Metal complexes for use in pet scans

Abstract

The present invention relates to a compound according to formula (I) or salt thereof: (I) where: R1 is selected from the group consisting of H, F, Cl, Br, I, sulfonic acid, sulfonate, C1-C6 alkyl, C2-C6 alkenyl, C6-C12 aryl, and C1-C6 alkoxy; R2 is selected from the group consisting of Cl, Br, I and groups that can be joined via click chemistry; L is selected from the group consisting of a single bond, C1-C12 alkyl, C2-C12 alkenyl, unsubstituted or C1-C12 alkyl-substituted C6-C12 aryl, and C1-C6 alkoxy, wherein, in the event that L is a single bond, R2 and R1 are different. The invention also relates to a metal complex and a conjugate comprising the compound, and to methods for the preparation thereof.

Description

[0001] RWTH Aachen / Forschungszentrum Jülich GmbH Düsseldorf, January 21, 2026 Our reference: RD 42844 / AL

[0002] RWTH Aachen University, a public corporation

[0003] Templergraben 55, 52062 Aachen

[0004] Research Center Jülich GmbH

[0005] 52425 Jülich

[0006] Metal complexes for use in PET scans

[0007] The present application relates to compounds for the formation of metal complexes that are particularly suitable for use in positron emission tomography (PET) or radiotherapy. The invention comprises the compound itself, a method for its preparation, the resulting metal complex and methods for its preparation, and finally the compounds for use in in vivo diagnostic procedures with a PET scanner and / or a therapeutic procedure.

[0008] PET is an established nuclear medicine imaging technique based on the use of radiopharmaceuticals. These consist of a radioactive nuclide and a carrier, such as a metal complex, which binds specifically to target tissue. Metal complexes are particularly important because they form long-lasting and stable bonds between the metal ion and the ligand, withstanding physiological conditions. Such complexes could also be equipped with other radioactive nuclides and used for selective radiotherapy.

[0009] 45 Titanium complexes are promising candidates for PET scans due to their physical properties, such as their suitable half-life and the emission of positive beta rays. However, no stable in vivo titanium complex has yet been developed. 45A titanium complex is known that offers both the necessary stability and specific binding to target biomolecules for clinical applications. This limitation poses a significant challenge for the use of 45 Titanium is depicted in molecular imaging.

[0010] In particular, existing complexes are not stable against physiologically occurring chelating agents, such as citrates, or an exchange of the metal with physiologically abundant metals, such as iron, occurs. In both cases, this prevents the complex from reaching the target tissue with sufficient reliability.

[0011] Furthermore, such complexes must be relatively easy and quick to produce, as the handling of the nuclides requires special care due to their instability. It would also be desirable if the ligands used were capable of binding various nuclides used for diagnostics or therapy.

[0012] Soborg-Pedersen et al. (Molecules 2020, 25, 1104) describe how certain titanium(IV) ligands can be coupled to the prostate-specific membrane antigen (PSMA) via suitable chemical reactions to enable PET scans. This coupling typically occurs via a linker that ensures specific binding to the target protein. Although these ligands and their complexes exhibit a high affinity for PSMA, the stability of the complex under physiological conditions is not guaranteed.

[0013] Koller et al. (Angew. Chem. Int. Ed. 2022, 61, 202201211) describe titanium(IV) complexes based on an unsubstituted symmetrical CAM-TREN ligand (tricatecholamine-based tris(2-aminoethyl)amine), which can be stable under physiological conditions but do not offer a binding site for biomolecules. Furthermore, several substituted symmetrical CAM-TREN ligands are also known and can form stable titanium(IV) complexes. Due to their symmetry, such ligands can be synthesized relatively easily. However, these ligands lack the possibility of selective binding to biomolecules, as they cannot be specifically linked to a biolinker. Therefore, they are less suitable for applications requiring specific tissue targeting.

[0014] Compounds for applications in PET scans therefore still offer potential for improvement. Against this background, the object of the invention is to provide compounds with which particularly stable metal complexes can be obtained under physiological conditions and which allow selective coupling to molecules with binding sites for target tissue binding.

[0015] This problem according to the invention is solved by a compound according to claim 1, and furthermore by the method for preparing the compound according to claim 6, the metal complex according to claim 7, the method for preparing the metal complex according to claim 8, the conjugate according to claim 9, and the compounds for use according to claim 10. Preferred embodiments of the invention are specified in the dependent claims, in the description, or in the examples, wherein further features described or shown in the dependent claims, in the description, or in the examples may, individually or in any combination, constitute an object of the invention unless the context clearly indicates otherwise.

[0016] The invention therefore proposes a compound according to formula (I) or a salt thereof:

[0017]

[0018] where

[0019] RI is selected from the group consisting of H, F, Cl, Br, I, sulfonic acid, sulfonate, C1-C6 alkyl, C2-C6 alkenyl, C6-C12 aryl, and C1-C6 alkoxy,

[0020] R2 is selected from the group consisting of Cl, Br, I and groups connectable via click chemistry,

[0021] L is selected from the group consisting of a single bond, C1-C12 alkyl, C2-C12 alkenyl, unsubstituted or Cl-C12-alkyl-substituted C6-C12 aryl, and C1-C6 alkoxy, wherein, in the case where L is a single bond, R2 and RI are different.

[0022] It has been demonstrated that metal complexes exhibiting high stability under physiological conditions can be produced using such compounds. Furthermore, it is possible to synthesize conjugates that can also be converted into metal complexes capable of selectively binding to biomolecules. This allows for the precise targeting of specific tissue types, thereby expanding diagnostic and therapeutic options in oncology. In particular, it has been shown that these complexes are significantly more hydrolytically stable compared to, for example, corresponding imines. While not bound to a specific theory, it is assumed that the strong chelating effect of this compound enhances its stability against other compounds, such as citrate.In particular, complexation can be carried out in the final step of conjugate production, which allows for particularly good integration of radionuclides into the conjugates. Furthermore, it has been shown that various residues can be coupled to the compound of the present invention without impairing the stability of the complex. This makes it possible to produce different conjugates from the same base compound, each tailored to different applications. It has also been shown that different metals can be stably bound to the same compound under physiological conditions, enabling both diagnostic imaging and therapy with the same conjugate. In particular, metal complexes of such compounds are stable in both artificial blood plasma and human plasma.Without being bound to any theory, it is assumed that in particular no transmetallation occurs with a calculated excess factor of 10 compared to the metal complex. 7 This results in particularly stable application in blood. Furthermore, it ensures that metal complexes of such compounds are metabolized normally in the bodies of test subjects after injection, meaning they are transported rapidly through the body without binding to healthy cells and, in particular, without accumulating in any body parts during metabolism. This can potentially enable a comparatively safe application.

[0023] The field of click chemistry is well-known and deals with a group of chemical reactions that proceed efficiently, selectively, and under mild conditions to form stable covalent bonds. It is based on the idea of ​​quickly and easily joining molecular building blocks without generating unwanted byproducts. Typical click chemistry reactions include the azide-alkyne cycloaddition, the Diels-Alder reaction with inverse electron demand, and the thiol-maleimide coupling. These reactions are characterized by high chemoselectivity and biocompatibility, which is why they are frequently used in bioconjugation, materials science, and drug development. Groups that can be joined via click chemistry can thus be understood, in particular, as functional groups that can bind to each other specifically and efficiently as pairs to form stable covalent links.

