side chain of Asn, Trp, Asp, Lys, 3-(4-piperidinyl)-Ala, Glu, or Ser, or R5Pis Lys(PGChel);

[0529] R6Pis an amino acid side chain of 4CF3-Phe, 1Me-Trp, BIP, 2Nal, 1 Nal, D-Ala, Ala, or 4F-Phe, or R6Pis a protected amino acid side chain of Trp, 7Aza-Trp, 5F-Trp, 5MeO-Trp, Asn, 5OH-Trp, 7Me-Trp, 7MeO-Trp, or 7CI-Trp;

[0530] R7Pis

[0531] (i) an amino acid side chain of 3Pya, 4Pya, Lys(Me)3, Ala, or D-Ala,

[0532] (ii) a protected amino acid side chain of His, Gin, Lys, Glu, Arg, Orn, or Ser, or

[0533] (iii) selected from the group consisting of , ndently

[0534] 3, 5,10, 12, or 14;

[0535] R8Pis an amino acid side chain of D-Ala or Ala, or R8Pis a protected amino acid side chain of Asp, Asn, or Thr;

[0536] R9Pis an amino acid side chain of 1 Me-T rp, D-Ala, Ala, 4F-Phe, 1 Nal, or 2Nal, or R9Pis a protected amino acid side chain of Trp, 7Aza-Trp, 5F-Trp, 5MeO-Trp, 7CI-Trp, 5OH-Trp, 7Me-Trp, or 7MeO-Trp;

[0537] R10Pis an amino acid side chain of Pro, D-Ala, Ala, trans4Fluoro-Pro, cis4Fluoro-Pro, Pip, 5,5-diMe-Pro, Aze, R-3Me-Aze, ACI, or 3Me2-Aze, or R10Pis a protected amino acid side chain of trans4OH-Pro, cis4OH-Pro, trans4NH2-Pro, or cis4NH2-Pro; m is 0;

[0538] PG1is H or a carboxylic acid protecting group;

[0539] PG2is H or a thiol protecting group;

[0540] PG3is H or an amino protecting group;

[0541] PG4is H or a hydroxyl protecting group;

[0542] PGChelis a protecting group; wherein at least one of R4P, R5P, or R7Pis substituted with a PGChelor PGChel- containing group; wherein each backbone nitrogen atom or alpha carbon is optionally substituted with a methyl group;

[0543] (B) deprotecting the resin-bound peptide of Formula IV, or a pharmaceutically acceptable salt thereof, to form a deprotected intermediate, wherein the deprotected intermediate is not substituted with a PGChelor PGChel-containing group; and

[0544] (C) reacting the deprotected intermediate with an optionally protected Chelator, ChelatorFree, to provide the resin-bound peptide of Formula III.

[0545] In an embodiment, the process further comprising the steps of (A) providing a resin-bound peptide of Formula IV:

[0546] (IV), or a pharmaceutically acceptable salt thereof, wherein: P1pis Ac;

[0547] P2pis C(O)-D2P;

[0548] D2Pis the resin;

[0549] R1Pis a protected amino acid side chain of Trp;

[0550] R2Pis a protected amino acid side chain of Thr; R3Pis an amino acid side chain of t-Bu-Ala;

[0551] B1is Ci alkylene;

[0552] C1is Ci alkylene;

[0553] Vs" 2

[0554] A1aPand A1bPare eachPG;

[0555] R4Pis a protected amino acid side chain of 3-(4-piperidinyl)-Ala; R5Pis a protected amino acid side chain of Asn;

[0556] R6Pis an amino acid side chain of 2Nal;

[0557] R7Pis selected from the group consisting of

[0558] R8Pis a protected amino acid side chain of Asp;

[0559] R9Pis a protected amino acid side chain of Trp;

[0560] R10Pis an amino acid side chain of Pro; m is 0;

[0561] PG1is H or a carboxylic acid protecting group;

[0562] PG2is H or a thiol protecting group;

[0563] PG4is H or a hydroxyl protecting group;

[0564] PGChelis a protecting group; wherein each backbone nitrogen atom or alpha carbon is optionally substituted with a methyl group;

[0565] (B) deprotecting the resin-bound peptide of Formula IV, or a pharmaceutically acceptable salt thereof, to form a deprotected intermediate, wherein the deprotected intermediate is not substituted with a PGChelor PGChel-containing group; and

[0566] (C) reacting the deprotected intermediate with an optionally protected Chelator, ChelatorFree, to provide the resin-bound peptide of Formula III.

[0567] In an embodiment,

[0568] R1Pis an amino acid side chain of Trp that is protected with a Boc group;

[0569] R2Pis an amino acid side chain of Thr that is protected with a t-Bu group;

[0570] R3Pis an amino acid side chain of NMe-tBuAla;

[0571] R4Pis an amino acid side chain of PipA(acetic);

[0572] R5Pis an amino acid side chain of Asn that is protected with a trityl group;

[0573] R6Pis an amino acid side chain of 2Nal;

[0574] R7Pis an amino acid side chain of Lys substituted with 4-methyltrityl or the chelator DOTA;

[0575] R8Pis an amino acid side chain of Asp that is protected with a t-Bu group;

[0576] R9Pis an amino acid side chain of Trp that is protected with a Boc group; and

[0577] R10Pis an amino acid side chain of Pro.

[0578] In an embodiment, m is 0; P1Pis:

[0579] P2pis C(O)NH2;

[0580] R1Pis an amino acid side chain of Trp that is protected with a Boc group;

[0581] R2Pis an amino acid side chain of Thr that is protected with a t-Bu group;

[0582] R3Pan amino acid side chain of NMe-tBuAla;

[0583] A1aPand A1bPare each

[0584] B1is CH2;

[0585] C1is CH2;

[0586] R4Pis an amino acid side chain of PipA(acetic);

[0587] R5Pis an amino acid side chain of Asn that is protected with a trityl group;

[0588] R6Pis an amino acid side chain of 2Nal;

[0589] R7Pis

[0590] R8Pis an amino acid side chain of Asp that is protected with a t-Bu group;

[0591] R9Pis an amino acid side chain of Trp that is protected with a Boc group; and

[0592] R10Pis an amino acid side chain of Pro.

[0593] In an embodiment, PGChelis an amino protecting group.

[0594] In another embodiment, PGChelis 4-methyltrityl (Mtt).

[0595] In an embodiment, PGChelis 1-(4,4-dimethyl-2,6-dioxocyclohexylidene)ethyl (Dde).

[0596] In still another embodiment, PGChelis 1-(4,4-dimethyl-2, 6-dioxocyclohex-1-ylidene)- 3-methylbutyl (ivDde).

[0597] In yet another embodiment, deprotecting the resin-bound peptide of Formula IV is performed in the presence of hexafluoroisopropanol (HFIP) or trifluoroacetic acid (TFA).

[0598] In another embodiment, deprotecting the resin-bound peptide of Formula IV is performed in the presence of hydrazine.

[0599] In still another embodiment, deprotecting the resin-bound peptide of Formula IV is performed in the further presence of a trialkylsilane and dichloromethane.

[0600] In an embodiment, trialkylsilane is triisopropylsilane (TIS) or triethylsilane (TES).

[0601] In another embodiment, ChelatorFreecomprises an unprotected carboxylic acid group.

[0602] In yet another embodiment, ChelatorFreehas the following structure:

[0603] In still another embodiment, the reaction of the deprotected intermediate with ChelatorFreeis performed in the presence of a coupling agent.

[0604] In an embodiment, the coupling agent is (7-Azabenzotriazol-1- yloxy)tripyrrolidinophosphonium hexafluorophosphate (PyAOP).

[0605] In another embodiment, the reaction of the deprotected intermediate with ChelatorFreeis performed in the further presence of a base.

[0606] In some embodiments, the base is a tertiary amine, carbonate, or bicarbonate.

[0607] In another embodiment, ChelatorFreehas following structure:

[0608] In still another embodiment, the reaction of the deprotected intermediate with ChelatorFreeis performed in the presence of a base.

[0609] In some embodiments, the base is a tertiary amine, carbonate, or bicarbonate.

[0610] In other embodiments, ChelatorFreehas the following structure:

[0611] In another embodiment, the reaction of the deprotected intermediate with ChelatorFreeis performed in the presence of a coupling agent.

[0612] In yet another embodiment, the coupling agent is N, N’ -diisopropylcarbodiimide (DIG), A / ,A / -dicyclohexylcarbodiimide (DCC), 1-(3-dimethylaminopropyl)-3-ethylcarbodiimide (EDC), 1-[bis(dimethylamino)methylene]-1 / - / -1 ,2,3-triazolo[4,5-b]pyridinium 3-oxid hexafluorophosphate (HATU), O-(1 / - / -6-Chlorobenzotriazole-1-yl)-1 ,1 ,3,3-tetramethyluronium hexafluorophosphate (HCTU), [benzotriazol-1-yloxy(dimethylamino)methylidene]- dimethylazanium;hexafluorophosphate (HBTU), or 2-(1 / - / -benzotriazole-1-yl)-1 , 1 ,3,3- tetramethylaminium tetrafluoro bo rate (TBTU).

[0613] In an embodiment, the reaction between the deprotected intermediate with ChelatorFreeis optionally performed in the further presence of an additive.

[0614] In some embodiments, the additive is Oxyma.

[0615] In another embodiment, the reaction of the deprotected intermediate with ChelatorFreeis performed in still the further presence of a base.

[0616] In some embodiments, the base is a tertiary amine, carbonate, or bicarbonate. In some embodiments, the base is DIPEA.

