Title of Invention | AN IMPROVED PROCESS FOR PREPARING HIGH PURITY ETHYL-(R)-4-CYANO-3-HYDROXY BUTYRIC ACID ESTER/BUTYRATE |
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Abstract | A process for the preparation of alkyl-(R)-4-cyano-3-hydroxybutyrate of Formula I and Formula I A; OH O Formula I Where R represents lower alkyl group with 1-4 carbon atoms OH O (R) v ^QEt Formula la Esters of Formula I and Formula I A are known to be commercially important as intermediates in the synthesis of pharmaceuticals for treatment of hyperlipidemia. |
Full Text | FORM2 THE PATENTS ACT, 1970 (39 of 1970) & The Patents Rules, 2006 PROVISIONAL SPECIFICATION (See section 10; rule 13) 1. Title of the invention. - "AN IMPROVED PROCESS FOR PREPARING HIGH PURITY ETHYL-(R)-4-CYANO-3-HYDROXY BUTYRIC ACID ESTER/BUTYRATE" 2. Applicant(s) (a) NAME : (b) NATIONALITY : (c) ADDRESS : ARCH PHARMALABS LIMITED An Indian Company "H" Wing, 4th floor, Tex Centre, Off Saki Vihar Road, Chandivali, Andheri (East), Mumbai-400 072, India. 3. PREAMBLE TO THE DESCRIPTION The following specification describes the invention. FIELD OF INVENTION The present invention relates to the process for the preparation of alkyl-(R)-4-cyano-3-hydroxybutyrate of Formula I. The present invention relates more particularly to ethyl-(R)-4-cyano-3-hydroxy butyric acid esters. Formula I where R represents lower alkyl group with 1 -4 carbon atoms OH O Formula la BACKGROUND OF THE INVENTION 4-substituted-3-hydroxybutyric ester derivatives more particularly ethyl-(R)-4-cyano-3-hydroxy butyric acid ester of Formula I are known to be commercially important intermediate in the synthesis of pharmaceuticals for hypolipidemic agents in the treatment of hyperhpidemias. They are also called lipid-Iowering drugs (LLD) or agents. Methods for the preparation of lower alkyl esters of (R)-4-cyano-3-hydroxy butyric acid are disclosed for example in JP-A-2001114739, WO2004/031131, WO2000/046186 and US5430171. Acta Chem.Scand.,B37,341(1983) reports a method for producing a 4-cyano-3-hydroxybutyrate from 4-bromo-3-hydroxy butyrate that requires protecting the hydroxyl group with a protecting group prior to reaction with sodium cyanide. 2 Recent routes to synthesize 4-cyano-3-hydroxybutyrate esters involve the uncatalysed chemical reaction of 4-bromo or 4-chloro-3-hydroxybutyrate ester, without protection of hydroxyl group with a cyanide salt. However by-products are formed under the basic conditions created by basic cyanide anion, which are particularly problematic to remove from the product. US5430171 discloses a method for increasing the optical purity of lower alkyl esters (e.g. ethyl, propyl or n-butyl ester) by making the use of tert-butyl (S)-4-halogeno-3-hydroxy butyrate which is obtained as solid that can be used upon recrystallisation. The prior art WO2005/018579 discloses a method for the preparation of 4-substituted-3-hydroxybutyric acid derivatives by halohydrin dehalogenase catalyzed conversion of 4-halo-3-hydroxybutyric acid derivatives. It states that when the cyanide is provided by a cyanide salt, the reaction mixture is typically bufferd or acidified or both to provide the desired pH. Suitable acids for the acidification of basic cyanide salts solutions include organic acids, for example carboxylic acids, sulphonic acids, phosphoric acid, acidic salts like dihydrogen phosphate salts, bisulphate salts and the like. It further comprises purification of the product if needed. US6140527 describes an alternative approach for the treatment of crude lower alkyl esters of (R)-4-cyano-3-hydroxybutyric acid that involves removal of the dehydrated by-products, such as 4-hydroxycrotonic acid esters formed during processing, by chemical reaction, which renders these components water soluble and extractable. But the process results in low yield which makes it commercially undesirable. The purification of a crude lower alkyl esters of (R ) -4-cyano-3-hydroxy butyric acid formed from the cyanation of lower alkyl esters of (S)-4-chloro-3- 3 hydroxybutyric acid by distillation was disclosed in JP-A-19970254804 and US5908953. US5908953 discloses that besides unreacted starting material, additional unwanted process impurities could result, such as crude lower alkyl esters of(R )- 4-cyano-3 -hydroxybutyric acid which may include hydroxy acryl ate, cyanoacrylate, 3-cyanobutyrolactone, 3-hydroxybutyrolactone, 3-cyano-4-hydroxybutyrate lower alkylester, 3,4-dicyanobutyrate lower alkyl ester and high