[0024] This makes it possible to attach various residues that selectively bind to biomolecules to the complex after the compound has been produced.

[0025] Preferably, the compound according to formula (I) may have the following formula (I*):

[0026]

[0027] where RI, R2, and L are defined as before.

[0028] Preferably, R2 may be selected from Cl, Br, I and from groups connectable via click chemistry, wherein the groups connectable via click chemistry are selected from the group consisting of ethinyl, azidoyl, norborneyl, tetrazinyl, maleimidyl and cyclooctinyl.

[0029] Preferably, R2 is selected from Cl, Br, I, ethynyl, azidoyl, and cyclooctynyl, particularly from Br and azidoyl. Preferably, L is selected from the group consisting of a single bond, C1-C12 alkyl, Cl-C12-alkyl-substituted C6-C12 aryl, preferably from a single bond and Cl-C12-alkyl-substituted C6-C12 aryl. Particularly preferably, L is selected from a single bond or C1-C12-alkyl-substituted phenyl. Particularly preferably, the C1-C12-alkyl-substituted phenyl has the following formula (L*), where * and ** represent points of attachment to the catechol residue and to R2, respectively, with * preferably representing the connection to the catechol residue and ** the connection to R2:

[0030]

[0031] (L*)

[0032] It may be particularly preferred that n in formula (L*) is selected from 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11 and 12.

[0033] The preferred linkers ensure that in the resulting conjugates, the residue selectively binding to the biomolecule has a distance from the complex that does not negatively affect the selectivity of the residue.

[0034] Preferably, R2 may be selected from Br and L is selected from a single bond.

[0035] Preferably, R2 is selected from azidoyl and L is selected from the group consisting of C1-C6 alkyl, Cl-C12-alkyl-substituted C6-C12 aryl, preferably Cl-C12-alkyl-substituted C6-C12 aryl. Particularly preferably, R2 is selected from azidoyl and L is a Cl-C12-alkyl-substituted phenyl according to formula (L*). Preferably, RI is selected from H or C1-C6 alkenyl, preferably H.

[0036] Preferably, formula (I) may be provided that it is protonated, in particular singly, doubly or triply protonated, and together with an anion forms the salt of the compound, wherein the anion is preferably selected from the group consisting of chloride, bromide, iodide, nitrate, sulfate, phosphate, carbonate and organic carboxylates, in particular acetate.

[0037] Preferably, the salt may have the following formula (1a)

[0038]

[0039] where X is selected from the group consisting of chloride, bromide, iodide, nitrate, sulfate, phosphate, carbonate and organic carboxylates, in particular acetate,

[0040] where k, n and m are integers and 3 · k = n · m.

[0041] Preferably, the salt may have the following formula (la*).

[0042]

[0043] (la*)

[0044] where X is selected from the group consisting of chloride, bromide, iodide, nitrate, sulfate, phosphate, carbonate and organic carboxylates, in particular acetate,

[0045] where k, n and m are integers and 3 · k = n · m.

[0046] Preferably, the salt may have the formula (1a) or formula (1a*), X is selected from chloride, k is equal to 1, n is equal to 3 and m is equal to 1.

[0047] The invention further proposes a method for producing the compound, wherein the method comprises the steps:

[0048] i) Protecting an amino group of tris(2-aminoethyl)amine with a protecting group reagent to obtain a compound according to formula (II), where R3 is a protecting group:

[0049] H2N

[0050] R— NH N—

[0051] NH2

[0052]

[0053] (II)

[0054] ii) Reaction of the compound according to formula (II) with a compound according to formula (III) to form a compound according to formula (IV):

[0055]

[0056] (III) iii) Reduction of imine groups to secondary amines in the compound according to formula (IV), deprotection of the protected amino group, and optionally adjustment of the pH value, to obtain a compound according to formula (V)

[0057] HN

[0058]

[0059] iv) Reaction of the compound according to formula (V) with a compound according to formula (VI) to form the compound according to formula (I) or the salt thereof:

[0060]

[0061] Preferably, the process may include the steps: i) Protecting an amino group of tris(2-aminoethyl)amine with a protecting group reagent to obtain a compound according to formula (II), wherein R3 is a protecting group:

[0062] H2N

[0063] R— NH N—

[0064] NH2

[0065]

[0066] (II)

[0067] ii) Reaction of the compound according to formula (II) with a compound according to formula (III*) to form a compound according to formula (IV*):

[0068]

[0069] iii) Reduction of imine groups to secondary amines in the compound according to formula (IV*), deprotection of the protected amino group, and optional adjustment of the pH value, while obtaining a compound according to formula (V*)

[0070]

[0071] (V*)

[0072] iv) Reaction of the compound according to formula (V) with a compound according to formula (VI) to form the compound according to formula (I*) or the salt thereof:

[0073] ,2

[0074]

[0075] (VI).

[0076] It may preferably be provided that R 3 a protecting group selected from the group consisting of tert-butyloxycarbonyl (Boc), triphenylmethyl (Trityl), banzyloxycarbonyl (Cbz), fluorenylmethyleneoxycarbonyl (Fmoc) and allyloxycarbonyl (Alloc), wherein R3 is in particular a Boc or Trityl protecting group.

[0077] Preferably, the protecting group reagent may be selected from the group consisting of di-Zc / V-butyldicarbonate (BOC₂O), benzyl chloride, fluorenyl methoxycarbonyl chloride (Fmoc-Cl), or N-(9-fluorenyl methoxycarbonyloxy)succinimide (Fmoc-OSu), particularly di-Zc / V-butyldicarbonate. Preferably, process step i) may be carried out in an organic solvent, particularly an organic solvent selected from the group consisting of polar organic solvents, preferably chloroform, tetrahydrofuran (THF), ethanol, dimethyl sulfoxide (DMSO), and dichloromethane (DCM), more preferably chloroform, tetrahydrofuran, ethanol, and dimethyl sulfoxide.

[0078] It is preferably provided that process step i) is carried out at a temperature in a range of > -50°C to < 50°C, preferably > -30°C to < 30°C or > -10°C to < 25°C, for example at -5°C, 0°C, 5°C, 10°C, 15°C or 20°C.

[0079] Preferably, in process step i) the tris(2-aminoethyl)amine and the protecting group reagent are reacted in a molar ratio of > 1:1 to < 10:1, preferably 2:1 to < 9:1, > 3:1 to < 8:1 or > 4:1 to < 7:1, for example 5:1 or 6:1.

[0080] Preferably, process step i) may include a purification step after the reaction in which, in particular, the compound according to formula (II) is separated from excess tris(2-aminoethyl)amine and by-products, especially by distillation, filtration and / or extraction.

[0081] Preferably, it may be provided that in process step ii) the compound according to formula (II) and the compound according to formula (III) are reacted in a molar ratio of > 1:1 to < 1:3, preferably 1:1.5 to < 1:2.5, for example 1:2.

