Title of Invention

AN IMPROVED PROCESS FOR PREPARATION OF CEFTIOFUR INTERMEDIATE

Abstract

AN IMPROVED PROCESS FOR PREPARATION OF CEFTIOFUR INTERMEDIATE. An improved method for manufacture of 7-aminoO-(2-furanylcarbonylthiomethyI)-3-cephem-4-carboxylic acid of formula (I), a key intermediate for the third generation cephalosporin antibiotic, ceftiofur. The method proposes a selective bronsted acid, the molar proportion of the acid employed, the medium of reaction and the temperature of reaction in providing 7-amino-3-(2-furanylcarbonylthiomethyl)-3-cephem-4-carboxylic acid (I) in high yield and purity. To The Controller of Patents The Patent Office At Mumbai

Full Text

FORM -2 THE PATENTS ACT, 1970 (39 OF 1970) COMPLETE SPECIFICATION ( See Section 10 ; rule 13) (1) TITLE OF INVENTION AN IMPROVED PROCESS FOR PREPARATION OF CEFTIOFUR INTERMEDIATE (2) (a) LUPIN LIMITED, (b) 159, CST Road, Kalina, Santacruz (East), Mumbai - 400 098, State of Maharashtra, India, (c) an Indian company The following specification particularly describes the nature of this invention and the manner in which it is to be performed. FIELD OF INVENTION The present invention provides an improved method for manufacture of 7-amino-3-(2- furanylcarbonylthiomethyl)-3-cephem-4-carboxylic acid of formula (I), a key intermediate for the third generation cephalosporin antibiotic, ceftiofur. BACKGROUND OF THE INVENTION 7-Amino-3-(2-furanylcarbonylthiomethyl)-3-cephem-4-carboxyIic acid of formula (I) which is a key intermediate of ceftiofur has been synthesized by any of the following three methods, viz, I. Journal of Antibiotics (1974, 573-578; Essery J.M. et. al) teaches a general method for preparation of 3-thiomethyI cephalosporin derivatives comprising reaction of 7-amino cephalosporanic acid and a thiol carboxylic acid, in an aqueous medium and in the presence of a phosphate buffer. Apart from the general method described in scherae-l for preparation of 7-amino-3-thiomethylsubstituted cephalosporanic acid, there are, however no enabling disclosures therein for preparation of 7-amino-3-(2-furanylcarbonylthiomethyl)-3-cephem-4-carboxyiic acid of formula (I). The yields reported for preparation of various 7-amino-3-thiomethylsubstituted-3-cephem cephalosporin compounds however are quite low (40-47%), rendering them commercially less attractive. 2 Scheme-!: Method for preparation of 7-amino-3-(2-thiomethylsubstituted)-3-cephem-4-carboxylic acid as described in Journal of Antibiotics (1974, 573-578) II. US Patent No 4,464,367 (Labeeuw, B. et. al) discloses a method for preparation of the compound of formula (I) utilising the method described in Journal of Antibiotics (1974, 573-578; Essery J.M. et. al). However, here again apart from mentioning that compound (I) can be prepared by the general method described in Journal of Antibiotics (1974, 573- 578; Essery J.M. et. al) the patent fails to give any experimental details of how compound (I) can be specifically prepared. III. US Patent No. 4,397,330 (Sacks C.E. et al) contains the first specific disclosure for a method of preparation for the compound of formula (I), which is summarized in scheme- II, comprising reaction of 7-amino cephalosporanic acid and thiofuroic acid in a water immiscible solvent such as ethyl acetate at pH 6.4 ± 0.2 and at a temperature of 65°C. Even though, this patent gives details of experimental conditions for preparation of compound (I) as would be evident from preparation 1, column 4 of the patent, there is however no mention as to how the pH is maintained or any mention about the yield and quality of the product. 3 Scheme-11: Method for preparation of 7-amino-3-(2-fnranylcarbonylthiomethyl)-3-cephem-4-carboxylic acid (I) as described in US Patent No. 4,397,330. Moreover, since cephalosporins are susceptible to thermal degradation it is observed that at elevated temperatures of 65 °C and above, the product obtained is highly coloured which calls for extensive purification that is not only time-consuming but also costly. IV. US Patent No. 6,476,220 (Handa, V.K. et. al) teaches a method for preparation of (1) comprising, reaction of 7-arninocephaIosporanic acid and 2-thiofuroic acid in the presence of boron trifluoride in alkyl acetate as solvent at ambient temperature and which is summarized in