Synthesis of compounds binding grpr

Abstract

Disclosed herein are methods of synthesizing compounds binding to GRPR. Additional compounds useful in such a synthesis are also disclosed.

Description

[0001] PAT059784-PCT-SEC01

[0002] SYNTHESIS OF COMPOUNDS BINDING GRPR

[0003] FIELD OF THE INVENTION

[0004] The present invention relates to synthesis of compounds binding GRPR. In particular, the synthesis of NeoB, which is useful for treating cancer.

[0005] BACKGROUND

[0006] Breast cancer is the most common cancer and the leading cause of cancer death for women worldwide. The global incidence is 85.8 to 91.6 cases per 100,000, whereas mortality rates range from 17.4 to 20.1 deaths per 100,000 (DeSantis et al. Breast cancer statistics, 2015: Convergence of incidence rates between black and white women. CA Cancer J Clin; 66(1):31-42 ; Hashim et al. The global decrease in cancer mortality: trends and disparities. Ann Oncol; 27(5):926-33 ; Torre et al. Global Cancer Incidence and Mortality Rates and Trends--An Update. Cancer Epidemiol Biomarkers Prev; 25(1 ):16-27; Heer et al. The incidence of breast cancer in Canada 1971-2015: trends in screening-eligible and young-onset age groups. Can J Public Health; 111 (5):787-793).

[0007] Despite progress in new treatment methods, there is still a need to provide improved clinical treatments of breast cancer. NeoB is a compound which can be complexed with a radionuclide to provide a therapeutic agent for the treatment of cancer. An efficient synthesis of NeoB would be important for supplying drugs to fight cancer.

[0008] SUMMARY

[0009] The disclosure provides a method of preparing a compound of formula (I) the method comprising a) synthesizing a compound of formula (II) PAT059784-PCT-SEC01 b) reacting the compound of formula (II) by additional synthetic steps to form a compound of formula (I); wherein polymer support; and

[0010] PG1is a protecting group for an amine of an amino acid.

[0011] DETAILED DESCRIPTION

[0012] The present disclosure relates to a method of synthesis of NeoB, with structure shown in formula (I).

[0013] The NeoB compound is a new generation bombesin analogue which binds to the GRPR with high affinity (half maximal inhibitory concentration (IC50) 1-2 nM, Nock et alJ. Nucl. Med. 2017; 58(1):75-80) and shows low internalization, consistent with the antagonistic behavior of the peptide. The NeoB compound contains in its structure a DOTA metal-chelator which allows for radiolabeling with different radionuclides including gallium-68 (for PET imaging), lutetium-177 (for radionuclide therapy) and other relevant radionuclides, which makes the theranostic use of NeoB possible, without affecting receptor affinity, internalization properties or biodistribution. In non-clinical models, [68Ga]Ga-NeoB and [177Lu]-Lu NeoB have shown high affinity to the GRPR which is overexpressed in breast, prostate, gastrointestinal stromal tumors (GIST) and gliomas (including glioblastoma) (Flores et al. 2010, supra, Morgat et al, J. Nucl. Mec / .2017;58(9):1401-1407), as well as low degree of internalization upon binding to the specific receptor.

[0014] The ability of the radiolabeled compound to target the GRPR expressing tumor has been confirmed in in vivo imaging and biodistribution studies in tumor models. [177Lu]Lu-NeoB is rapidly PAT059784-PCT-SEC01 cleared from the blood, quickly eliminated through the renal system, with no retention in kidneys. Background radioactivity is observed in GRPR-expressing tissues (mostly pancreas), which however decreases over time, consistently with a GRPR antagonist profile. On the contrary, tumor radioactivity is persistent, with detectable uptake values up to 7 days after injection.

[0015] In one aspect, the disclosure provides a method of preparing a compound of formula (I) the method comprising a) synthesizing a compound of formula (II) b) reacting the compound of formula (II) by additional synthetic steps to form a compound of formula (I); wherein polymer support; and

[0016] PG1is a protecting group for an amine of an amino acid.

