AN IMPROVED PROCESS FOR THE PREPARATION OF MELPHALAN AND ITS
SALTS
Field Of The Invention
The present invention relates to a novel process for preparation of highly pure Melphalan and its pharmaceutically acceptable salt having a purity of > 99 % which is simple, convenient, economical, industrially viable and avoids use of hazardous chemicals. Background Of The Invention
Melphalan, chemically known as 4-[bis(2-chloroethyl)amino]-L-phenylalanine, is represented by Formula (I)
(Formula Removed)
Melphalan hydrochloride, sold under the trade name Alkeran®, is a well established cytotoxic agent belonging to the class of nitrogen mustard alkylating agents, which is active against selective human neoplastic diseases such as multiple myeloma and ovarian cancer.
Melphalan was first disclosed in US 3032584 and US 3032585. Several processes for the preparation of Melphalan have been reported in the literature such as those described in US 3032585, US 3032584, US 20090240074 and FR 1360836.
The process for the synthesis of Melphalan, disclosed in US 3032584, involves the use of a key intermediate, 4-aminophenylalanine, prepared from L-phenylalanine. The Scheme is summarized below:
(Formula Removed)
a)Nitration; b)Phthalic anhydride;c) Ethanol; d)Ethyl acetate; e) Glacial Acetic Acid;f)POCl3
Dry pyridine HC1 Methanol Ethylene oxide
reflux Pd/CaCO3
The key intermediate 4-aminophenylalanine has two active amino groups, one at the alpha carbon to the carboxylic acid function (glycinic amino group) and the other at the para position of the phenyl ring (aromatic amino group). All the processes, known in the art, disclose the need to protect the glycinic amino group so as to selectively introduce the hydroxyethyl or chloroethyl group on to the aromatic amino group. The protecting groups commonly used in the prior art are acetyl, formyl, and phthaloyl groups.
US 3032585 also discloses a process for the synthesis of Melphalan from N-acetyl-DL-phenylalanine which comprises resolution of racemic mixture of N-acetyl-DL-phenylalanine brucine or cincodine salt by means of crystallization. Basifying the separated L-isomer followed by esterification, reduction, hydroxyethylation, chlorination and hydrolysis to yield Melphalan. The scheme is summarized below
(Formula Removed)
a) Brucine/ b)Hydrolysis;c) Esterification; d) glycinic amine e) reduction; f) Hydroxyethylation;
Cinchonidine; protection;
g) Chlorination; h) Hydrolysis;
US 20090240074 discloses a process for the preparation of Melphalan which involves the regiospecific hydroxyethylation of the aromatic amino group without protecting the glycinic amino group of p-aminophenylalanine. The process demonstrated in this invention involves regiospecific reaction parameters to obtain 4-(bis(2-chloroethyl)amino)phenylalanine or its alkyl ester without any protection of the glycinic amino group. The scheme is summarized below.
(Formula Removed)
a) Nitration; b) Reduction;c) Hydroxyethylation; d) Base treatment; e) chlorination
FR 1360836 describes preparation of Melphalan by hydroxyethylation of aniline using ethylene oxide to give N,N-bis(hydroxyethyl) aniline, chlorinating the latter with phosphorus oxychloride to give bis-(2-chloroethyl) aniline which is formylated in the para positon, followed by cyclizing it into the azlactone with hippuric acid and acetic anhydride, followed by reducing the azlactone with zinc dust in hydrochloric acid and acidic hydrolysis to yield melphalan hydrochloride. The scheme is summarized below.
(Formula Removed)
a)POCl3; b) DMF; c) Hippuric Acid; d) Zn dust; e) hydrolysis;
POCl3 Acetic HC1
anhydride
From the foregoing, it would be apparent that the reported methods for the preparation of Melphalan suffer from one or more of the following disadvantages or limitations viz.
a) More Number of steps involved in the process.
b) Use of ethylene oxide which is harmful, potentially carcinogenic, irritant and moreover requires special handling and safety precautions.
c) Use of Phosphorous oxychloride which is corrosive and irritant and requires special handling and safety precautions
d) Formation of several byproducts/impurities, which may be generated due to the use of ethylene oxide and Phosphorous oxychloride. The structures of the impurities formed may be represented by following Formulas.
