Method for synthesizing melphalan

Abstract

The present invention relates to a method for producing melphalan (4-[bis(2-5 chloroethyl)amino]-L-phenylalanine) of formula (I), which comprises protecting the carboxy and amino groups of the amino acid group of 4-amino-L-phenylalanine by converting the aromatic amino group of the 4-amino-L-phenylalanine to a compound of formula: -N(CHCHOS(O) n O - ) group (where n is 1 or 2), followed by reaction with a reagent capable of converting the group to —N(CHCHOS(O) n O - The present invention also provides novel intermediates useful in the preparation of melphalan. TIFF2023508071000033.tif53165

Description

[Technical Field]

[0001] FIELD OF THE INVENTION The present invention relates to a synthetic method for preparing melphalan (4-[bis(2-chloroethyl)amino]-L-phenylarnine), currently commercially available as the hydrochloride salt under the name Alkera™. [Background technology]

[0002] Background of the Invention Melphalan, having formula (I), is a chemotherapeutic agent belonging to the group of nitrogen mustard alkylating agents. It inhibits DNA replication by alkylating DNA guanine bases and forming stable bonds between two DNA strands. Melphalan can be used to treat various tumors, including multiple myeloma, ovarian cancer, and amyloidosis. Melphalan is also used in pediatrics for the treatment of retinoblastoma.

[0003] [ka]

[0004] U.S. Pat. No. 3,032,584, assigned to the National Institute of Research and Development, relates to a method for preparing melphalan, which comprises heating a compound of the following formula with a chlorinating agent selected from the group consisting of phosphorus oxychloride (POCl) and thionyl chloride (SOCl):

[0005] [ka]

[0006] where R1 is hydrogen or -COOC2H5, R2 is hydrogen, R3 is a -CHO group or a -CH3CO group, and R2 and R3 together represent a group of the formula:

[0007] [ka]

[0008] Compounds of the general formula:

[0009] [ka]

[0010] It is prepared by reacting a compound of the formula: with ethylene oxide:

[0011] [ka]

[0012] In particular, U.S. Pat. No. 3,032,584 illustrates a method for the synthesis of melphalan, which includes: a) In the presence of nitric acid and sulfuric acid, D,L-phenylalanine of the formula:

[0013] [ka]

[0014] Nitration of the compound of formula (I) provides p-nitro-D,L-phenylalanine of formula (II):

[0015] [ka]

[0016] b) Esterification of p-nitro-D,L-phenylalanine with phthalic anhydride to provide N-phthaloyl-p-nitrophenylalanine of the formula:

[0017] [ka]

[0018] c) Esterification of the carboxylic acid group of N-phthaloyl-p-nitrophenylalanine with ethanol to provide ethyl-N-phthaloyl-p-nitrophenylalanine of the formula:

[0019] [ka]

[0020] d) Hydrogenation of the nitro group of ethyl-N-phthaloyl-p-nitrophenylalanine to provide ethyl-N-phthaloyl-p-aminophenylalanine of the formula:

[0021] [ka]

[0022] e) Reaction of ethyl-N-phthaloyl-p-aminophenylalanine with ethylene oxide to provide ethyl-N-phthaloyl-p-bis-(2-hydroxyethyl)-aminophenylalaninate of the formula:

[0023] [ka]

[0024] f) Chlorination of the -OH group of ethyl-N-phthaloyl-p-bis-(2-hydroxyethyl)-aminophenylalaninate with POCl to provide ethyl-N-phthaloyl-p-bis-(2-chloroethyl)-aminophenylalaninate of the formula:

[0025] [ka]

[0026] g) Ethyl-N-phthaloyl-p-bis-(2-chloroethyl)-aminophenylalaninate is treated with concentrated hydrochloric acid, followed by removal of the protecting group with saturated sodium acetate solution to give (S)-melphalan (I) (L enantiomer) as the hydrochloride salt (monohydrochloride).

