Synthesis of a precursor of radiopharmaceutical products

Abstract

The present disclosure is directed to a method for synthesizing a precursor of radiopharmaceutical products, CTT1298. CTT1298 is a precursor of [18F]CTT1057, a radioligand imaging (RLI) agent useful in the diagnostic of prostate cancer, and a key intermediate in the synthesis of other radiopharmaceutical products useful in the treatment of prostate cancer, like [177Lu]Lu-CTT1401, and [177Lu]Lu-CTT1403 which are radioligand therapeutic (RLT) agents.

Description

[0001] SYNTHESIS OF A PRECURSOR OF RADIOPHARMACEUTICAL PRODUCTS

[0002] FIELD OF THE INVENTION

[0003] The present disclosure relates to a method for synthesizing a precursor of radiopharmaceutical products, CTT1298. CTT1298 is a precursor of [18F]CTT1057, a radioligand imaging (RLI) agent useful in the diagnostic of prostate cancer, and a key intermediate in the synthesis of other radiopharmaceutical products useful in the treatment of prostate cancer, like [177Lu]Lu- CTT1401 , and [177Lu]Lu-CTT1403 which are radioligand therapeutic (RLT) agents.

[0004] In particular, the present disclosure relates to a method for synthesizing CTT1298 in high purity, which can be performed on a large scale.

[0005] BACKGROUND

[0006] Prostate-specific membrane antigen is a transmembrane protein, also known as folate hydrolase or glutamate carboxypeptidase II. From all the known PSMA-overexpressing tumors, prostate cancer is the one in which the role of PSMA has been most extensively studied. Prostate cancer remains the cancer with the second highest mortality in the United States (US), and the third leading cause of cancer-related death in Europe in men (Siegel RL, Miller KD, Jemal A (2017) Cancer Statistics, 2017. CA Cancer J Clin; 67(1 ):7-30, Malvezzi M, Carioli G, Bertuccio P, et al (2019) European cancer mortality predictions for the year 2019 with focus on breast cancer. Ann Oncol; 30(5):781 -7). It also remains the most diagnosed cancer with an estimated increase of 9,960 new cases with a total of 174,650 in 2019 (Siegel RL, Miller KD, Jemal A (2018) Cancer Statistics, 2018. CA Cancer J Clin; 68(1 ):7-30, Siegel RL, Miller KD, Jemal A (2019) Cancer statistics, 2019. CA Cancer J Clin; 69(1 ):7-34). Most of the diagnosed cases are in more developed regions due to the use of PSA testing, but there is only modest variation in mortality rates globally which is driven by metastatic, and often castration-resistant disease (Bray F, Ren JS, Masuyer E, et al (2013). Int J Cancer; 132:1133-45). Subsequent treatment is multifaceted and may involve observation, surgery (prostatectomy), radiation therapy (external beam or brachytherapy), hormonal therapy, chemotherapy. The differential expression of PSMA from tumor to non-tumor tissue has resulted in numerous targeted strategies involving both disease localization using PSMA-PET imaging as well as therapeutic intervention. Correct identification of disease location and extent determines treatment decisions for patients with prostate cancer. Identification of distant metastatic disease at the early stages of prostate cancer is thus important in planning prostate cancer management.

[0007] Novel PET (positron-emission tomography) radiotracers are currently being developed as PET imaging is an enticing choice since it offers the potential to both stage patients and provide insight into tumor biology. Among the various PET probes available, [18F]CTT1057 is a promising novel PS MA-targ eting18F-labeled PET imaging agent (WO2014143736). Unlike most other PSMA agents labelled with either68Ga or18F (e.g. [68Ga]Ga-PSMA-11 , [18F]PSMA1007, [18F]DCFPyL) which share a urea backbone, [18F]CTT1057 is based on a phosphoramidate scaffold that irreversibly binds to PSMA with high nanomolar affinity, which may account for a higher and prolonged tumor uptake (Behr SC, Aggarwal R, VanBrocklin HF, et al (2019) Phase I Study of CTT1057, an18F-Labeled Imaging Agent with Phosphoramidate Core Targeting Prostate-Specific Membrane Antigen in Prostate Cancer. J Nucl Med; 60(7):910-6).

[0008] Clinical trials using [18F]CTT1057 are ongoing, this compound is currently tested in Phase ll / lll for the detection of PSMA-positive tumors. The Phase-I study in 20 prostate cancer patients (n = 5 primary staging and n = 15 metastatic-castration resistant prostate cancer (mCRPC)) has shown an acceptable safety profile without any radiotracer-related adverse reactions. The Phase-I study also demonstrated that metastatic lesions are detected with higher sensitivity on [18F]CTT 1057 imaging than on conventional imaging (Behr et al 2019).

[0009] The phosphoramidate scaffold is also present in radioligand therapeutic (RLT) agents useful in the treatment of prostate cancer like [177Lu]Lu-CTT1401 , and [177Lu]Lu-CTT1403.

[0010] The synthesis of [18F]CTT1057, [177Lu]Lu-CTT1401 , and [177Lu]Lu-CTT1403 typically involves a key precursor / intermediate which is CTT1298 (Pentapotassium (3S,10S,15S)-22-amino-5- oxido-5, 12, 17-trioxo-6-oxa-4, 11 ,16-triaza-5A5-phosphadocosane-1 ,3, 10, 15-tetracarboxylate, CAS number = 1628718-07-9). The latter is a potassium salt of the following formula:

[0011]

[0012] In particular, in the synthesis of [18F]CTT1057, this compound is the chemical precursor for the production of the RLI agent. CTT 1298 reacts with a p-18fluorobenzoic acid succinimidyl ester to produce [18F]CTT1057.

[0013] Because it is the precursor, it is important that CTT1298 is highly pure, as it is not convenient to have extended purification steps after production of the RLI agent. The synthesis of CTT1298 is therefore a key step in the production of RLI and RLT agents.