(Formula Removed)
Impurity C (P' is Hydrogen or protecting group) Impurity D
e) No effective purification process of Melphalan or its intermediates is reported in the literature to remove the impurities.
The impurities formed during the prior art processes are very hard to remove, therefore there formation should be minimized during the process itself. Therefore there is a need to provide a simple, convenient, economical, industrially viable commercial process for the preparation of Melphalan, which avoids use of hazardous chemicals and results in the formation of Melphalan, in particular Melphalan hydrochloride of pharmacopoeial grade having a purity of greater than 99%. Summary of Invention
In one embodiment the present invention provides a novel process for preparing a highly pure Melphalan of Formula (I) or its pharmaceutically acceptable salt.
(Formula Removed)
comprising the steps of; a) reductively alkylating a compound of Formula (II), wherein R is C1-C6 Alkyl and P is a suitable protecting group in the presence of a triflate and a base to obtain a compound of Formula III in a single step, wherein R and P is as defined above
(Formula Removed)
b) deprotection of a compound of Formula (III) to a compound of Formula (IV)
(Formula Removed)
c) optionally converting the compound of Formula (IV) to its acid addition salt
d) converting the compound of Formula (IV) or its acid addition salt to Melphalan of Formula (I) and
e) optionally Converting Melphalan to its pharmaceutically acceptable salt
In another embodiment the present invention provides a process for preparing a highly pure Melphalan of Formula (I) or its pharmaceutically acceptable salt.
(Formula Removed)
comprising the steps of;
a) providing a mixture of compound of Formula IV and a suitable solvent
b) converting the compound of Formula (IV) to its acid addition salt
c) isolating the acid addition salt of compound of Formula (IV)
d) converting the acid addition salt of compound of Formula (IV) to Melphalan of Formula (I) and
e) optionally Converting Melphalan to its pharmaceutically acceptable salt
In yet another embodiment the present invention provides a process for preparing a highly pure Melphalan of Formula (I) or its pharmaceutically acceptable salt.
(Formula Removed)
comprising the steps of;
a) deprotecting a compound of Formula (III)), wherein R is C1-C6 Alkyl and P is a suitable
protecting group, in the presence of hydrazine Hydrate to a compound of Formula (IV)
(Formula Removed)
b) optionally converting the compound of Formula (IV) to its acid addition salt
c) converting the compound of Formula (IV) or its acid addition salt to Melphalan of Formula (I) and
d) optionally Converting Melphalan to its pharmaceutically acceptable salt Detailed Description of The Invention
Examples of R in Compound of Formula II
(Formula Removed)
may include C1-C6 Alkyl such as Methyl, ethyl, propyl. The protecting group P along with Nitrogen may be selected from the group comprising of following structures:
(Formula Removed)
The compound of formula II may be obtained by any of the methods known in the art. The reductive alkylation of compound of Formula (II) may be carried out in the presence of a suitable triflate reagent. The term "Triflate" herein referred to any reagent having Trifluoromethanesulfonate group. The suitable triflate reagent may be selected from the group comprising of methyl triflate, ethyl triflate, chloroethyl triflate, trifluoromethyl triflate, and 2,2,2-trifluoroethyl triflate.
The reductive alkylation of compound of Formula (II) may be carried out in the presence of a suitable base such as Organic Base or Inorganic Base.
The organic base may be selected from the group comprising of C1-C4 alkyl ammonia; mono, di or tri C1- C4 alkyl amine such as triethyl amine, diisipropropyl ethyl amine; mono, di or tri hydroxy C1-C4 alkyl amine; morpholine; thiomorpholine; piperidine; N,N-dimethylaniline; pyridine; hydrazines and pyrrolidine.
The inorganic base may be selected from the group comprising of metal carbonate such as lithium carbonate, sodium carbonate, potassium carbonate, barium carbonate, calcium carbonate and magnesium carbonate; metal bicarbonate such as sodium bicarbonate, potassium bicarbonate, barium bicarbonate, calcium bicarbonate and magnesium bicarbonate and metal hydroxide such as sodium hydroxide, potassium hydroxide, barium hydroxide, calcium hydroxide and magnesium hydroxide.