scheme-III. Even though the product is obtained in good yield and purity, however it suffers from a limitation in that it is utilizes a hazardous reagent like boron trifluoride, which requires elaborate precautions while handling. Scheme-Ill: Method for preparation of 7-amino-3-(2-furanylcarbonylthiomethyl)-3-cephem-4-carboxylic acid (I) as described in US Patent No. 6,476,220. Apart from the above methods, which either utilize a Lewis acid or a phosphate buffer for reaction of thiofuroic acid with 7-amino cephalosporanic acid, there are no other reports of methods for preparation of (I). Various other methods are .known in the literature for displacement of the 3-acetoxy group of a cephalosporanic acid by a sulphur nucleophile. These include, 4 a) US Patent No. 4,144,391 (Hatfield L.D et. al) which teaches a method for displacement of the acetoxy group of a cephalosporanic acid with a sulphur nucleophile in an organic solvent, under essentially anhydrous conditions by heating at elevated temperatures between 70-120°C. The synthesis of cephalosporin compounds such as cefamandoie, cefazolin, ceftezole, cefazaflur etc is achieved through this method. b) US Patent No. 3,278,531 (Cox J.S.G et. al) which teaches a method for displacement of the acetoxy group of cephalosporanic C with a sulphur nucleophile in an aqueous mixture of water miscible solvent at pH 5-8 at elevated temperatures between 35-70°C to give 3-substituted thio derivatives of cephalosporin C. c) US Patent No. 4,472,574 (Hug Rudolph) which teaches a method for preparation of ceftriaxone by reaction of 7-amino cephalosporanic acid with 2,5-dihydro-6-hydroxy-3- mercapto-2-methyI-5-oxo-as-triazine in presence of boron trifluoride or its complex in a polar organic solvent such as acetonitrile. All the above methods, are either carried out in the presence of a Lewis acid such as boron trifluoride or in the absence of an acid at an elevated temperature. One of the widely used reagents which is utilized for the displacement of the acetoxy group at 3-methyl position of 7-amino cephalosporanic acid are the Bronsted acids such as sulphuric acid, sulfonic acids, such as methanesulfonic acid, para-toluene sulfonic acid, trifluormethane sulfonic acid etc. Such methods are described herein below, a) US Patent No. 4,376,200 (T. Ozasa et. al), which teaches a method for heterocyciic thiomethylation at the 3-position of 7-amino cephalosporanic acid is carried out in the absence of a solvent and in the presence of a large excess of sulphuric acid. Cephalosporin compounds like cefamandoie and cefazolin are prepared by this method. The reaction is carried out by dissolving 7-amino cephalosporanic acid in concentrated sulfuric acid or a mixture thereof with polyphosphoric acid and carrying out the reaction 5 in ice-cold conditions or at elevated temperatures below 45°C. The product is isolated, by pouring the mixture into ice-cold water. Scheme-IV: Method for preparation of 7-amino-3-substitutedthiomethyl-3-cephem-4-carboxylic acid as described in US Patent No. 4,376,200. This patent mentions that 7-amino-3-heterocyclic thiomethyl-A3-cephem-4-carboxyiic acid thus prepared is obtained with yields of 80-90% however, there is no mention about the purity of the compound prepared by this method. b) US Patent No. 4,312,986. discloses a method for preparing 7-(substituted)-amino-3-substituted thiomethyl-A3-cephem-4-carboxylic acid comprising, reaction of a 7-(substituted)-amino-3-substituted-A3-cephem-4-carboxylic acid with a thiol compound in the presence of a protonic acid or a Lewis acid other than boron trifluoride, the chemistry of which is depicted herein below in scheme-V. R = thiol compoun residue R1 = hydrogen, C]_4 alkoxy group R = amino group or protected amino group Scheme-V: Method for preparation of 7-(substituted)-amino-3-subs1ituted thiomethyl-Δ3 cephem-4-carboxylic acid as described in US Patent No. 4,312,986. 