[0027] U.S. Pat. No. 3,032,585, assigned to the National Institute of Research and Development, relates to an improvement over the method disclosed in U.S. Pat. No. 3,032,584, in which the improvement is the optical resolution of N-acetyl-p-nitro-D,L-phenylalanine using brucine or p-nitro-N-phthaloyl-D,L-phenylalanine using cinchonidine to obtain N-acetyl-p-nitro-L-phenylalanine and p-nitro-N-phthaloyl-L-phenylalanine, respectively, and presents synthetic steps similar to those disclosed in U.S. Pat. No. 3,032,584.

[0028] China Patent Application Publication No. 101100440, assigned to Zhuzhou Municipal De Chemical Co., Ltd., discloses a method for preparing melphalan starting from (S)-4-nitro-phenylalanine ethyl ester whose amino group is protected as tert-butyl carbamate; after the protection reaction, the method follows the same method as disclosed in U.S. Pat. No. 3,032,585, with the only difference being that the concentration of hydrochloric acid in the final deprotection reaction of the amino and carboxy moieties is in the range of 2M-6M instead of 12M.

[0029] WO 2009 / 117164, assigned to Navinta LLC, discloses a method comprising hydroxyethylation of the amino group on the phenyl ring of a protected p-aminophenylalanine of the formula:

[0030] [ka]

[0031] Here, R1 is hydrogen or a C1-C6 straight or branched alkyl chain, provided that the amino group of the amino acid moiety (glycine NH2) does not need to be protected. Summary of the Invention [Problem to be solved by the invention]

[0032] Thus, known methods for the synthesis of melphalan require a hydroxyethylation step of p-amino-L-phenylalanine, either in protected or free form. Such a step is carried out using ethylene oxide as the alkylating agent, but ethylene oxide is a gas and poses safety concerns, especially when used on an industrial scale.

[0033] Therefore, there remains a felt need to provide a method for the synthesis of melphalan that does not require the use of ethylene oxide. [Means for solving the problem]

[0034] Description of the Invention Applicants have found that melphalan (I) can be advantageously synthesized in the optically pure L-isomer via a process involving regiospecific bisulfate-alkylation of the aromatic amino group of 4-amino-L-phenylalanine. Thus, in a first aspect, the present invention provides melphalan (I):

[0035] [ka]

[0036] In the synthesis method of the compound of the present invention, the aromatic amino group of 4-amino-L-phenylalanine in which the carboxyl group and the amino group of the amino acid group are protected is converted into a compound of the following formula: -N(CHCHOS(O) n O - ) group (where n is 1 or 2), followed by reaction with a reagent capable of converting the group to —N(CHCHOS(O) n O -)2 group to a -N(CH2CH2Cl)2 group. DETAILED DESCRIPTION OF THE INVENTION

[0037] More specifically, the method of the present invention comprises the following steps: a) reaction of a protected 4-amino-L-phenylalanine of formula (II) with 1,3,2-dioxathiolane-2,2-dioxide (also called "ethylene sulfate") of formula (IIIa) or with 1,3,2-dioxathiolane-2-oxide (also called ethylene sulfite) of formula (IIIb):

[0038] [ka]

[0039] wherein R1 is a carboxy protecting group, one of R2 and R3 is hydrogen and the other is an amino protecting group, or R2 and R3 together form an amino protecting group with the nitrogen atom to which they are attached.

[0040] [ka]

[0041] The reaction is carried out in the presence of an inorganic base, preferably a carbonate or bicarbonate, more preferably NaHCO, KHCO, or CsCO, to provide the protected 4-(bis-(2-ethylsulfite)-amino-L-phenylalanine or protected 4-(bis-(2-ethylsulfite)-amino-L-phenylalanine of formula (IV).

[0042] [ka]

[0043] where R1, R2 and R3 are as defined above and X is OS(O) n O -where n is as defined above and M + or M 2+ is a metal cation, preferably Na + , K. + or Cs + ;Mg 2+ or Ca 2+ , more preferably Na + , K. + or Cs + , and even more preferably Na + is.