The reductive alkylation of compound of Formula (II) may be carried out in the presence of a suitable solvent. Suitable solvent may be selected from the group comprising of water; alcohols, such as methanol, ethanol and isopropanol; nitriles, such as acetonitrile ; chlorinated hydrocarbons, such as methylene chloride, ethylenedichloride ; dipolar aprotic solvents, such as dimethylsulfoxide and dimethylformamide ; esters, such as ethyl acetate and isopropyl acetate; cyclic ethers, such as dioxane and tetrahydrofuran ; ketone such as acetone, diisobutyl ketone, -cyclohexanone, methylcyclohexanone, methyl ethyl ketone, methyl isobutyl ketone, acetylacetone and mixtures thereof.
The reductive alkylation of compound of Formula (II) may be carried out at about ambient temperature to about reflux temperature. The ambient temperature may be at about room temperature, which may range from about 20° to about 35°C.
The reductive alkylation of compound of Formula (II) may be carried out for about 2 hour to about 8 hours.
In general, the deprotection of compound of Formula III
(Formula Removed)
may be carried out in the presence of suitable acid such as hydrochloric acid, hydrobromic acid, nitric acid and sulfuric acid, to obtain compound of Formula (IV)
(Formula Removed)
The deprotection of compound of Formula III may be carried out in the presence of Hydrazine Hydrate in a suitable solvent. Suitable solvent may be selected from the group comprising of water; alcohols, such as methanol, ethanol and isopropanol; nitriles, such as acetonitrile ; chlorinated hydrocarbons, such as methylene chloride, ethylenedichloride ; dipolar aprotic solvents, such as dimethylsulfoxide and dimethylformamide ; esters, such as ethyl acetate and isopropyl acetate; cyclic ethers, such as dioxane and tetrahydrofuran ; ketone such as acetone, diisobutyl ketone, cyclohexanone, methylcyclohexanone, methyl ethyl ketone, methyl isobutyl ketone, acetylacetone and mixtures thereof.
The deprotection of compound of Formula III in the presence of Hydrazine Hydrate may be carried out at about ambient temperature i.e. about room temperature, which may range from about 20° to about 35°C.
The deprotection of compound of Formula III in the presence of Hydrazine Hydrate may be carried out for about 12 hour to about 48 hours, preferably 24 hours.
The compound of Formula (IV) may optionally be converted to its acid addition salt such as hydrochloride, hydrosulfide and para-toluenesulfonate salt
(Formula Removed)
The acid addition salt of compound of Formula IV may be prepared by treating the compound of Formula IV with respective acid in the presence of suitable solvent. Suitable solvent
may be selected from the group comprising of water; alcohols, such as methanol, ethanol and isopropanol; nitriles, such as acetonitrile ; chlorinated hydrocarbons, such as methylene chloride, ethylenedichloride ; dipolar aprotic solvents, such as dimethylsulfoxide and dimethylformamide ; esters, such as ethyl acetate and isopropyl acetate; cyclic ethers, such as dioxane and tetrahydrofuran; ketone such as acetone, diisobutyl ketone, cyclohexanone, methylcyclohexanone, methyl ethyl ketone, methyl isobutyl ketone, acetylacetone and mixtures thereof.
The acid addition salt of compound of Formula IV may be prepared at about ambient temperature i.e. about room temperature, which may range from about 20° to about 35°C.
The acid addition salt of compound of Formula IV may be prepared for about 1 hour to about 4 hours, preferably 2 hours.
Isolation of the acid addition salt of compound of Formula IV, may be accomplished by one or more of concentration, crystallization, precipitation, cooling, filtration, centrifugation or a combination thereof.
The compound of Formula IV or its acid addition salt may be converted to Melphalan of Formula I by acid hydrolysis in the presence of suitable acid such as Hydrochloric acid.
(Formula Removed)
Melphalan as obtained by the process of present invention may be converted to its acid addition salt such as Melphalan Hydrochloride.
Melphalan Hydrochloride as obtained by the process of present invention has the purity of > 99 % with the Impurities A, B, C and D either not detectable or less that 0.1%.