[0082] It is preferable that process step ii) is carried out in an organic solvent, in particular in an alcohol, water, tetrahydrofuran, DMSO or mixtures thereof, most preferably methanol, ethanol, water and DMSO. It is preferable that process step ii) is carried out at a temperature in the range of > 0°C to < 90°C, preferably > 5°C to < 60°C, > 10°C to < 30°C or > 20°C to < 25°C, for example at room temperature.

[0083] Preferably, in process step iii), the compound according to formula (IV) is dissolved in an organic solvent, in particular in a mixture of methanol and tetrahydrofuran, and treated with a protecting group removal compound and an imine group reduction compound. It is understood that the protecting group removal compound depends on which protecting group was used in the previous steps. For example, the protecting group removal compound may be an acid or a base.

[0084] Preferably, the compound used to reduce the imine group is a borohydride, preferably sodium borohydride. In this case, it is particularly preferred that the compound according to formula (IV) is dissolved in a mixture of methanol and tetrahydrofuran and treated with sodium borohydride. It is further preferred that the solution is subsequently treated with an acid, preferably HCl, and in particular with HCl in an organic solvent such as methanol. For example, an intermediate of the following formula (Va) can be formed, where k, n, m, and X are defined as for formula (aa) and 2 • k = n • m.

[0085] R 1

[0086] HO

[0087] k · X m· H3N +

[0088] OH

[0089]

[0090] R 1 (

[0091]

[0092] Va)

[0093] Preferably, the pH value can be adjusted, especially after adding an acid to the solution, for example NaHCO3.

[0094] Preferably, it may be provided that in process step v) in a first step the compound according to formula (V) and the compound according to formula (VI) are reacted in a molar ratio of > 1:0.75 to < 1:1.25, preferably 1:0.9 to < 1:1.1, for example 1:1.

[0095] It may preferably be provided that process step v) is carried out in an organic solvent, in particular in an alcohol, tetrahydrofuran or mixtures thereof, most preferably methanol.

[0096] It is preferably possible that process step v) is carried out at a temperature in a range of > 0°C to < 90°C, preferably > 5°C to < 60°C, > 10°C to < 30°C or > 20°C to < 25°C, for example at room temperature.

[0097] Preferably, in process step v), the reaction is carried out in a second step with a compound for reducing the imine groups. Preferably, the compound for reducing the imine group is a borohydride, preferably sodium borohydride. Particularly preferably, in this case, this reaction takes place in a mixture of methanol and tetrahydrofuran, which is treated with sodium borohydride. It is also preferably that the solution is subsequently treated with an acid, preferably HCl, and in particular with HCl in an organic solvent such as methanol.

[0098] It may be preferably provided that the salt of formula (1a) is formed as an intermediate. It may also be preferably provided that the pH value is adjusted, in particular after the solution is treated with an acid, for example with NaHCO3, while retaining the compound according to formula (1).

[0099] The invention further proposes a metal complex according to formula (VII).

[0100] M q+ M' u+ Z (v · Y w )

[0101] (VII)

[0102] where

[0103] Z is a compound of the following formula (Vila)

[0104]

[0105] (Vila)

[0106] where

[0107] RI, R2, and L are defined as before,

[0108] where M is a metal cation in the oxidation state q+, where q is an integer selected from 2, 3 or 4,

[0109] where M' is a metal cation in the oxidation state u+, where u is an integer selected from 1, 2 or 3, or where M' represents one to three protons and u+ is the total charge of these protons, or where M' is absent and u+ is zero,

[0110] where Y w an anion or cation with a charge w is

[0111] where v and w are integers and q + u - 6 = -v · w, where Y is absent in the case that q + u = 6. For the purposes of the present invention, a metal complex is understood to be a chemical compound comprising at least one metal atom and one or more ligands. The ligands are molecules or ions that provide electron pairs and are bound to the metal center via coordinate bonds.

[0112] In accordance with the present invention, the metal complex according to formula (VII) thus comprises at least one metal atom, which is present as a metal cation in oxidation state 2, 3, or 4. Additionally, a further metal cation may be present in the metal complex, which is present in the u+ oxidation state, i.e., 1, 2, or 3. Furthermore, the metal complex comprises a tris-(2-aminoethyl)amine-based ligand Z of formula (Vila), which may have multiple coordinate bonds to the metal atoms, thus coordinating them. In formula (Vila), ligand Z is depicted as having a 6-fold negative charge, whereby this charge may be localized differently depending on the coordinate bond to the metal atoms. If only the first metal is present in the metal complex, ligand Z may also have a 6-fold negative charge. Alternatively, in this case, the ligand may be singly, doubly, or triply protonated.This refers to the case where M' represents one to three protons. In this case, M' contributes to a one to three positive charge, M'. u+ This corresponds to 1H + , 2H + or 3H + .

[0113] Overall, the complex consisting of the metal(s) and the ligand can have a residual charge which is balanced by corresponding anions or cations Y".

[0114] Preferably, Z may be a compound of the following formula (Vila*).

[0115]

[0116] (Vila*)

[0117] Where RI, R2, and L are defined as before.

[0118] Preferably, M and / or M' may be chelated by ligand Z. For the purposes of the present invention, the term "chelated" means that the metal has multiple coordinate bonds to ligand Z.

[0119] Preferably, M may have coordinate bonds with ligand Z to oxygen atoms of ligand Z, preferably without any coordinate bonds to the nitrogen atoms. The oxygen atoms are preferably the catecholate oxygen atoms of ligand Z. Particularly preferably, M may be six-fold coordinated by the catecholate oxygen atoms of ligand Z.

[0120] Preferably, M', as a metal, has coordinate bonds with ligand Z to oxygen and nitrogen atoms of ligand Z. The oxygen atoms are preferably the ortho-oxygen atoms of the catecholate residues of ligand Z. Particularly preferably, M' is three-fold coordinated by the catecholate oxygen atoms of ligand Z. The nitrogen atoms are preferably the nitrogen atoms of the tris(2-aminoethyl)amine backbone of ligand Z. Preferably, M' is three-fold or four-fold coordinated by the nitrogen atoms of ligand Z. Further preferably, M' is three-fold coordinated by the catecholate oxygen atoms of ligand Z and three-fold or four-fold coordinated by the nitrogen atoms of ligand Z.

[0121] In a preferred embodiment, the metal complex has the following formula (Vllb)

[0122] N

[0123]

[0124] where

[0125] RI, R2, M, M', u, Y, v and w are defined as before.

[0126] Preferably, M may be a radionuclide. For the purposes of the present invention, a radionuclide can be understood to be an atom that undergoes spontaneous radioactive decay and emits ionizing radiation.

[0127] It may preferably be provided that M q+ a hard or medium-hard cation according to the HSAB principle. Preferably, it can be provided that M q+ selected from the group consisting of Fe 2+ , Co 2+ , Ni 2+ , Zn 2+ , Cu 2+ , Mn 2+ , CD 2+ , Pb 2+ , Al 3+ , Sc 3+ , Y 3+ , Ln 3+ , La 3+ , Ce 3+ , Sm 3+ , Lu 3+ , Ga 3+ , In 3+ , Fe 3+ , Co 3+ , Cr 3+, Mn 3+ , Ru 3+ , Rh 3+ , Zr 4+ , Hf 4+ , Ti 4+ , Sn 4+ , Ce 4+ , Ru 4+ , and Os 4+ It may be particularly preferable that M q+ selected from the group consisting of Ga 3+ , Ln 3+ , Lu 3+ , Ti 4+ and Sn 4+ .