[0617] It is to be understood that when a variable group Rop, R1P, R2P, R3P, R4P, R5P, R6P, R7P, R8P, R9P, or R10Pof the compound of Formula IV is the side chain of an amino acid that forms a cycle with the peptide backbone (e.g., Pro), the corresponding amino acid nitrogen of the peptide backbone forms part of the cyclic group.

[0618] III. Equivalents and scope

[0619] While various disclosure embodiments have been particularly shown and described in the present disclosure, it will be understood by those skilled in the art that various changes in form and details may be made without departing from the spirit and scope of the embodiments disclosed herein and set forth in the appended claims.

[0620] Those skilled in the art will recognize or be able to ascertain using no more than routine experimentation, many equivalents to the specific embodiments described herein. The scope of the present disclosure is not intended to be limited to the above description, but rather is as set forth in the appended claims.

[0621] Where ranges are given, endpoints are included. Furthermore, it is to be understood that unless otherwise indicated or otherwise evident from the context and understanding of one of ordinary skill in the art, values that are expressed as ranges can assume any specific value or subrange within the stated ranges in different embodiments of the disclosure, to the tenth of the unit of the lower limit of the range, unless the context clearly dictates otherwise.

[0622] In addition, it is to be understood that any particular embodiment of the present disclosure that falls within the prior art may be explicitly excluded from any one or more of the claims. Since such embodiments are deemed to be known to those of ordinary skill in the art, they may be excluded even if the exclusion is not set forth explicitly herein. Any particular embodiments of compositions disclosed herein can be excluded from any one or more claims, for any reason, whether or not related to the existence of prior art.

[0623] All cited sources, for example, references, publications, databases, database entries, and art cited herein, are incorporated into this application by reference, even if not expressly stated in the citation. In case of conflicting statements of a cited source and the instant application, the statement in the instant application shall control.

[0624] Section and table headings are not intended to be limiting.

[0625] EXAMPLES

[0626] List of Abbreviations

[0627] Amino acids and building blocks

[0628] • Na-(((9H-fluoren-9-yl)methoxy)carbonyl)-1-(tert-butoxycarbonyl)-L-tryptophan (W)

[0629] • (((9H-fluoren-9-yl)methoxy)carbonyl)-L-threonine (T)

[0630] • (((9H-fluoren-9-yl)methoxy)carbonyl)-L-isoleucine (I)

[0631] • N-(((9H-fluoren-9-yl)methoxy)carbonyl)-S-trityl-L-cysteine (C)

[0632] • (S)-2-((((9H-fluoren-9-yl)methoxy)carbonyl)amino)-3-(tritylamino)propanoic acid (N)

[0633] • Na-(((9H-fluoren-9-yl)methoxy)carbonyl)-Np-(tert-butoxycarbonyl)-L-histidine (H)

[0634] • (S)-2-((((9H-fluoren-9-yl)methoxy)carbonyl)amino)-4-((3-methylpentan-3-yl)oxy)-4- oxobutanoic acid (D)

[0635] • (((9H-fluoren-9-yl)methoxy)carbonyl)-L-proline (P)

[0636] • N2-(((9H-fluoren-9-yl)methoxy)carbonyl)-N6-(1-(4,4-dimethyl-2,6- dioxocyclohexylidene)ethyl)-L-lysine (K(Dde))

[0637] • N2-(((9H-fluoren-9-yl)methoxy)carbonyl)-N6-(1-(4,4-dimethyl-2,6- dioxocyclohexylidene)ethyl)-D-lysine (D-Lys(Dde)) • N2-(((9H-fluoren-9-yl)methoxy)carbonyl)-N6-[1 -(4,4-dimethyl-2, 6-dioxocyclohex-1 - ylidene)-3-methylbutyl)-L-lysine (K(ivDde))

[0638] • N2-(((9H-fluoren-9-yl)methoxy)carbonyl)-N6-[1 -(4,4-dimethyl-2, 6-dioxocyclohex-1 - ylidene)-3-methylbutyl]-D-lysine (D-Lys(ivDde))

[0639] • N2-(((9H-fluoren-9-yl)methoxy)carbonyl)-N6-(tert-butoxycarbonyl)-D-lysine (D- Lys(Boc))

[0640] • (S)-2-((((9H-fluoren-9-yl)methoxy)carbonyl)amino)-3-(naphthalen-2-yl)propanoic acid (2Nal)

[0641] • 2-(4,7,10-tris(2-(tert-butoxy)-2-oxoethyl)-1 ,4,7,10-tetraazacyclododecan-1-yl)acetic acid (DOTA(tBu)3)

[0642] • 2,2’,2”-(10-(2-((2,5-dioxopyrrolidin-1-yl)oxy)-2-oxoethyl)-1 ,4,7,10- tetraazacyclododecane-1 ,4,7-triyl)triacetic acid (DOTA-NHS)

[0643] • (S)-4-((((9H-fluoren-9-yl)methoxy)carbonyl)amino)-6,6-dimethyl-5-oxoheptanoic acid (gE)

[0644] • 3-((tert-butoxycarbonyl)amino)propanoic acid (Boc-betaAla)

[0645] • (S)-2-((((9H-fluoren-9-yl)methoxy)carbonyl)amino)pent-4-enoic acid (AllylG)

[0646] • (S)-2-((((9H-fluoren-9-yl)methoxy)carbonyl)amino)-3-azidopropanoic acid (DapN3)

[0647] • (S)-2-((((9H-fluoren-9-yl)methoxy)carbonyl)amino)pent-4-ynoic acid (Pra)

[0648] General Procedure

[0649] The peptides described herein were synthesized according to the generalized solidphase peptide synthesis (SPPS) process (Merrifield, R. B., J. Am. Chem. Soc. 1963, 85, 2149-2154). The peptides were assembled from the C-terminus to the / V-terminus on insoluble support (resin). The a-amino group of each amino acid was protected by the basesensitive 9-Fluorenylmethyloxycarbonyl (Fmoc) group, while the functional side chains were protected by acid sensitive groups, unless otherwise stated.

[0650] The synthesis was initiated using an insoluble support [i.e., Fmoc-Rink Amide 4- Methylbenzhydrylamine (MBHA) resin] to which the C-terminal amino acid in the sequence was attached. The protected amino acids were attached sequentially to the peptide chain resulting in fully protected peptides attached to the solid support resin. The lysine8side chain was additionally capped with 1 ,4,7,10-tetraazacyclododecane-1 ,4,7,10-tetraacetic acid (DOTA), a chelating moiety.

[0651] The crude peptide was obtained by simultaneous cleavage of the peptide from the resin and removal of the side chain protecting groups through acidolysis using trifluoroacetic acid (TFA), resulting in the C-terminal amide form of the fully deprotected peptide. A global constraint (macrocyclization) was applied via a thioacetal bridge between the cysteine residues.

[0652] A purification scheme using reversed phase-high performance liquid chromatography (RP-HPLC) was used to generate the acetate salt form of the final peptide.

[0653] Synthesis of Linear Protected Peptide

[0654] Peptides were synthesized on Fmoc-Rink-MBHA resin. The Fmoc protecting group was initially removed (i.e., deprotected) from the Fmoc-Rink Amide MBHA resin with DMF and piperidine. The synthesis employed standard Fmoc / DIC SPPS chemistry and the amino acid side chains were protected with acid-labile protecting groups. / V-Fmoc deprotection steps were performed using piperidine in DMF. Oxyma-buffered piperidine / DMF was used for the Fmoc removal during the Cys10cycle to minimize the possible Trp11- Pro12diketopiperazine formation. Couplings were performed with DIC as the activator and Oxyma as the additive. Following the coupling of Trp1and Fmoc deprotection, acetylation of the / V-terminus was performed using acetic anhydride (Ac2O) I diisopropylethylamine (DIPEA) I DMF. Selective deprotection of the Lys8(Mtt) sidechain was performed using hexafluoroisopropanol (HFIP) / triisopropylsilane (TIS) / dichloromethane (DCM). Optionally, selective deprotection of the Lys8(Dde) or Lys8(ivDde) sidechain was performed using 2% hydrazine / DMF. The tri-t-Bu-protected 1 ,4,7,10-tetraazacyclododecane-1 ,4,7,10-tetraacetic acid (DOTA(OtBu)3-OH) coupling was performed under basic conditions with (7- Azabenzotriazol-1-yloxy) tripyrrolidinophosphonium hexafluorophosphate (PyAOP) I DIPEA. Completion of these steps results in a protected peptide anchored onto the resin.

[0655] Qualitative reaction monitoring was performed using the ninhydrin / chloranil tests. These tests measure residual, resin-bound amino groups. A negative test result indicates absence of free amines (i.e., complete coupling), and the process can then proceed to the next coupling step. A positive test result indicates incomplete coupling; thus, prolonged coupling or re-coupling of the Fmoc amino acid may be performed.

[0656] After assembly of the peptide sequence was completed and final deprotection was performed, the peptide on resin was washed with DMF and isopropyl alcohol (IPA) and then dried using a gentle stream of nitrogen gas (N2).

[0657] Cleavage of Linear Protected Intermediate Peptide from Resin and Global Deprotection

[0658] Cleavage of the peptide from solid support and global deprotection was performed in a cleavage solution mixture composed of trifluoroacetic acid (TFA), water (H2O), thioanisole, and dithiothreitol (DTT). The peptide-resin was added to the cold cleavage solution and stirred for 30 min at ambient temperature. The solution was then heated to 40 °C for 2-4 hours to complete deprotection of the DOTA moiety while monitoring the reaction progress by liquid chromatography-mass spectrometry (LC-MS).

[0659] The depleted resin was filtered off and rinsed with additional TFA. The filtrate and rinse were combined and concentrated by rotary evaporation under reduced pressure to approximately half the initial volume. The resulting concentrate was precipitated by quick addition to cold 1 :1 methyl tert-butyl ether (MTBE):hexanes. The precipitate was filtered, washed with MTBE / hexanes, and dried under vacuum.