Detailed experimental parameters suitable for this novel process of making melphalan are provided by the following examples, which are intended to be illustrative and not limiting of all possible embodiments of the invention. Reference example 1
To a stirred solution of 4-amino-N-phthaloyl-L-phenylalanine methyl ester in 165 ml
water and 88 ml acetic acid was added ethylene oxide (35g) at 0-5°C and stirred reaction mixture
at RT for 12h. The Reaction was monitored by TLC. After completion of reaction, reaction
mixture was poured into 1100 ml water, neutralized pH to 7-7.5 with NaHCCO3, followed by
extraction with 220 ml of DCM. The organic layer was washed with water, dried over Na2SO4,
concentrated under vacuum to get dark brown gummy mass.
Weight: 13.8g Yield: 99 % Impurity C: 2.0% Reference example 2
To a stirred solution of Crude 4-bis(2-hydroxyethyl)amino-L-phenylalanine methyl ester in 70 ml toluene, 8 ml POCl3 was added dropwise at room temperature. The reaction was heated to reflux at 100-110°C for 2hrs. The reaction was monitored by TLC. On completion solvent was evaporated under vacuum to get a gummy mass. The Gummy mass was dissolved in water and pH adjusted to 7.0 with saturated NaHCO3 solution, followed by extraction with DCM. The DCM layer so obtained was washed with water, dried over Na2SO4, and concentrated under vacuum to get crude. The crude product was crystallized in Isopropyl: n-butanol (140 ml, 1:1) to get pure product. Weight: 9.5g Yield: 68% Reference example 3
A solution of 9g of 4-[bis(2-chloroethyl)amino]-N-phthaloyl-L-phenylalanine methyl ester in 90 ml cone. HC1 was refluxed for 10-12 hours. The reaction mixture was cooled to 25-30°C and filtered to separate phthalic acid. The aqueous solution was evaporated to dryness in vacuo and the residue dissolved in 60 ml methanol. 4-bis(2-chloroethyl)amino-L-phenylalanine was precipitated by addition of 15 ml Diethylamine: Methanol mixture (1:1) to a pH of 7 at 0-5°C. The precipitated product was stirred for 2 hours at RT, filtered, washed thoroughly with 50 ml methanol and dried at 30-35°C for 10-12 hours. Weight: 4.6g Yield: 75% Reference example 4
To a solution of 1 g of 4-bis(2-chloroethyl)amino-L-phenylalanine in 8 ml ethanol was
added 1.2 ml ethanolic HC1 at 25-30°C for 3-4hrs. The reaction mixture was heated to 80°C for
10-15 minutes. The reaction progress was monitored by HPLC. On completion of reaction the
reaction mixture was cooled to RT. The reaction mixture was further cooled to 0-5°C for 2-3
hours under stirring. The precipitated solid was filtered under vacuum and washed with 10 ml
diethyl ether.
Weight: 0.6g
Yield: 54%
Purity: 97.57%
Impurity A: 0.7%
Impurity D: 1.15%
Example-1
Preparation of 4-[bis(2-chloroethyl)aminol-N-phthaloyl-L-phenylalanine methyl ester
To a stirred solution of 0.5 g of 4-amino-N-phthaloyl-L-phenylalanine methyl ester in 50 ml acetone was added 4.26 g of K2CO3. Reaction mixture was stirred at RT for 15 min, then added 13.1 g of 2-chloroethyl trifluoromethanesulfonate dropwise. Reaction mixture was heated at 50-60°C for 4h. Solvent was evaporated under vacuum to get gummy mass which was dissolved in 200 ml dichloromethane. Dichloromethane layer washed with water and brine, dried over Na2SO4, concentrated under vacuum to get crude product which was crystallized in 60 ml methanol to get pure product. Weight 0.35 g HPLC Purity: >98.0% Example-2 Preparation of 4-bis(2-chloroethyl)amino-L-phenylalanine methyl ester
To a stirred solution of 10 g of 4-[bis(2-chloroethyl)amino]-N-phthaloyl-L-phenylalanine methyl ester in 60 ml methanol was added 1.39 g of hydrazine hydrate. Reaction mixture was stirred at room temperature for 24h. Precipitated solid was filtered off and washed with methanol. Water was added to filtrate and the product was extracted with 160 ml toluene. The toluene layer was washed with water and brine and concentrated under vacuum to get crude gummy mass. Crude product was taken in 150 ml acetone, added 4.18 g of p-toluenesulfonic acid (PTSA), stirred for 2h at RT. Precipitated product as PTSA salt was filtered and washed with acetone. PTSA Salt of product was taken in water, neutralized with bicarbonate solution, extracted product with toluene thrice, combined toluene layer was washed with water and brine, evaporated under vacuum to get pure product. Weight: 0.49 g Purity: >98.0% Example-3
Preparation of 4-bis(2-chloroethyl)amino-L-phenylalanine hydrochloride (Melphalan hydrochloride)
A solution of 2 g of 4-bis(2-chloroethyl)amino-L-phenylalanine methyl ester in 20 ml
cone. HC1 was heated at 100°C for 3-4hrs. On completion of reaction the reaction mixture was
cooled to RT, and diluted with 20 ml DM water. The pH was adjusted to 0.5 with sodium acetate,
and filtered off. The precipitate was washed with water and finally with 12 ml acetone to get pure
Melphalan hydrochloride.