[0128] Preferably, M may be a radionuclide selected from Ti, Cu, Ga, Y, Sn or Lu, in particular selected from 45 Ti, 64 Cu, 68 Ga, 86 Y, 117m Sn and 177 Lu, especially preferred 45 Ti and 117m It may be preferred that, where M' u+ selected from the group consisting of Na + , Ca 2+ , Sr 2+ , CD 2+ , Sc 3+ , Y 3+ and Ln 3+ or La 3+ , preferably Na + , Ca 2+ and Sr 2+ , more preferred Na+ and Ca 2+ .

[0129] It may preferably be provided that Y w selected from the group consisting of chloride, bromide, iodide, nitrate, sulfate, phosphate, carbonate, organic carboxylates, especially acetate, sodium, potassium, calcium, magnesium and mixtures thereof.

[0130] The invention further proposes a process for producing the metal complex according to formula (VII), wherein a compound according to formula (I) or the salt thereof is reacted with a source for the metal cation M and optionally a source for the metal cation M'.

[0131] Preferably, the compound according to formula (I) or the salt thereof may be dissolved in a solution, in particular in a physiologically safe solvent, for example in water or in dimethyl sulfoxide (DMSO).

[0132] Preferably, the source for the metal cation M and optionally M' may be provided in a physiologically safe solvent, for example in water or in dimethyl sulfoxide (DMSO).

[0133] Preferably, the compound according to formula (I), the source of the metal cation M, and optionally M' are stirred together in a physiologically safe solvent, for example, water or dimethyl sulfoxide (DMSO). The reaction time is particularly preferably less than or equal to 10 minutes, preferably less than or equal to 5 minutes, for example, 1 minute, 2 minutes, 3 minutes, or 4 minutes. It is also preferred that the metal complex is purified and isolated by column chromatography, in particular by HPLC.

[0134] The invention further proposes a conjugate of a compound of formula (I) or of its salt or of the metal complex according to formula (VII) with a compound of formula (VIII):

[0135] R 2

[0136] A

[0137] (VIII)

[0138] where R2' is a group that can be coupled to R2 and A is a residue that binds specifically to a biomolecule.

[0139] It may be particularly preferred that the biomolecule is selected from biomolecules that bind specifically to proteins of cancer cells, especially cancer cells with a slow glucose metabolism.

[0140] The invention further proposes the preparation of the conjugate of the metal complex. It is particularly preferred that the conjugate of the metal complex be prepared from the conjugate of the compound of formula (I) or its salt. The metal complex can be prepared in the same way as the metal complex from the compound of formula (I) or its salt.

[0141] The invention further proposes the compound according to formula (I) or its salt, the metal complex according to formula (VII), or the conjugate with the compound according to formula (VIII) for use in an in vivo diagnostic procedure using a PET scanner and / or a therapeutic procedure, in particular for the in vivo diagnosis and / or therapy of cancer. Further advantages and advantageous embodiments of the invention are illustrated by the examples and explained in the following description. It should be noted that the examples are for descriptive purposes only and are not intended to limit the invention in any way.

[0142] Examples

[0143]

[0144] Synthesis of compounds of formula (VI) starting from a compound of formula (X):

[0145] / =O / =O

[0146] R 2 / 4— Z

[0147] L— / V- OH X— C y— OH

[0148]

[0149] OH OH

[0150] (VI). (X)

[0151] Here, X is a functional group specified below, depending on the reaction. For the subsequent reaction, the compound of formula (X) can initially be protected. A selection of possible reactions is described below.

[0152] Hydroxy protection a

[0153] z=O

[0154] X— 6 O

[0155] \ R

[0156]

[0157] OR

[0158] a

[0159] 2,3-Dihydroxybenzaldehyde of formula X is dissolved in dry N,N-dimethylformamide at 0 °C. Solid potassium carbonate and sodium bromide are added to this solution, followed by the slow addition of RY (C1–C6 alkyl or benzyl). The reaction mixture is heated to room temperature and stirred for 16 h. Water is then added and extracted with ethyl acetate. The combined organic phases are washed with water and saturated sodium chloride solution, dried over sodium sulfate, and the solvent is removed under vacuum. The product is purified by column chromatography. The ether-protected derivative of formula (a) is obtained.

[0160] Catechol protection as an acetal b

[0161]

[0162] b

[0163] A solution of 2,3-dihydroxybenzaldehyde of formula (X) in dry acetonitrile is treated with X2R (e.g., 1,3-dibromopropane) and a catalytic amount of p-toluene sulfonic acid monohydrate. The reaction mixture is stirred at room temperature for 3 h. After complete conversion (checked by thin-layer chromatography), saturated sodium bicarbonate solution is added and extracted with ethyl acetate. The combined organic phases are dried over sodium sulfate and concentrated under vacuum. The residue is redissolved and purified by column chromatography. The acetal-protected derivative of formula (b) is obtained.

[0164] Aldehyde fermentation c

[0165]

[0166] OH

[0167] c

[0168] To a solution of 2,3-dihydroxybenzaldehyde of formula (X) in absolute toluene, ethylene glycol and p-toluene sulfonic acid monohydrate are added under argon. The reaction mixture is heated to reflux using a Dean-Stark apparatus and stirred for 4 h, during which time the water formed is removed azeotropically. After cooling to room temperature, the mixture is treated with saturated sodium bicarbonate solution and the phases are separated. The organic phase is washed with water, dried over sodium sulfate, and the solvent is removed under reduced pressure. The residue is redissolved and purified by column chromatography over silica gel. The acetal-protected derivative of formula (c) is obtained.

[0169] Complete protection of

[0170]

[0171] d

[0172] First, 2,3-Dihydroxybenzaldehyde of formula (X) is reacted as described to give the dibenzyl-protected derivative of formula (a or b). The intermediate thus obtained is then reacted without further purification according to the aldehyde protection to give the corresponding acetal (c). After work-up as described in Example 1, the fully protected compound of formula (d) is obtained.

[0173] Functionality of the protected connection:

[0174] Suzuki clutch on the

[0175]

[0176] To a solution of the fully protected compound of formula (d) (where X is a halide) in degassed 1,4-dioxane / water, the corresponding arylboronic acid, potassium carbonate, and a catalytic amount of a palladium complex are added. Palladium(O) or palladium(II) complexes, in particular Pd(PPh3)2Cl2, Pd(dppf)Cl2, or Pd(OAc)2 in combination with phosphine ligands, can be used as catalysts. The reaction mixture is evacuated three times and filled with argon, then heated at 90 °C with stirring for 16 h. After cooling to room temperature, the mixture is diluted with water and extracted with ethyl acetate. The combined organic phases are washed with water and saturated sodium chloride solution, dried over sodium sulfate, and concentrated under vacuum. The residue is redissolved and purified by column chromatography over silica gel.The coupled compound of formula (e) is obtained, which after deprotection corresponds to a compound of formula (VI).

