|Title of Invention||
AN IMPROVED PROCESS FOR PERPARATION OF TYROSINE-NCA
|Abstract||Tyrosine-N-carboxy anhydride (Tyrosine-NCA, I) is one of the four amino acid building blocks used in the preparation of glatiramer acetate. The present invention describes a process for preparation of tyrosine-NCA by industrially convenient, environmentally friendly and safe process involving the reaction of triphosgene and tyrosine. Tyrosine-NCA obtained by this process is > 99.0% pure with <0.01% chloride content and substantially free from tyrosine impurity.|
An Improved Process for Preparation of Tyrosine-NCA
Field of the Invention
Tyrosine-N-carboxy anhydride (Tyrosine-NCA, I) is one of the four amino acid building blocks used in the preparation of glatiramer acetate. The present invention describes a process for preparation of tyrosine-NCA by industrially convenient, environmentally friendly and safe process involving the reaction of triphosgene and tyrosine. Tyrosine-NCA obtained by this process is > 99.0% pure with
Background of the Invention
Glatiramer acetate is a synthetic peptide polymer used in the treatment of relapsing multiple sclerosis. (M. M. Mouradain, Pharmacology & Therapeutics, 98, 245-255, 2003). It is a random polymer of L-alanine, L-tyrosine, L-Glutamic acid, L-lysine and is prepared by polymerization N-carboxy anhydrides (NCAs) of L-Tyrosine, L-alanine, L-5-benzyl L-glutamic acid and L-s-trifluoroacetyl lysine. The above polymerization reaction is highly sensitive, and the final polymer quality depends on the quality of input amino acid NCAs. We found that, whenever above amino acid NCAs do not meet the stringent quality specifications, glatiramer acetate obtained failed in average molecular weight and amino acid composition specifications. In order to obtain glatiramer acetate meeting to specifications, we use NCAs, which are to be >99% pure and chloride content Amino acid N-carboxyanhydrides (amino acid -NCAs) are chemically 3-substituted oxazolin-2, 5-diones. Leuchs first prepared NCAs in 1906 via intermolecular cyclization
of N-alkyl or N-aryloxycarbonyl amino acid halides. Hence these are also known as Leuchs anhydrides (Leuchs H., Chem. Ber., 41, 1721, 1906). This method involves preparation of alkoxy aryl carbamates, conversion to acid halides, and thermally induced cyclization. This method is obsolete and of historical interest only. Amino acid -NCAs are highly unstable at room temperature and needs to be stored around ~20°C. Since the first preparation of NCAs, many different procedures have been reported. Fuchs-Farthing is the most popular method for preparation of amino acid-NCAs (III) both at academic and industrial level (Farthing, A., J. Chem. Soc, 3213-3217, 1950; Fuchs F. Chem. Ber., 55, 2943, 1922). This preparation, involves reaction of amino acid (II) with phosgene in variety of solvents (Scheme 1). Many variants of phosgenation such as phosgenation of amino acid copper complexes, N-trimethylsilyloxcarbony amino acid trimethylsilyl ester and N-carboxy amino acid sodium salts (T. J. Blacklock, R. Hirschmann, and D. F. Verber, Peptides, Volume 9, pp39, academic press, 1987) are reported. Use of phosgene is major disadvantage in these methods. Phosgene is highly hazardous gas, and requires specialized handling and personal protection equipment. Hence it not preferred method in the industry.
In order to avoid phosgene, many substitutes are developed; diphosgene and triphosgene are generally used substitutes.