boiling uncharacterized compounds. It also describes a purification method for lower alkyl esters of (R)-4-cyano-3-hydroxybutyric acid that involves distillation of a crude mixture in the presence of a solvent that has a boiling point of 50-160°C at 10 torr. Using such distillation methods, the decomposition of starting material is said to be minimized that otherwise causes loss in ester production. The disadvantages of the various processes disclosed in the prior art are as follows: 1) excess sodium cyanide used for the reaction is hydrolyzed by using acid forming highly poisonous hydrogen cyanide during the hydrolysis, 2) Side products like acrylate are generated by dehydration due to the highly acidic hydrogen on a position for the carboxy group and the corresponding acid by hydrolysis of ester group. 3) In case of hydrolysis of sodium cyanide using sulphuric acid, increase in the acidity results the hydrolysis of the esters that gives rise to unwanted side products. 4) The purification involves high vacuum distillation of crude product which is prone to generate additional impurities which are formed due to the high temperature conditions during distillation. 5) Distillation also leads to low yield, high cost of production, thermal decomposition of the product. Moreover hydrogen cyanide generates some 4 polymeric impurities which lead to colour development in the product and also in subsequent intermediates of Atorvastatin. It appears that the prior processes have not provided for a method to minimize or eliminate the liberation of free hydrogen cyanide. Neutralizing agents other than acids were tried to deactivate sodium cyanide. While working on this, it was found that use of sodium hypochlorite that is usually used to neutralize sodium cyanide causes undesired oxidation of ethyI-(S)-4-chloro-3-hydroxy butyrate into ethyl-(S)-4-chloro-3-oxo butyrate of the formula II. Accordingly, there is a need for a safe and efficient method for producing on industrial scale non-racemic chiral 4-substituted-3-hydroxybutyric acid esters that not only avoids vacuum distillation but also affords product of required quality. In the present process distillation, which leads to impurities due to excessive heating, has been avoided. Thus, in the present invention, improvement is better than the predictable use of the prior art elements according to their established functions. The present invention is based on the combined principle of use of ferrous sulphate for the removal of cyanide ion and the use of EDTA for the removal of heavy metals. The present invention avoids the cumbersome procedure of distillation and simultaneously yields the product in high purity. OBJECT OF THE INVENTION It is an object of the present invention to provide an improved process for the preparation of lower alkyl-(R)-4-Cyano-3-hydroxybutyrate. 5 It is another object of the present invention to provide a commercially useful process for the preparation of lower alkyl-(R)-4-Cyano-3-hydroxybutyrate. It is yet another object of the present invention to provide an improved process for the preparation of ethyl-(R)-4-cyano-3-hydroxy butyric acid ester/butyrate. It is yet another object of the present invention to provide an enzymatic process for the preparation of subsequent statin intermediates thereof. It is yet another object of the present invention to provide a modified work up of the cyanation reaction. It is yet another object of the present invention to provide a process which avoids distillation. It is yet another object of the present invention to provide a product with lighter color and low moisture content. It is yet another object of the present invention to provide a product which contains no appreciable amount of cyanide content to affect the subsequent intermediates. It is yet another object of the present invention to provide a product with high yield and high optical and chemical purity. It is a further object of the present invention to facilitate the preparation of the next intermediate required for the preparation of the statin drug. SUMMARY OF THE INVENTION According to an aspect of the invention, there is provided an improved process for the preparation of alkyl-(R)-4-cyano-3-hyciroxybutyrate of Formula I particularly ethyl-(R)-4-cyano-3-hydroxybutyrate is provided which comprises the steps of: i. Providing ethyl -(S)-4-chIoro-3-hydroxy butyrate; ii. Contacting said ethyl -(S)-4-chloro-3-hydroxy butyrate with sodium cyanide in the presence of