6 The method essentially consists reaction of 7-amino cephalosporanic acid, with a thiol compound in a non-aqueous solvent in the presence of a Bronsted acid (protonic acid) such as methanesulfonic acid, perchloric acid or a Lewis acid such as stannic chloride or anhydrous zinc chloride at -20 to +80°C, and in a time ranging between 1.0 to 4.0 hours. The product 7-(substituted)-amino-3-substituted thiomethyl-A3- cephem-4-carboxylic acid is isolated after adjusting to pH 4.0. The non-aqueous solvents that can be employed are selected from aliphatic saturated mono or dicarboxylic acid, a nitrile, a nitroalkane or a sulfolane. The patent also states that the Bronsted/Lewis acid is employed in a molar ratio of 2-10 moles per mole of 7-(substituted)-amino-3- cephem-4-carboxylic acid From the description it can be noted that group R of the cephalosporin thio substituent at the 3-methyI position is preferably nitrogen containing heterocyclic group, which contains at least one nitrogen atom with or without oxygen or sulfur atom. These 3-thiomethyl-substituted intermediates disclosed therein are employed for manufacture of cephalosporin antibiotics, such as cefamandole, cefbuperazone, cefmenoxime, ceforanide, cefmetazole, cefminox, cefonicid, cefoperazone, cefotetan, cefotiam, cefpiramide etc. In particular, there is no mention about synthesis of compounds wherein R is an oxygen containing heterocyclic ring, such as a furan derivative. Moreover the patent does not describe compounds where there is an intervention of a carbonyl group between the heterocyclic ring and the sulfur atom at the 3-position of the cephalosporins nucleus i.e. compound (I). In their attempt for extending the method described in US 4,312,986, for synthesis of 7-amino-3-(2-furanylcarbonyIthiomethyl)-3-cephem-4-carboxylic acid (I) comprising reaction of 7-amino cephalosporanic acid (II) with 2-thioruroic acid (III) in a non-aqueous organic solvent (acetic acid) in the presence of methanesulfonic acid at 50°C (as per example 1, column II) it was found that, 7 i) there was only 17% conversion to the desired product of formula (I) as evidenced by HPLC, ii) total impurities between 75-80% were formed in the reaction, iii) the product isolated with a yield of 16% was dark in colour and had a purity of only 79% and also containing 19-21% of impurities, Herein it is worth mentioning that the presence of a carbonyl group interposed between a sulfur atom and a furan ring system in the 3-thioftiroylmethyl substituent of 7-amino-3-(2-furanyIcarbonylthiomethyl)-3-cephem-4-carboxylic acid (I) makes the compound (I) very labile and susceptible to fission of the sulfur-carbon bond of the carbonyl group leading to the formation of the thiol compound and the dimeric compound in solution. The structure of the impurities arising out of fission of the sulfur - carbonyl bond and dimerisation are given herein below as compounds (IV) and (V) respectively which probably explains the low conversion and formation of high level of impurities. The effect is fess pronounced in cephalosporin compounds, which do not possess a carbonyl group interposed between the sulphur atom and the heterocyclic group, therefore these compounds are formed with high conversion and low level of impurities and therefore with higher yield and purity. 8 Thus to summarize, a) Synthesis of 7-amino-3-(2-ftjranylcarbonyIthiomethyl)-3-cephem-4-carboxylic acid (I) has been carried out under neutral conditions as described in US Patent No. 4,937,330 and Journal of Antibiotics (1974, 573-578) or under acidic conditions in presence of boron trifluoride as described in US Patent No. 6,476,220. b) Yield or purity of the compound (I) obtained by the methods described in US Patent No. 4,937,330 and Journal of Antibiotics (1974, 573-578) are not reported. c) Even though the yield and purity of the compound (I) synthesized by the method described in US Patent No. 6,476,220 is good, but however the method employs a hazardous reagent like boron trifluoride, which requires careful handling on industrial scale. d) Extension of the method described in US Patent No. 4,312,986 for synthesis of 7-amino- 3-(2-furanylcarbonylthiomethyl)-3-cephem-4-carboxyUc acid (I) gave compound (I) as a dark-brown compound with a yield of 16% and purity 79%. Thus there is a need for a practical, less hazardous method for preparation of 7-amino-3-(2-furanylcarbonyIthiomethyl)-3-cephem-4-carboxyIic acid (I) with good yield and purity and substantially free from impurities, which moreover, is free of the shortcomings associated with the prior art methods, The present inventors have found that compound (I) can be synthesized from 7-amino cephalosporanic