Indian Patents. 212050:2-MERCAPTO-5-PHENYL-1, 3, 4-OXADIAZOLYL-(Z)-4-BROMO-2-METHOXYIMINO BUTYRIC ACID DERIVATIVE AND PROCESS OF PREPARATION THEREOF

Title of Invention	2-MERCAPTO-5-PHENYL-1, 3, 4-OXADIAZOLYL-(Z)-4-BROMO-2-METHOXYIMINO BUTYRIC ACID DERIVATIVE AND PROCESS OF PREPARATION THEREOF
Abstract	Compounds of formula (I) wherein X is halogen and R1 is alkyl or phenyl, are useful for the preparation of cephalosporins of the formula (VI) through acylation and thiourea cyclisation.

Full Text	Field of Invention The present invention relates to a 2-mercapto-5-phenyl-l, 3,4-oxadiazolyl- (Z)-4-bromo-2-methoxyimino butyric acid derivative used in the preparation of cephalosporin antibiotics. The present invention also discloses the process of preparing novel thioester derivatives of the general formula (I) by reacting 4-halogeno-2~methoxyimino-3-oxo~butyric acid (II) with 5- substituted-!, 3,4-oxadiazole-2-thiol of formula (III). The invention also discloses the use of the new intermediate (1) for the preparation of cephalosporanic antibiotics (V^) in excellent yields and purity wherein X represents halogen (CL Br and I) R1 represents C1-C4 alkyl or phenyl Background Art Acid chlorides, anhydrides, esters, amide etc, are reported in the chemical literature for activation of carboxylic acid of formula (IV). Activation in the form of acid chloride required protection and deprotection of NH2 group. Activation of 2- (2-aminothiazol-4-yI)-2-methoxyiminoacetic acid (IV) by S02C12/DMF is reported in US patent 5,856, 502 and activation of SOCIz/DMF is reported in US patent 5,037, 988. These processes suffers with the limitation of poor by moderate yields along with the use of solvents like benzene and stringent conditions required for carrying out the reactions at commercial scale. In US patent No.4,576,749 and 4,548,748 the acid of formula (IV) have also been activated by reacting with 1-hydroxybenzotriazole (HOBT) or 2-mercaptobenzothiazole (MBT) in the presence of dicyclohexylcarbodimide (DCC) to produce reactive ester of the acid (TV) which reacted to cephem moiety to prepare cephem antibiotics, but the processes are time consuming and with low yields, hence not suitable. US patent 4,767,852 discloses a process for production of cephems by acylating 7-ainino-3-cephem-4-carboxylic acid with 2-mercaptoben2othiazolyl-(Z)-2-(2-aminothiazol-4-yl)-2-methoxyiminoacetate (MAEM). Similarly, US PatNo,5,026,843 disclosed a process for preparing ceftriaxone disodium hemiheptahydrate by acylation of 7-amino-3-[[(2,5-dihydio-6-hydroxy-2-methyl-5-oxo-l,2,4-triazin-3yl)thio]methyl]3-cephem-4-carboxyU^ acid (ACT) by using MAEM as acylating agents in good yield and quality. Thus MAEM has become the standard acylating agent for the preparation of cephalosporins having an oximino group and a 2-aminothiazolyl group in 7-position of cephem compounds. However, the synthesis of MAEM from 2-(2-aminothiazol-4-yl)-2-methoxyiminoacetic acid (IV) and 2,2'-dithio-bis-benzothiazole involves use of costly condensing agent triphenylphosphine (TPP). Moreover, during condensation of MAEM with 7-amino-3-cephem-4-caiboxylic acid compound (V) , a toxic compound MBT is also produced as a byproduct, see e.g.. Chemical Abstracts, 111, 19243p (1989) which is difficult to remove completely. Thus it is evident that the procedures described in the prior art for preparation of these antibiotics are complex, involving protection, deprotection and are associated with toxic byproduct generation. Hence there is a need to develop new acylating agents which are capable of transferring the 2-aminothiazolyl moiety to cephem compounds of formula (V) in good yield but without producing this toxic byproduct. On the similar lines, a new thioester was reported by D.G.Walker, Tet. Lett. 1990, 31,6481 to acylate the cephem moiety to get cefepime sulfate but yields obtained by using this thioester wore in the range of 54-73% which cannot be considered as good yield to operate a process at commercial scale. The use of this thioester was reported in the Tet. Lett. 1990, 31, 6481 only for cefepime and not for other cephalosporins. This thioester was exploited in US patent No. 5,869,649 for making three other important cephem antibiotics. Synthesis of 4-halogeno - 2 - methoxyimino-3-oxo-butyric acid is reported in patent no. EP 0 030 294 and a large number of references are available in the patent literature disclosing the use of 4-halogeno-2-methoxyimino-3-oxo-butyric acid represented by formula (H) as the starting