[0660] Purification of the Crude Linear Intermediate Peptide

[0661] The linear intermediate was purified by single stage RP-HPLC. The crude linear intermediate was dissolved in acetic acid (AcOH) / H2O and stirred at 50 °C for 1 hour to promote decarboxylation of the carbamic acid intermediate (M + 44) of the tryptophan residue. The column was equilibrated with acetonitrile (ACN) before loading the solution onto the column. The eluent was collected and analyzed by HPLC. See Table 1 for the parameters of the method used for purification of the crude linear intermediate. The fractions containing the purified linear intermediate peptide that met the 95% purity specification were pooled and lyophilized to yield the linear intermediate as dry powder.

[0662] Table 1:

[0663] Solution-Phase Thioacetal Cyclization

[0664] The purified linear intermediate peptide was dissolved in 50% THF / H2O. Potassium carbonate (K2CO3) and Tris(2-carboxyethyl)phosphine hydrochloride (TCEP HCI) in H2O was added to the peptide solution. The solution was stirred for approximately 30 min. Diiodomethane (CH2I2) was added to the solution followed by K2CO3in H2O and the mixture was agitated by stirring for 18-24h. The progress of cyclization was monitored by LC-MS. Upon completion, excess CH2I2and THF was removed by rotary evaporation and the solution was acidified by addition of neat TFA.

[0665] Description of the Purification and Counter-Ion Exchange Processes

[0666] General The crude cyclized peptide from the previous step was purified by a two-step, preparative, reversed phase HPLC procedure, on C18 derivatized silica (Daisogel SP-120- 10-ODS-RPS).

[0667] The elution from the column was monitored by UV and the fractions obtained were analyzed by an in-process RP-HPLC test and combined in such a way that the purity complies with the requirements for in-process controls. Side fractions that do not meet the purity specification may be recycled through the same step of the process or discarded.

[0668] Purification by preparative reversed phase chromatography (RPC 1)

[0669] The crude cyclized peptide was diluted 1 :1 with water. The solution was filtered and applied to a preparative HPLC column that has been washed with methanol and equilibrated ACN. The product was eluted using a gradient of 0.1 M triethylammonium phosphate (TEAP) pH 2.25 buffers for mobile phase A and ACN for mobile phase B, with monitoring by UV at 280 nm. See Table 2 for the parameters of the RPC-1 purification method.

[0670] The sublots that meet the requirements for in-process controls (refer to Section 3.2.S.2.4 Control of Critical Steps and Intermediates) were pooled prior to the next step of the manufacturing process. This step was repeated twice to meet the desired product purity specification.

[0671] Table 2: RPC-1 purification method parameters

[0672] Purification by preparative reversed phase chromatography (RPC 2) / lyophilization

[0673] In the second stage of the purification, the pooled sublots of semi-purified product from the first purification step were diluted 1 :1 with water and loaded onto a preparative column, which was equilibrated with 0.2M aqueous HOAc and washed with 0.1 M ammonium acetate (NH4OAc). The product was eluted using a gradient of 0.2M aqueous HOAc for mobile phase A and ACN for mobile phase B, with monitoring by UV at 280 nm. See Table 3 for the parameters of the RPC-2 purification method. In this step, the counter ion was exchanged to form the acetate salt of PPL3571 drug substance. The resulting pure fractions that met the requirements for in-process controls (refer to Section 3.2.S.2.4 Control of Critical Steps and Intermediates) were filtered using a 0.45um Nylon filter, shell frozen and lyophilized to dryness to give the acetate salt of final peptide. Table 3: RPC-2 purification method parameters

[0674] Example 1 : Preparation of Peptide of CMP N0.:1

[0675] Ac-Trp-Thr-N-Me-Ala(tBu)-Cys-[3-(4-piperidinyl)]Ala-Asn-Nal(2')-Lys(DOTA)-Asp-Cys-Trp-

[0676] Pro-NH2, (Cys4^Cys10thioacetal bridge) (CMP N0.:1 )

[0677] Method Summary

[0678] The synthesis of CMP NO.1 (Peptide 1 ) was completed using generalized Fmoc solid-phase peptide synthesis techniques.

[0679] The peptide was synthesized on Rink Amide 4-Methylbenzhydrylamine (MBHA) using standard iterative and separate Fmoc deblocking and DIG coupling steps with washing in-between. The lysine8side chain was additionally conjugated with 1 ,4,7,10- tetraazacyclododecane-1 ,4,7,10-tetraacetic acid (DOTA), a chelating moiety (chelator). The crude peptide was obtained by cleavage / deprotection via acidolysis using trifluoroacetic acid (TFA), resulting in the C-terminal amide form of the fully deprotected peptide. A global constraint (macrocyclization) was applied via a thioacetal bridge between the cysteine residues. A purification scheme using reversed phase-high performance liquid chromatography (RP-HPLC) was used to generate the acetate salt form of the final peptide. Lyophilization of fractions (>95% purity) gave the final product as the acetate salt.

[0680] Experimental Method

[0681] Synthesis of Peptide 1 (Compound 153)

[0682] Swelling and Deblocking Resin: 206 g (179.2 mmol, 1 eq.) of Rink Amide MBHA resin (0.87 mmol / g loading) was soaked in DMF until desired swelling was achieved. The deblocking of the resin bound Fmoc group was performed by 20% piperidine in DMF. A colorimetric ninhydrin test (Kaiser Test) was performed to confirm deblocking of Fmoc and presence of free amine. The resin was washed with DMF.

[0683] Coupling of AA1: Fmoc-Pro-OH (2 eq., 121 g) was dissolved in DMF (1 .03 L) along with ethyl cyanohydroxyiminoacetate (oxyma) (2 eq., 51 g) as an additive. Pre-activation of the acid was accomplished by addition of DIC (2 eq, 157 mL). The resulting solution was added to the resin and allowed to react for 1.5 hours. The resin was washed with DMF x 5.

[0684] Capping Resin: Acetylation of any remaining resin-bound free amine (capping) was performed using a 20% Ac2O / 5% DIPEA / DMF solution. The resin was washed with DMF.

[0685] Coupling of AA2: Fmoc deblocking was completed with 20% piperidine / DMF x 2 (5 min, 20 min). A colorimetric Chloranil test, for secondary amines, was performed to confirm complete deblocking of the proline residue. Fmoc-Trp(Boc)-OH (2 eq., 189 g) was combined with oxyma (4 eq., 102 g) and DIC (2 eq, 56 mL) in DMF (1.03 L). The resulting solution was added to the resin and allowed to react for 1.6 hours. A chloranil test was performed to confirm the reaction was complete. The resin was washed with DMF x 8.

[0686] Coupling of AA3: Fmoc deblocking was completed with 20% piperidine / DMF. DMF washes were performed. A ninhydrin test was performed to confirm deblocking. Fmoc- Cys(Trt)-OH (2 eq., 210 g) was combined with oxyma (2 eq., 51 g) and DIC (2 eq, 56 mL) in DMF (1.03 L). The resulting solution was added to the resin and allowed to react for 1.5 hours. A ninhydrin test was performed to confirm the reaction was complete. Capping by acetylation with Ac2O / DIPEA / DMF was performed. The resin was washed with DMF x 6.

[0687] Coupling of AA4: Fmoc deblocking was completed with 10% piperidine / DMF with 0.5M oxyma / DMF, as an additive to minimize the possible Trp2-Pro1diketopiperazine formation. Deblocking was performed twice (5 min, 20 min). DMF washes were performed. A ninhydrin test was performed to confirm deblocking. Fmoc-Asp(t-Bu)-OH (2 eq., 148 g) was combined with oxyma (2 eq., 51 g) and DIC (2 eq, 56 mL) in DMF. The resulting solution was added to the resin and allowed to react for 4.7 hours. A chloranil test was performed to confirm the reaction was complete. The resin was washed with DMF x 6.

[0688] Coupling of AA5: Fmoc deblocking was completed with 20% piperidine / DMF. DMF washes were performed. A ninhydrin test was performed to confirm deblocking. Fmoc- Lys(Mtt)-OH (2 eq., 224 g) was combined with oxyma (2 eq., 51 g) and DIC (2 eq, 56 mL) in DMF (1.03 L). The resulting solution was added to the resin and allowed to react for 16.3 hours. A ninhydrin test was performed to confirm the reaction was complete. The resin was washed with DMF x 6.

[0689] Coupling of AA6: Fmoc deblocking was completed with 20% piperidine / DMF. DMF washes were performed. A ninhydrin test was performed to confirm deblocking. Fmoc-2-Nal- OH (2 eq., 157 g) was combined with oxyma (2 eq., 51 g) and DIC (2 eq, 56 mL) in DMF (1 .03 L). The resulting solution was added to the resin and allowed to react for 21 .2 hours. A ninhydrin test was performed to confirm the reaction was complete. The resin was washed with DMF x 3, then IPA x 3.

[0690] Coupling of AA7: Fmoc deblocking was completed with 20% piperidine / DMF. DMF washes were performed. A ninhydrin test was performed to confirm deblocking. Fmoc- Asn(Trt)-OH (2 eq., 214 g) was combined with oxyma (2 eq., 51 g) and DIC (2 eq, 56 mL) in DMF (1.03 L). The resulting solution was added to the resin and allowed to react for 2.8 hours. A ninhydrin test was performed to confirm the reaction was complete. The resin was washed with DMF x 6.