[0017] In some embodiments, the compound of formula (II) is synthesized by the reaction of a compound of formula (III) with an activated polymer support of formula (IV) to form the compound of formula (II) PAT059784-PCT-SEC01

[0018] * indicates an activated polymer support.

[0019] In some embodiments, the activated polymer support is 2-chlorotrityl resin.

[0020] In some embodiments, the step b) reacting the compound of formula (II) comprises the following steps in order:

[0021] (i) reaction of the compound of formula (ll)to cleave PG1 , followed by peptide coupling with PG2-Gly-OH

[0022] (ii) reaction of the product of step (i) to cleave PG2, followed by peptide coupling with PG3- Val-OH

[0023] (iii) reaction of the product of step (ii) to cleave PG3, followed by peptide coupling with PG4- Ala-OH

[0024] (iv) reaction of the product of step (iii) to cleave PG4, followed by peptide coupling with PG5- Trp(PG6)-OH

[0025] (v) reaction of the product of step (iv) to cleave PG5, followed by peptide coupling with PG7- Gln(PG8)-OH

[0026] (vi) reaction of the product of step (v) to cleave PG7, followed by peptide coupling with PG9- D-Phe-OH to give a product of formula (V) wherein PG1, PG2, PG3, PG4, PG5, PG7and PG9are protecting groups for an amine of an amino acid;

[0027] PG6is a protecting group for the indole nitrogen of tryptophan; and

[0028] PG8is a protecting group for the side chain amide nitrogen of glutamine.

[0029] In some embodiments, the step b) reacting the compound of formula (II) comprises:

[0030] (vii) reacting a compound of formula (V) to cleave PG9, followed by coupling reaction with a compound of formula (VI) to give a compound of formula (VII) PAT059784-PCT-SEC01 wherein PG9is a protecting group for an amine of an amino acid, and PG10is a protecting group for an amine.

[0031] In some embodiments, the step b) reacting the compound of formula (II) comprises:

[0032] (viii) reacting a compound of formula (VII) to cleave PG10, followed by coupling reaction with a compound of formula (VIII) to give a compound of formula (IX) PAT059784-PCT-SEC01 wherein PG10is a protecting group for an amine of an amino acid and PG11is a protecting group for a carboxylic acid.

[0033] In some embodiments, the step b) reacting the compound of formula (II) comprises: (ix) reacting a compound of formula (IX) to remove the polymer support and remove protecting groups PG6, PG8, and PG11to give a compound of formula (I)

[0034] In some embodiments, each protecting group for an amine of an amino acid is independently selected from the group consisting of fluorenylmethyloxycarbonyl (Fmoc), tertbutoxycarbonyl (Boc), Trityl, and benzyloxycarbonyl (CBz).

[0035] In some embodiments, each protecting group for an amine of an amino acid is the same, for example Fmoc. PAT059784-PCT-SEC01

[0036] In some embodiments, PG6is Boc and / or PG8is trityl.

[0037] In some embodiments, PG10is selected from the group consisting of fluorenylmethyloxycarbonyl (Fmoc), tert-butoxycarbonyl (Boc), Trityl, and benzyloxycarbonyl (CBz), for example Fmoc.

[0038] In some embodiments, PG11is selected from the group consisting of tert-butyl, benzyl, para-methoxybenzyl, methyl, ethyl, and isopropyl, for example tert-butyl.

[0039] In some embodiments, the step b) reacting the compound of formula (II) comprises the step:

[0040] (ix) reacting a compound of formula (IX) to remove the polymer support and remove protecting groups PG6, PG8, and PG11to give a compound of formula (I), and wherein step (IX) is performed in a single pot reaction, for example wherein the polymer support, PG6, PG8, and PG11can all be cleaved by reaction with acid and step (ix) comprises reaction with acid, for example wherein the polymer support is trityl resin, PG6is Boc, PG8is trityl, and PG11is tert-butyl.

[0041] General Definitions

[0042] 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’.

[0043] 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 %.