[0044] b) Substituting the sulfate or sulfite group, X, of compound (IV) with a chloride to provide the protected melphalan of formula (V).

[0045] [ka]

[0046] where R1, R2 and R3 are as defined above. c) Removal of the protecting groups R1-R3 to provide melphalan (I).

[0047] Preferably, R1 is a straight or branched lower alkyl group, more preferably a straight or branched C1-C6 alkyl group, more preferably ethyl. In one embodiment, R2 is hydrogen and R3 is a group of formula R4-C(O)-, where R4 is hydrogen or a straight or branched lower alkyl group, preferably a straight or branched C1-C6 alkyl group. In another embodiment, R2 and R3 together with the nitrogen atom to which they are attached represent a group of formula:

[0048] [ka]

[0049] In a preferred embodiment of the invention, R1 is ethyl and R2 and R3 together with the nitrogen atom to which they are attached form a group of formula (VI) as defined above. In a preferred embodiment, the protected 4-amino-L-phenylalanine of formula (II) is reacted with 1,3,2-dioxathiolane-2,2-dioxide (IIIa). The protected 4-amino-L-phenylalanine (II) can be obtained according to methods known in the art, in particular the compound of formula (IIa):

[0050] [ka]

[0051] The compound can be obtained by nitration and esterification reactions as disclosed in Bixue Xu & C., Bioorganic & Medicinal Chemistry, 17, (2009), 3118-3125, and by protection of the glycine nitrogen as disclosed in Tetrahedron Asymmetry, 22, Issue 2, (2011) 185-189.

[0052] Step a) is a linear or branched C5-C 10 Hydrocarbons, straight-chain or branched halogenated C1-C6 hydrocarbons, linear or cyclic C3-C 14 The reaction can be carried out in an organic solvent selected from ethers or C4-C6 esters, C2-C3 nitriles, dimethylformamide (DMF), dimethylacetamide (DMA), and dimethyl sulfoxide (DMSO). Preferably, the reaction is carried out in dichloromethane (DCM) or acetonitrile (ACN) at room temperature (25°C). At the end of the reaction, the solvent is evaporated and the residue is recovered with an alcohol, preferably ethanol, to obtain chemically and optically pure compound (IV).

[0053] Compounds of general formula (IV) and their use as intermediates for the synthesis of melphalan represent further aspects of the present invention. Particularly preferred compounds of formula (IV) are those in which R1 is ethyl, R2 and R3 together with the nitrogen atom to which they are attached represent a group of formula (VI) as defined above, and X is -OS(O)2O -and M + and M 2+ is compound (IVa) which is as defined above:

[0054] [ka]

[0055] Step b) can be carried out in two different ways. In a first embodiment [hereinafter "Embodiment A"], a compound of formula (IV), preferably protected 4-(bis-(2-ethylsulfate)-amino-L-phenylalanine (IVa), is first reacted with an inorganic chloride source, such as LiCl, NaCl, KCl, CaCl 2, MgCl or BaCl, preferably CaCl, MgCl or BaCl, even more preferably BaCl or CaCl, to give the protected 4-(bis-(2-chloroethyl)-amino-L-phenylalanine) of formula (V) as defined above, followed by crystallization, if desired, in a suitable solvent. The reaction with the inorganic chloride source is carried out in an organic solvent / water mixture, where the organic solvent is typically selected from ethyl acetate, dimethylformamide, and mixtures of water with tetrahydrofuran, methyltetrahydrofuran, acetonitrile, or alcohols, at a temperature typically in the range of 20° C. to 60° C., preferably at room temperature.