[0177] Suzuki coupling of a boron-functionalized compound of formula (d)

[0178]

[0179] To a solution of the fully protected compound of formula (d) (where X is a boronic acid residue) in degassed 1,4-dioxane / water, an aryl halide-containing linker (e.g., the corresponding aryl or heteroaryl bromide or iodide), potassium carbonate, and a catalytic amount of a palladium complex are added. Palladium^) or palladium(II) complexes, in particular Pd(PPh3)2Cl2, Pd(dppf)Cl2, or Pd(OAc)2 in combination with phosphine ligands, can be used as catalysts. The reaction mixture is evacuated three times and filled with argon, and then heated at 90 °C with stirring for 16 h. After cooling to room temperature, it is diluted with water and extracted with ethyl acetate. The combined organic phases are washed with water and saturated sodium chloride solution, dried over sodium sulfate, and concentrated under vacuum. The residue is dissolved again and purified by column chromatography over silica gel.The coupled compound of formula (e) is obtained, which after deprotection corresponds to a compound of formula (VI).

[0180] Alternative linker introduction based on o-vanilinyl:O OH

[0181]

[0182] Under constant stirring and simultaneous introduction of a strong stream of hydrogen chloride, 9 g of paraformaldehyde and 6 g of anhydrous zinc chloride are dissolved in 100 mL of concentrated hydrochloric acid, whereupon a solution of 30 g of o-vanillin in 150 mL of benzene is added. The introduction of hydrogen chloride is continued for 4 h, the temperature being constantly maintained at approximately 20 °C by cooling. The blackish-red reaction mixture is poured onto ice with the simultaneous addition of 100 mL of benzene. The separated benzene phase is freed from resinous products by filtration and washed twice with water. After drying over sodium sulfate, the benzene is distilled off, and the resulting brownish-black crude product is pressed onto clay. 5-Chloromethyl-o-vanillin is obtained by recrystallization twice from ligroin (boiling range 100–120 °C), which, after deprotection of the methyl ether, corresponds to a compound of formula (VI).

[0183] Azide formation from alkyl halide in the linker

[0184] q

[0185] R

[0186] OR

[0187]

[0188] A compound of formula (e) in which the linker group introduced via Suzuki is a terminal alkyl bromide group of the form -(CH2) n -Br is dissolved in dimethylformamide. Sodium azide is added to this solution. The reaction mixture is stirred at 80 °C for 16 h. After cooling to room temperature, water is added and extracted with ethyl acetate. The combined organic phases are washed with water and saturated sodium chloride solution, dried over sodium sulfate, and carefully concentrated under vacuum. The reduced solution of the residue is purified by column chromatography over silica gel. The azide-functionalized compound of formula (f) is obtained, in which the substituent introduced via Suzuki has a terminal azide group -(CH2) n-N3 exhibits, which after deprotection corresponds to a compound of formula (VI).

[0189] Instead of an alkyl bromide, an alkyl chloride or alkyl iodide can also be reacted analogously, with reaction times and temperature adjusted to obtain the corresponding azide. Azides are classified as potentially explosive, which is why the solvent is never completely removed.

[0190] Instead of the compound of formula (e), 5-chloromethyl-o-vanillin can also be reacted accordingly.

[0191] BOC route

[0192] Synthesis of BOC-TREN compound according to formula (II)

[0193] BOC2O

[0194] - ►

[0195] DCM

[0196]

[0197] TREN BOC-TREN

[0198] A solution of BOC2O (1.2 mL, 5.5 mmol, 1.0 eq.) in DCM (80 mL) was diluted to a solution of TREN (5.1 mL, 35 mmol, 6.4 eq.) in DCM (100 mL) using a syringe pump with a flow rate of 24 mLh -1 The mixture was added at room temperature with continuous stirring. The reaction was stirred for three hours and concentrated under reduced pressure. The residue was dissolved in distilled water (10 mL) and extracted with DCM (6 x 15 mL). The organic phase was dried over MgSch. The solution was concentrated under reduced pressure to obtain a clear oil. Yield: 792 mg, 3.2 mmol, 58.4%

[0199] 1 H NMR (400 MHz, CDC13): 3.16 (m, 2H, b'), 2.74 (t, 4H, b), 2.53 (m, 6H, a / a'), 1.42 (s, 9H, h').

[0200] Synthesis of (BOC)(CIm)2-TREN compound according to formula (IV)

[0201]

[0202] BOC-TREN BOC-(Clm)2-TREN

[0203] 2,3-Dihydroxybenzaldehyde (0.9625 g, 7.0 mmol, 2 eq.) was added to a solution of BOC-TREN (0.8571 g, 3.5 mmol, 1 eq.) in methanol (25 mL). The solution turned brown. No precipitate was observed, indicating that no (CIm)3-TREN was formed as a byproduct. The filtrate was concentrated under reduced pressure and dried under high vacuum. The desired (BOC)(CIm)2-TREN was obtained as a brown resin.

[0204] Yield: 1.5605 g, 3.2 mmol, 99.7%

[0205] J H-NMR(400 MHz, DMSO-d6): 8.39 (s, 2H, c), 6.78 (m, 2H, f), 6.70 (m, 2H, d), 6.53 (t, 2H, e), 3.63 (t, 4H, b), 2.95 (m, 2H, b'), 2.82 (t, 2H, a'), 2.59 (t, 4H, a), 1.34 (s, 9H, h').

[0206] Synthesis of (CAm)₂-TREN · 3 HCl – compound according to formula (V)

[0207]

[0208] BOC-(Clm)2-TREN (CAm)2-TREN ■ 3 HCl NaBH4 (0.2425 g, 6.4 mmol, 2 eq.) was added to a solution of (BOC)(CIm)2-TREN (1.4447 g, 3.2 mmol, 1 eq.) in THF (25 mL) and methanol (12 mL). The solution was stirred overnight and concentrated under reduced pressure, yielding a light beige solid. This was dissolved in a small amount of methanol, and the pH of the resulting solution was adjusted to 1 with concentrated hydrochloric acid. A white solid was precipitated and removed by filtration. The resulting solution was then added dropwise to ether (500 mL) with stirring, forming a white precipitate. The liquid phase was decanted, and the precipitate was washed with ether (2 x 200 mL). The remaining liquid from the suspension was removed under reduced pressure and dried in high vacuum, resulting in a cream-colored solid.

[0209] JH-NMR(400 MHz, DMSO-d6): 9.13 (br s, 3H, g'), 8.40 (br s, 2H, g), 6.97 (d, 2H, f), 6.88 (d, 2H, d), 6.67 (t, 2H, e), 4.15 (s, 4H, c), 3.12 (s, 2H, b'), 3.05 (s, 4H, b), 2.78 (br s, 6H, a / a').