material. EP 0030294 and WO 00 0063214 discloses the condensation of the 4- Statement of Invention The present invention provides a 2-mercapto-5-phenyl-l, 3,4-oxadiazolyl- {Z)-4-bromo-2-methoxyimino butyric acid derivative used in the preparation of cephalosporin antibiotics. The present invention also discloses the process of preparing novel thioester derivatives of the general formula (I) by reacting 4-halogeno-2~methoxyiniino-3~oxo-butyric acid (II) with 5- substituted-h 3.4-oxadia7-ole-2-thiol of formula (III). The invention also discloses the use of the new intermediate (1) for the preparation of cephalosporanic antibiotics (VT) in excellent yields and purity Detailed Description of the Invention The present invention provides new thioesters of 4-halogeno-2-methoxyimino-3-oxo-butyric acid of general fonnula (I). The synthesis of compound (I) is achieved by preparing activated complex of 4-halogeno-2-methoxyimino-3-oxo-butyric acid (H) with DMF-POCI3 followed by the reaction with thio-oxadiazoles of the general formula (HI) in organic solvent in presence of an organic base at the temperature between -30°C and +20°C- The reactive active ester is obtained quantitative yields (95-99%). product (Vn) which is formed during this reaction has also been controlled in the process. Surprisingly this side reaction has never been mentioned in the literature. In an embodiment, in the compound of formula (I), X is chloro, bromo or iodo. In another embodiment the organic solvent is selected from the group comprising dichloromethane, tetrahydrofuran, dioxane, N,N-dimethylformamide, acctonitrile and mixtures thereof. In still another embodiment the organic base is selected from the group comprising triethylamine, diethylamine, tributylamine, pyridine, N-alkylanilines, and mixtures thereof. The compound (I) so obtained is reacted with 7-amino cephem carboxylic acid of general foramla (V) in two different methods and both the methods lead to same product with comparable yields and purity. Using above mentioned thioester the cephalosporin antibiotics obtained are of high purity (90-99%), The method gives an excellent yield (70-95%) of cephalosporin without necessitating the protection of the amino group of the acylating agents, and the toxic byproduct 2-mercaptoben20thiazole is not produced. The cephalosporin antibiotic were synthesized by following two methods: Method-I The reactive thioester (I) was reacted with 7-aminocephem compound (V) in organic solvent in the presence of base to obtained condensed product, which was not isolated and is directly cyclised with thiourea in mixture of water and a polar organic solvent like tetrahydrofuran, dimethylfonnamide, dioxane, alcohol to obtain desired cephalosporanic antibiotics of very good purity and excellent yields. Method -II In this approach, starting from active ester of formula (I) final product was prepared in one pot reaction. The process comprises cyclization of active ester in the first step and in same reactor addition of amino cephem compound in mixture of water and a polar organic solvent like tetrahydrofuran, dimethylformamide, dioxane, alcohols to obtain desired cephalosporanic antibiotics of equally good purity and yields as compared to first approach. This approach provides a simple , cheap and commercially viable method without the necessity of isolating thioester and without producing any toxic byproduct namely 2-mercaptobenzothiazole. The substituent R2 in cephem compound (V) and (VI) represents hydrogen, methyl, acetyloxymethyl, methoxymethyl, 2,5-dihydro-6-hydroxy-2-methyl-5-oxo-l,2,4-triazine-3- thiol, furanyl-2-carbonyl thiol or a standard cephalosporin substituents. R3 in cephem compound (V) and (VI) represents hydrogen , salt or a ester group which can be easily removed e.g. p-methoxybenzyl , p-nitrobenzyl , diphenylmethyl , phenacyl , trimethylsilyl etc. In an embodiment of the present invention the organic base may be selected from the group consisting of triethylamine, N-methylmorpholine, pyridine, N-methylanilines, 1,5- diazabicyclo[4.3.0] non-5-ene, l,4-diazabicyclo[2*2.2]octane, 4-dimethylaminopyridine, and mixtures thereof. Many other beneficial results can be obtained by applying disclosed invention in a different manner or by modifying the invention with the scope of disclosure. However, V since the major characteristic feature of the present invention resides in the use of novel reactive thioester derivatives of 4-bromo-2-methoxyimino-3-oxo-butyric acid of the general formula (I) in preparing the cephalosporin antibiotics, the technical scope of the present invention should not be limited to the following examples. The following examples are provided to illustrate but not to limit the claimed invention. EXPERIMENTAL Example -1 Synthesis of 2- mercapto- 5 - phenyl - 1, 3, 4 - oxadiazolyl - (Z) - 4- bromo - 2- methoxyimino-3-oxo-butyrate (I). Phosphorus oxy chloride (25,6g) was added slowly to N, N-dimethyl formamide (12.2g) at 0 to -5°C Stirred for 30 minutes. Acetonitrile (200 ml) was added followed by 4-bromo-2-methoxyimino-3-oxo-butyric acid (25.0g) and 5-phenyl-l,3,4-oxadiazole-2-thiol (19.8g). Pyridine (44.1ml) was slowly added to the flask at -10°C. The progress of the reaction was monitored by HPLC, After the disappearance of the starting material, the reaction mass was poured into ice-water, white colored solid separated out which was filtered and washed with water. Dried under vacuum to obtain 40.8 gm of thioester with HPLC purity (96.0 - 98.0%) Melting point : 139-140 °C ^HNMR (DMS0-d6) : 8 4.1 (3H,s4Sr-Oa;y, 4.3(2H,s3iQiCO) 7.6-7.9(5H, m, - C^s) ^°C-NMR(CDCl3) : 5 30.2,65.8,121.3,127.7,129.7,134.1,147.5,147.8,156.3,160.2 186.1. Example 2 3-Acetyloxymethyl-7-[(ZH2-aminothiazolyl-4-yl)-2-(methoxyimino)acetam cephem-4-carboxylic acid (Cefotaxime acid). Method-I A mixture of THF (250ml) and water (150ml) and N,N-dimethylacetamide (25.0ml) was stirred under inert atmosphere. At 0° - 5°C, 7-aminocephalosporanic acid (25.0g) and 2-mercapto-5-phenyl-l,3,4-oxadiazolyl-(20-4-bromo-2-methoxyinuno-3oxo-butyrate(46.0^^ were added. Triethylamine (20.4g) was slowly added to reaction by maintaining pH 7.0 to 8.0. The reaction was checked by HPLC. After 6-8 hrs., the reaction mixture was extracted by methylene chloride(200x3). The aqueous layer is subjected for charcoal treatment Thiourea (18.4g) and sodium acetate (4.2g) were added to the filtered aqueous layer and stirred for 1.0 hr to get the cefotaxime which was isolated with subsequent acidification of the aqueous layer with dil. HCl at 10°C to pH 3.0. The solid separated was filtered, washed with water and ethylacetate and then dried under vacuum at 40-45°C to get Cefotaxime, 40.9g (yield 98%). ' HPLC (purity) = 98-99% Method-n 2-Mercapto-5-phenyl-l,3,4-oxadiazolyl-(Z)-4-bromo-2-methoxyimino-3-oxo-butyrate (46.0g.) was taken in a mixture of tetrahydrofuran (250ml) and water (150ml). The solution was cooled to lO°C and the thiourea (20.47g) and sodium acetate (4.32g) were added. The reaction mixture was stirred for 1.0 hr. 7-amino cephalosporanic acid (25.0g) was added followed by slow addition of triethylamine (20.4g) the progress of the reaction was monitored by HPLC. The reaction was completed in 6-8 hr. The reaction mixture was extracted with dichloromethane (3 X 200 ml). The aqueous layer was acidified with dil. HCl to obtain cefotaxime, 38,0g. was extracted with dichloromethane (3 x 100ml). The aq. layer was separated and treated with charcoal (0,2g), Thiourea (10.9g) is added to the solution and stirred for LO hr. till cyclisation is over . A solution of sodium-2-ethylhexanoate (30,5g) in acetone was added at 10-15°C and stirred for L5 hours (400ml) of acetone was added in 1 hour at 10-15°C to complete the crystallization. The product was filtered under N2 atmosphere and wet cake was dissolved in mixture of water and acetone (1:2), and cooled to -lO°C. Colored impurities were separated. The solution was decanted and diluted with acetone (600ml) at 18-20°C. Precipitated solid was filtered under N2 and washed with acetone (20ml). Dried under vacuum at 40-45°C to get pure Ceftriaxone sodium 25.5g. HPLC (purity): 98.0% for 2-3 hours at a pH of 7.0-8,5 mamtained by triethylamine to get clear solution. The reaction mixture was monitored by HPLC. After completion of reaction, 200ml water was added and pH was adjusted to 7.0. The aqueous layer was separated, charcoalizied and treated with sodium-2-ethylhexanoate (30.5g) in acetone, reaction was proceeded by same method as mentioned in method-I to get crude ceftriaxone sodium (24.0g). mercapto-5-phenyl-13,4-oxadiazolyHZ)-4-bromo-2-methoxyimmo-3-oxo-butyr^ were added to a mixture of THF (35ml) and watcir (35ml) at temperature 5^C. The pH of reaction was maintained at 7,5 to 8.5 by addition of TEA during the reaction- After completion of reaction, the reaction was extracted with methylene chloride (25ml x 3). The aqueous layer was diluted with 15ml THF and thiourea was added to the aqueous and stirring was continued for 30 