[0014] The synthesis of this intermediate has been described before, for example in WO 2022 / 207906 A1. The final chemical step of the CTT1298 synthesis is a classical hydrogenation step to remove protecting groups, generally performed in THF on the milligram scale.

[0015] As clinical trials are ongoing, it becomes necessary to produce large quantities of this compound with high purity. However, when the deprotection step is performed on a big scale using the above mentioned process, problems arise. Indeed, the purity of the product decreases with large scale synthesis. In particular, when the deprotection step is performed on several dozens of grams of product, the purity can drop lower than 90%, which is not advisable for the production of radiopharmaceutical products.

[0016] It is therefore relevant to provide a reproductible method for synthesizing CTT 1298 with high purity, preferably higher than 95%, on a large scale, like several grams.

[0017] SUMMARY

[0018] The inventors unexpectedly found out that by switching the solvent from THF to a substituted cyclic ether, like 2-methyl-THF, during the deprotection step, the purity of CTT1298 can be improved. In particular, it is possible to achieve high purity of the compound, more than 95% or 97%, even on a large scale.

[0019] The inventors hypothesize that when THF is used as a solvent, it can react with the deprotected product to form an impurity, which is the following compound of formula (III)

[0020] Wherein X is H or a counterion X+, like K+. Compound of formula (III) can be in free acid or salt form. When the compound of formula (III) is in free acid form, X is H. When the compound of formula (III) is in a salt form, COOX represents COO X+. In this case, X is a positive counterion X+. X can be selected from alkali metals, like K.

[0021] The formation of this impurity therefore reduces the purity of the compound of formula (I). On the other hand, when a substituted cyclic ether, like 2-methyl-THF, is used during the deprotection step, the formation of the impurity of formula (III) is prevented. Thus, the change of solvent in the deprotection step prevents the formation of the impurity and allows for a high purity of the compound of formula (I), for example more than 95% or 97%.

[0022] Thus, the present disclosure relates to a method for synthesizing a compound of formula (I),

[0023] said method comprising a step of deprotecting a compound of formula (II) wherein PG1 , PG2 and PG3 are each independently a protecting group, said deprotection being done by hydrogenation in a solvent which is a substituted cyclic ether, and, preferably, in the presence of a metal-based catalyst.

[0024] The disclosure also relates to compound of formula (I) obtained or obtainable, preferably directly obtained or directly obtainable, by the method.

[0025] The disclosure also relates to a compound of formula (I), which is more than 90% pure, preferably more than 93% pure, and more preferably more than 95% pure, even more preferably more than 96%, 97%, 98%, or 99%.

[0026] The disclosure also relates to a compound of formula (I) for use in the production of a radiopharmaceutical product, preferably a radioligand product, more preferably, a radioligand imaging (RLI) agent, e.g.18F-CTT1057 (i.e. Vidoflufolastat (18F)), or a radioligand therapeutic (RLT) agent, e.g. comprising the molecule CTT1400, CTT1401 , CTT1402, or CTT1403, in particular, [177Lu]Lu-CTT1401 , or [177Lu]Lu-CTT1403. DETAILED DESCRIPTION

[0027] General Definitions

[0028] The use of the articles “a”, “an”, and “the” in both the description and claims are to be construed to cover both the singular and the plural, unless otherwise indicated herein or clearly contradicted by context. The terms “comprising”, “having”, “being of”, “including”, and “containing” are to be construed as open terms (i.e., meaning “including but not limited to”) unless otherwise noted. Additionally, whenever “comprising” or another open-ended term is used in an embodiment, it is to be understood that the same embodiment can be more narrowly claimed using the intermediate term “consisting essentially of’ or the closed term “consisting of’.

[0029] The term “about” or “ca.” has herein the meaning that the following value may vary for ± 20%, preferably ± 10%, more preferably ± 5%, even more preferably ± 2%, even more preferably ± 1 %.

[0030] The expression “ compound X free from Y” has herein the meaning that the compound X comprises less than 5000 ppm of Y, preferably less than 1000 ppm of Y, and even more preferably less than 500 ppm, 100 ppm, 50 ppm, 10 ppm or 5 ppm .

[0031] As used herein the term “radiopharmaceutical” or “radiopharmaceutical compound” refers to a pharmaceutical compound which is labelled with a radionuclide element. Such radiopharmaceutical compound has binding affinity to a specific marker on target cells, for example, a receptor or a tumor antigen, and therefore includes a target ligand (or target binding moiety). Radiopharmaceutical compounds are useful as contrast agents in imaging techniques, such as PET scan or MRI scan, or as therapeutics in nuclear medicine, also known as radioligand therapy (RLT), or PRRT (peptide receptor radionuclide therapy).

[0032] The term "protecting group" refers to a functional group introduced into a molecule from a chemical functional group, in order to mask some or all of its reactivity. Masking (protecting) a chemical functional group on the molecule thus improves the selectivity of subsequent reactions. The term "protection" or "protected" thus refers to the state of the molecule after reaction with a protecting group. Deprotection refers to the step of releasing some or all of the protective groups from a protected molecule, and preferably obtaining the molecule in its original state prior to its protection by the compounds of the invention. The skilled person will be able to identify protecting groups PG1 , PG2, PG2’ and PG3 that are particularly suitable for the desired function, as described for example in Greene's Protective Groups in Organic Synthesis by Peter G. M. Wuts, Publisher: Wiley-Blackwell; Edition: 5th Edition (December 23, 2014) or in Amio Acid-Protecting groups A. Isidro-Llobet et al. Chem. Rev. 2009, 109, 6, 2455-2504.