[0691] Coupling of AA8: Fmoc deblocking was completed with 20% piperidine / DMF. DMF washes were performed. A ninhydrin test was performed to confirm deblocking. Fmoc- [cHex(4-Aza-4-Boc)]Ala-OH (2 eq., 178 g) was combined with oxyma (2 eq., 51 g) and DIC (2 eq, 56 mL) in DMF (1 .03 L). The resulting solution was added to the resin and allowed to react for 18.7 hours. A ninhydrin test was performed to confirm the reaction was complete. The resin was washed with DMF x 6.

[0692] Coupling of AA9: Fmoc deblocking was completed with 20% piperidine / DMF. DMF washes were performed. A ninhydrin test was performed to confirm deblocking. Fmoc- Cys(Trt)-OH (2 eq., 210 g) was combined with oxyma (2 eq., 51 g) and DIC (2 eq, 56 mL) in DMF (1.03 L). The resulting solution was added to the resin and allowed to react for 5.2 hours. A ninhydrin test was performed to confirm the reaction was complete. Capping by acetylation with Ac2O / DIPEA / DMF was performed. The resin was washed with DMF x 6.

[0693] Coupling of AA10: Fmoc deblocking was completed with 20% piperidine / DMF. DMF washes were performed. A ninhydrin test was performed to confirm deblocking. Fmoc-M-Me- P-t-Bu-Ala-OH (2 eq., 137 g) was combined with oxyma (2 eq., 51 g) and DIC (2 eq, 56 mL) in DMF (1.03 L). The resulting solution was added to the resin and allowed to react for 16.3 hours. A ninhydrin test was performed to confirm the reaction was complete. The resin was washed with DMF x 6.

[0694] Coupling of AA11: Fmoc deblocking was completed with 20% piperidine / DMF. DMF washes were performed. A chloranil test was performed to confirm deblocking. Fmoc-Thr(t- Bu)-OH (2 eq., 143 g) was combined with oxyma (2 eq., 51 g) and DIC (2 eq, 56 mL) in DMF (1 .03 L). The resulting solution was added to the resin and allowed to react for 19.8 hours. A chloranil test was performed to confirm the reaction was complete. The resin was washed with DMF x 3. The AA11residue was subjected to recoupling. Fmoc-Thr(t-Bu)-OH (1 eq., 71 g) was combined with oxyma (1 eq., 26 g) and DIC (1 eq, 28 mL) in DMF (503 mL). The resulting solution was added to the resin and allowed to react for 5.5 hours. A chloranil test was performed to confirm the reaction was complete. The resin was washed with DMF x 3.

[0695] Coupling of AA12: Fmoc deblocking was completed with 20% piperidine / DMF. DMF washes were performed. A ninhydrin test was performed to confirm deblocking. Fmoc- Trp(Boc)-OH (2 eq., 224 g) was combined with oxyma (2 eq., 51 g) and DIC (2 eq, 56 mL) in DMF. The resulting solution was added to the resin and allowed to react for 16.3 hours. A ninhydrin test was performed to confirm the reaction was complete. The resin was washed with DMF x 6.

[0696] / V-terminal Capping: Fmoc deblocking was completed with 20% piperidine / DMF. DMF washes were performed. A ninhydrin test was performed to confirm deblocking. The resin was washed with DMF (3 x 1.7 L). Capping was performed using a capping solution of 20% AC2O / 5% DIPEA in DMF (1.7 mL). The capping solution was added to the resin and the mixture was agitated for 15 minutes. The resin was washed with DMF (3 x 1.7 L) then IPA (3 x 1.7 L).

[0697]

[0698] Scheme 1 : Deprotection of Lys8(Mtt) and chelator coupling.

[0699] Mtt Deprotection: 1 ,1 ,1 ,3,3,3-Hexafluoro-2-propanol (HFIP) (824 mL) and Triisopropyl silane (TIPS) (103 mL) were combined in DCM (1133 mL) and added to the resin and the mixture was agitated for 1 hour. This step was repeated and the combined resin and deprotection cocktail was agitated for 2 hours. A ninhydrin test was performed to confirm deprotection. The resin was washed with DCM (3 x 1 min), 5% DIPEA / DMF (3 x 1 min), and DMF (3 x 1 min). Scheme 1. Dde or ivDde Deprotection: Optionally, 1-(4,4-dimethyl-2,6-dioxocyclohex-1- ylidene)ethyl (Dde) or 1-(4,4-dimethyl-2,6-dioxocyclohex-1-ylidene)isovaleryl (ivDde) was used in place of Mtt. Deprotection conditions for Dde and ivDde consist of the following: A solution of 2% hydrazine monohydrate in A / ,A / -dimethylformamide (DMF) was added to the resin-bound peptide and the mixture was agitated for 5 minutes. This step was repeated twice more to ensure complete deprotection of the Dde or ivDde group from the Lys sidechain. A ninhydrin test was performed to confirm deprotection. The resin was washed with DCM (3 x 1 min), 5% DIPEA / DMF (3 x 1 min), and DMF (3 x 1 min). Chelator Coupling: DOTA(Ot-Bu)3-OH (2 eq., 205 g) was combined with PyAOP (2 eq., 186 g) and DIPEA (2 eq, 124 mL) in DMF (1.03 L) then added to the resin and agitated for 19.0 hours. The resin was washed with DMF. The coupling was repeated with DOTA(Ot- BU)3-OH (0.9 eq., 93 g), PyAOP (0.9 eq., 84 g), and DIPEA (0.9 eq, 56 mL) in DMF (1.03 L) which was added to the resin and agitated for 21 .3 hours. The resin was washed with DMF (3 x 1 min) and IPA (3 x 1 min). The crude resin was dried under a stream of nitrogen (N2). See Scheme 1.

[0700] Resin Cleavage and DOTA Deprotection: Cleavage of the peptide from solid support and global deprotection was performed in a mixture of TFA, H2O, and thioanisole, in a ratio of 96:2:2 (v / v), and 100 mg / mL DTT at a concentration of 5 mL / g resin. The cleavage solution was mixed and cooled in a dry ice bath to -10 °C. The peptide-resin was added to the cold cleavage solution and stirred for 30 min at ambient temperature. The solution was then heated to 40 °C for 2-4 hours with reaction monitoring by LC-MS or HPLC. Samples for monitoring were prepared by adding 100 pL of the reaction mixture to 1 .3 mL of 20% ACN / water in a microcentrifuge tube. The solution was filtered with a 0.2 pm syringe filter into a sample vial. The sample was decarboxylated by heating to 60°C for 3-5 minutes then subjected to LC-MS / HPLC screening. Exact conditions are found in Table 4.

[0701] Table 4: IPC HPLC Method

[0702] Crude Peptide Isolation: the depleted resin was filtered off and rinsed with additional TFA. The filtrate and rinse were combined in a round-bottom flask and concentrated by rotary evaporation under reduced pressure to approximately half the initial volume. The resulting concentrate was precipitated by quick addition to cold 1 :1 MTBE:hexanes (100 mL per gram starting peptide-resin). The precipitate was filtered through a medium sintered glass funnel, washed three times with MTBE, and dried in vacuo. Cleavage was performed in four sublots, totaling 726 g of peptide resin to produce 450 g of crude linear peptide.

[0703] Linear Purification: The linear intermediate peptide was purified by single stage RP- HPLC. Conditions are listed in Table 5. The crude linear intermediate was dissolved in 10% ACOH / H2O (50 mL / g crude) and decarboxylated by heating to 50 °C for 1 hour. The column was equilibrated with 5% ACN before loading the solution onto the column. The gradient was applied, and the eluent was collected in 50 mL fractions and analyzed by HPLC. Fractions of purity >85% (Analytical Method 2) were pooled and lyophilized to give the purified linear intermediate as a solid. Table 5: RPC-1 HPLC Method

[0704] Thioacetal Cyclization: In a narrow-necked vessel the linear peptide was dissolved in 50% THF / H2O at a concentration of 10.0 g / L. TCEP HCI (1 .5 eq) was added to the peptide solution followed by K2CO3(3 eq., 0.81 M). The pH was verified to be 4<pH<7 with pH paper. The reaction vessel was sealed with Parafilm and stirred for 30 min. CH2I2(10 eq.) was added to the solution followed by K2CO3(3 eq., 0.81 M). The pH was verified to be >7 with pH paper. The reaction was resealed with parafilm and vortexed vigorously overnight. Additional TCEP (1.5 eq) was added as needed, and pH adjusted to 8-9 with K2CO3(0.81 M). Upon completion, excess CH2I2and THF were removed by rotary evaporation and the solution was acidified by addition of neat TFA. (See Scheme 2).

[0705]

[0706] Scheme 2: Disulfide disruption and thioacetal cyclization.

[0707] RP-HPLC Purification: Purification of Peptide 1 was performed in a three-stage process using two successive purifications with TEAP buffer, followed by acetic acid buffer. Front and rear shoulders were segregated and saved separately for re-purification. Table 6: HPLC Method 1

[0708] Primary Purification

[0709] RPC-1 was performed using HPLC Method 1 (Table 6). Pooling criteria for fraction analysis was >80% giving a pool purity of >85%. RPC-2 was performed using HPLC Method 2 (Table 7). Pooling criteria for fraction analysis was >95% fraction purity, giving a pool purity of 97%. RPC-3 was performed using HPLC Method 3 (Table 8). Pooling criteria was >95% fraction purity, giving a pool purity of 98%. The overall recovery yield over the three stages was 43%.

[0710] Front Shoulder Reprocessing

[0711] Front shoulder side fractions resulting after primary purification were combined and repurified using HPLC Method 1 (Table 6). Maximum pool purity achieved was 90%.