acid (II) by reaction with thiofuroic acid (III) in the presence of an Bronsted acid and alkyl acetate as solvent as described in scheme-VI. 9 Scheme-VI: Method for preparation of 7-amino-3-(2-furanylcarbonyl1hiomethyl)-l-cephem-4-carboxylic acid (I) as described in present invention. Among the Bronsted acids tried were paratoluene sulfonic acid, trifluoroacetic acid, trifluoromethane sulfonic acid, methanesulfonic acid and sulphuric acid. It was found that methanesulfonic acid was the preferred acid as the conversion and yield was higher as compared to other Bronsted acids. The conversion of 7-amino cephalosporanic (II) acid to 7-amino-3-(2-furanylcarbonylthiomethyl)-3-cephem-4-carboxylic acid (I) employing sulphuric acid was only 70-80% with 20-30% of associated impurities and purity of isolated compound (I) was also lower i.e. below 93.5%. When methanesulfonic acid was used as the Bronsted acid instead of sulfuric acid, there was not only a improvement in the conversion of (I) between 80 to 90% but most importantly, the isolated product i.e. 7-amino-3-(2-furanylcarbonylthiomethyI)-3-cephem-4-carboxylic acid (I) was found to possess high purity of more than 96% substantially free of impurities and which also exhibited high stability. Similarly, when instead of methanesulfonic acid, the above mentioned reaction was carried out in the presence of other bronsted acids like p-toluenesulfonic acid, trifluoromethane sulfonic acid etc. very little displacement at the 3a - position of the cephem compound took place and the reaction led to formation of predominant amounts of unidentified impurities. 7-amino-3-(2-furanylcarbonylthiomethyl)-3-cephem-4-carboxylic acid of formula (I) formed in the reaction was only between 5-30% and could not be isolated from the reaction mixture. 10 The quantity of methanesulfonic acid employed is not catalytic but a large excess of 18-20 moles is required. It was expected that with the large amount of methanesulfonic acid used, there would be higher level of impurities with lower conversion resulting in lower yield and low purity of the product, but the results obtained were surprisingly found to be contrary. The yield and quality of 7-amino-3-(2-furanyIcarbonylthiomethyl)-3-cephem-4-carboxylic acid (I) and formation of associated impurities was also found to be highly dependent on the molar proportion of methanesulfonic acid employed per mole of 7-amino cephalosporanic acid (II), the medium and temperature of the reaction. The reaction medium also found to play a significant role in the conversion of (I) and the in the formation of impurities. Water-immiscible solvents such as alkyl acetates, chlorinated hydrocarbons etc and water-miscible solvents such as nitriles were tried out. The inventors found out that carrying out the reaction in alkyl acetates preferably ethyl acetate resulted in higher conversion of compound (I) with low impurity formation. With other solvents the impurity formation was high in the range of 65-75% giving a low conversion between 25-35%. The product (I) was isolated with good yield and purity substantially free from impurities. The selection of the bronsted acid, the molar proportion of the acid employed, the medium of reaction and the temperature of reaction in providing 7-amino-3-(2-fiiranylcarbonyIthiomethyl)-3-cephem-4-carboxylic acid (I) in high yield and purity, therefore forms the basis of the present invention. SUMMARY OF THE INVENTION An aspect of the present invention provides a simple, cost effective method for the manufacture of 7-amino-3-(2-njranylcarbonylthiomethyI)-3-cephem-4-carboxylic acid, a key intermediate of ceftiofur of formula (I) 11 employed in molar proportion of 1.2 to 3.0 moles per mole of compound (II), in the presence of ethyl acetate as solvent in the presence of a large excess of methanesulfonic acid, employed in molar proportions of 18 to 20 moles per mole of compound (II), and at a temperature between 25 °C to 35 °C, preferably between 28 °C to 32 °C, followed by quenching the reaction mixture with water and adjusting.the pH to 5.8 ± 0.2 to give 7-amino-3-(2-ruranylcarbonylthiomethyl)-3-cephem-4-carboxylic acid, of formula (I) having high purity and substantially free from impurities. DETAILED DESCRIPTION OF THE INVENTION Thiofuroic acid (III) was prepared by the method described in US Patent No. 4,397,330 comprising reaction of furoyl chloride (VI) with sodium sulphide at pH 8-9 in an aqueous medium and isolated by extraction with ethyl acetate at pH 1.5-2.0. The mixture of thiofuroic acid in ethyl acetate was used as such for the preparation of 7-amino-3-(2-furanylcarbonylthiomethyl)-3-cephem-4-carboxylic acid (I). 