[0033] As used herein, the term “alkyl”, by itself or as part of another substituent, refers to a linear or branched alkyl functional group having preferably from 1 to 12 carbon atoms, more preferably 1 to 6 carbon atoms, and even more preferably 1 to 4 carbon atoms. Suitable alkyl groups include methyl, ethyl, n-propyl, / -propyl, n-butyl, / -butyl, s-butyl and f-butyl, pentyl and its isomers (e.g. n-pentyl, / so-pentyl), and hexyl and its isomers (e.g. n-hexyl, / so-hexyl). The expression “(di)methyl substituted compound” refers to a compound which can be substituted with a methyl or a dimethyl group.

[0034] As used herein, the terms “ambient temperature” refers to a temperature of 20° C.±5° C. (I. e. , 15-25° C).

[0035] As used herein, the term “substituted” refers to a compound wherein one or more hydrogen atom has been replaced by an atom or a group different from hydrogen. In particular, the terms “substituted cyclic ether” refers to a cyclic ether group wherein one or more hydrogen has been substituted by an atom or a group different from hydrogen, for example an alkyl group. In this case, the substituted cyclic ether is an alkyl substituted cyclic ether.

[0036] As used herein, the term “purity” when used in relation to compound of formula (I), refers to the purity of the compound itself, and does not referto the enantionmerically purity. If the compound is 100% pure, it means that only the compound of formula (I) is present. The purity can be determined by HPLC, in particular reversed phase achiral HPLC. The column used can be a HPLC column containing porous silica-based particles comprising phenyl-hexyl groups. The size of the porous silica-based particles can be from 1.5 to 10 pm. In particular, the purity of the compound of formula (I) can be determined using the following HPLC method:

[0037] The method for synthesizing a compound of formula (I)

[0038] The present disclosure relates to a method for synthesizing a compound of formula (I), CTT1298, said method comprising a step of deprotecting a compound of formula (II) wherein PGi, PG2 and PG3 are each independently a protecting group, said deprotection being done by hydrogenation in a solvent which is a substituted cyclic ether, and, preferably, in the presence of a metal-based catalyst.

[0039] This method makes it possible to obtain a highly pure compound of formula (I). According to an embodiment, the compound of formula (I) is more than 90%, preferably more than 93% pure, and more preferably more than 95% pure, even more preferably more than 96%, 97%, 98%, or 99% pure. For example, the compound of formula (I) can be more than 90% pure, for example more than 91 %, 92%, 93%, 94%, 95%, 96%, 97%, 98%, 99%, 99.5% or 99.9% pure. Preferably, the compound of formula (I) can be more than 95% pure. The purity of the compound can be determined by HPLC as mentioned herein.

[0040] The yield of this hydrogenation step can be more than or equal to 80%, preferably more than 85%.

[0041] According to an embodiment, the substituted cyclic ether solvent is selected from the group consisting of alkyl substituted tetrahydrofuran, preferably a C1-C4 alkyl substituted tetrahydrofuran; alkyl substituted 1 ,4-dioxane, preferably a C1-C4 alkyl substituted 1 ,4-dioxane; and mixtures thereof. The alkyl substituted tetrahydrofuran can be a (di)methyl substituted tetrahydrofuran or a (di)methyl substituted 1 ,4-dioxane. According to an embodiment, the substituted cyclic ether solvent is selected from the group consisting of 2-methyl tetrahydrofuran, 2,5-dimethyl tetrahydrofuran, 2-methyl-1 ,4-dioxane, 2,5-Dimethyl-1 ,4- dioxane. Preferably the substituted cyclic ether solvent is 2 methyl THF.

[0042] The protecting groups PG1, PG2, and PG3 are removable by hydrogenation, i.e. the protecting groups PG1, PG2 and PG3 are released when the compound of formula (II) is treated with hydrogen (H2) and, optionally, a catalyst. The obtained product therefore has free -NH2, - COOH and -(PO)-OH functions. The person skilled in the art will be able to identify protecting groups PG1, PG2 and PG3 that are particularly suitable for the desired function. PG1, PG2 and PG3 are protecting groups that are labile in the same conditions of hydrogenation. These protecting groups are well-know in the art and are described, for example, in Greene's Protective Groups in Organic Synthesis by Peter G. M. Wuts, Publisher: Wiley-Blackwell; Edition: 5th Edition (December 23, 2014), in particular at pages 686-837 for the carboxyl protecting groups, at pages 895-1194 for the amino protecting group and at pages 1203-1263 for the phosphoramidate protecting groups. PGi is a carboxyl protecting group. Each of the protecting groups PGi can be independently selected from the group consisting of a benzyl, phenacyl, N-Phtalimidomethyl, 9-anthrylmethyl, 2-(9,10-Dioxo)anthrylmethyl, piperonyl, trimethyl silyl, and p-methoxybenzyl (PMB).

[0043] PG?is an amino protecting group. The group NH-PG2 can be selected from the group consisting of 1 ,1-dimethylpropynyl carbamate, vinyl carbamate, allyl carbamate, cinnamyl carbamate, N- Hydroxypiperidinyl carbamate, 4,5-Diphenyl-3-oxazolin-2-one, benzyl carbamate, substituted benzyl carbamate (like p-nitrobenzyl carbamate, 3,4-dimethoxy-6-nitrobenzyl carbamate, 2,4- dichlorobenzyl carbamate), 5-benzioxazolylmethyl carbamate, 9-anthrylmathyl carbamate, diphenylmethyl carbamate, isocotinyl carbamate, S-benzyl carbamate, N-Allyl, N-o-nitrobenzyl- N-Di(p-methoxyphenyl)methyl, N-triphenylmethyl, N-(p-methoxyphenyl)diphenylmethyl-N- Diphenyl-4-pyridylmethyl, N-benzylidene, N-nitro, N-oxide, N-benzylsulfonyl, and N- phenacylsulfonyl.

[0044] PG3 is a phosphoramidate protecting group. PG3 can be selected from the group consisting of benzyl, phenyl, 2-Methylphenyl and 2,6-dimethylphenyl.