[0044] The term "treating" or "treatment" as used herein comprises a treatment relieving, reducing or alleviating at least one symptom in a subject or effecting a delay of progression of a disease. For example, treatment can be the diminishment of one or several symptoms of a disorder or complete eradication of a disorder, such as cancer. Within the meaning of the present disclosure, the term "treat" also denotes to arrest, delay the onset (i.e., the period prior to clinical manifestation of a disease) and / or reduce the risk of developing or worsening a disease. As used herein in the context the disclosed combination therapy, the term “treatment” encompasses the administration of the radiopharmaceutical compound, optionally in combination with a CDK4 / 6 inhibitor and / or the PAT059784-PCT-SEC01 endocrine treatment. Such treatment may comprises one or more administrations of the radiopharmaceutical compound over a determined period.

[0045] As used herein “breast cancer” refers to the most common cancer and the leading cause of cancer death for women worldwide. The term breast cancer also includes its subtypes based on the presence or absence of the ER and progesterone receptor (PgR), and the expression and amplification of HER2: HR-positive (HR+; ER+, PgR+ and HER2-), HER2-positive (HER2+) and triple-negative (TN; ER-, PR- and HER2-).

[0046] As used herein the term “radiopharmaceutical” or “radiopharmaceutical compound” refers to a pharmaceutical compound which is labelled with a radionuclide element, typically of metallic nature. 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).

[0047] The terms “tumor” and “cancer” are used interchangeably herein, e.g., both terms encompass solid and liquid, e.g., diffuse or circulating, tumors. As used herein, the term “cancer” or “tumor” includes premalignant, as well as malignant cancers and tumors and benign cancers. The term "cancer" as used herein includes primary malignant cells or tumors (e.g., those whose cells have not migrated to sites in the subject's body other than the site of the original malignancy or tumor) and secondary malignant cells or tumors (e.g., those arising from metastasis, the migration of malignant cells or tumor cells to secondary sites that are different from the site of the original tumor).

[0048] As used herein, the phrase “therapeutically effective amount” of a compound refer to an amount of the compound that will elicit a desired therapeutic response in at least a sub-population of subjects, for example, ameliorate the symptoms, alleviate conditions, slow or delay disease progression, or prevent a disease, at a reasonable benefit / risk ratio applicable to any medical treatment.

[0049] The term "subject" or "patient" as used herein is intended to include animals, which are capable of suffering from or afflicted with a cancer or any disorder involving, directly or indirectly, a cancer. Examples of subjects include mammals, e.g., humans, apes, monkeys, dogs, cows, horses, pigs, sheep, goats, cats, mice, rabbits, rats, and transgenic non6WO 2021 / 171261 PCT / IB2021 / 051643 human animals. In an embodiment, the subject is a human, e.g., a human suffering from, at risk of suffering from, or potentially capable of suffering from cancers.

[0050] In the chemical formulae, the wavy line represents the attachment point of the moiety. PAT059784-PCT-SEC01

[0051] The radiopharmaceutical compound for use in the combination therapy of the disclosure

[0052] EXAMPLES

[0053] All starting materials were commercially available unless otherwise mentioned.

[0054] METHODS

[0055] NMR experiments were performed on a 500 MHz NMR spectrometer, at room temperature in DMSO-d6 solvent.

[0056] Mass spectrometry (MS) experiments were performed with a Thermoscientfic Orbitrap Exploris 240; Mass range m / z 150-2250; ion source ESI; Polarity: both, positive ion (V): 3500; Negative ion (V): 2500; vaporizer temperature :350 C; ion transfer tube temperature: 350 C; aux gas (Arb): 15; Sheath Gas (Arb): 40.

[0057] HPLC method:

[0058] Column: C18 1 .7 pm

[0059] Column Dimension: 2.1 x 100 mm

[0060] Column Temperature :80°C

[0061] Injection volume: 1 .00 pL

[0062] Flow rate: 0.5 mL / min

[0063] Gradient: hold 5% B for 0.2 min; from 5% to 98% B in 9.2 min

[0064] Eluent A: water + 0.05% TFA

[0065] Eluent B: acetonitrile + 0.04% TFA

[0066] Example 1 : Synthesis of NeoB

[0067] PAT059784-PCT-SEC01

[0068] Synthesis of dipeptide Fmoc-His-DMH

[0069] The synthesis of dipeptide (1a) is shown below: .