12 In a typical embodiment of the present invention, 7-amino cephalosporanic acid (II) is suspended in an inert organic solvent, to which methanesulfonic acid is added. To the resulting mixture is added thiofuroic acid (III) and the progress of the reaction is monitored by HPLC. After completion of the reaction, 7-amino-3-(2-furanylcarbonylthiomethyI)-3-cephem-4-carboxylic acid (I) is isolated by quenching with water followed by adjusting the pH between 5.6 and 6.0. The method for preparation of 7-amino-3-(2-furanylcarbonylthiomethyI)-3-cephem-4-carboxylic acid (I) as per the present invention is summarized in Scheme-VII for ready reference. 13 Scheme-VII: Method of preparation of 7-Amino-3-(2-furanylcarbonylthiomethyl)-3-cephem-4-carboxylic acid (I) as per the present invention, The reaction of 7-amino cephalosporanic acid (II) and thiofuroic acid (III) to give 7-amino-3-(2-furanylcarbonylthiomethyl)-3-cephem-4-carboxylic acid (I) was found to be dependent on the following parameters: a) selection of Bronsted acid. b) molar proportion of the Bronsted acid. c) temperature of the reaction medium. d) solvent medium. 14 a) Selection of Bronsted acid: The conversion of compound (II) to give compound (I) was found by the present inventors to be dependent on the bronsted acid employed. Bronsted acids such as sulphuric acid, trifluoroacetic acid, para toluenesulfonic acid, trifluoromethanesulfonic acid and methanesulfonic acid were tried out for achieving the said conversion but methanesulfonic acid was found to be the Bronsted acid of choice since the conversion of compound (I) was high, associated impurities were low thereby giving good yield (65-69%) and purity (above 96%). The results have been summarised in Table-I. Table-I: Effect of Bronsted acid in the conversion of 7-amino cephalosporanic acid to 7-amino-3-(2-furanylcarbonylthiomethyl)-3-cephem-4-carboxyhc acid (I). No Bronsted acid Conversion (%) Impurity formation Purity of compound(I) (%) (%) I Methanesulfonic acid 85-90 5-15 above 96 2 Sulphuric acid 70-80 20-30 93 T j Trifluoroacetic acid No 24.36 Not isolated. conversion 4 p-Toluenesulfonic acid 0.15 21.9 Gummy solid formed during reaction, not isolated. 5 Trifluoromethanesulfonic acid 27,55 49.22 Gummy solid formed during reaction, not isolated. Thus it will be evident that methanesulfonic acid is the preferred acid as the yield, conversion and purity of the compound (I) is higher. 15 b) Molar proportion of methanesulfonic acid: The effect of the molar proportion of methanesulfonic acid employed per mole of 7-amino cephalosporanic acid and its role on the rate of conversion, impurity formation and purity of the compound is summarized in Table-II. Table-II: Effect of molar ratio of methanesulfonic acid on the conversion of 7-amino cephalosporanic acid to 7-amino-3-(2-fitranylcarbonylthiomethyl)-3-cephem-4-carboxylic acid (I). No Molar Proportion of methanesulfonic acid per mole of 7-Amino cephalosporanic acid (II) Conversio n (%) Impurity formation (%) Purity of compound (I) (%) 1. 10.0 moles 38-40 {unreacte d compound (II):28%) 30-35 Gummy material isolated. 2. 12.0 moles 65 (unreacte d compound (II):6.0% } 20-25 85-87 3, 20.0 moles 86 7-8 96-98 It is evident from Table-II, that when the molar proportion of methanesulfonic acid per mole of the compound (II) is 10.0, the conversion of 7-amino-3-(2-furanylcarbonylthiamethyl)-3-cephem-4-carboxylic acid (I) is quite low (38-40%) with higher proportion of associated impurities (30-35%) and also the reaction does not go to completion. Increasing the molar proportion of methanesulfonic acid to 12 moles per mole of compound (II) improves the conversion of compound (1) and lowers impurity formation but the purity of the isolated compound (I) is however low (85%). A molar proportion of 18 - 20 per mole of the compound (I) was found to be optimum as the impurity formation was lower (7-8%) with concomitant rise in conversion of compound (I) thus giving higher yield (65-69%) and purity above 96%. 