[0210] Trityl route

[0211] Synthesis of trityl-TREN compound according to formula (II)

[0212]

[0213] TREN

[0214] A solution of trityl chloride (1.5321 g, 5.5 mmol, 1.0 eq.) in DCM (150 mL) was slowly and vigorously stirred to give a solution of TREN (5.1 mL, 35 mmol, 6.36 eq.) in DCM (200 mL). The reaction solution was stirred for one hour and concentrated under reduced pressure until approximately 100 mL remained. The solution was washed with 10% NaOH (100 mL) and salt solution (50 mL). The organic phase was dried with MgSch and concentrated under reduced pressure to obtain a beige oil.

[0215] Yield: 1.9279 g, 4.962 mmol, 90.2%

[0216] 1 H NMR (400 MHz, DMSO-6): 7.41 (m, 6H, j'), 7.29 (m, 6H, i'), 7.19 (m, 3H, h'), 2.51 (m, 6H, a,a'), 2.27 (t, 4H, b), 2.06 (t, 2H, b').

[0217] Synthesis of (Trityl)(CIm)2-TREN - compound according to formula (IV)

[0218]

[0219] Trityl-TREN Trityl-(Clm)2-TREN

[0220] Trityl-TREN (1.3498 g, 3.5 mmol, 1 eq.) was dissolved in methanol (50 mL) and 2,3-dihydroxybenzaldehyde (0.9597 g, 6.95 mmol, 2 eq.) was added. The solution was stirred overnight and concentrated under reduced pressure. A brown solid was obtained.

[0221] 1 H-NMR(400 MHz, DMSO-6): 8.35 (s, 2H, c), 7.37-7.12 (m, 15H, h' / i' / j'), 6.80-6.51 (s, 2H, c), 6.79 (m, 2H, f), 6.65 (m, 2H, d), 6.53 (m, 2H, e), 3.58 (s, 6H, a / a'), 2.64 / 2.68 (s, 6H, a / a').

[0222] Synthesis of (CAm)₂-TREN · 3 HCl – compound according to formula (V)

[0223]

[0224] Trityl-(Clm)2-TREN (CAm)2-TREN ■ 3 HCl (Trityl)(CIm)2-TREN (2.0096 g, 3.2 mmol, 1 eq.) was dissolved in THF (70 mL) and methanol (50 mL). NaBH4 (0.2426 g, 6.4 mmol, 2 eq.) was added and the reaction solution was stirred overnight. The next day, the reaction solution was concentrated under reduced pressure. The residue was dissolved in methanol (55 mL) and the pH was adjusted to 1 by adding concentrated hydrochloric acid. The solution was added dropwise to stirring THF (500 mL), forming a light brown precipitate. The liquid phase was decanted and the precipitate was washed with fresh THF (2 x 200 mL). The liquid phase of the suspension was removed under reduced pressure and dried in high vacuum, yielding a beige solid. Since the yield of the preceding product (Trityl)(CIm)2-TREN could not be determined, no yield could be calculated for this step.

[0225] J H-NMR(400 MHz, DMSO-6): 9.15 or 9.03 (br s, 2H or 3H, g or g'), 6.97 (d, 2H, f), 6.87 (d, 2H, d), 6.67 (t, 2H, e), 4.15 (s, 2H, c), 3.12 (s, 4H, b), 3.05 (s, 2H, b'), 2.74 (s, 6H, a / a').

[0226] Synthesis starting from (CAm)₂-TREN · 3 HCl – compound according to formula (V)

[0227] Synthesis of (5-Br-CIm)(CAm)2-TREN - intermediate step

[0228]

[0229] (5-Br-Clm)-(CAm)₂-TREN₂-5-bromo-2,3-dihydroxybenzaldehyde (0.6413 g, 2.9 mmol, 1 eq.) and NaHCO₃ (244.5 mg, 2.9 mmol, 1 eq.) were added to a solution of (CAm)₂-TREN₂-• 3 HCl (1.4762 g, 2.9 mmol, 1 eq.) in methanol (100 mL). The reaction was stirred overnight. The following day, the solution was concentrated under reduced pressure. The brown solid was further dried under high vacuum.

[0230] ¹H-NMR(400 MHz, DMSO-d6): 6,93 (m, 3H, f / f'), 6,86 (m, 3H, d / d'), 6,67 (m, 2H, e), 5,49 (s, 1H, c'), 4,13 (s, 4H, c), 3,07 (s, 2H, b'), 3,02 (s, 4H, b), 2,68 / 2,72 (s, 6H, a / a').Synthese von (5-Br-CAm)(CAm)2-TREN - Verbindung nach Formel (I)

[0231] (5-Br-Clm)(CAm)₂-TREN

[0232]

[0233] (5-Br-CAm)(CAm)2-TREN • 3 HCl NaBH₄ (120.4 mg, 3.1 mmol, 1 eq.) was added to a solution of (5-Br-CIm)(CAm)2-TREN (1.8297 g, 3.1 mmol, 1 eq.) in THF (50 mL) and methanol (50 mL). The reaction was stirred for two days. The reaction solution was concentrated under reduced pressure and dissolved in methanol (50 mL). The solution was added dropwise to stirring ether (500 mL) so that the product precipitated as a brown solid. The liquid phase was decanted and the precipitate washed with fresh ether (2 x 200 mL). The liquid phase of the suspension was concentrated under reduced pressure. The brown solid was dried under high vacuum.

[0234] ESI-MS: deprotonated fragment [(5-Br-CAm)(CAm)2-TREN]:

[0235] Theo, m / z: 589.1667. Exp. m / z: 589.1877.

[0236] JH-NMR(400 MHz, DMSO-6): 9.70 (s, 3H, h / h'), 9.22 (s, 2H, g'), 9.16 (s, 3H, i / i'), 8.43 (s, 2H, g), 6.99 (d, 3H, f / f), 6.88 (d, 3H, d / d'), 6.67 (t, 2H, e), 4.14 (s, 6H, c / c'), 3.10 (s, 2H, b'), 3.04 (s, 4H, b), 2.72 / 2.73 (s, 6H, a / a'). 13 C-NMR(100 MHz, DMSO-6): 147.02 (6'), 145.59 (6), 144.25 (5'), 144.22 (5), 122.02 (9 / 9'), 119.25 (8), 118.80 (4 / 4'), 116.67 (7 / 7'), 109.66 (8'), 51,06 (1), 49,66 (1'), 44,96 / 45,12 (3 / 3'), 43,71 (2'), 36,52 (2).

[0237] Synthesis of [Ca(DMF)₂[Fe(H₃)(5-Br-CAm(CAm)₂TREN)Cl₂]₂ – Verbindung nach Formel (VII)

[0238] (5-Br-CAm)(CAm)2-TREN • 3 HC1 (83.8 mg, 0.12 mmol, 1 eq), FeCl3· 6 H₂O (31.9 mg, 0.12 mmol, 1 eq) and CaH2 (32.8 mg, 0.72 mmol, 6 eq) were dissolved in DMF (3.6 mL). The solution was stirred at 100 °C for 10 minutes. Single crystals of the compound were obtained by slow diffusion of benzene into the DMF solution. The structure exhibited the following structural formula, which was determined by X-ray crystallography:

[0239] [Ca(DMF)₂[Fe(H₃)(5-Br-CAm)(CAm)₂TREN]Cl₂]₂

[0240]

[0241] The stability of the complex in solution can be demonstrated using UV-Vis spectroscopy. Stability towards exchange with other metals (transmetallation) can also be shown using UV-Vis spectroscopy, from which the stability of the complexes under physiological conditions can be deduced. For this purpose, the UV-Vis spectrum of the complex can be recorded and compared with the UV-Vis spectrum after the complex has been exposed to a metal salt-containing solution. For X-ray structure analysis, a crystal of the compound was measured with a Rigaku XtaLAB Synergy-DW VHF using a HyPix-Arc 100 detector, and the measurement data were reduced using CrysAlisPro 1.171.44.80a. The crystallographic data are given in Table 1. The atomic positions obtained are given in Table 2.