halohydrin dehydrogenase; iii. contacting the reaction mixture of step (ii) with ferrous sulphate at a controlled rate; 6 iv. Contacting EDTA with the mixture of step (iii); v. Extracting said cyano product using an organic solvent; vi. And optionally, treating with charcoal followed by azeotropic distillation. DETAILED DESCRIPTION OF THE INVENTION An improved process is provided for the preparation of optically pure lower alkyl (R) - 4-cyano-3-hydroxybutyric acid esters more particularly ethyl-(R) - 4-cyano-3-hydroxybutyric acid esters. The process minimizes the generation of free hydrogen cyanide, eliminates the need for distillation, and minimizes the formation of heat-generated impurities. The process is safe to the personnel, simpler in unit operations, scalable to industrial production, results in a highly pure cyanobutyrate intermediate valuable for subsequent statin compound synthesis in a highly economical manner. The present invention has the following advantages over the existing process known in the art: 1) Exposure to free hydrogen cyanide is minimized due to complex formation by using ferrous sulphate. 2) The complex formation is faster than the time required for the expulsion of hydrogen cyanide which avoids the exposure to hydrogen cyanide and longer time cycle. 3) Controlled addition of ferrous sulphate gradually brings down the pH from alkaline to acidic thereby limits the risk of HCN generation at acidic pH as used in the prior art. 4) Ethyl-(R)-4-cyano-3-hydroxybutyrate having the GC purity of 99.8-99.9%, optical purity of 99.9% having Ethyl-(S)-4-cyano-3-hydroxybutyrate lesser than 0.1%, moisture content in the range of 0.16-0.19%. 5) No purification using distillation thus reducing a unit operation. 7 In one aspect, the present invention relates to cyanation of ethyl-(S)-4-chloro-3-hydroxybutyrate using sodium cyanide in presence of halohydrin dehydrogenase. The cyanation reaction between ethyl-(S)-4-chIoro-3-hydroxybutyrate and sodium cyanide is illustrated in Scheme 1. Ethyl -(S)-4-chloro-3-Hydroxy butyrate Ethy, _(R)-4-cyano-3-Hydroxy butyrate Scheme 1 In one specific aspect, the cyanation is accomplished over a time period of about 8-10 hrs. In another aspect, the temperature of the cyanation reaction is maintained at about 40-45°C and the pH of the cyanation reaction is maintained from about 5.5 to about 9.0. or from about 6.0 to about 8.5, or from about 6.5 to about 8.0. In one specific aspect, the pH is maintained from about 6.9 to about 7.8 or from about 7.0 to about 7.5. In another aspect, the process is carried out till ethyl-(S)-4-chloro-3-hydroxybutyrate is consumed completely. In one aspect, the salt of a strong acid and weak base is a salt that comprises the acid component selected from the group consisting of: sulphuric acid, phosphoric acid, nitric acid, hydrochloric acid, etc,; and the weak base component is selected from the group consisting of: ferrous, cuprous, cadmium, zinc, nickel, cobalt, etc. Examples of such salts include: ferrous sulphate, cuprous sulphate, calcium sulphate, cadmium sulphate, zinc sulphate, nickel sulphate, cobalt sulphate, In yet another aspect, the salt of a strong acid and weak base is contacted with the cyanation mixture described above at a slow rate such that the liberation of hydrogen cyanide gas is controlled or minimized. In another aspect, EDTA (Ethylenediaminetetraacetic acid) is contacted with the prior mixture of cyanate and butyrate. This step may be followed by charcoal treatment. The product may be then isolated by using an organic solvent of suitable polarity such as ethyl acetate or another solvent of comparable polarity, or a mixture of an organic solvent and water to provide a solvent mixture of suitable polarity comparable to ethyl acetate. The product may be optionally concentrated under reduced pressure to get the concentrate. . The concentrate is optionally charcolized again, and washed with ethyl acetate if needed. Any moisture that may be trapped inside may be removed azeotropically using hexane as solvent which is removed easily by separation. Further details of the invention are illustrated below in the following non-limiting examples EXAMPLES Example 1 The enzyme halohydrin dehydrogenase (3.94g) was charged into a suitable assembly well equipped with the arrangement for pH measurement followed by the addition of 25% aqueous sodium cyanide (NaCN) solution to adjust the pH between 7.0-7.5. Ethyl-(S)-4-chloro-3-hydroxybutyrate (400 