[0045] Preferably, the deprotection is performed in the presence of a catalyst, preferably a metal - based catalyst. The skilled person is able to determine which catalyst to use depending on the nature of the protecting groups PGi, PG2 and PG3 present in the compound of formula (II). The catalyst is chosen among hydrogenation catalyst, like metal-based catalyst. Examples of metalbased catalysts include platinum group element (i.e., ruthenium, osmium, rhodium, iridium, palladium, platinum) catalysts. The metal catalyst may be composed of a metal alone (e.g., palladium black), or may be a metal supported on a carrier. As the carrier, a known one can be used and, for example, activated carbon, silica, alumina, zeolite and the like can be mentioned. Of these, activated carbon is preferable from the aspects of easy availability and the like. From the aspects of catalyst activity, the metal catalyst is preferably one wherein a metal is supported on a carrier. Examples of the palladium catalysts include Pd(OH)2, palladium carbon, silica- supported palladium catalyst, alumina-supported palladium catalyst and the like. According to an embodiment, the metal-based catalyst is palladium carbon wherein palladium(O) is supported on activated carbon.

[0046] The metal amount of the metal-based catalyst to be used between 1 and 25 wt% compared to the weight of the compound of formula (II), preferably between 5 and 15 wt%, and preferably between 8 and 12 wt%. The amount of metal can be comprised between 100 to 25000 ppm, or between 1000 and 20000 ppm or between 5000 and 15000 ppm .

[0047] The deprotection reaction can be performed at a temperature comprised between 10°C and the boiling point of the solvent. For example, the deprotection reaction can be performed at a temperature comprised between 10 and 110°C, or between 20 and 100°C, or between 10 and 30°C. According to an embodiment, the hydrogenation is performed at room temperature.

[0048] The hydrogenation is generally performed at a hydrogen pressure not less than the atmospheric pressure. The upper limit of the hydrogen pressure is determined by the pressure vessel and the like to be used. According to an embodiment, the hydrogenation is performed using H2at a pressure between 1 and 20 bars, preferably between 5 and 15 bars, and more preferably between 8 and 12 bars.

[0049] The hydrogenation is preferably performed using a base. The base can be selected from the group consisting of carbonate salts, hydrogenocarbonate salts, and potassium-based bases. Examples of suitable bases include carbonate or hydrogenocarbonate salts, like K2CO3, and KHCO3. Preferably, the base is a potassium-based base, like KOH, K2CO3 or KHCO3.. The quantity of base used can be from 2.5 equivalents (compare to the compound of formula (II)) to 5 equivalents.

[0050] The quantity of the compound (II) used in the deprotection steps can be at least 1g, at least 5g, at least 10g, at least 25g, at least 40g, or at least 50g. It can be comprised between 5 and 100g, or between 50 and 80g.

[0051] While the time of hydrogenation may vary depending on the amount of the compound of formula (II), the quantity of the base, the catalyst and the solvent, as well as temperature, hydrogen pressure and the like, it is preferably not less than 30 minutes, more preferably not less than 4 hr, and preferably not more than 48 hr, more preferably not more than 32 hr. According to an embodiment, the time of hydrogenation is comprised between 4 and 5h.

[0052] After the hydrogenation, the crude product can be purified using one or more of the following techniques: filtration, washing with an organic solvent, liquid / liquid extraction, treatment with a metal scavenger, treatment with adsorbent material, recrystallization. These purification steps can be implemented by any technique known by the person skilled in the art. After the hydrogenation, filtration can be performed. The pore size of the filter used can be comprised between 0,05pm and 5pm, it can be a microfiltration.

[0053] The crude product can be washed with an organic solvent using liquid / liquid extraction. The organic solvent used can be selected from THF, ethyl acetate, diethyl ether, or pentane. Preferably, the organic solvent used for washing and liquid-liquid extraction is THF.

[0054] The crude product can be treated with a metal scavenger to remove the metal-based catalyst used for hydrogenation. Examples of metal scavenger that can be used include thiol functionalized silica, dimercaptotriazine functionalized silica, amine functionalized silica, cysteine functionalized silica, diamine functionalized silica, DOTA functionalized silica, imidazole functionalized silica, thiourea functionalized silica, triamine functionalized silica, and triaminetetraacetate sodium salt functionalized silica. In particular, when a palladium-based catalyst is used, dimercaptotriazine functionalized silica can be used as a palladium-scavenger.

[0055] Examples of adsorbent material that can be used include activated charcoal, zeolites and clays. Preferably, the adsorbent material is activated charcoal.

[0056] According to an embodiment, the crude product obtained after hydrogenation is purified using the following steps:

[0057] (I) Filtration,

[0058] (II) Liquid / liquid extraction,

[0059] (iii) Treatment with a metal scavenger, and

[0060] (iv) Microfiltration.

[0061] After purification, the compound of formula (I) can be freeze dried.

[0062] The purity of the compound of formula (I) can be determined using HPLC.

[0063] According to an embodiment, the method comprises, before the deprotection step, at least one of the following steps.

[0064]

[0065] All these steps can be implemented by any technique known by the person skilled in the art.

[0066] All the protecting groups PGi, PG2 and PG3 are as described above. PG1 is stable in the conditions used in steps 1-5. It is only deprotected during the last hydrogenation step. PG 3 is stable in the conditions used in steps 3-5.

[0067] PG2’ is an amino protecting group. Representative examples of amino protecting groups include, but are not limited to, t-butyloxycarbonyl (Boc), 9-fluorenyl methoxycarbonyl (Fmoc), allyloxycarbonyl (alloc), N-(1-(4,4-dimethyl-2,6-dioxocyclohexylidene)ethyl) (Dde), 1-(1- Adamantyl)-1 -Methylethoxycarbonyl (Adpoc), N-(1 -(4,4-dimethyl-2,6-dioxocyclohex-1 - ylidene)-3-methylbutyl) (IvDde), monomethoxytrityl (MMt) and 4-methyltrityl (Mtt).