[0712] Rear Shoulder Repurification

[0713] Rear shoulder side fractions resulting from primary purification were combine and repurified using HPLC Method 3 (Table 7). Analysis was performed by bracketing fractions, giving a pool purity of 98%. Counter Ion Exchange and Lyophilization: Sublots of the Peptide 1 TFA salt were dissolved in 1000 mL 10% ACN / 0.2%TFA / water and loaded onto C18 RP-HPLC media. Counter-ion exchange was performed by passing 0.2 M NFUOAc for 20 minutes before applying the gradient shown below (Table 9). Fractions were selected to give a pool purity of >97% and lyophilized to give 16 g of Peptide 1 as the acetate salt.

[0714] Table 9: Ion-exchange Method

[0715] Results

[0716] SPPS of Peptide 1 on a 179.2 mmol scale produced 726 g of peptide-resin (179 mmol, theoretical 815 g, yield 85.9%). TFA cleavage / deprotection of 721 g peptide-resin produced 450 g of crude peptide 1 (yield 122%). Crude purity by Analytical Method 1 across 6 sublots ranged from 26-42%. Purification of 443 g of the crude linear peptide 1 generated 130 g of linear peptide 1 intermediate of >85% purity (Overall yield 35%).

[0717] Cyclization / purification of 128 g linear peptide 1 intermediate gave 31 g of the TFA salt. The cyclization process provided a crude purity of 85% using THF / water as the medium and 60% when ACN / water was used. Cyclization / purification yield was 24.1% and overall yield is 8.4%.

[0718] Synthesis of Peptide 2 (Indium (III) Labeling)

[0719] Feasibility 1 g Scale Experiment

[0720] In a 2-L Erlenmeyer flask equipped with a stir bar, 1 .0 g (0.48 mmol) of purified Peptide 1 TFA salt was dissolved in 100 mL 0.2M NH4OAc (adjust to 4.9 pH with acetic acid). While vortexing, (5 eq, 0.53 g, 2.4 mmol) I nCI3 was added to give a heterogenous mixture with fine white precipitate, which homogenized upon heating. The reaction temperature was raised to 60 °C (30 minutes heating) and held at 60 °C for 1 hour. The mixture was allowed to cool to ambient temperature. The solution was filtered through a fine sintered glass funnel and purified by RP-HPLC with HPLC Method 4, achieving 96.0% purity. A second purification was performed with a more shallow gradient (HPLC Method 5), to achieve 97.2% purity. Lyophilization produced 604 mg of Peptide 2 acetate in a 57% yield.

[0721] Table 10: HPLC Method 4

[0722] Table 11: HPLC Method 5

[0723] Scale-up

[0724] The indium chelation reaction was scaled-up to 8.7 g (4.8 mmol) of purified Peptide 2 TFA salt using the previously described method. Unlike the 1 g scale, the fine white precipitate did not homogenize upon heating; instead, a biphasic mixture was formed. The mixture was allowed to cool to ambient temperature and 1000 mL of ACN was added but failed to homogenize. The solution was passed through a fine fritted filter and diluted with 4.6 L of 3% acetic acid / water for purification by RP-HPLC.

[0725] Peptide 2 was purified in two stages, followed by counter-ion conversion as shown in Tables 12-14 below.

[0726] Table 12: HPLC Method 6

[0727] Table 13: HPLC Method 7

[0728] Table 14: Ion-exchange Method Final Lyophilization

[0729] Sublots of Peptide 2 were reconstituted together in 700 mL 20% ACN / H2O. The solution was passed through a 0.45 pm nylon filter and lyophilized to give Peptide 2 as the acetate salt.

[0730] Results

[0731] Peptide 1 TFA salt was chelated with ln3+to give chelated Peptide 2 acetate (99% purity) in 58% yield across the chelation process. Overall yield across all steps, including synthesis, was 4.9%.

[0732] Synthesis of Peptide 3 (Heavy Label)

[0733] Method

[0734] Resin-bound peptide 3; 4.1 g of peptide-resin was used to synthesize peptide 3 in the same manner as peptide 1 on an estimated 1 .0 mmol scale. Cleavage and deprotection gave 1.7 g of crude linear peptide 3 with a crude purity of 43.1 % (81.4% yield). Purification of the crude linear peptide was performed with HPLC Method 8 (Table 15). Lyophilization of the main pool produced 439 mg linear peptide (94% purity) and lyophilization of the side cut produced 163 mg of linear peptide (80% purity). The recovery yield was 26% and 10% respectively. Table 15: HPLC Method 8

[0735] Cyclization was performed at a 300 mg scale on linear peptide 3 (purity >90%) using the aforementioned procedure. Initial purification gives a purity of 98.3% with a single pass of HPLC Method 1 . All main fraction pools were combined and processed with HPLC Method 3, to convert TEAP to TFA, and lyophilized to give 212 mg of peptide 3 TFA salt in 10.1% overall yield (97.6% purity).

[0736] Analytical Methods Analytical Method 1 (HPLC): designed for analysis of the crude linear peptide intermediate. The method was designed to utilize a wide gradient window to allow for observation of distant impurities.

[0737] Table 16: Analytical Method 1 (HPLC) Analytical Method 2 (HPLC): designed for general analysis of the peptide, analysis of intermediates, in-process fraction analysis, and as the Release Method for peptide 3 and peptide 2. It provides a gradient slope of 1% / min.

[0738] Table 17: Analytical Method 2 (HPLC)

[0739] Analytical Method 3 (UPLC): was developed for cyclization reaction monitoring and fraction analysis during purifications.

[0740] Table 18: Analytical Method 3 (HPLC)

[0741] Synthesis of Peptide 4 (Compound 447)

[0742] The synthesis of peptide 4 was conducted in a similar fashion as to the synthesis of peptide 1 with an exception to the conditions utilized for the coupling of AA8. The alternate conditions are provided below.

[0743] Peptide 4 - Coupling of AA8: Fmoc deblocking was completed with 20% piperidine / DMF. DMF washes were performed. A ninhydrin test was performed to confirm deblocking. Fmoc-3-[cHex(4-Aza-4-CH2COOtBu)]Ala-OH (2 eq., 182 g) was combined with oxyma (2 eq., 51 g) and DIC (2 eq, 56 mL) in DMF (~1.0 L). The resulting solution was added to the resin and allowed to react for at least 16 hours. A ninhydrin test was performed to confirm the reaction was complete. The resin was washed with DMF x 6.

Claims

CLAIMS1 . A process for preparing a cyclic peptide of Formula I:or a pharmaceutically acceptable salt thereof, wherein:P1is selected from: H, -L1-Chelator,D1is selected from H, CH3, C(O)OH, and -NR”-Chelator;L1is absent or selected fromwherein the amino group of L1connects to the carbonyl group of P1or Chelator to form an amide bond;P2is selected from C(O)NH2, C(O)OH,P3is selected from H, Ac, -L3-Chelator,L3is absent or independently selected fromwherein the carbonyl group of L3connects to an amine group of P2to form an amide bond;D3is independently selected from: CH3, C(O)OH, -NR”-Chelator, andX is halogen;R° is an amino acid side chain of a natural amino acid or an amino acid side chain of an unnatural amino acid;R1is an amino acid side chain of a natural amino acid or an amino acid side chain of an unnatural amino acid;R2is an amino acid side chain of a natural amino acid or an amino acid side chain of an unnatural amino acid;R3is an amino acid side chain of a natural amino acid or an amino acid side chain of an unnatural amino acid;B1is C1-6 alkylene;C1is C1-6 alkylene;A1is selected from:wherein w is selected from 1 , 2, or 3;R4is an amino acid side chain of a natural amino acid or an amino acid side chain of an unnatural amino acid, both of which are optionally substituted with Chelator, CH2C(O)OH, or C(O)(CH2CH2O)P(CH2)2N(CH3)3+, wherein the Chelator is optionally substituted to the amino acid side chain through a Linker;R5is an amino acid side chain of a natural amino acid or an amino acid side chain of an unnatural amino acid, both of which are optionally substituted with Chelator, wherein the Chelator is optionally substituted to the amino acid side chain through a Linker;R6is an amino acid side chain of a natural amino acid or an amino acid side chain of an unnatural amino acid;R7is selected from:(i) an amino acid side chain of a natural amino acid,(ii) an amino acid side chain of an unnatural amino acid, or(iii) selected from the group consisting ofwherein L4is absent or independently selected from:wherein the carbonyl group of L4connects to an amine group of R7to form an amide bond;R8is an amino acid side chain of a natural amino acid or an amino acid side chain of an unnatural amino acid;R9is an amino acid side chain of a natural amino acid or an amino acid side chain of an unnatural amino acid;R10is an amino acid side chain of a natural amino acid or an amino acid side chain of an unnatural amino acid; m is 0 or 1 ; each n, q, and u are independently an integer from 0 to 16; each p is independently an integer from 0 to 24;each s is independently an integer from 0 to 16; each t is independently 1 , 2, 3, 4, 5, or 6; each R’ is independently selected from H, C(O)OH, (CH2)0H and NHAc; and each R” is independently selected from H and CH3; wherein each backbone nitrogen atom or alpha carbon is optionally substituted with a methyl group. wherein either the cyclic peptide of Formula I does not comprise a Chelator, or at least one of R4, R5, or R7is substituted with a Chelator or Chelator-containing group, wherein said process comprises reacting a linear peptide of Formula II:or a pharmaceutically acceptable salt thereof, under conditions that produce a reaction between A1aand A1bto afford the compound of Formula I, wherein:A1aand A1bare each selected from:wherein either the linear peptide of Formula II does not comprise a Chelator, or at least one of R4, R5, or R7is substituted with a Chelator or Chelator-containing group, wherein each backbone nitrogen atom or alpha carbon is optionally substituted with a methyl group.