[0242] Table 1

[0243] Empirical formula C₇₂H₁₁₀Br₂Ca₂Cl₄Fe₂N₁₄O₂₀

[0244] Formula weight 1985.222

[0245] Temperature / K 100.15

[0246] Crystal system Monoclinic

[0247] Space group P2i / c

[0248] a / A 18.0488(7)

[0249] b / A 18.0568(6)

[0250] c / A 15.0381(6)

[0251] ß / ° 113.184(5)

[0252] Volume / A 3 4505.2(3)

[0253] Z 2

[0254] ρ calc g / cm 3 1,463

[0255] μ / mm -1 6,313

[0256] F(000) 2064.1

[0257] Crystal size / mm 3 0.08 x 0.08 x 0.005

[0258] Radiation Cu Kα (λ = 1.54184)

[0259] 20 Area for data collection / ° 7.24 to 88.98

[0260] Index range -16 <h < 16, -14 <k < 16, -13 < 1 < 13

[0261] Collected Reflexes 17052

[0262] Independent reflexes 3479 [R int = 0.0665, R sigma = 0.0523]

[0263] Data / Restraints / Parameters 3479 / 526 / 498

[0264] Goodness-of-fit on F 2 1.089

[0265] Finale R Indices [I>=2σ (I)] R1= 0.0864, wR2= 0.2376

[0266] Finale R Indices [all data] R1= 0.1106, wR2= 0.2539

[0267] Größter diff. peak / hole / e A -3 0.90 / -0.57Tabelle 2: Fraktionelle Atomkoordinaten (×10 4 )

[0268] Atom x y z Atom x y z Fel 6724.5(10) 4729.1(10) 6058.5(13) C38 6179(4) 4779(4) 8528(6) Cal 4769.6(13) 4385.8(13) 5840.7(17) C39 6697(5) 4740(4) 9498(5) Br2 7784.2(16) 8320.4(15) 5557(2) C40 7525(5) 4697(4) 9755(4) Br3 6223(3) 4823(3) 10392(3) C52 5642(9) 2753(8) 6735(10) Brl 4191(15) 2251(16) 2700(30) C42 3426(9) 4718(8) 6846(11) C12 10205(3) 5736(3) 8138(3) C12 8629(8) 2348(9) 6413(12) Cll 8156(3) 2584(3) 3790(4) C25 8307(4) 6074(5) 5486(6) 032 6035(4) 4770(4) 6863(5) C30 8366(4) 6842(5) 5511(6) Oll 6881(4) 3661(4) 5935(5) C29 7736(5) 7269(4) 5544(7) 031 7591(4) 4766(4) 7379(5) C28 7048(4) 6927(5) 5552(6) 022 6368(4) 5785(4) 5584(5) C27 6990(4) 6160(5) 5527(6) 012 5613(4) 4450(4) 4920(5) C26 7619(5) 5733(4) 5494(6) 021 7548(4) 4986(5) 5516(6) N43 3178(8) 4471(10) 7465(12) 051 5083(5) 3186(5) 6305(6) C14 7169(7) 2214(7) 5531(11) 041 4069(5) 4573(5) 6811(6) C32 9717(8) 3838(9) 8883(11) NI 3 7902(5) 2673(6) 5737(8) C24 8965(8) 5574(9) 5431(11) N33 8849(6) 3994(6) 8667(8) C3 10088(8)3940(9) 7043(11) N23 9193(6) 4989(7) 6216(8) C31 9775(8) 3268(9) 8201(11) C15 6415(4) 2624(4) 4892(6) Cll 9358(8) 2784(9) 6539(13) C20 5814(5) 2305(3) 4091(6) C22 9746(8) 4427(9) 6128(12) C19 5131(4) 2710(4) 3548(5) C55 6233(10) 1561(8) 7264(12) CI8 5047(4) 3435(4) 3806(5) C54 4821(10) 1695(9) 6013(13) C17 5648(4) 3754(3) 4607(6) C45 2391(12) 4729(16) 7440(18) C16 6332(4) 3349(4) 5150(5) C44 3716(15) 4060(20) 8290(20) N53 5579(8) 2025(7) 6667(9) C72 7857(15) 7786(13) 8313(17) NI 9490(6) 3447(7) 7168(10) 071 8473(15) 8146(15) 8414(16) C34 8727(7) 4600(8) 9271(10) N73 7805(10) 7037(13) 8172(9) C35 7835(3) 4694(4) 9043(6) C75 7091(12) 6627(13) 8019(14) C36 7317(4) 4733(4) 8073(5) C74 8480(13) 6645(13) 8137(16) C37 6489(4) 4776(4) 7816(4) Synthesis of a conjugate a compound of formula (I) and a compound of formula (VIII):

[0269]

[0270] (VIII)

[0271] In this case, R2' is a group that can be coupled to R2 and A is a residue that binds specifically to a biomolecule.

[0272] Click response with PSMA

[0273]

[0274] A PSMA ligand with a terminal alkyne group and an azide-functionalized compound of formula (I) or a deprotected variant are dissolved in a mixture of water and tert-butanol. The solution is treated with copper sulfate pentahydrate (5 mol%) and sodium ascorbate (10 mol%) and purged under nitrogen for 10 min. The reaction mixture is allowed to stand at room temperature with stirring for 16 h.

[0275] After completion of the reaction (monitored by HPLC or TLC), the solvent is partially removed under reduced pressure, and the residue is diluted with water. The crude mixture is purified by reversed-phase column chromatography. After removal of the organic solvent under vacuum, the triazole-linked PSMA conjugate ligand is obtained. The Click reaction can generally be carried out with terminal alkyne PSMA ligands and azide-functionalized compounds, using other mixtures of water and organic solvents, such as dimethyl sulfoxide / water or dimethylformamide / water, as well as other copper sources and reducing agents.

[0276] Simulation of the bonding of the conjugate to a biomolecule:

[0277] Simulations have shown that corresponding conjugates can bind to biomolecules.

[0278] methodology

[0279] The protein structure of a PSMA receptor (PDB ID: 5O5T) was prepared using UCSF ChimeraX visualization and a Python script for automated error correction, simplification, and validation. This reduced the structure from 26,515 to 4,875 atoms while preserving the binding pocket. Software used included ChimeraX, Python (with RDKit and MolBar for validation), Avogadro for ligand assembly, and xTB (GFN-FF / xTB) for optimizations.