[0056] Then, in step c), the protected 4-(bis-(2-chloroethyl)-amino-L-phenylalanine (V) is treated with an acid of pH<1 in water at a temperature in the range of 85-115°C, preferably 110°C, to provide an acidic aqueous solution containing melphalan (I) bis-hydrochloride. The acid can be inorganic or organic and is typically selected from hydrochloric acid, sulfuric acid, citric acid, methanesulfonic acid, toluenesulfonic acid, acetic acid, perchloric acid, or mixtures thereof. Finally, melphalan can be crystallized by increasing the pH of the acidic aqueous solution; preferably, melphalan is crystallized as the hydrochloride salt (monohydrochloride) by increasing the pH to a value in the range of 5 to about 8.5, preferably 7.5 to 8.5. The pH increase can be achieved using an organic or inorganic base, typically an organic amine or ammonia; according to a preferred embodiment, the base is ammonia.

[0057] In a second embodiment (hereinafter "embodiment B"), step b) is carried out as follows: First, a compound of formula (IV), preferably protected 4-(bis-(2-ethylsulfate)amino-L-phenylalanine (IVa), is desulfated using absolute ethanol and sulfuric acid, thereby obtaining protected 4-(bis-(2-hydroxyethyl)amino-L-phenylalanine of formula (VII):

[0058] [ka]

[0059] wherein R1, R2, and R3 are as defined above, optionally followed by crystallization in a suitable solvent. The reaction is typically carried out at a temperature in the range of 70-90°C, preferably 80°C, using an amount of sulfuric acid in the range of 0.4-2 equivalents relative to the protected 4-(bis-(2-ethylsulfate)-amino-L-phenylalanine (IVa).

[0060] The resulting protected 4-(bis-(2-hydroxyethyl)-amino-L-phenylalanine (VII) is then reacted with POCl or SOCl to provide the compound of formula (V), which is subjected to step c) as exemplified above. The reaction with POCl or SOCl is carried out in an organic solvent which may be selected from toluene and halogenated hydrocarbons, preferably dichloromethylene or trichloromethylene, at a temperature ranging from room temperature to 110° C. Preferably, the solvent is toluene and the reaction temperature is room temperature.

[0061] Therefore, the method of the present invention is advantageous because it avoids the use of ethylene oxide. Specifically, with regard to the use of 1,3,2-dioxathiolane-2,2-dioxide (IIIa), the first advantage is due to the use of 1,3,2-dioxathiolane-2,2-dioxide (IIIa) to carry out the bis-alkylation of protected 4-amino-L-phenylalanine (II). In fact, 1,3,2-dioxathiolane-2,2-dioxide (IIIa) can be used in a significantly lower amount relative to ethylene oxide (approximately 2.05 eq relative to protected 4-amino-L-phenylalanine (II) compared to approximately 40 eq of ethylene oxide required to carry out the same reaction). 1,3,2-dioxathiolane-2,2-dioxide (IIIa) can be used in a stoichiometric amount relative to protected 4-amino-L-phenylalanine (II) and is completely decomposed in the reaction. It should also be understood that 1,3,2-dioxathiolane-2,2-dioxide (IIIa) is cheaper than ethylene oxide and is not included in the list of toxic gases. Furthermore, alkylation with 1,3,2-dioxathiolane-2,2-dioxide (IIIa) contemplates the use of organic solvents, which do not promote hydrolysis of the protecting groups on the amino and carboxyl groups of the amino acid moiety.

[0062] The second advantage relates in particular to step b), embodiment A. Indeed, the use of inorganic chlorides as chlorinating agents to carry out the chlorination of 4-(bis-(2-ethylsulfate)-amino-L-phenylalanine (IVa) avoids the use of SOCl or POCl and, therefore, the need to quench the release of hydrochloric acid and its reaction with organic bases, which often leads to the production of toxic gases such as SO. When inorganic chlorides are used, the waste product of the chlorination reaction is inorganic sulfate, which has low toxicity; moreover, inorganic sulfate is sparingly soluble and can be removed from the reaction mixture by simple filtration. [Example]