16 c) Effect of temperature: The reaction rate was found to be dependent on the temperature of the reaction medium after addition of methane sulfonic acid. The reaction was quite slow at lower temperature i.e. below 25°C, requiring more than 5.0 hours for the reaction to go to completion. However the reaction rate was considerably accelerated with increase in temperature. The optimum temperature was found to be between 28-35°C, but preferably 30 + 2 °Q as the time required is between 2-3 hours for the reaction to go to completion. d) Reaction Medium: The solvent employed as the reaction medium is selected from a water-immiscible or a water-miscible organic solvent such as a chlorinated solvent, alkyl acetate, nitriles but preferably alkyl acetate. When the reaction was carried out in chlorinated solvents such as dichloromethane or nitriles such as acetonitirile, low conversion (25-30%) of (I) was obtained with concurrent formation of very high level of impurities (30-40%). The effect of solvents or, the conversion of compound (I) and formation of impurities is summarized in Table-Ill. Table-Hi: Effect of (he reaction medium on the conversion of 7-am'mo cephalosporanic acid to 7-amino-3-(2-furanylcarbonylthiomethy})-3-cephem-4-carboxylic acid (!) No Solvent employed Conversion (%) Impurity formed (%) Purity of compound (I) % 1. Dichloromethane 23.38 76.24 Gummy solid, not isolated 2. Acetonitrile 31.48 68.40 Gummy solid, not isolated 3. Ethyl acetate 85-90 5-15 Above 96% Alkyl acetate was preferred as the solvent of choice as the conversion was quite high between 85-90% with impurity formation between 10-15%. Alkyl acetate preferably ethyl acetate was selected as the solvent of choice for carrying out the reaction since compound (II) dissolved easily in ethyl acetate and also the reaction was facile with the reaction going to completion in 2-3 hours. 17 The volume of ethyl acetate employed can be between 5-20 times volume per gram of compound (II), but preferably 10-18 times of ethyl acetate. The optimum amount of thiofuroic acid (III) required for the reaction to go to completion was found to be between 1.2 -2.0 moles per mole of the compound (II). A slight excess of compound (III) was required for the reaction to go to completion. The mixture of thiofuroic acid (III) in ethyl acetate obtained during the preparation of (III) is used as such for the reaction. In a specific embodiment, 7-amino cephalosporanic acid (II) is suspended in ethyl acetate [18 volumes per gram of (I)] and cooled between -10 and -15° C and methanesulfonic acid (20 mo)es) is added slowly to the mixture. A mixture of thiofuroic acid (1.2 moles) in ethyl acetate is added to the mixture and the reaction mixture agitated at 30 ± 2 ° C with intermittent HPLC monitoring. The reaction mixture is quenched with water, and the pH of the reaction mixture is adjusted to pH 5,8 ± 0.2 by addition of 25% aqueous ammonia solution at a temperature of 28 ± 2 °C. The compound of formula (I) is allowed to separate out completely by agitating the mixture at 28 + 2 ° C for 60-120 minutes and filtered. The compound of formula (I) prepared by the present method has the following characteristics as shown in Table-Ill. Table-Ill: Stability of 7-amino-3-(2-furanylcarbonylthiomethyl)-3-cephein-4-carboxytic acid (I) prepared by the present invention. Purity 96-98% Total Impurities 2.0-4.0% Storage Stability Stable for 90 days at 40° + 2° C & Rh 75% + 5% with a drop in assay from 96. 13 to 95.56% The invention is further illustrated by the following non-limiting examples. 18 Example-1 Preparation of 7-amino-3-(2-furanylcarbonylthiomethyl)-3~cephem-4-carboxylic acid (I) from 7-amino cephalosporanic acid (II) using methanesulfonic acid 1- amino cephalosporanic acid (lOOg; 0.3676 moles) was added to ethyl acetate (1800ml). The reaction mixture was cooled to -10 to -12 °C and methanesulfonic acid (706.6gms; 7.3527 moles) was added to it in 45 minutes, maintaining the temperature below -10 °C. Thiofuroic acid (56.47gms; 0.4411 moles in 325ml of ethyl acetate) was added to the reaction mixture. The reaction mixture was stirred for three hours at 25 + 2 °C. The progress of the reaction was monitored by HPLC. The reaction