[0070] MW: 522.74 MW: 744.98

[0071] Fmoc protection PAT059784-PCT-SEC01

[0072] Intermediate 1c (5.07 g, 9.699 mmol, 1.0 eq) was dissolved in with DCM (50 ml), a clear colorless solution was obtained. To the mixture triethylamine (1.352 ml, 9.699 mmol, 1.0 eq) was added. The mixture was stirred for 5min and then Fmoc-NHS was added. (3.90 g, 11 .561 mmol, 1 .2 eq), the reaction mixture was stirred for 1 h, according to HPLC the reaction was complete. The reaction mixture was evaporated to dryness to obtain 1b as a white foam, (9.52g, purity 82.4%) the product was used without any purification in the next step.

[0073] Characterization of 1 b: HPLC (method 1) retention time (rt) 6.50 min; HRMS 745.4410 (M+H).

[0074] Trityl-Removal

[0075] Intermediate 1b (5.86 g, 7.866 mmol) was mixed with Trifluoroacetic acid (51 ml), triisopropylsilane (4 ml), and water (3 ml)). The thin brown Suspension was stirred for 1 h. Suspension turns light brown-beige after a few minutes. According to HPLC the reaction was complete in 1 h. The Reaction mixture was poured over to 200mL cooled (0°C) water, a suspension with heavy looking particles was obtained. Suspension left to stir for 30min and filtered of (Filtration 1 min 42sek), the filter cake was washed 2x with 50mL Water. And then dried under vacuum at 35°C until constant weight to obtain 1a (5.06g) according to HPLC the purity of 1a was 74% with main impurity to be residual amount of cleaved Trt.

[0076] Characterization of 1a: HPLC (method 1) rt 4.91 min; HRMS 503.3698.

[0077] Resin loading.

[0078] Note: The Reaction is done in a dried reactor under nitrogen at Room Temperature 20-25°C

[0079] In a 50mL dried SPPS Reactor 2-chlorotrityl chloride resin 2a (6.00 g, 9.6 mmol) was mixed with

[0080] DCM (Swelling) (50 ml, 777.138 mmol) and left to stir for 30min. The suspension was drained PAT059784-PCT-SEC01 under nitrogen pressure. To the resin a solution of 1a (4.918 g, 5.088 mmol), DIPEA (6.707 ml, 38.400 mmol) and DCM (35 ml) and was added, to the suspension was added a second portion of DIPEA (3.3 ml, 19.2 mmol) in 35 ml of DCM, the reaction mixture was stirred for 2h under nitrogen and then the solid phase reactor was drained and then to the resin was added 40 ml of a solution of DCM / MeOH / DIPEA 17:2:1 and stirred for 60min. The solid phase reactor was drained, and the resin was washed; 2 times with 50mL DCM; 2 times with 50mL DMF; 2 times with 50mL DCM; 3 times with 50mL isopropanol and 3 times with 50mL Diisopropylether. At the end of the washes, the resin was partially dried by passing nitrogen for 15min, the resin was then dried under vacuum at 35°C to yield 7.97 g of 3a. The Fmoc loading determination was 0.5 mmol / g (4.0 mmol, 80 % yield).

[0081] Solid Phase Peptide Synthesis

[0082] The SPPS process was executed in a 4 mmols scale (8 gx0.5 mmol / g). One coupling cycle is described, the rest of the cycles were performed following the same conditions (See table 1 below).