2. The process of claim 1 , wherein:P1is selected from H, Ac,independently 9, 10, 11 , 12, or 13;D1is CH3or C(O)OH;X is halogen;R1is selected from the group consisting of an amino acid side chain of Trp, 2Nal, 1 Nal, 4CF3-Phe, 7Aza-Trp, 1Me-Trp, 5OH-Trp, BIP, 5OMe-Trp, 4F-Phe, 3Pya, 4Pya, PAF, MAF, OAF, 5Qui, 7MeO-Trp, 7Me-Trp, 5F-Trp, 7CI-Trp, D-Ala, and Ala;R2is selected from the group consisting of an amino acid side chain of Thr, D-Ala, Ala, and Lys;R3is selected from the group consisting of an amino acid side chain of He, Env, CHA, CBA, Nle, Tbg, THPG, Chg, 2Nal, 1 Nal, 2CF3-Phe, D-Ala, Ala, Leu, t-Bu-Ala, a-tert-amylGly, Allo-lle, Lys(C12), Lys(C14), and Lys(C16);B1is C1-6 alkylene;C1is C1-6 alkylene;A1is selected from the group consisting ofR4is selected from the group consisting of an amino acid side chain of Asn, D-Ala, Ala, DAB-4-NHCOC5HH , DAB-4-NHCOC7H15, Asp, Ser, Lys(DOTA), Lys, 3-(4-piperidinyl)-Ala, 3-(1-morpholinyl)-Ala, 3Pya, 4Pya, Glu, Pip(CH2CO2H)Ala, Pip(PegNMe3)Ala, and Pip(GAE-DOTA)Ala;R5is selected from the group consisting of an amino acid side chain of Asn, Ala, D- Ala, Trp, Asp, Lys, Lys(DOTA), 3Pya, 4Pya, 3-(4-piperidinyl)-Ala, 3-(1-morpholinyl)-Ala, Glu, and Ser;R6is selected from the group consisting of an amino acid side chain of Trp, 4CF3- Phe, 1Me-Trp, 7Aza-Trp, BIP, 2Nal, 1 Nal, D-Ala, Ala, 4F-Phe, 5F-Trp, 5MeO-Trp, Asn, 5OH- Trp, 7Me-Trp, 7MeO-Trp, and 7CI-Trp;(i) selected from the group consisting of an amino acid side chain of 3Pya, 4Pya, Lys(Me)3, His, Ala, D-Ala, Gin, Lys, Glu, Arg, Orn, and Ser; or(ii) selected from the group consisting of12, or 14;R8is selected from the group consisting of an amino acid side chain of Asp, D-Ala, Ala, Asn, and Thr;R9is selected from the group consisting of an amino acid side chain of Trp, 7Aza- Trp, 1 Me-Trp, D-Ala, Ala, 4F-Phe, 1 Nal, 2Nal, 5F-Trp, 5MeO-Trp, 7CI-Trp, 5OH-Trp, 7Me- Trp, and 7MeO-Trp;R10is selected from the group consisting of an amino acid side chain of Pro, D-Ala, Ala, trans4Fluoro-Pro, cis4Fluoro-Pro, trans4OH-Pro, cis4OH-Pro, Pip, 5,5-diMe-Pro, trans4NH2-Pro, cis4NH2-Pro, Aze, R-3Me-Aze, ACI, and 3Me2-Aze; m is 0; and wherein each backbone nitrogen atom or alpha carbon is optionally substituted with a methyl group.

3. The process of claim 1 or claim 2, wherein:P1is Ac;P2is C(O)NH2or C(O )OH;R1is an amino acid side chain of Trp;R2is an amino acid side chain of Thr;R3is an amino acid side chain of t-Bu-Ala;B1is Ci alkylene;C1is Ci alkylene;R4is an amino acid side chain of 3-(4-piperidinyl)-Ala or Pip(CH2CO2H);R5is an amino acid side chain of Asn;R6is an amino acid side chain of 2Nal;R7is selected from the group consisting ofR8is an amino acid side chain of Asp;R9is an amino acid side chain of Trp;R10is an amino acid side chain of Pro; m is 0;VSHA1aand A1bare each ; and wherein each backbone nitrogen atom or alpha carbon is optionally substituted with a methyl group.

4. The process of claim 1 or claim 2, wherein: vSHVSH(i) A1ais and A1bis5. The process of claim 4, wherein:VSHVSHA1ais and A1bis ; and the process comprises combining the linear peptide of Formula II with a compound selected from:to form a group having a structure selected from:wherein Lv, independently for each occurrence, is a leaving group.

6. The process of any one of claims 1 , 4, or 5, further comprising the step of deprotecting and cleaving a resin-bound peptide of Formula III:(III), or a pharmaceutically acceptable salt thereof, from a resin; wherein:P1pis selected from: H, -L1p-Chelatorp,D1Pis selected from H, CH3, C(O)O-PG1, and -NR”-Chelatorp; L1Pis absent or selected fromwherein the amino group of L1Pconnects to the carbonyl group of P1por Chelatorpto form an amide bond; P2pis selected from C(O)-D2P,D2Pis the resin;L2Pis absent or selected from:P3pis selected from H, an amino protecting group, Ac, -L3p-Chelatorp,L3Pis absent or independently selected fromwherein the carbonyl group of L3Pconnects to an amine group of P2pto form an amide bond;D3Pis independently selected from: CH3, C(O)O-PG1, -NR”-Chelatorp, andX is halogen;Ropis an optionally protected amino acid side chain of a natural amino acid or an optionally protected amino acid side chain of an unnatural amino acid;R1Pis an optionally protected amino acid side chain of a natural amino acid or an optionally protected amino acid side chain of an unnatural amino acid;R2Pis an optionally protected amino acid side chain of a natural amino acid or an optionally protected amino acid side chain of an unnatural amino acid;R3Pis an optionally protected amino acid side chain of a natural amino acid or an optionally protected amino acid side chain of an unnatural amino acid;B1is C1-6 alkylene;C1is C1-6 alkylene;A1aPand A1bPare each selected from:R4Pis an optionally protected amino acid side chain of a natural amino acid or an optionally protected amino acid side chain of an unnatural amino acid, both of which are further optionally substituted with Chelatorp, CH2C(O)O-PG1, or C(O)(CH2CH2O)p(CH2)2N(CH3)3+, wherein the Chelatorpis optionally substituted to the amino acid side chain through a Linker;R5Pis an optionally protected amino acid side chain of a natural amino acid or an optionally protected amino acid side chain of an unnatural amino acid, both of which are optionally further substituted with Chelatorp, wherein the Chelatorpis optionally substituted to the amino acid side chain through a Linker;R6Pis an optionally protected amino acid side chain of a natural amino acid or an optionally protected amino acid side chain of an unnatural amino acid;R7Pis selected from:(i) an optionally protected amino acid side chain of a natural amino acid,(ii) an optionally protected amino acid side chain of an unnatural amino acid, or(iii) the group consisting ofwherein L4is absent or independently selected from:wherein the carbonyl group of L4connects to an amine group of R7Pto form an amide bond;R8Pis an optionally protected amino acid side chain of a natural amino acid or an optionally protected amino acid side chain of an unnatural amino acid;R9Pis an optionally protected amino acid side chain of a natural amino acid or an optionally protected amino acid side chain of an unnatural amino acid;R10Pis an optionally protected amino acid side chain of a natural amino acid or an optionally protected amino acid side chain of an unnatural amino acid; m is 0 or 1 ; each n, q, and u are independently an integer from 0 to 16; each p is independently an integer from 0 to 24; each s is independently an integer from 0 to 16;each t is independently 1 , 2, 3, 4, 5, or 6; each R’” is independently selected from H, C(O)O-PG1, (CH2)O-PG4and NHAc; and each R” is independently selected from H and CH3;PG1is H or a carboxylic acid protecting group;PG2is H or a thiol protecting group;PG3is H or an amino protecting group;PG4is H or a hydroxyl protecting group;Chelatorpis an optionally protected Chelator; wherein each backbone nitrogen atom or alpha carbon is optionally substituted with a methyl group. wherein either the resin-bound peptide of Formula III does not comprise a Chelatorp, or at least one of R4P, R5P, or R7Pis substituted with a Chelatorpor Chelatorp-containing group; to provide a linear peptide of Formula II.