mixture was cooled to 0 °C and quenched slowly with 400 ml of chilled water, below 10 °C. Sodium dithionite solution (5gms in 50 ml of demineralized water and EDTA (0.5g dissolved in lOOml of demineralized water) was added to the mixture. The pH of the reaction was adjusted to 2.0 by addition of 25% aqueous ammonia solution (350ml) at 0-15 °C and iurther adjusted to pH 5.8 ± 0.2 by adding 15% aqueous ammonia solution at a temperature of 25-27°C. The product (I) slowly starts precipitating out and the mixture is further agitated at same temperature. The solid was filtered off and washed with ethyl acetate (800 ml) followed by water (2400 ml). The wet cake was taken in water and dissolved by adding 56 ml of triethylamine (pH= 9-9.5) while maintaining the temperature between 4-5 °C. The aqueous solution was optionally agitated with activated carbon and filtered. The pH of the filtrate was adjusted to pH 5.8 very slowly by addition of 15% aqueous orthophosphoric acid at 28-30 °C. The product was filtered off and washed with 250 ml of water followed by 125 ml of acetone and dried under reduced pressure to obtain 82 g (65.6%) of 7-amino-3-{2-furanylcarbonylthiomethyl)-3-cephem-4-carboxylic acid (I) having purity 96.13%. ExampIe-2 Preparation of 7-amino-3-(2-furanylcarbonylthiomethyl)-3-cephem-4-carboxylic acid (I) from 7-amino cephalosporanic acid (II) using sulphuric acid. 1- amino cephalosporanic acid (lOg; 0.03676 moles) was added to ethyl acetate (lOOrnl). The reaction mixture was cooled to -10 to -12 °C and sulphuric acid (54.0gms; 0.551 19 moles) was added to it in 45 minutes, maintaining the temperature below -10 °C. Thiofuroic acid (5.65gms; 0.4411 moles in 325ml of ethyl acetate) was added to the reaction mixture. The reaction mixture was stirred for three hours at 25 + 2 °C. The progress of the reaction was monitored by HPLC. The reaction mixture was cooled to 0 °C and quenched slowly with 40 ml of chilled water;, below 1.0 C, Sodium dithionite solution (O.5gms in 5.0 ml of demineralized water and EDTA (0.5g dissolved in 10ml of demineralized water) was added to the mixture. The pH of the reaction was adjusted to 2.0 by addition of 25% aqueous ammonia solution (35ml) at 0-15 C and further adjusted to pH 5.8 ± 0.2 by adding 15% aqueous ammonia solution at a temperature of 25-27°C. The product (I) slowly starts precipitating out and the mixture is further agitated at same temperature. The solid was filtered off and washed with ethyl acetate (80 ml) followed by water (240 ml). The wet cake was taken in water and dissolved by adding 5.6 ml of triethylamine (pH: 9-9.5) while maintaining the temperature between 4-5 C. The aqueous solution was optionally agitated with activated carbon and filtered. The pH of the filtrate was adjusted to pH 5.8 very slowly by addition of 15% aqueous orthophosphoric acid at 28-30 °C. The product was filtered off and washed with 25ml of water followed by 12,5ml of acetone and dried under reduced pressure to obtain 9.4 g (75.6%) of 7-amino-3-(2-furanylcarbonylthiomethyl)-3-cephem-4-carboxylic acid (I) having purity 93.49%. 20 We claim, 1. A process for preparation of 7-amino-3-(2-furanylcarbonyUhiomethyl)-3-cephem-4- carboxylic acid of formula (I)-comprising, reaction of 7-amino cephalosporanic acid of formula (II) and thiofuroic acid of formula (III), employed in molar proportion of 1.2 to 2.0 moles per mole of compound (II), in the presence of ethyl acetate as solvent and in the presence of a large excess of methanesulfonic acid, and at a temperature between 28 °C to 32 °C to give 7-amino-3-(2-ruranylcarbonyithiomethyl)-3-cephem-4-carboxylic acid of formula (I) possessing high purity, substantially free of impurities and high stability. 2. A process according to claim I, wherein the molar proportion of methanesulfonic acid is between 18-20 moles per mole of the compound of formula (II). 3. A process for preparation of 7-amino-3-(2-ruranylcarbonyIthiomethyI)-3-cephem-4- carboxylic acid of formula (I) substantially as hereindescribed and illustrated with reference to the accompanying examples. Dated this 10th day of December 2003 21

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991-mum-2002-form 3(15-11-2002).pdf

991-mum-2002-form 4(12-12-2003).pdf

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