[0083] Table 1 : Conditions for SPPS PAT059784-PCT-SEC01

[0084] Example process of 2 Coupling (Coupling of Fmoc-Val-OH)

[0085] Coupling

[0086] In a separate flask 3.68g Fmoc-VAL-OH was mixed with 3.04g 0-(7-Azabenzotriazol-1-yl)- N,N,N',N'-tetramethyluronium-hexafluorophosphate HATU and all dissolved with 64mL Dimethylformamide. To the Solution 1.14g Diisopropylethylamine DIPEA was added, and yellow solution left for max. 10min at RT under stirring. The solution added to the peptide resin, the suspension was stirred for 3h. The completion of the reaction was monitored by Kaiser and TNBS tests. After the coupling reaction was complete the solid phase reactor was drained and the resin was washed 1X64 ml of DMF

[0087] Capping

[0088] To the resin was added 64ml of a solution of Acetic anhydride / Pyridine 1 :1 (VA / ), the suspension was stirred for 30min. Solution drained with Nitrogen pressure and Resin washed 4x64mL Dimethylformamide.

[0089] Fmoc cleavage

[0090] 64 ml of 25% 4-Methylpiperidine in Dimethylformamide Solution was added, the suspension was stirred for 5min, the solid phase reactor was drained and then as second portion of 64 ml of 25% 4- Methylpiperidine in Dimethylformamide solution was added and stirred for at least 15min, the solid phase reactor was drained and then the resin was washed 6 times with 64mL of DMF.

[0091] Next coupling started

[0092] Note: over the weekend a dry down process was performed after Fmoc removal by washing the Support 4x64mL Isopropanol and 4x64mL Diisopropylether drying for ca. 15min under nitrogen and overnight at 35°C under vacuum. Due to the 50% TFA Solution for IPC with MS Protecting PAT059784-PCT-SEC01 groups can be removed and Mass of product with and without protecting groups have to be looked for.

[0093] W = 13.91 g according to resin weight gain (14.34 g) a process the SPPS efficiency is 97% (Non corrected for content).

[0094] Cleavage and Global Deprotection (GD)

[0095] Peptide resin intermediate [27a] (11.45g, 3.2 mmol) was placed in solid phase reactor (SPR), then 60 ml of Dichloromethane was added, the suspension was stirred for 30min and then SPR was drained.

[0096] To the Resin 70mL of Cleavage Solution containing Trichloroacetic acid / Triisopropylsilane / Water 88 / 7 / 5 (V / V / V) was added and stirred for 4h, the reaction was monitored by HPLC. The SPR was drained and the peptide solution was added dropwise to a reactor with 210 ml of pre-cooled (0- 5°C) Diisopropylether, the suspension was filtered and the filter cake was washed with 2x60 ml of Diisopropylether and dried under vacuum at 35°C, after drying 5.83 g, of crude-NeoB was obtained, the reaction yield calculated as free base is 116%, this higher yield could be explained by the presence of TFA as counter ion. The purity of the crude NeoB was 70% and its identity was confirmed by mass spectrometry. PAT059784-PCT-SEC01

[0097] Characterization of crude NeoB: HPLC (method 1) rt 3.65 min; MS 1575.8.

[0098] Prep-HPLC purification and Lyophilization.

[0099] Crude NeoB is purified with gradient elution over Kromasil Cw 10um 100A reversed phase silica using water, acetonitrile and trifluoroacetic acid as mobile phases.

[0100] 505.9mg crude NeoB are dissolved in 27.5ml solvent A and 1 ml solvent B resulting in a turbid orange solution and passed over 0.2um Teflon syringe filter resulting in a transparent feed solution. Filtration rate is slow, and pressure needs to be exercised.

[0101] A 20x250mm column is slurry-packed and tracer-tested before use (N / L > 10000, 0.7 < T < 1 .3) and equilibrated with >= 5 column volumes of 98%vol Solvent A and 2% Solvent B. Feed solution is loaded on the column, and filter and the feed lines are purged with 10ml Solvent A. Gradient elution is performed with 18.9ml / min total flow according to a time program:

[0102] Composition of mobile phases is as follows:

[0103] Solvent A Solvent B

[0104] Purified Water in g 900 100

[0105] Acetonitrile in g 78.6 707.4

[0106] Trifluoroacetic acid in g 1 .49 1 .49 PAT059784-PCT-SEC01

[0107] Time / min % Vol Solvent B

[0108] 0 2

[0109] 5 2

[0110] 70 70

[0111] 71 100

[0112] 90 100

[0113] 91 2

[0114] 100 2

[0115] Fractions are collected according to UV signal, analyzed by HPLC, and pooled in Riches, Dilutes and Waste. Yield of HPLC step is estimated via weighted HPLC signals. Acetonitrile is stripped from the pooled Rich fractions in a Rotavapor (water bath at 35°C and final vacuum at 50mbar). Residue is frozen with dry ice and lyophilized in a flask. Resulting in 111 mg of NeoB, 111 mg of NeoB with a purity of 98.4 % was obtained, its identity was confirmed by mass spectrometry and by co-injection with a NeoB reference standard the efficiency of the purification process was 64%.

[0116] Characterization of neoB: HPLC rt 3.75; HRMS 1575.8289.

[0117] 1H NMR (500 MHz, DMSO-d6) 6 14.30 (br s, 2H), 13.61 - 11.72 (m, 2H), 10.76 (br s, 1 H), 9.96 (s, 1 H), 8.97 (d, J = 1 .2 Hz, 1 H), 8.90 (br s, 1 H), 8.43 (br d, J = 7.4 Hz, 1 H), 8.30 (br d, J = 7.8 Hz, 1 H), 8.23 (br t, J = 5.5 Hz, 1 H), 8.17 (br d, J = 8.3 Hz, 1 H), 8.05 (br d, J = 4.7 Hz, 2H), 7.68 (br d, J = 8.3 Hz, 2H), 7.62 (br d, J = 8.5 Hz, 5H), 7.60 - 7.54 (m, 5H), 7.34 - 7.28 (m, 5H), 7.28 - 7.23 (m, 9H), 7.22 - 7.16 (m, 3H), 7.17 - 7.12 (m, 1 H), 7.22 - 7.11 (m, 1 H), 7.03 (t, J = 7.0 Hz, 1 H), 6.95 (t, J = 7.1 Hz, 1 H), 6.77 (br s, 1 H), 4.65 - 4.57 (m, 1 H), 4.56 - 4.51 (m, 1 H), 4.57 - 4.48 (m, 1 H), 4.36 (quin, J = 7.1 Hz, 3H), 4.30 (br d, J = 5.2 Hz, 5H), 4.22 - 4.16 (m, 1 H), 4.14 (br dd, J = 8.1 , 6.6 Hz, 2H), 4.09 - 4.01 (m, 3H), 4.07 - 4.01 (m, 1 H), 3.97 (br dd, J = 15.2, 5.6 Hz, 3H), 3.97 - 3.92 (m, 2H), 3.87 - 3.77 (m, 10H), 3.77 - 3.65 (m, 18H), 3.62 (br s, 4H), 3.35 (br s, 9H), 3.19 - 3.06 (m, 21 H), 3.02 (br dd, J = 13.7, 4.9 Hz, 4H), 2.99 - 2.83 (m, 7H), 2.07 (s, 1 H), 1 .99 - 1 .97 (m, 1 H), 2.03 - 1 .91 (m, 2H), 1 .88 - 1 .78 (m, 1 H), 1 .69 - 1 .60 (m, 1 H), 1 .56 - 1 .45 (m, 1 H), 1 .35 - 1 .22 (m, 3H), 1 .22 - 1 .17 (m, 4H), 1 .15 - 1 .05 (m, 2H), 1 .05 - 1 .02 (m, 1 H), 0.85 (brt, J = 6.3 Hz, 5H), 0.85 - 0.72 (m, 15H). PAT059784-PCT-SEC01

[0118] Conclusions

[0119] • A new synthetic strategy for the production of NeoB has been developed

[0120] • The side chain attachment was performed on the amino acid Histidine (His)

[0121] • The side attachment avoids the need of fragment condensation in solution, this means that the new synthesis uses just solid phase synthesis.

[0122] • The new process gave an excellent overall yield 51%. This yield could be further improved with process development.

Claims

PAT059784-PCT-SEC01CLAIMSWhat is claimed is:1 . A method of preparing a compound of formula (I)the method comprising a) synthesizing a compound of formula (II)b) reacting the compound of formula (II) by additional synthetic steps to form a compound of formula (I); whereinpolymer support; andPG1is a protecting group for an amine of an amino acid.