7. The process of any one of claim 2, 4, or 5, further comprising the step of deprotecting and cleaving a resin-bound peptide of Formula III:(HI), or a pharmaceutically acceptable salt thereof, from a resin; wherein:P1Pis selected from: H, Ac,independently 9, 10, 1 1 , 12, or 13;D1Pis selected from CH3and C(O)O-PG1;P2pis selected fromD2Pis the resin;X is halogen;R1Pis an amino acid side chain of 2Nal, 1 Nal, 4CF3-Phe, 1 Me-Trp, 4F-Phe, 5Qui, D- Ala, or Ala, or R1Pis a protected amino acid side chain of Trp, 7Aza-Trp, 5OH-Trp, BIP, 5OMe-Trp, 3Pya, 4Pya, PAF, MAF, OAF, 7MeO-Trp, 7Me-Trp, 5F-Trp, or 7CI-Trp;R2Pis an amino acid side chain of D-Ala or Ala, or R2Pis a protected amino acid side chain of Thr or Lys;R3Pis an amino acid side chain of He, Env, CHA, CBA, Nle, Tbg, THPG, Chg, 2Nal, 1 Nal, 2CF3-Phe, 2PhEt-Ala, D-Ala, Ala, Leu, t-Bu-Ala, a-tert-amylGly, Allo-lle, Lys(C12), Lys(C14), or Lys(C16);B1is C1-6 alkylene;C1is C1-6 alkylene;A1aPand A1bPare each selected from:, , COC5Hn , DAB-4- NHCOC7H15, 3-(1-morpholinyl)-Ala, 3Pya, 4Pya, or Pip(PegNMe3)Ala, or R4Pis a protected amino acid side chain of Asn, Asp, Ser, Lys(DOTA), Lys, 3-(4-piperidinyl)-Ala, Glu, Pip(CH2CO2H)Ala, or Pip(GAE-DOTA)Ala;R5Pis an amino acid side chain of Ala, D-Ala, 3Pya, 4Pya, or 3-(1-morpholinyl)-Ala, or R5Pis a protected amino acid side chain of Asn, Trp, Asp, Lys, Lys(DOTA), 3-(4- piperidiny l)-Ala, Glu, or Ser;R6Pis an amino acid side chain of 4CF3-Phe, 1 Me-Trp, BIP, 2Nal, 1 Nal, D-Ala, Ala, or 4F-Phe, or R6Pis a protected amino acid side chain of Trp, 7Aza-Trp, 5F-Trp, 5MeO-Trp, Asn, 5OH-Trp, 7Me-Trp, 7MeO-Trp, or 7CI-Trp;R7Pis(i) an amino acid side chain of 3Pya, 4Pya, Lys(Me)3, Ala, or D-Ala,(ii) a protected amino acid side chain of His, Gin, Lys, Glu, Arg, Orn, or Ser, or(iii) selected from the group consisting ofpendently 3, 5,10,12, or 14, and wherein DOTA is optionally protected with three PG1groups or one LG1group;R8Pis an amino acid side chain of D-Ala or Ala, or R8Pis a protected amino acid side chain of Asp, Asn, or Thr;R9Pis an amino acid side chain of 1 Me-T rp, D-Ala, Ala, 4F-Phe, 1 Nal, or 2Nal, or R9Pis a protected amino acid side chain of Trp, 7Aza-Trp, 5F-Trp, 5MeO-Trp, 7CI-Trp, 5OH-Trp, 7Me-Trp, or 7MeO-Trp;R10Pis an amino acid side chain of Pro, D-Ala, Ala, trans4Fluoro-Pro, cis4Fluoro-Pro, Pip, 5,5-diMe-Pro, Aze, R-3Me-Aze, ACI, or 3Me2-Aze, or R10Pis a protected amino acid side chain of trans4OH-Pro, cis4OH-Pro, trans4NH2-Pro, or cis4NH2-Pro; m is 0;PG1is H or a carboxylic acid protecting group;PG2is H or a thiol protecting group;PG3is H or an amino protecting group;PG4is H or a hydroxyl protecting group;LG1is an amine reactive leaving group; wherein each backbone nitrogen atom or alpha carbon is optionally substituted with a methyl group; andwherein either the resin-bound peptide of Formula III does not comprise DOTA, or at least one of R4P, R5P, or R7Pis substituted with DOTA or a DOTA-containing group; to provide a linear peptide of Formula II8. The process of claim 3, further comprising the step of deprotecting and cleaving a resin-bound peptide of Formula III:(HI), or a pharmaceutically acceptable salt thereof, from a resin; wherein:P1Pis Ac;P2Pis C(O)-D2P;D2Pis the resin;R1Pis a protected amino acid side chain of Trp;R2Pis a protected amino acid side chain of Thr;R3Pis an amino acid side chain of t-Bu-Ala;B1is Ci alkylene;C1is Ci alkylene;A1aPand A1bPare eachR4Pis a protected amino acid side chain of 3-(4-piperidinyl)-Ala or Pip(CH2CO2H)Ala;R5Pis a protected amino acid side chain of Asn;R6Pis an amino acid side chain of 2Nal;R7Pis selected from the group consisting ofonally protected with three PG1groups or one LG1group;R8Pis a protected amino acid side chain of Asp;R9Pis a protected amino acid side chain of Trp;R10Pis an amino acid side chain of Pro; m is 0;PG1is H or a carboxylic acid protecting group;PG2is H or a thiol protecting group;PG4is H or a hydroxyl protecting group;LG1is an amine reactive leaving group; wherein each backbone nitrogen atom or alpha carbon is optionally substituted with a methyl group; and wherein either the resin-bound peptide of Formula III does not comprise DOTA, or at least one of R4P, R5P, or R7Pis substituted with DOTA or a DOTA-containing group; to provide a linear peptide of Formula II.

9. The process of any one of claims 6-8, wherein the resin is Rink amide MBHA resin.

10. The process of any one of claims 6-9, wherein the deprotection and cleavage of the resin-bound peptide of Formula III is performed under acidic conditions.11 . The process of any one of claims 6-10, wherein each protecting group is an acid- labile protecting group.

12. The process of any one of claims 6-1 1 , wherein the deprotection and cleavage of the resin-bound peptide of Formula III is performed in the presence of a reducing agent.

13. The process of any one of claims 6-12, wherein the deprotection and cleavage of the resin-bound peptide of Formula III is performed in the presence of a nucleophilic scavenger.

14. The process of any one of claims 6-13, wherein the deprotection and cleavage of the resin-bound peptide of Formula III is performed in the presence of trifluoroacetic acid (TFA), thioanisole, and dithiothreitol (DTT).

15. The process of any one of claims 6 or 9-14, further comprising the steps of (A) providing a resin-bound peptide of Formula IV:(IV), or a pharmaceutically acceptable salt thereof, wherein:D1Pis selected from H, CH3, C(O)O-PG1, and -NR”-PGChel;L1Pis absent or selected fromwherein the amino group of L1Pconnects to the carbonyl group of P1Pto form an amide bond or the amino group of L1Pforms a covalent bond with PGChel; P2pis selected from C(O)-D2P,D2Pis a resin;L2Pis absent or selected from:P3pis selected from H, an amino protecting group, Ac, -|_3P-PGChel,L3Pis absent or independently selected fromwherein the carbonyl group of L3Pconnects to an amine group of P2pto form an amide bond;D3Pis independently selected from: CH3, C(O)O-PG1, -NR”-PGChel, andX is halogen;Ropis an optionally protected amino acid side chain of a natural amino acid or an optionally protected amino acid side chain of an unnatural amino acid;R1Pis an optionally protected amino acid side chain of a natural amino acid or an optionally protected amino acid side chain of an unnatural amino acid;R2Pis an optionally protected amino acid side chain of a natural amino acid or an optionally protected amino acid side chain of an unnatural amino acid;R3Pis an optionally protected amino acid side chain of a natural amino acid or an optionally protected amino acid side chain of an unnatural amino acid;B1is C1-6 alkylene;C1is C1-6 alkylene;A1aPand A1bPare each selected from:R4Pis an optionally protected amino acid side chain of a natural amino acid or an optionally protected amino acid side chain of an unnatural amino acid, both of which are further optionally substituted with PGChel, CH2C(O)O-PG1, or C(O)(CH2CH2O)p(CH2)2N(CH3)3+, wherein the PGChelis optionally substituted to the amino acid side chain through a Linker;R5Pis an optionally protected amino acid side chain of a natural amino acid or an optionally protected amino acid side chain of an unnatural amino acid, both of which are optionally further substituted with PGChel, wherein the PGChelis optionally substituted to the amino acid side chain through a Linker;R6Pis an optionally protected amino acid side chain of a natural amino acid or an optionally protected amino acid side chain of an unnatural amino acid;R7Pis selected from:(i) an optionally protected amino acid side chain of a natural amino acid,(ii) an optionally protected amino acid side chain of an unnatural amino acid, or(iii) the group consisting ofwherein L4is absent or independently selected from:wherein the carbonyl group of L4connects to an amine group of R7Pto form an amide bond;R8Pis an optionally protected amino acid side chain of a natural amino acid or an optionally protected amino acid side chain of an unnatural amino acid;R9Pis an optionally protected amino acid side chain of a natural amino acid or an optionally protected amino acid side chain of an unnatural amino acid;R10Pis an optionally protected amino acid side chain of a natural amino acid or an optionally protected amino acid side chain of an unnatural amino acid; m is 0 or 1 ; each n, q, and u are independently an integer from 0 to 16; each p is independently an integer from 0 to 24; each s is independently an integer from 0 to 16; each t is independently 1 , 2, 3, 4, 5, or 6; each R’” is independently selected from H, C(O)O-PG1, (CH2)O-PG4and NHAc; and each R” is independently selected from H and CH3;PG1is H or a carboxylic acid protecting group;PG2is H or a thiol protecting group;PG3is H or an amino protecting group;PG4is H or a hydroxyl protecting group;PGChelis a protecting group; wherein at least one of R4P, R5P, or R7Pis substituted with a PGChelor PGChel- containing group; wherein each backbone nitrogen atom or alpha carbon is optionally substituted with a methyl group;(B) deprotecting the resin-bound peptide of Formula IV, or a pharmaceutically acceptable salt thereof, to form a deprotected intermediate, wherein the deprotected intermediate is not substituted with a PGChelor PGChel-containing group; and(C) reacting the deprotected intermediate with an optionally protected Chelator, ChelatorFree, to provide the resin-bound peptide of Formula III.