Diphosgene (trichlomethylchloroformate, TCF) is high boiling (127-128° C for TCF, versus 8.2°C for phosgene) hence easy to handle and is less toxic than phosgene. Some
amino acid NCAs were prepared using diphosgene at a small scale by reacting amino acid with diphosgene (Katakai R., Iizuka Y., J. Org. Chem., 50, 715-716, 1985). However, diphosgene is not available in quantities required at industrial scale. Triphosgene (bistrichloromethyl carbonate) is crystalline compound and is less hazardous than phosgene and diphosgene. In the recent times it has become a popular substitute of phosgene and is available abundantly at a cheap price. Daly and Poche for the first time prepared amino acid NCAs using triphosgene, their paper describes synthesis of stearyl glutamate, DL-2-aminostearic acid, 5-benzyl L-glutamate, O-benzyl-L-tyrosine, L-phenyl alanine, L-leucine, L-alanine in THF in 58.5-89.5% yield (Daly, W.H. & Poche, D., Tetrahedron Lettres, 29, 5859-5862, 1988), later Wilder and Mobashery (Wilder, R., and Mobashery, S, Journals of Organic Chemistry, 57, 2755-56, 1992) reported the synthesis of L-valine, O-benzyl-L-tyrosine, L-phenylalanine, 5-benzyl L-glutamatic acid, glycine, Boc-L-lysine in 65-83% yield in anhydrous ethyl acetate and triethylamine system using triphosgene.
Recent, US patents 6,479,665 (2002) and 6, 603,016 (2002) gives a very general method of preparation of a,p,y amino acid NCAs using phosgene, diphosgene, triphosgene in presence of unsaturated organic compound, such as oc-pinene in order to trap liberated hydrochloric acid and less than 1000 mbar to give a,p,y amino acid NCAs free of chlorides. US patents 6,479,665, has the disadvantage of creating negative pressure, which creates process-engineering difficulties. Similarly, US patent 6,603,016 procedures involves an additional process chemical such as a-pinene to trap hydrogen chloride liberated in the reaction. Which increases the cost of production. In addition, both these patents do not mention anything regarding the purity of NCAs, and amount of free amino acid in the NCAs obtained by the above processes. These quality specifications are highly important to produce glatiramer acetate meeting quality specifications.
Tyrosine -NCA was prepared using phosgene (Astbury, W.T., Dalgliesh, C.E., Darmon, S.E., Sutherland, G.B.B.M., Nature, 162, 596,1948; Hirschmann et al., J. Am. Chem. Soc. 93, 2746-2754, 1971). However, none of the above methods describe, tyrosine-NCA prepared using triphosgene having >99.0% assay,
tyrosine. Present invention describes a commercial process for preparation of tyrosine-NCA from tyrosine (IV) and triphosgene (V) that is economically viable, robust, and scalable linearly without using toxic phosgene gas as shown in the scheme 2.
Detailed Description of the Present Invention
Moisture causes polymerization of amino acid NCAs. Therefore, the moisture present in tyrosine can also cause polymerization of tyrosine NCA formed during the reaction media. To prevent polymerization, vacuum dried tyrosine with moisture content One of other difficulties in the process is choice of solvent and the purity of it. The critical parameter is content of moisture in the solvent. Solvents such as ethyl acetate, dioxane, tetrahydrofuran, acetonitrile are used with moisture content less than 0.01%. In this invention, solvents are dried using desiccants such as calcium chloride, molecular
sieves for overnight, and then double distilled, checked for moisture content. Solvents with moisture content less than 0.01% are only used in the process.
During the reaction of triphosgene with tyrosine at the refluxing temperature, if the vent is kept open, the atmospheric air is sucked, and moisture entered into the reaction vessel induces polymerization of tyrosine-NCA formed in the reaction. To control moisture-induced polymerization during the reaction, the reaction is conducted in presence of inert atmosphere. The inert atmosphere is created by nitrogen or argon, preferable by nitrogen gas.
The reaction of triphosgene with tyrosine liberates hydrogen chloride, this react with free tyrosine to give tyrosine hydrochloride. The formation of hydrochloride salt hinders progress of reaction and invariable results in tyrosine- NCA having chloride impurities. Liberated toxic gases are neutralized by the scrubber. The reservoir of the scrubber is filled with alkalis such as ammonia, alkali metal hydroxides.
Mode of addition of triphosgene is critical to achieve highly pure tyrosine-NCA. When triphosgene is added in single lot, the reaction is incomplete. In order to force the increase reaction to completion, triphosgene is added in the lots. However, handling triphosgene in the lots is not convenient. To solve this problem, a solution of triphosgene is in the solvent of reaction is made and added in lots.