[0063] The invention is explained in more detail in the experimental part below. Experimental Department Commercially available reagents and solvents of the following purity were used: - L-phenylalanine (purity >99%); - Concentrated nitric acid (≧65%); - concentrated sulfuric acid (≥96%); - Sodium hydroxide (purity >99%); - Absolute ethanol (GC purity >99%); - Thionyl chloride (purity >98%); - Ethanol (GC purity ≥ 95%), (industrial grade); - N-carbethoxyphthalimide (purity ≥ 96%); - acetonitrile (purity ≥ 98%); - Anhydrous cesium carbonate (purity ≥ 96%); - 10% w / w Pd on activated carbon; - Ethyl acetate (GC purity >95%), (technical grade); - 1,3,2-dioxathiolane 2,2-dioxide (purity ≥ 95%); - dichloromethane (amil. stab. purity ≥ 98%); - sodium bicarbonate (purity ≥ 95%); - barium chloride dihydrate (purity ≥ 99%); - Sodium chloride (purity ≥ 95%), (industrial grade); - HCl 37%, commercially available; - Hydrogen was generated on-site using a hydrogen generator.

[0064] Reference example - Synthesis of N-phthalimido-4-amino-L-phenylalanine ethyl ester (IIa)

[0065] Example 1 4-Nitro-L-phenylalanine monohydrate [Synthesized according to Bixue Xu & C. Bioorganic & Medicinal Chemistry 17 (2009) 3118-3125] L-Phenylalanine monohydrate (50 g, 302.7 mmol) was dissolved in 85% v / v H2SO4 (150 mL) and cooled to 10 °C. The resulting solution was added dropwise with stirring to a mixture of concentrated HNO3 and concentrated H2SO4 (76.5 mL, 1.4 / 1.1 vol / vol) (prepared and cooled to room temperature). The resulting reaction solution was stirred at room temperature for 5 h, then the pH was adjusted to 2-3 with 40% NaOH, and the resulting precipitate was collected by filtration. The wet precipitate was recrystallized from 700 mL of water to give 4-nitro-L-phenylalanine monohydrate as a pale yellow powder (65.9 g, 95%).

[0066] Example 2 4-Nitro-L-phenylalanine ethyl ester hydrochloride [Synthesized according to Bixue Xu &C. Bioorganic & Medicinal Chemistry 17 (2009) 3118-3125] 4-Nitro-L-phenylalanine (65.9 g, 287.8 mmol) was suspended in 300 mL of absolute ethanol and cooled to 0° C. The resulting mixture was stirred for 10 minutes. Thionyl chloride (91.5 mL, 149.9 g, 4.4 eq) was slowly added dropwise to the reaction mixture with stirring, maintaining the internal temperature below 10° C. After the addition was complete, the resulting mixture was heated at 80° C. for 4 hours, then concentrated to 50 mL, and ethyl ether (250 mL) was slowly added at room temperature to give a white precipitate, which was collected by filtration and dried (70.4 g, 95%).

[0067] Example 3 N-phthalimido-4-nitro-L-phenylalanine ethyl ester [This synthesis was carried out according to the procedure disclosed in Tetrahedron Asymmetry, 22, Issue 2, (2011) 185-189, with the difference that the reaction solvent was acetonitrile instead of water and the inorganic base was cesium carbonate instead of sodium carbonate.] 4-Nitro-L-phenylalanine ethyl ester hydrochloride (60 g, 234.4 mmol) was suspended in 420 mL of acetonitrile with stirring at room temperature, and then anhydrous CsCO (2.0 eq, 152.7 g) was added to the suspension. A solution of N-carbethoxyphthalimide (53.9 g, 1.05 eq) in 240 mL of acetonitrile was added over 15 min, and the resulting reaction mixture was heated at 40 °C for 24 h. The reaction mixture was filtered on a sintered glass filter, and the cake was washed with 500 mL of acetonitrile. The mother liquor was concentrated to dryness, and a yellow oily residue was crystallized by adding methanol (5 vol / dried residue). The resulting suspension was cooled to 0 °C for 1 h and filtered. The wet product was dried under full vacuum at 35 °C for 18 h (yield: 61.5 g, 75%).