2. The method of claim 1 , wherein the compound of formula (II) is synthesized by the reaction of a compound of formula (III) with an activated polymer support of formula (IV) to form the compound of formula (II)PAT059784-PCT-SEC01*indicates an activated polymer support.

3. The method of claim 1 or 2, wherein the activated polymer support is 2-ch lorotrityl resin.

4. The method of any one of claims 1-3, wherein the step b) reacting the compound of formula (II) comprises the following steps in order:(i) reaction of the compound of formula (ll)to cleave PG1 , followed by peptide coupling with PG2-Gly-OH(ii) reaction of the product of step (i) to cleave PG2, followed by peptide coupling with PG3- Val-OH(iii) reaction of the product of step (ii) to cleave PG3, followed by peptide coupling with PG4- Ala-OH(iv) reaction of the product of step (iii) to cleave PG4, followed by peptide coupling with PG5- Trp(PG6)-OH(v) reaction of the product of step (iv) to cleave PG5, followed by peptide coupling with PG7- Gln(PG8)-OH(vi) reaction of the product of step (v) to cleave PG7, followed by peptide coupling with PG9- D-Phe-OH to give a product of formula (V)wherein PG1, PG2, PG3, PG4, PG5, PG7and PG9are protecting groups for an amine of an amino acid;PG6is a protecting group for the indole nitrogen of tryptophan; andPG8is a protecting group for the side chain amide nitrogen of glutamine.

5. The method of any one of claims 1-4, wherein the step b) reacting the compound of formula (II) comprises:(vii) reacting a compound of formula (V) to cleave PG9, followed by coupling reaction with a compound of formula (VI) to give a compound of formula (VII)PAT059784-PCT-SEC01wherein PG9is a protecting group for an amine of an amino acid, and PG10is a protecting group for an amine.

6. The method of any one of claims 1 -5, wherein the step b) reacting the compound of formula (II) comprises:(viii) reacting a compound of formula (VII) to cleave PG10, followed by coupling reaction with a compound of formula (VIII) to give a compound of formula (IX)PAT059784-PCT-SEC01wherein PG10is a protecting group for an amine of an amino acid and PG11is a protecting group for a carboxylic acid.

7. The method of any one of claims 1 -6, wherein the step b) reacting the compound of formula (II) comprises:(ix) reacting a compound of formula (IX) to remove the polymer support and remove protecting groups PG6, PG8, and PG11to give a compound of formula (I)8. The method of any one of claims 1 -7 wherein each protecting group for an amine of an amino acid is independently selected from the group consisting of fluorenylmethyloxycarbonyl (Fmoc), tert-butoxycarbonyl (Boc), Trityl, and benzyloxycarbonyl (CBz).

9. The method of claim 8, wherein each protecting group for an amine of an amino acid is the same, for example Fmoc.PAT059784-PCT-SEC0110. The method of any one of claims 4-9, wherein PG6is Boc and / or PG8is trityl.11 . The method of any one of claims 5-10, wherein PG10is selected from the group consisting of fluorenylmethyloxycarbonyl (Fmoc), tert-butoxycarbonyl (Boc), Trityl, and benzyloxycarbonyl (CBz), for example Fmoc.

12. The method of any one of claims 6-11 , wherein PG11is selected from the group consisting of tert-butyl, benzyl, para-methoxybenzyl, methyl, ethyl, and isopropyl, for example tert-butyl.

13. The method of any one of claims 7-12, wherein the step b) reacting the compound of formula (II) comprises the step:(ix) reacting a compound of formula (IX) to remove the polymer support and remove protecting groups PG6, PG8, and PG11to give a compound of formula (I), and wherein step (IX) is performed in a single pot reaction, for example wherein the polymer support, PG6, PG8, and PG11can all be cleaved by reaction with acid and step (ix) comprises reaction with acid, for example wherein the polymer support is trityl resin, PG6is Boc, PG8is trityl, and PG11is tert-butyl.

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