g) was then added at 40-45°C keeping the pH in the range of 7.0-7.5 using 25% aqueous sodium cyanide NaCN solution. After complete addition of ethyl-(S)-4-chloro-3-hydroxybutyrate, reaction mass was kept under stirring at 40-45°C for 8-10 hours till ethyl-(S)-4-chloro-3-hydroxybutyrate was fully consumed. The unreacted sodium cyanide was neutralized by the addition of ferrous sulphate solution having the pH of 3.0 when it starts complex formation. The free hydrogen cyanide if any was flushed off using nitrogen which was absorbed in ferrous sulphate solution which minimizes exposure to hydrogen cyanide. The sludge was removed by filtration. The filtrate was treated with 8g of EDTA which removed the metallic impurities of iron. The product was then extracted in ethyl acetate and charcolised with 5% charcoal. The filtrate was concentrated under vacuum. The 9 water trapped was then removed azeotropically using lit of hexane. The product (306 g) was separated from hexane layer. GC purity of the product to be 99.8%-99.9%, %, optical purity of 99.9% having S enantiomer lesser than 0.1 % with moisture content of 0.16-0.19%. We Claim: 1. A process for the preparation of alkyI-(R)-4-cyano-3-hydroxybutyrate of Formula I in high optical purity of about 99.9%, having S enatiomer less than about 0.1% and low moisture content of about 0.16-0.19%, while minimizing the level of hydrogen cyanide production, which comprises the steps of: i. Providing alkyl -(S)-4-chloro-3-hydroxy butyrate; ii. Contacting said alkyl-(S)-4-chloro-3-hydroxy butyrate with a metal cyanide in the presence of halohydrin dehydrogenase; iii. contacting the reaction mixture of step (ii) with the salt of a strong acid and a weak base at a controlled rate; iv. Contacting EDTA with the mixture of step (iii); v. Extracting said cyano product using an organic solvent; vi. And optionally, treating with charcoal followed by azeotropic distillation in the presence of a non-polar solvent. OH O Formula I 2. The process for the preparation of alkyl-(R)-4-cyano-3-hydroxybutyrate of Formula I as claimed in claim 1, wherein said alkyl-(R)-4-cyano-3-hydroxybutyrate of Formula I is ethyl-(R)-4-cyano-3-hydroxybutyrate (Formula la). 10 Formula la 3. The process for the preparation of alkyl-(R)-4-cyano-3-hydroxybutyrate of Formula I as claimed in claim 1, wherein said metal cyanide is selected from the group consisting of: sodium cyanide, potassium cyanide, magnesium cyanide or calcium cyanide. 4. The process for the preparation of alkyl-(R)-4-cyano-3-hydroxybutyrate of Formula I as claimed in claim 1, wherein the pH of the mixture of step (ii) is maintained at a range from about 5.5 to about 9.0. 5. The process for the preparation of alkyl-(R)-4-cyano-3-hydroxybutyrate of Formula I as claimed in claim 1 wherein the salt of a strong acid and a weak base is selected from the group consisting of, ferrous sulphate, cuprous sulphate, zinc sulphate, nickel sulphate, cadmium sulphate, cobalt sulphate. 6. The process for the preparation of alkyl-(R)-4-cyano-3-hydroxybutyrate of Formula I as claimed in claim 1 wherein the nonpolar solvent of step (vi) is a hydrocarbon containing 5-8 carbon atoms. 7. The process for the preparation of alkyl-(R)-4-cyano-3-hydroxybutyrate of Formula I as claimed in claim 6 wherein the nonpolar solvent is selected from the group consisting of: pentane, hexane, heptane, octane, isopentane, isoheptane, and toluene. Saloni Rastogi OfS. Majumdar&Co. (Agents for the applicant) Dated this 21st day of July 2008 11 |
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1543-MUM-2008-ABSTRACT(17-12-2008).pdf
1543-MUM-2008-ABSTRACT(GRANTED)-(6-1-2012).pdf
1543-MUM-2008-CANCELLED PAGES(3-10-2011).pdf
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Patent Number | 250502 | ||||||||||||
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Indian Patent Application Number | 1543/MUM/2008 | ||||||||||||
PG Journal Number | 02/2012 | ||||||||||||
Publication Date | 13-Jan-2012 | ||||||||||||
Grant Date | 06-Jan-2012 | ||||||||||||
Date of Filing | 21-Jul-2008 | ||||||||||||
Name of Patentee | ARCH PHARMALABS LIMITED | ||||||||||||
Applicant Address | H WING, 4TH FLOOR, TEX CENTRE, OFF SAKI VIHAR ROAD, CHANDIVALI, ANDHERI EAST, MUMBAI. | ||||||||||||
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PCT International Classification Number | CO7C2/00 | ||||||||||||
PCT International Application Number | N/A | ||||||||||||
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