[0068] Step 1 : starting material IV is treated with a reducing agent to reduce the carboxylic acid function to an alcohol function. This step can be performed by 1 ) first producing an anhydride, for example by using a chloroformate and a base, and then 2) using an hydride, like NaBH4or LiBH4, to reduce the anhydride function to an alcohol function. The chloroformate can be an alkyl chloroformate like isobutyl chloroformate and the base can be 4-Methyl morpholine.

[0069] Step 2: first intermediate V is treated with the phosphite VI, and then the -OH function is protected with PG3. In compound VI, R can be any organic substituent like an alkyl or an aryl group. According to an embodiment, R is an aryl group, like phenyl.

[0070] Step 3: intermediate VII reacts with compound VIII (wherein Xr is an anion, like a halide, for example Cl- or Br) and CCI4to form intermediate IX, this can be done in basic conditions, for example by using N,N-Diisopropylethylamine.

[0071] Step 4: first PG2’ is selectively removed to form a free amine function which then reacts with compound X to form compound XI. When PG2’ is a Boc protecting group, the selective deprotection can be performed using an acid, like TFA. The reaction with compound XI can be done using a coupling reagent and a base. Examples of coupling agent that can be used include benzotriazol-1-yl-oxytripyrrolidinophosphonium hexafluorophosphate (PyBOP), 1 - [Bis(dimethylamino)methylene]-1 H-1 ,2,3-triazolo[4,5-b]pyridinium 3-oxid hexafluorophosphate (HATU), 2-(1 H-Benzotriazole-1-yl)-1 ,1 ,3,3-tetramethyluronium tetrafluoroborate (TBTU), 2- (1 H-benzotriazol-1-yl)-1 ,1 ,3,3-tetramethyluronium hexafluorophosphate (HBTU), 2-chloro-4,6- dimethoxy-1 ,3,5-triazine (CDMT), N-[(5-Chloro-3-oxido-1 H-benzotriazol-1 -y I )-4- morpholinylmethylene]-N-methylmethanaminium hexafluorophosphate (HDMC), 1 -Cyano-2- ethoxy-2-oxoethylidenaminooxy)dimethylamino-morpholino-carbenium hexafluorophosphate (COMU), dimethylamino(triazolo[4,5-b]pyridin-3-yloxy)methylidene]- dimethylazanium;tetrafluoroborate (TATU), N,N,N’,N’-tetramethyl-S-(1-oxido-2- pyridyl)thiouronium tetrafluoroborate (TOTT), N-Ethoxycarbonyl-2-ethoxy-1 ,2-dihydroquinoline (EEDQ), 1-Propanephosphonic anhydride (T3P), and 4-(4,6-dimethoxy-1 ,3,5-triazin-2-yl)-4- methyl-morpholinium chloride (DMTMM). Examples of bases that can be used include N,N- Diisopropylethylamine (DIPEA), N,N-Diisopropylethylamine ('Pr2Net), triethylamine (TEA), 4- methylmorpholine (NMM), imidazole, pyridine, and collidine. Step 5: first PG2’ is selectively removed to form a free amine function which then reacts with compound XII to form compound II. When PG2’ is a Boc protecting group, the selective deprotection can be performed using an acid, like TFA. The reaction with compound XII can be done using a coupling reagent and a base like mentioned in step 4.

[0072] According to an embodiment, the method comprises, before the deprotection step, all the steps 1 to 5.

[0073] Compound of formula (I)

[0074] The disclosure also relates to a compound of formula (I) obtained or obtainable, preferably directly obtained or directly obtainable, by the method according to any of the preceding claims.

[0075] The disclosure also relates to compound of formula (I) which is more than 90%, preferably more than 93% pure, and more preferably more than 95% pure, even more preferably more than 96%, 97%, 98%, or 99% pure. For example, the compound of formula (I) can be more than 90% pure, for example more than 91 %, 92%, 93%, 94%, 95%, 96%, 97%, 98%, 99%, 99.5% or 99.9% pure. Preferably, the compound of formula (I) can be more than 95% pure The purity of the compound can be determined by HPLC as mentioned herein.

[0076] The compound of formula (I) can be free from tetrahydrofuran residue and free from 1 ,4 dioxane residue.

[0077] The compound of formula (I) can be free from the compound of formula (III) wherein X is H or a counterion X+, like K+.

[0078] Compound of formula (III) can be in free acid or salt form. When the compound of formula (III) is in free acid form, X is H. When the compound of formula (III) is in a salt form, COOX represents COO X+. In this case, X is a positive counterion X+. X can be selected from alkali metals, like K.

[0079] The disclosure also relates to composition comprising a compound of formula (I) and at least one carrier. The compound of formula (I) or the composition can be used in the production of a radiopharmaceutical product, preferably a radioligand product. The radioligand can be a radioligand imaging (RLI) agent or a radioligand therapeutic (RLT) agent. The RLI can be18F- CTT1057 (i.e. Vidoflufolastat (18F)). The RLT can be [177Lu]Lu-CTT1401 or [177Lu]Lu-CTT1403.

[0080] The compound of formula (I) or the composition can be used in the production of a precursor of a radiopharmaceutical product like CTT1400, CTT1401 , CTT1402 or CTT1403.

[0081] Embodiments

[0082] 1 . A method for synthesizing a compound of formula (I), said method comprising a step of deprotecting a compound of formula (II) wherein PGi, PG2 and PG3 are each independently a protecting group, said deprotection being done by hydrogenation, in the presence of a metal-based catalyst, and in a solvent which is a substituted cyclic ether.

[0083] 2. The method according to embodiment 1 , wherein the compound of formula (I) is more than 90% pure, preferably more than 93% pure, and more preferably more than 95% pure, even more preferably more than 96%, 97%, 98%, or 99% pure.