Weight: 0.74g
Purity: 99.57% Impurity A: 0.07% Impurity D: Not detectable

We claim:
1) A process for preparing a highly pure Melphalan of Formula (I) or its pharmaceutically
acceptable salt.
(Formula Removed)
comprising the steps of;
a) reductively alkylating a compound of Formula (II), wherein R is C1-C6 Alkyl and P
is a suitable protecting group in the presence of a triflate and a base to obtain a
compound of Formula III in a single step, wherein R and P is as defined above
(Formula Removed)
b) deprotection of a compound of Formula (III) to a compound of Formula (IV)
(Formula Removed)
c) optionally converting the compound of Formula (IV) to its acid addition salt
d) converting the compound of Formula (IV) or its acid addition salt to Melphalan of Formula (I) and
e) optionally Converting Melphalan to its pharmaceutically acceptable salt
2) A process for preparing a highly pure Melphalan of Formula (I) or its pharmaceutically
acceptable salt.
(Formula Removed)
comprising the steps of;
a) providing a mixture of compound of Formula IV and a suitable solvent
b) converting the compound of Formula (IV) to its acid addition salt
c) isolating the acid addition salt of compound of Formula (IV)
d) converting the acid addition salt of compound of Formula (IV) to Melphalan of Formula (I) and
e) optionally Converting Melphalan to its pharmaceutically acceptable salt
3) A process for preparing a highly pure Melphalan of Formula (I) or its pharmaceutically acceptable salt.
(Formula Removed)
comprising the steps of;
a) deprotecting a compound of Formula (III)), wherein R is C1-C6 Alkyl and P is a suitable
protecting group, in the presence of hydrazine Hydrate to a compound of Formula (IV)
(Formula Removed)
b) optionally converting the compound of Formula (IV) to its acid addition salt
c) converting the compound of Formula (IV) or its acid addition salt to Melphalan
of Formula (I) and
d) optionally Converting Melphalan to its pharmaceutically acceptable salt
4) The process as claimed in claims 1 and 3, wherein R in Compound of Formula II-IV is
Methyl, ethyl or propyl.
5) The process as claimed in claims I and 3, wherein P along with Nitrogen in Compound of
Formula II and III is selected from the group comprising of following structures:
(Formula Removed)
6) The process as claimed in claim 1, wherein triflate reagent is selected from the group
comprising of methyl triflate, ethyl triflate, chloroethyl triflate, trifluoromethyl triflate, and 2,2,2-
trifluoroethyl triflate.
7) The process as claimed in claim 1, wherein base is Organic Base or Inorganic Base.
8) The process as claimed in claim 7, wherein the organic base is selected from the group
comprising of C1-C4 alkyl ammonia; mono, di or tri C1- C4 alkyl amine such as triethyl amine,
diisipropropyl ethyl amine; mono, di or tri hydroxy C1-C4 alkyl amine; morpholine;
thiomorpholine; piperidine; N,N-dimethylaniline; pyridine; hydrazines and pyrrolidine.