[0280] Preparation steps

[0281] The process began with initial structural simplification: Unnecessary components such as the AA chain in the protein, most water molecules, sugar derivatives (NAG, BMA, MAN), and calcium were removed, while chloride / zinc ions near the binding site and water residue 1233 were retained; this was done using the Python function `pdbcleaning` or ChimeraX selection / delete commands. Alternative conformations were reduced to A (`removeduplicates`), element names were validated (`checkElements`), and amino acid codes were checked (`checkAmino Acids`). Residues were trimmed asymmetrically around the binding pocket (10–20 Å radius around co-crystallized ligand 9OT, visualized in ChimeraX), with `cutpdb` performing cuts at alpha carbon atoms to preserve peptide bonds (special treatment for proline) and minimize fragment count.

[0282] Hydrogen addition and validation

[0283] Hydrogen atoms were added in ChimeraX via Tools > Structure Editing > Add Hydrogen, with protonation states based on pKa values ​​(e.g., deprotonated Asp / Glu, protonated Lys / Arg); terms were saturated with CH3 groups via build modify commands. Validation decomposed the PDB structure into residues using RDKit (pdbtoresidue), generated MolBars (molbarproof), and verified unique structures for each residue type, with manual review of representative cases. Final conversion to XYZ was performed via pdbtoxyz.

[0284] Torsion-based method

[0285] The torsion-based ligand matching approach (Approach 2) used a custom Python script (fitligand, developed with Christopher Zurek) for inside-out matching: Rotatable bonds were identified, torsion angles were varied in 30° increments from the anchor outwards, the ligand was inserted into the protein, and steric collisions were evaluated via fractional coordination numbers (calculatefrac-tionalCNs, >1 = overlap). The lowest collision angle per bond was selected, and clash-free conformer ensembles were generated (65 for CI, 16 for C2, etc.). Dispersion was disabled for linearity. Ensembles were optimized with GFN-FF (protein backbone fixed), and the lowest-energy complex was separated / re-optimized for association-free energy.

[0286]

[0287] ΔG assoc = G system — G ligand — G protein (with G = vibrations neglected). This outperformed random sampling (GOAT / TTConf) and enabled fits for all linker variants C1-C5 in the PSMA pocket.

[0288]

[0289] The simulated results show that Ti(IV)-based PSMAs can adopt collision-free geometries that are geometrically well adapted to the narrow PSMA binding channel, thus providing strong structural evidence for a favorable interaction of this system with the receptor.

[0290] Steric complementarity

[0291] A torsion-guided placement protocol of the target molecule into the PSMA receptor demonstrates that, for ligands C1-C3, the Ti(IV) complex, the linker, and the PSMA target can be arranged along the extended entry funnel and within the binding pocket without significant steric collisions, even under strict geometric constraints. By systematically varying the torsion angles along the methylene linker, these ligands can follow the sterically predetermined course of the entry channel and the active site.

[0292] Electrostatics and directed interactions

[0293] In the generated conformers, the PSMA binding anchor fragment remains oriented to interact with the known polar and charged residues in the PSMA binding pocket, consistent with electrostatically dominated contacts, hydrogen bonds, and 7t-7t interactions typical of urea-based PSMA ligands. The reduced receptor model retains the crucial charged and hydrogen-bonding features of the active site, such that the identified low-voltage conformers of C1-C3 satisfy steric constraints and align the donor / acceptor and charged groups of the ligand to electrostatically complementary regions, thus supporting their suitability for high-affinity binding.

Claims

Patent claims 1. Compound according to formula (I) or salt thereof: where RI is selected from the group consisting of H, F, Cl, Br, I, sulfonic acid, sulfonate, C1-C6 alkyl, C2-C6 alkenyl, C6-C12 aryl, and C1-C6 alkoxy, R2 is selected from the group consisting of Cl, Br, I and groups connectable via click chemistry, L is selected from the group consisting of a single bond, C1-C12 alkyl, C2-C12 alkenyl, unsubstituted or Cl-C12-alkyl-substituted C6-C12 aryl, and C1-C6 alkoxy, wherein, in the case where L is a single bond, R2 and RI are different.

2. Compound or salt thereof according to claim 1, wherein R2 is selected from Cl, Br, I, Ethynyl, Azidoyl and Cyclooctinyl, in particular from Br and Azidoyl.

3. Compound or salt thereof according to claim 1 or 2, wherein L is selected from the group consisting of a single bond, C1-C12 alkyl, C1-C12-alkyl-substituted C6-C12 aryl, preferably a single bond and C1-C12-alkyl-substituted C6-C12 aryl.

4. Compound or salt thereof according to any one of claims 1 to 3, wherein RI is selected from H or C1-C6 alkenyl, preferably H.

5. Compound or salt thereof according to any one of claims 1 to 4, wherein the salt has the following formula (1a) where X is selected from the group consisting of chloride, bromide, iodide, nitrate, sulfate, phosphate, carbonate and organic carboxylates, in particular acetate, where k, n and m are integers and 3 · k = n · m.

6. Method for producing the compound according to any one of claims 1 to 5, wherein the method comprises the steps: i) Protecting an amino group of tris(2-aminoethyl)amine with a protecting group reagent to obtain a compound according to formula (II), where R3 is a protecting group: H2N R— NH N— NH2 (II)ii) Reacting the compound according to formula (II) with a compound according to formula (III) to form a compound according to formula (IV): iii) Reduction of imine groups to secondary amines in the compound according to formula (IV), deprotection of the protected amino group, and optionally adjustment of the pH value, to obtain a compound according to formula (V) (V) iv) Reacting the compound according to formula (V) with a compound according to formula (VI) to form the compound according to formula (I) or the salt thereof according to any one of claims 1 to 5:

7. Metal complex according to formula (VII) M q+ M' u+ Z (v · Y w ) (VII) where Z is a compound of the following formula (Vila) R 1 where RI, R2, and L are defined as in the preceding claims, where M is a metal cation in the oxidation state q+, where q is an integer selected from 2, 3 or 4, where M' is a metal cation in the oxidation state u+, where u is an integer selected from 1, 2 or 3, or where M' represents one to three protons and u+ is the total charge of these protons, or where M' is absent and u+ is zero, where Y w an anion or cation where v and w are integers and q + u - 6 = - v · w, where Y is absent in the case that q + u = 6.

8. Method for producing the metal complex according to claim 7, wherein a compound according to formula (I) or the salt thereof according to any one of claims 1 to 5 is reacted with a source for the metal cation M and optionally a source for the metal cation M'.

9. Conjugate of a compound of formula (I) or of the salt thereof according to any one of claims 1 to 5 or of the metal complex according to formula (VII) according to claim 7 with a compound of formula (VIII): y A (VIII) where R2' is a group that can be coupled to R2 and A is a residue that binds specifically to a biomolecule.

10. Compound according to formula (I) or the salt thereof according to any one of claims 1 to 5, the metal complex according to formula (VII) according to claim 7 or the conjugate with the compound according to formula (VIII) according to claim 9 for use in an in vivo diagnostic procedure using a PET scanner and / or a therapeutic procedure, in particular for in vivo diagnosis and / or therapy of cancer.

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