16. The process of any one of claims 7 or 9-14, further comprising the steps of (A) providing a resin-bound peptide of Formula IV:(IV), or a pharmaceutically acceptable salt thereof, wherein:P1pis selected from: H, Ac,independently 9, 10, 1 1 , 12, or 13;D1Pis selected from CH3and C(O)O-PG1;X is halogen;R1Pis an amino acid side chain of 2Nal, 1 Nal, 4CF3-Phe, 1 Me-Trp, 4F-Phe, 5Qui, D- Ala, or Ala, or R1Pis a protected amino acid side chain of Trp, 7Aza-Trp, 5OH-Trp, BIP,5OMe-Trp, 3Pya, 4Pya, PAF, MAF, OAF, 7MeO-Trp, 7Me-Trp, 5F-Trp, or 7CI-Trp;R2Pis an amino acid side chain of D-Ala or Ala, or R2Pis a protected amino acid side chain of Thr or Lys;R3Pis an amino acid side chain of He, Env, CHA, CBA, Nle, Tbg, THPG, Chg, 2Nal, 1 Nal, 2CF3-Phe, 2PhEt-Ala, D-Ala, Ala, Leu, t-Bu-Ala, a-tert-amylGly, Allo-lle, Lys(C12), Lys(C14), or Lys(C16);B1is C1-6 alkylene;C1is C1-6 alkylene;A1aPand A1bPare each selected from:, , COC5Hn, DAB-4- NHCOC7H15, 3-(1-morpholinyl)-Ala, 3Pya, 4Pya, or Pip(PegNMe3)Ala, or R4Pis a protected amino acid side chain of Asn, Asp, Ser, Lys(DOTA), Lys, 3-(4-piperidinyl)-Ala, Glu, Pip(CH2CO2H)Ala, or R4Pis Pip(GAE-PGChel)Ala;R5Pis an amino acid side chain of Ala, D-Ala, 3Pya, 4Pya, or 3-(1-morpholinyl)-Ala, or R5Pis a protected amino acid side chain of Asn, Trp, Asp, Lys, 3-(4-piperidinyl)-Ala, Glu, or Ser, or R5Pis Lys(PGChel);R6Pis an amino acid side chain of 4CF3-Phe, 1Me-Trp, BIP, 2Nal, 1 Nal, D-Ala, Ala, or 4F-Phe, or R6Pis a protected amino acid side chain of Trp, 7Aza-Trp, 5F-Trp, 5MeO-Trp, Asn, 5OH-Trp, 7Me-Trp, 7MeO-Trp, or 7CI-Trp;R7Pis(i) an amino acid side chain of 3Pya, 4Pya, Lys(Me)3, Ala, or D-Ala,(ii) a protected amino acid side chain of His, Gin, Lys, Glu, Arg, Orn, or Ser, or(iii) selected from the group consisting of, wherein each s is independently3, 5,10, 12, or 14;R8Pis an amino acid side chain of D-Ala or Ala, or R8Pis a protected amino acid side chain of Asp, Asn, or Thr;R9Pis an amino acid side chain of 1 Me-T rp, D-Ala, Ala, 4F-Phe, 1 Nal, or 2Nal, or R9Pis a protected amino acid side chain of Trp, 7Aza-Trp, 5F-Trp, 5MeO-Trp, 7CI-Trp, 5OH-Trp, 7Me-Trp, or 7MeO-Trp;R10Pis an amino acid side chain of Pro, D-Ala, Ala, trans4Fluoro-Pro, cis4Fluoro-Pro, Pip, 5,5-diMe-Pro, Aze, R-3Me-Aze, ACI, or 3Me2-Aze, or R10Pis a protected amino acid side chain of trans4OH-Pro, cis4OH-Pro, trans4NH2-Pro, or cis4NH2-Pro; m is 0;PG1is H or a carboxylic acid protecting group;PG2is H or a thiol protecting group;PG3is H or an amino protecting group;PG4is H or a hydroxyl protecting group;PGChelis a protecting group; wherein at least one of R4P, R5P, or R7Pis substituted with a PGChelor PGChel- containing group; wherein each backbone nitrogen atom or alpha carbon is optionally substituted with a methyl group;(B) deprotecting the resin-bound peptide of Formula IV, or a pharmaceutically acceptable salt thereof, to form a deprotected intermediate, wherein the deprotected intermediate is not substituted with a PGChelor PGChel-containing group; and(C) reacting the deprotected intermediate with an optionally protected Chelator, ChelatorFree, to provide the resin-bound peptide of Formula III.

17. The process of any one of claims 8 or 9-14, further comprising the steps of(A) providing a resin-bound peptide of Formula IV:(IV), or a pharmaceutically acceptable salt thereof, wherein:P1pis Ac; P2pis C(O)-D2P;D2Pis the resin;R1Pis a protected amino acid side chain of Trp;R2Pis a protected amino acid side chain of Thr;R3Pis an amino acid side chain of t-Bu-Ala;B1is Ci alkylene;C1is Ci alkylene;A1aPand A1bPare eachR4Pis a protected amino acid side chain of 3-(4-piperidinyl)-Ala;R5Pis a protected amino acid side chain of Asn;R6Pis an amino acid side chain of 2Nal;R7Pis selected from the group consisting ofR8Pis a protected amino acid side chain of Asp;R9Pis a protected amino acid side chain of Trp;R10Pis an amino acid side chain of Pro; m is 0;PG1is H or a carboxylic acid protecting group;PG2is H or a thiol protecting group;PG4is H or a hydroxyl protecting group;PGChelis a protecting group; wherein each backbone nitrogen atom or alpha carbon is optionally substituted with a methyl group;(B) deprotecting the resin-bound peptide of Formula IV, or a pharmaceutically acceptable salt thereof, to form a deprotected intermediate, wherein the deprotected intermediate is not substituted with a PGChelor PGChel-containing group; and(C) reacting the deprotected intermediate with an optionally protected Chelator, ChelatorFree, to provide the resin-bound peptide of Formula III.

18. The process of any one of claims 15-17, wherein PGChelis an amino protecting group.

19. The process of any one of claims 15-18, wherein PGChelis 4-methyltrityl (Mtt), 1-(4,4- dimethyl-2,6-dioxocyclohexylidene)ethyl (Dde), or 1-(4,4-dimethyl-2, 6-dioxocyclohex-1- ylidene)-3-methylbutyl (ivDde).

20. The process of claim 19, wherein deprotecting the resin-bound peptide of Formula IV is performed in the presence of hexafluoroisopropanol (HFIP), trifluoroacetic acid (TFA), or hydrazine.21 . The process of claim 20, wherein deprotecting the resin-bound peptide of Formula IV is performed in the further presence of a trialkylsilane and dichloromethane.

22. The process of claim 21 , wherein the trialkylsilane is triisopropylsilane (TIS) or triethylsilane (TES).

23. The process of any one of claims 15-22, wherein ChelatorFreecomprises an unprotected carboxylic acid group.

24. The process of any one of claims 15-23, wherein ChelatorFreeis the following structure:

25. The process of claim 23 or claim 24, wherein the reaction of the deprotected intermediate with ChelatorFreeis performed in the presence of a coupling agent.

26. The process of claim 25, wherein the coupling agent is (7-Azabenzotriazol-1- yloxy)tr’pyrrolidinophosphonium hexafluorophosphate (PyAOP), N,N'- diisopropylcarbodiimide (DIG), A / ,A / -dicyclohexylcarbodiimide (DCC), 1-(3- dimethylaminopropyl)-3-ethylcarbodiimide (EDC), 1-[bis(dimethylamino)methylene]-1 / - / - 1 ,2,3-triazolo[4,5-b]pyridinium 3-oxid hexafluorophosphate (HATU), O-(1 / - / -6- Chlorobenzotriazole-1-yl)-1 ,1 ,3,3-tetramethyluronium hexafluorophosphate (HCTU), [benzotriazo 1-1 -yloxy(dimethylamino)methylidene]-dimethylazanium; hexafluorophosphate (HBTU), 2-(1 / - / -benzotriazole-1-yl)-1 ,1 ,3,3-tetramethylaminium tetrafluoroborate (TBTU), or similar.

27. The process of claim 26, wherein the reaction of the deprotected intermediate with ChelatorFreeis performed in the further presence of a base.

28. The process of any one of claims 15-23, wherein ChelatorFreeis the following structure:

29. The process of claim 28, wherein the reaction of the deprotected intermediate with ChelatorFreeis performed in the presence of a base.

30. The process of claim 29, wherein the base is a tertiary amine, carbonate, or bicarbonate.31 . The process of any one of claims 15-23, wherein ChelatorFreeis the following structure:

32. The process of claim 30, wherein the reaction of the deprotected intermediate with ChelatorFreeis performed in the presence of a coupling agent.

33. The process of claim 32 wherein the coupling agent is (7-Azabenzotriazol-1- yloxy)tripyrrolidinophosphonium hexafluorophosphate (PyAOP), N,N'- diisopropylcarbodiimide (DIG), A / ,A / -dicyclohexylcarbodiimide (DCC), 1-(3- dimethylaminopropyl)-3-ethylcarbodiimide (EDC), 1-[bis(dimethylamino)methylene]-1 / - / - 1 ,2,3-triazolo[4,5-b]pyridinium 3-oxid hexafluorophosphate (HATU), O-(1 / - / -6- Chlorobenzotriazole-1-yl)-1 ,1 ,3,3-tetramethyluronium hexafluorophosphate (HCTU), [benzotriazo 1-1 -yloxy(dimethylamino)methylidene]-dimethylazanium; hexafluorophosphate (HBTU), or 2-(1 / - / -benzotriazole- 1-yl)- 1 ,1 , 3, 3-tetramethylaminium tetrafluoro bo rate (TBTU).

34. The process of claim 32, wherein the reaction of the deprotected intermediate with ChelatorFreeis optionally performed in the further presence of an additive.

35. The process of claim 34, wherein the additive is Ethyl (2Z)-2-cyano-2- (hydroxyimino)acetate (Oxyma), 1 / - / -1 ,2,3-Benzotriazol-1-ol (HOBt), 1-Hydroxy-7- azabenzotriazole (HOAt), or similar.

36. The process of claim 34, wherein the reaction of the deprotected intermediate withChelatorFreeis performed in still the further presence of a base.

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