9) The process as claimed in claim 7, wherein the inorganic base is selected from the group
comprising of metal carbonate such as lithium carbonate, sodium carbonate, potassium carbonate,
barium carbonate, calcium carbonate and magnesium carbonate; metal bicarbonate such as
sodium bicarbonate, potassium bicarbonate, barium bicarbonate, calcium bicarbonate and
magnesium bicarbonate and metal hydroxide such as sodium hydroxide, potassium hydroxide,
barium hydroxide, calcium hydroxide and magnesium hydroxide.
10) The process as claimed in claim 1, wherein the reductive alkylation of compound of Formula II is carried out in the presence of a suitable solvent.
11) The process as claimed in claim 10, wherein suitable solvent is selected from the group comprising of water; alcohols, such as methanol, ethanol and isopropanol; nitriles, such as acetonitrile; chlorinated hydrocarbons, such as methylene chloride, ethylenedichloride; dipolar aprotic solvents, such as dimethylsulfoxide and dimethyl formamide; esters, such as ethyl acetate and isopropyl acetate; cyclic ethers, such as dioxane and tetrahydrofuran; ketone such as acetone, diisobutyl ketone, cyclohexanone, methylcyclohexanone, methyl ethyl ketone, methyl isobutyl ketone, acetylacetone and mixtures thereof.
12) The process as claimed in claim 1, wherein the reductive alkylation of compound of Formula II is carried out at about ambient temperature to about reflux temperature.
13) The process as claimed in claim 1, wherein the deprotection of compound of Formula III
(Formula Removed)
is carried out in the presence of suitable acid such as hydrochloric acid, hydrobromic acid, nitric acid and sulfuric acid, to obtain compound of Formula (IV)
(Formula Removed)
14) The process as claimed in claim 3, wherein the deprotection of compound of Formula III is carried out in the presence of a suitable solvent.
15) The process as claimed in claim 14, wherein suitable solvent is selected from the group comprising of water; alcohols, such as methanol, ethanol and isopropanol; nitriles, such as acetonitrile; chlorinated hydrocarbons, such as methylene chloride, ethylenedichloride; dipolar aprotic solvents, such as dimethylsulfoxide and dimethylformamide ; esters, such as ethyl acetate
and isopropyl acetate; cyclic ethers, such as dioxane and tetrahydrofuran; ketone such as acetone, diisobutyl ketone, cyclohexanone, methylcyclohexanone, methyl ethyl ketone, methyl isobutyl ketone, acetylacetone and mixtures thereof.
16) The process as claimed in claim 3, wherein the deprotection of compound of Formula HI is carried out at about ambient temperature i.e. about room temperature.
17) The process as claimed in claim 1, wherein the acid addition salt is hydrochloride, hydrosulfide or para-toluenesulfonate salt.
18) The process as claimed in claim 1, wherein the acid addition salt of compound of Formula IV
is prepared by treating the compound of Formula IV with respective acid in the presence of suitable solvent.
19) The process as claimed in claim 18, wherein suitable solvent is selected from the group comprising of water; alcohols, such as methanol, ethanol and isopropanol; nitriles, such as acetonitrile; chlorinated hydrocarbons, such as methylene chloride, ethylenedichloride; dipolar aprotic solvents, such as dimethylsulfoxide and dimethylformamide; esters, such as ethyl acetate and isopropyl acetate; cyclic ethers, such as dioxane and tetrahydrofuran; ketone such as acetone, diisobutyl ketone, cyclohexanone, methylcyclohexanone, methyl ethyl ketone, methyl isobutyl ketone, acetylacetone and mixtures thereof.
20) The process as claimed in claim 1, wherein the compound of Formula IV or its acid addition salt is converted to Melphalan of Formula I by acid hydrolysis.
(Formula Removed)
21) The process as claimed in claim 1, wherein Melphalan as obtained is converted to its acid
addition salt such as Melphalan Hydrochloride.
22) The process as claimed in claim 1, wherein Melphalan Hydrochloride as obtained has the purity of > 99 % with the Impurities A, B, C and D either not detectable or less that 0.1%.