[0084] 3. The method according to embodiment 1 or 2, wherein the substituted cyclic ether solvent is selected from the group consisting of alkyl substituted tetrahydrofuran, alkyl substituted 1 ,4-dioxane, and mixtures thereof.

[0085] 4. The method according to any of the preceding embodiments, wherein the substituted cyclic ether solvent is selected from the group consisting of 2-methyl tetrahydrofuran, 2,5-dimethyl tetrahydrofuran, 2-methyl-1 ,4-dioxane, 2,5-Dimethyl-1 ,4-dioxane, preferably the substituted cyclic ether solvent is 2 methyl THF.

[0086] 5. The method according to any of the preceding embodiments, wherein said deprotection is performed using a base, preferably a carbonate or hydrogenocarbonate salt, more preferably K2CO3 or KHCO3.

[0087] 6. The method according to any of the preceding embodiments, wherein each of the protecting groups PG1 and PG3 is a benzyl group.

[0088] 7. The method according to any of the preceding embodiments, wherein the protecting group PG2 is a benzyl carbamate group.

[0089] 8. The method according to any of the preceding embodiments, wherein the catalyst is palladium on carbon.

[0090] 9. The method according to embodiment 8, wherein the quantity of the catalyst is between 1 and 25 wt%, preferably between 5 and 15 wt%, and preferably between 8 and 12 wt%. 10. The method according to any of the preceding embodiments, wherein the hydrogenation is performed using H2at a pressure between 1 and 20 bars, preferably between 5 and 15 bars, and more preferably between 8 and 12 bars.

[0091] 11. The method according to any of the preceding embodiments, wherein said deprotection is performed at a temperature between 10 and 30°C, preferably at ambient temperature.

[0092] 12. The method according to any of the preceding embodiments, wherein the quantity of compound (II) is at least 1g.

[0093] 13. The method according to any of the preceding embodiments, wherein the crude product obtained after hydrogenation is purified using the following steps: i) Filtration, ii) Liquid / liquid extraction, iii) Treatment with a metal scavenger, and iv) Microfiltration.

[0094] 14. A compound of formula (I) obtainable by the method according to any of the preceding embodiments.

[0095] 15. A compound of formula (I) which is more than 90% pure, preferably more than 93% pure, and more preferably more than 95% pure, even more preferably more than 96%, 97%, 98%, or 99%. 16. The compound of formula (I) according to embodiment 15 which is free from the compound of formula (III) wherein X is H or a counterion X+, like K+.

[0096] 17. A composition comprising a compound of formula (I) according to embodiment 15 or 16, and at least one carrier.

[0097] 18. The compound of formula (I) according to any one of embodiments 14 to 16 for use in the production of a radiopharmaceutical product, preferably a radioligand product, more preferably, a radioligand imaging (RLI) agent, or a radioligand therapeutic (RLT) agent.

[0098] EXAMPLES

[0099] In the present section, the abbreviations used are the following: Boc-Glu-OBn 1 -Benzyl N-(tert-Butoxycarbonyl)-L-glutamate

[0100] CBz-AH-acid N-Carbobenzoxy-e-aminocaproic acid

[0101] CCI4 Carbon tetrachloride

[0102] DCM Dichloromethane

[0103] DIPEA N,N-diisopropylethylamine

[0104] DMF Dimethylformamide

[0105] H2 Hydrogen gas

[0106] H2O Water

[0107] HBTU O-(Benzotriazol- 1 -y I )-N , N ,N’ , N’-tetramethyluronium hexafluorophosphate

[0108] H-Glu(OBn)-OBn*HCI Dibenzyl L-Glutamate Hydrochloride iBCF Isobutyl chloroformate

[0109] K2CO3 Potassium carbonate

[0110] MeOH Methanol

[0111] Me-THF 2-methyl-tetrahydrofuran

[0112] NaBH4 Sodium borohydride

[0113] NMM N-Methylmorpholine

[0114] Pd / C Palladium on charcoal paste

[0115] RT Room Temperature

[0116] TEA Triethylamine

[0117] TFA Trifluoroacetic Acid

[0118] THF Tetrahydrofuran

[0119] Example 1: Synthesis of compound of formula (I) - CTT1298

[0120] CTT1298 was synthesized according to the scheme below in a 6-step procedure starting from 1 -Benzyl N-(tert-Butoxycarbonyl)-L-glutamate.

[0121]

[0122] Step 1 : Synthesis of Benzyl N-(tert-butoxycarbonyl)-5-hvdroxy-L-norvalinate - Intermediate A

[0123] To 375 g of 1 -Benzyl N-(tert-Butoxycarbonyl)-L-glutamate solubilized in tetrahydrofuran, 4- methylmorpholine is added. The reaction mixture is stirred until homogeneity and cooled down to -20°C ±3°C.

[0124] Temperature is maintained below -15°C during isobutyl chloroformate introduction and for the next approximately 20 minutes. Sodium borohydride and methanol are added, keeping the exotherm and off gas under control.

[0125] Then the reaction mixture is hydrolyzed with an aqueous solution of hydrochloric acid, keeping the temperature below 5°C. After hydrolysis, reaction mixture is concentrated under vacuum. The obtained aqueous solution is extracted with diisopropylic ether and the organic phases are washed by an aqueous acidic solution, water, a saturated sodium hydrogen carbonate aqueous solution successively and finally by a saturated sodium chloride aqueous solution. The resulting organic phase containing crude intermediate A is concentrated and dried under vacuum. The crude product is dissolved in dichloromethane and purified using silica gel chromatography. The eluting solvents are n-heptane and ethyl acetate. The solution containing purified intermediate A is concentrated under vacuum to obtain a yellow oil.