[0068] Example 4 N-phthalimido-4-nitro-L-phenylalanine ethyl ester 4-Nitro-L-phenylalanine ethyl ester hydrochloride (60 g, 234.4 mmoL) was suspended in 480 mL of 2-methyl-THF with stirring at room temperature, and then aqueous KHCO3 solution (10% w / V; 260 mL, 1 M) was added to the suspension with stirring. The phases were allowed to separate and the aqueous phase was removed. N-carbethoxyphthalimide (51.3 g, 1.0 eq) was added and the resulting reaction mixture was heated at 55° C. for 6 hours. After 6 hours, the temperature was lowered to 20±5° C. and triethylamine (8.17 mL; 58.6 mmol) was added to the reaction mixture (stirred for 6 hours). The reaction mixture was washed with 1 M HCl (260 mL) and brine (260 mL). The resulting solution was used directly in the preparation of N-phthalimido-4-amino-L-phenylalanine ethyl ester (IIa) - Example 6.

[0069] Example 5 N-phthalimido-4-amino-L-phenylalanine ethyl ester (IIa) N-phthalimido-4-nitro-L-phenylalanine ethyl ester (50 g, 142.8 mmol) was dissolved in ethyl acetate (500 mL) with stirring at room temperature. Once dissolution was complete, 10% Pd on activated carbon (2 g, 13% mol) was added, and the mixture was stirred at room temperature under a hydrogen atmosphere (0.4 bar) for 3 hours. Upon completion of the reaction, the catalyst was filtered off, and the solution was concentrated to dryness. The resulting crude product (46.3 g, 100%) was used in further synthetic steps without further purification.

[0070] Example 6 N-phthalimido-4-amino-L-phenylalanine ethyl ester (IIa) N-phthalimido-4-nitro-L-phenylalanine ethyl ester (solution obtained in Example 4) was kept stirring at room temperature. Ammonium formate / phosphate buffer solution (ammonium formate: 73.7 g; 85% phosphoric acid: 22.3 mL in 260 mL water) was added to the mixture along with 10% Pd on activated carbon (4 g). The mixture was stirred at 85°C for 4.5 hours. After the reaction was complete, the catalyst was filtered off and the phases were separated. The organic phase was concentrated to dryness and the crude product was recrystallized from isopropanol (7 v / w at -10°C). Yield 94.6%; 52.13 g.

[0071] Examples according to the present invention Example 7 [Step a)] - N-phthalimido-4-(bis-2-ethylsulfate)amino-L-phenylalanine ethyl ester (IVa) N-phthalimido-4-amino-L-phenylalanine ethyl ester (IVa) (45 g, 138.9 mmol) was suspended in 315 mL of dichloromethane (DCM) or acetonitrile (ACN), and sodium bicarbonate (23.9 g; 284.7 mmol) was added to the suspension in portions at room temperature (RT). 1,3,2-Dioxathiolane 2,2-dioxide (IIIa) (43.1 g; 347.3 mmol) was dissolved in DCM (135 mL) and slowly added to the reaction mixture (1 h). The resulting reaction mixture was stirred at RT for 18 h. After completion of the reaction, DCM was evaporated under vacuum and replaced with absolute ethanol (450 mL). The solid precipitate was collected by filtration under a nitrogen atmosphere and dried at 40 °C for 24 h (yield: 77.0 g; 90%).

[0072] Example 8 [Step b), Embodiment A] - N-phthalimido-4-(bis-2-chloroethyl)amino-L-phenylalanine ethyl ester N-phthalimido-4-(bis-2-ethylsulfate)-amino-L-phenylalanine (70 g; 113.6 mmol) was suspended at RT in ethyl acetate (700 mL) pre-saturated with water, followed by the addition of dimethylformamide (35 mL). The mixture was stirred at RT for 20 min, and then barium chloride dihydrate (83.2 g; 340.8 mmol) was added in two successive portions (5 min). The reaction was stirred at RT for 18 h and then filtered on a sintered glass filter to remove the solid sulfate. The ethyl acetate organic phase was washed twice with brine (2 × 200 mL) and dried under vacuum. Yield: 46.8 g; 92%.