There are number of methods described in the literature to determine the purity of NCAs, however, we found procedure of Berger et al., involving titration of tyrosine_NCA with sodium methoxide in presence of thymol blue indicator is accurate, simple and precise (Berger, A., Sela, M, Katachlski, E., Analytical Chemistry, 25, 1554-1555, 1953). Chlorides content is determined by argentometry. Free tyrosine in tyrosine is determined by thin layer chromatography using ninhyrin detection system.
Accordingly, the main objective of the present invention is to provide an improved process for the preparation of tyrosine-NCA of formula I possessing very high purity.
Another objective of the present invention is to provide an improved process for the preparation of tyrosine-NCA possessing very high purity, with >99.0% assay, chlorides content Still another objective of the present invention is to provide an improved process for the preparation of tyrosine-NCA possessing very high purity, with >99.0% assay, chlorides content Still another objective of the present invention is to provide an improved process for the preparation tyrosine-NCA possessing very high purity, with >99.0% assay, chlorides content Statement of the Invention.
The present invention describes a process for preparation of highly pure tyrosine-NCA suitable for preparation of glatiramer acetate. The invention involves reaction of purified tyrosine with triphosgene, wherein triphosgene is added in lots as solution in purified solvent. Tyrosine-NCA obtained by this process is >99.0% pure and contains Accordingly the present invention has been developed based on our finding that the qualities of input amino acid -NCAs influence the average molecular weight and amino acid analysis of glatiramer acetate.
The details of the invention are described in examples given below which are provided to illustrate the invention only and therefore should not be construed to limit the scope of the present invention.
Example 1: Preparation of tyrosine-NCA
10L tetrahydrofuran (MCO.01%), powdered and vacuum dried tyrosine (500g, MC Example 2: Preparation of tyrosine-NCA in acetonitrile
Powdered and vacuum dried tyrosine (lOg, MC
Yield: 5.1g (44.8%), assay = 99.4%, Chlorides = 0.01%, free tyrosine Powdered and vacuum dried tyrosine (lOg, MC Advantages of Present Invention:
1. In the present process hazardous phosgene is replaced with triphosgene and
liberated gases are fed to a scrubber, hence it is safe and environmental friendly.
2. The process is suitable for a commercial preparation
3. The process produces tyrosine-NCA of purity of > 99%, chlorides free tyrosine
1. An improved process for the preparation of tyrosine-NCA of formula (I)
Which comprises reacting purified tyrosine with triphosgene as a solution in suitable purified solvents, and which is added in portions at a temperature in the range 0-120°C to obtain the compound of the formula (I), tyrosine-NCA with high purity and which is suitable for preparation of glatiramer acetate.
2. A process as claimed in claim 1 wherein the purified solvent employed is selected
from organic solvents, acetonitrile, dioxan, ethyl acetate, tetrahydrofyran, and
preferably tetrahydrofyran and moisture content of purified solvent is less than
3. A process as claimed in claim 1 wherein the moisture content of purified tyrosine
employed is less than 4. A process as claimed in claim 1 wherein triphosgene is added as a solution in
purified solvent in lots.
5. A process as claimed in claims 1 wherein the preferred temperature of the
reaction is 50 to 80 °C.
6. A process as claimed in claim 1, wherein liberated toxic gases from the reaction
between tyrosine and triphosgene are neutralized by a scrubber, and the reservoir
of the scrubber is filled with ammonia, alkali metal hydroxides such sodium hydroxide etc. in inert atmosphere created by gases such as argon or nitrogen.
7. A process as claimed in claim 1 wherein tyrosine-NCA of purity >99.0% is
8. A process claimed as in claim 1, wherein free chloride content tyrosine-NCA
9. A process claimed as in claim 1, wherein the content of free tyrosine is in tyrosine-NCA.
10. An improved process for the preparation of tyrosine-NCA of the formula (I)
substantially as herein described with reference to the Examples 1 to 3.
|Indian Patent Application Number||1085/CHE/2005|
|PG Journal Number||48/2011|
|Date of Filing||08-Aug-2005|
|Name of Patentee||NATCO PHARMA LIMITED|
|Applicant Address||NATCO PHARMA LIMITED NATCO HOUSE ROAD NO.2, BANJARA HILLS HYDERABAD.|
|PCT International Classification Number||C07C 229/00|
|PCT International Application Number||N/A|
|PCT International Filing date|