[0126] Step 2: Synthesis of Benzyl 5-{[(benzyloxy)(oxo)-A5-phosphanyl1oxy}-N-(tert-butoxycarbonyl)- L-norvalinate - Intermediate B

[0127] 180g of intermediate A are solubilized in pyridine. Then a pyridine solution containing 128 ml_ of diphenylphosphite is added while maintaining the temperature below 0°C. The reaction mixture is stirred for 4h. The end of the reaction is controlled by HPLC with a limit for intermediate A below 7%.

[0128] 104 mL of benzyl alcohol are then added maintaining the temperature below 0°C. When the addition is completed, reaction mixture is stirred for at least 15h, allowing the temperature to reach ambient conditions.

[0129] Then the reaction mixture is poured on water. The aqueous phase is extracted by diisoproylic ether. The resulting organic phase is first washed by an acidic aqueous solution and then by water and a saturated sodium hydrogen carbonate aqueous solution successively. The organic phase containing intermediate B is concentrated under vacuum. The crude product is dissolved in dichloromethane and purified using silica gel chromatography. The eluting solvents are n- heptane and ethyl acetate. The solution containing purified intermediate B is concentrated under vacuum to obtain a yellow oil.

[0130] Step 3: Synthesis of Dibenzyl N-[(benzyloxy)({(4S)-5-(benzyloxy)-4-[(tert- butoxycarbonyl)amino1-5-oxopentyl}oxy)phosphoryl1-L-qlutamate - Intermediate C

[0131] To 175g of intermediate B solubilized in dichloromethane, 141g of H-Glu(OBn)-OBn- HCI and carbon tetrachloride are added and then N,N-Diisopropylethylamine. The reaction mixture is stirred for at least 4 hours.

[0132] The end of the reaction is controlled by HPLC with a limit for intermediate B below 2%.

[0133] After concentration under vacuum, the crude reaction media is solubilized in ethyl acetate and washed with a saturated ammonium chloride aqueous solution. The organic phase is then washed by water and by a saturated sodium chloride aqueous solution successively. The remaining organic phase is concentrated under vacuum to obtain a yellow oil intermediate C.

[0134] Step 4: Synthesis of Dibenzyl N-[(benzyloxy){[(4S)-5-(benzyloxy)-4-{(4S)-5-(benzyloxy)-4- [(tert-butoxycarbonyl)amino1-5-oxopentanamido}-5-oxopentyl1oxy}phosphoryl1-L-qlutamate - Intermediate D

[0135] To 250g of intermediate C solubilized in dichloromethane, trifluoroacetic acid is added and the reaction mixture is stirred for at least 4 hours. Debocylation completion is controlled by HPLC with a limit for intermediate C below 2%.

[0136] Reaction mixture is concentrated under vacuum and the obtained residue diluted in ethyl acetate. In the first place, the solution is washed with a sodium hydrogen carbonate saturated aqueous solution and then with a sodium chloride saturated aqueous solution. The organic phase is concentrated under vacuum to obtain yellow oil.

[0137] 116g of Boc-Glu-Obn are solubilized in N,N-dimethylformamide. HBTU and triethylamine are added. After a few minutes the yellow oil obtained previously is added to the reaction mixture which is maintained under agitation for at least 2 hours.

[0138] The reaction mixture is then diluted in ethyl acetate and the organic phase washed successively with an acidic aqueous solution, water and sodium hydrogen carbonate saturated aqueous solution. The residual organic phase containing crude intermediate D is concentrated under vacuum. Crude intermediate D is dissolved in dichloromethane and purified using silica gel chromatography. The eluting solvents are n-heptane and ethyl acetate. The isolated intermediate D is then dried under vacuum to obtain a white to light yellow solid. Step 5: Synthesis of Dibenzyl N-[(benzyloxy)({(12S,17S)-17-[(benzyloxy)carbonyl1-12- [(benzyloxy)carbonyl1-3, 10, 15-trioxo-1 -phenyl-2-oxa-4, 11 ,16-triazaicosan-20- yl}oxy)phosphoryl1-L-qlutamate - Intermediate E

[0139] To 200g of intermediate D solubilized in dichloromethane, trifluoroacetic acid is added and the reaction mixture is stirred for at least 12 hours. Debocylation is controlled by HPLC with a limit for intermediate D below 8%.

[0140] Reaction mixture is concentrated under vacuum and the obtained residue diluted in ethyl acetate. In the first place the solution is washed with a sodium hydrogen carbonate saturated aqueous solution and then with a sodium chloride saturated aqueous solution. The organic phase is concentrated under vacuum to obtain yellow oil.

[0141] 52g of CBz-AH-acid is solubilized in N,N-dimethylformamide. HBTU and triethylamine are added. After a few minutes the yellow oil obtained previously is added to the reaction mixture which is stirred for at least 2 hours. End of peptide coupling is controlled by HPLC with a limit for the debocylated intermediate below 2%.

[0142] The reaction mixture is diluted in ethyl acetate and the organic phase washed successively with an acidic aqueous solution, water and sodium hydrogen carbonate saturated aqueous solution. The organic phase containing crude intermediate E is then concentrated under vacuum. Crude intermediate E is dissolved in dichloromethane and purified using silica gel chromatography. The eluting solvents are n-heptane and ethyl acetate. The fractions containing intermediate E are concentrated and dried under vacuum. The solid obtained is solubilized in dichloromethane and processed with activated charcoal. The solids are removed by filtration on cellulose and the filtrate is concentrated. A final crystallization in ethyl acetate is performed to obtain pure intermediate E (beige to yellow oil).

[0143] Step 6: Synthesis of Pentapotassium (3S,10S,15S)-22-amino-5-oxido-5,12,17-trioxo-6-oxa- 4,11 ,16-triaza-5A5-phosphadocosane-1 ,3,10,15-tetracarboxylate - CTT1298 (CAS = 1628718- 07-9)

[0144] To 45g of intermediate E solubilized in 2-methyltetrahydrofuran, purified water and potassium carbonate (2.5 equivalents) are added. The reaction mixture is purged from air before and after introduction of catalytical palladium on carbon paste (10% metal w / w). Then hydrogen is introduced at a pressure of 10±1 bar while stirring the reaction mixture. Hydrogenation lasts for at least 4 hours at ambient temperature. Reaction completion is controlled by NMR and HPLC with a limit for intermediate E below 1 %.