[0073] Example 9 [Step b), Embodiment A] - N-phthalimido-4-(bis-2-chloroethyl)amino-L-phenylalanine ethyl ester N-phthalimido-4-(bis-2-ethylsulfate)-amino-L-phenylalanine (70 g; 113.6 mmol) was suspended in acetonitrile (700 mL). Anhydrous calcium chloride was added, and the mixture was stirred at 60° C. for 13 hours, then filtered over a sintered glass filter to remove the solid sulfate. The solvent was removed under vacuum. Yield: 49.8 g; 98%.

[0074] Example 10 [Step b), Embodiment B] - N-phthalimido-4-(bis-2-hydroxyethyl)amino-L-phenylalanine ethyl ester (Va) N-phthalimido-4-(bis-2-ethylsulfate)-amino-L-phenylalanine (70 g; 113.6 mmol) was suspended in absolute ethanol (700 mL) at room temperature. Concentrated H2SO4 (12.1 mL; 227.2 mmol) was slowly added dropwise to the reaction mixture with stirring. After the addition was complete, the mixture was heated at 80 °C for 1 h. The ethanol was evaporated under vacuum, and the oily residue was dissolved in methylene chloride (300 mL). The resulting organic solution was washed twice with 5% w / vol sodium bicarbonate solution, dried over magnesium sulfate, and evaporated to dryness under vacuum. The oily residue was recrystallized from ethyl acetate (yield 45.9 g; 98%).

[0075] Example 11 [Step c, embodiment B] N-phthalimido-4-(bis-2-hydroxyethyl)amino-L-phenylalanine ethyl ester (Va) to N-phthalimido-4-(bis-2-chloroethyl)amino-L-phenylalanine ethyl ester (VIIa) N-phthalimido-4-(bis-2-hydroxyethyl)amino-L-phenylalanine ethyl ester (Va) (50 g, 121.4 mmol) was dissolved in toluene (500 mL). Freshly distilled POCI3 (37.2 g; 22.7 mL, 242.8 mmol) was added slowly (1 h) to the reaction mixture at RT. The reaction was heated at 110 °C for 1 h, and then the solvent was removed under vacuum (yield: 48.9 g; 90%).

[0076] Example 12 [Step c] - Melphalan (I) hydrochloride N-phthalimido-4-(bis-2-chloroethyl)amino-L-phenylalanine ethyl ester (VIIa) (50 g; 111.6 mmol) was dissolved in 37% w / w hydrochloric acid (200 mL) and then heated under reflux for 24 h. The reaction mixture was cooled to room temperature and stirred at 20–25 °C for 8 h. The solid residue (phthalic acid) was removed by filtration, and ammonia solution (33% w / w, 16.1 M) was added to the mother liquor at 0 °C until a pH in the range of 8.0–8.4 was reached. The resulting solid melphalan was filtered, redissolved in 1 M HCl (120 mL) at 0 °C, and then treated with 1 M ammonia until a pH in the range of 8.0–8.4 was reached. The solid precipitate was filtered and dried under vacuum at 40 °C for 24 h (23.6 g; 90%).

Claims

1. Melphalan (I): 【Chemical 1】 The method for synthesizing the compound of formula (1) is as follows: ２ CH ２ OS (O) ｎ O － ) ２ (where n is 1 or 2), followed by reaction with a reagent capable of converting the —N(CH ２ CH ２ OS (O) ｎ O － ) ２ The group is -N(CH ２ CH ２ Cl) ２ The method comprises converting the compound to a group.