[0145] The reaction mixture is filtered and the crude is treated as follows. The solution is allowed to decant and the organic layer is discarded. The aqueous phase is washed with tetrahydrofuran, then concentrated under vacuum to remove organic solvents. The obtained aqueous residue is then treated with 3.2g of a metal scavenger (i.e. Dimercaptotriazine functionalized silica) The solution is filtered on 0.2pm and freeze dried. The obtained bulk material is stored in amber glass vials.

[0146] Nuclear magnetic resonance spectra were recorded on a AVANCE I Bruker spectrometer, using residual solvent peak for calibration.

[0147] 1H-NMR (300 MHz, MeOD / D2O (9 / 1 )) : 5 4.05-4.16 (m, 2H); 3.49 (m, 1 H), 3.69-3.75 (m, 2H), 2.94 (m, 2H), 2.38-1 .32 (m, 20H) Exchangable NH, NH2 were not visible

[0148] 13C-NMR (75 MHz, MeOD / D2O (9 / 1 )): 5 182.9; 181.4; 179.1 ; 178.3; 176.1 ; 174.9; 64.5; 56.7; 55.4; 54.7; 39.4; 35.4; 33.8; 32.2; 32.1 ; 28.3; 27.6; 27.0; 26.8; 25.1 ; 24.7

[0149] 31P-NMR (162 MHz, D2O): 5 7.4

[0150] The mass spectrometry (MS / MS) study has been performed on spectrometer Agilent 6230 on a sample content of 500 pg / mL solubilized in water.Calc for C21H32K5N4O10P = ; Exp = 774.9964 (potassium salt)

[0151] The purity of CTT1298 is checked by HPLC using the following method: Example 2 : Comparison of different conditions - Step 6

[0152] Intermediate E has been treated according to the above-mentioned process to provide CTT1298, with different conditions and at different scale in order to determine the influence of the solvent of the process on the purity of the obtained product. The results are summarized in the table 1 below.

[0153] Table 1

[0154] (1 ) After reprocessing with activated charcoal

[0155] The results show that the solvent has an important impact on the purity of the obtained product.

[0156] In the case where a substituted cyclic ether is used, the purity is drastically improved.

[0157] When THF is used, the purity of the product is not very high and it decreases with the scale of the reaction. In particular, it drops below 90% at a big scale if no further reprocessing is performed. On the contrary, when Me-THF is used, the purity is always above 95%, and even above 97%. Moreover, when Me-THF is used, it is easier to seperate the organic phase from the water phase during the liquid-liquid extraction. The good results of example 2c have been reproduced several times.

[0158] In the comparative examples, increasing the pressure to 10 bars with THF is expected to lead to even lower purity of the compound of formula (I), because, typically, higher pressure is increasing the reactivity of the reaction and would favor the formation of the side product.

Claims

Claims1 . A method for synthesizing a compound of formula (I),said method comprising a step of deprotecting a compound of formula (II)wherein PGi, PG2 and PG3 are each independently a protecting group, said deprotection being done by hydrogenation, in the presence of a metal-based catalyst, and in a solvent which is a substituted cyclic ether.

2. The method according to claim 1 , wherein the compound of formula (I) is more than90% pure, preferably more than 93% pure, and more preferably more than 95% pure, even more preferably more than 96%, 97%, 98%, or 99% pure.

3. The method according to claim 1 or 2, wherein the substituted cyclic ether solvent is selected from the group consisting of alkyl substituted tetrahydrofuran, alkyl substituted 1 ,4-dioxane, and mixtures thereof.

4. The method according to any of the preceding claims, wherein the substituted cyclic ether solvent is selected from the group consisting of 2-methyl tetrahydrofuran, 2,5- dimethyl tetrahydrofuran, 2-methyl-1 ,4-dioxane, 2,5-Dimethyl-1 ,4-dioxane, preferably the substituted cyclic ether solvent is 2 methyl THF.

5. The method according to any of the preceding claims, wherein said deprotection is performed using a base, preferably a carbonate or hydrogenocarbonate salt, more preferably K2CO3 or KHCO3.

6. The method according to any of the preceding claims wherein each of the protecting groups PG1 and PG3 is a benzyl group.

7. The method according to any of the preceding claims wherein the protecting group PG2 is a benzyl carbamate group.

8. The method according to any of the preceding claims, wherein the hydrogenation is performed using H2at a pressure between 1 and 20 bars, preferably between 5 and 15 bars, and more preferably between 8 and 12 bars.

9. The method according to any of the preceding claims, wherein the quantity of compound (II) is at least 1g.

10. The method according to any of the preceding claims, wherein the crude product obtained after hydrogenation is purified using the following steps: i) Filtration, ii) Liquid / liquid extraction, iii) Treatment with a metal scavenger, and iv) Microfiltration.

11. A compound of formula (I) obtainable by the method according to any of the preceding claims.

12. A compound of formula (I)which is more than 90% pure, preferably more than 93% pure, and more preferably more than95% pure, even more preferably more than 96%, 97%, 98%, or 99%.

13. The compound of formula (I) according to claim 12 which is free from the compound of formula (III)wherein X is H or a counterion X+.

14. A composition comprising a compound of formula (I) according to claim 12 or 13, and at least one carrier.

15. The compound of formula (I) according to any one of claims 12 to 14 for use in the production of a radiopharmaceutical product, preferably a radioligand product, more preferably, a radioligand imaging (RLI) agent, or a radioligand therapeutic (RLT) agent.

Images