2. 10. The method of claim 1, comprising the steps of: a) by reaction of the protected 4-amino-L-phenylalanine of formula (II) with 1,3,2-dioxathiolane-2,2-dioxide of formula (IIIa) or with 1,3,2-dioxathiolane-2-oxide of formula (IIIb) in the presence of an inorganic base: 【Chemistry 2】 Here, R １ is a carboxy protecting group, and R ２ and R ３ one of R is hydrogen and the other is an amino protecting group, or ２ and R ３ together with the nitrogen atom to which they are attached form an amino protecting group: 【Chemistry 3】 providing a protected 4-(bis-(2-ethylsulfite)amino-L-phenylalanine or 4-(bis-(2-ethylsulfite)amino-L-phenylalanine of formula (IV): 【Chemistry 5】 Here, R １ , R ２ and R ３ is as defined above, and X is OS(O) ｎ O － where n is 1 or 2, M ＋ or M ２＋ is a metal cation, b) substituting the -X group of the compound of formula (IV) with chlorine to provide a protected melphalan of formula (V): 【Chemistry 6】 Here, R １ , R ２ and R ３ is as defined above, c) Protecting group R １ -R ３ is removed to provide melphalan (I).

3. 3. The method of claim 2, wherein in step a), the protected 4-amino-L-phenylalanine of formula (II) is reacted with the 1,3,2-dioxathiolane 2,2-dioxide (IIa).

4. In the compound of formula (II), R １ is a linear or branched C １ -C ６ alkyl, and R ２ is hydrogen, and R ３ is the formula R ４ is a group of —C(O)—, where R ４ is hydrogen or a straight or branched C １ -C ６ alkyl, or R ２ and R ３ The method of claim 2 or 3, wherein taken together with the nitrogen atom to which they are attached, represent a group of the formula: 【Chemistry 7】

5. R １ is ethyl, and R ２ and R ３ The method of claim 4, wherein together with the nitrogen atom to which they are attached, form a group of formula (VI) as defined in claim 4.

6. The step b) is a step of oxidizing the compound of formula (IV) in a solution of LiCl, NaCl, KCl, CaCl2, MgCl ２ , or BaCl ２ 5. The process according to any one of claims 2 to 4, wherein the process is carried out by reacting a compound of formula (V) as defined in claim 2 with

7. Step b) comprises desulfating the compound of formula (IV) defined in claim 2 using absolute ethanol and sulfuric acid, thereby obtaining the protected 4-(bis-(2-hydroxyethyl)-amino-L-phenylalanine of formula (VII): 【Chemistry 8】 Here, R １ , R ２ and R ３ is as defined in claim 2 or 3, and then compound (VII) and POCl ３ or SOCl ２ 5. The process according to any one of claims 2 to 4, which is carried out by reacting with a compound selected from the group consisting of methyl, ...

8. 4. The method of any one of claims 2 to 3, wherein step c) is carried out by treating the protected melphalan of formula (V) with an acid in water at a temperature ranging from 85 to 115°C to a pH of <1 to provide an acidic aqueous solution comprising melphalan (I) bis-hydrochloride, and then increasing the pH to crystallize the melphalan.

9. 9. The process of claim 8, wherein the pH is increased to a value in the range of 7.5 to 8.5 to crystallize the melphalan to its hydrochloride salt.

10. Compound of formula (IV): 【Chemistry 9】 In the formula, R １ is a linear or branched C 1 -C 6 alkyl; R ２ and R ３ is hydrogen and the other is a group of formula R 4 —C(O)—, where R 4 is hydrogen or a straight or branched C 1 -C 6 alkyl, or R ２ and R ３ together with the nitrogen atom form a group represented by the following formula (VI), and X is —OS(O) ｎ O － where n is 1 or 2, and M ＋ or M ２＋ is a metal cation. 【Chemistry 10】

11. R １ is ethyl, and R ２ and R ３ and together with the nitrogen atom to which they are attached represent a group of formula (VI): 【Chemistry 10】

12. X is -OS (O) ２ O － 12. The compound according to claim 10 or 11, wherein

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