to 45 min. to complete the cyclisation. After that pH was lowered to 3 by addition of IN HCL The solution is saturated by salt. The organic layer was separated and pH was further adjusted to 0.5 by concentrated HCL IPE (250ml) was added to precipitate the hydrochloride salt of Ceftiofur, 4.3g (yield 75.0%). HPLC (purity) : 98.0% WE CLAIM: 1. A 2-mercapto-5-phenyl-l, 3,4-oxadiazolyl- (Z)-4-bromo-2-methoxyimino butyric acid derivative used in the preparation of cephalosporin antibiotics, and represented by formula(I) 2. A process for preparing active thioester derivatives 2-mercapto-5-phenyl-l, 3,4 oxadiazolyl- (Z)-4-bromo-2-methoxyimino butyric acid represented by formula (I) as claimed in claim 1, said process comprising the step of reacting 4-halogeno-2- methoxyimino-3-oxo- butyric acid represented by formula(II) wherein X represents halogen(Cl, Br, I) wherein Rl represents C1-C4 alkyl or phenyl with thio-oxadiazole of formula(III) in the presence of DMF, phosphorous oxychloride, an organic base and an organic solvent at a temperature being maintained in the range of-30°C to +20°C. 3. A process as claimed in claim 2 wherein the organic solvent is selected from the group consisting of dichloromethane, tetrahydrofuran, dioxane, N,N-dimethylformamide, acetonitrile or mixtures thereof. 4. A process as claimed in claim 2 wherein the organic base is selected from the group consisting of triethylamine, diethylamine,tributylamine, pyridine,N-alkylanilines, or mixtures thereof. 5. A process for preparing a cephalosporin compound of formula (VI) wherein R2 represents H, CH3,CH2OCH3, CH2OCOCH3, or a conventional cephalosporin moiety, R3 is hydrogen, salt or carboxyl protecting group, said process comprising the step of reacting a compound of formula (V) wherein R2 and R3 are defined as above, R4 is hydrogen or silyl group, with a compound of formula (I) and thiourea wherein, X and Rl are defined as claimed in claim 1. 6. A process as claimed in claim5, wherein the compound of formula (I) is reacted with compound of formula (V) in a mixture of an organic solvent and water, in the presence of an organic base at a temperature in the range of 0°-30°C preferably at 15°C and the intermediate formed is treated in situ with thiourea to obtain cephalosporin antibiotic of formula (VI). 7. A process as claimed in claim 5, wherein the compound of formula (1) is reacted with thiourea in mixture of an organic solvent and water in the presence of an organic base at a temperature in the range of-5°C to 30°C, preferably atl5°C, followed by addition of cephalosporin compound of formula (VI) in situ, maintaining the pH between 7.0 to 8.5 by addition of a base to obtain the cephalosporin antibiotic of formula (VI). 8. A process as claimed in claim 5 wherein R2 is hydrogen, methyl, methoxymethyl, acetyloxymethyl, (2,5-dihydro-6-hydroxy-2-methyl-5-'oxo-l, 2,4-triazin-3-yl) thiomethyl, furylcarbonyl thiomethyl or a conventional cephalosporin moiety. 9. A process as claimed in claim 5 wherein R3 is hydrogen or alkali metal salt. 10. A process as claimed in claims 6 and 7 wherein the organic solvent used is selected from the group consisting of tetrahydrofuran, N,N-dimethylacetamide, N, N dimethylformamide, dioxane, alcohol, acetonitrile or mixtures thereof 11. A process as claimed in claims 6 and 7 wherein the organic base used is selected from the group consisting of triethylamine, N-methylmorpholine, pyridine, N methylanilines, 1, 5-diazabicyclo [4.3. 0]non-5-ene, 1,4-diazabicyclo [2.2. 2] octane, 4 dimethylaminopyridine or mixtures thereof. 12. A process as claimed in claims 6 and 7 v'herein said compound of formula (VI) is a syn isomer. 13. A 2-mercapto-5-phenyl-l, 3,4-oxadiazolyl- (Z)-4-bromo-2-methoxyimino butyric acid derivative used in the preparation of cephalosporin antibiotics, substantially as herein described with reference to the foregoing examples. 14. A process for preparing active thioester derivatives 2-mercapto-5-phenyl-l, 3,4 oxadiazolyl- (Z)-4-bromo-2-methoxyimino butyric acid, substantially as herein described with reference to the foregoing examples.

Full Text

Field of Invention
The present invention relates to a 2-mercapto-5-phenyl-l, 3,4-oxadiazolyl- (Z)-4-bromo-2-methoxyimino butyric acid derivative used in the preparation of cephalosporin antibiotics. The present invention also discloses the process of preparing novel thioester derivatives of the general formula (I) by reacting 4-halogeno-2~methoxyimino-3-oxo~butyric acid (II) with 5- substituted-!, 3,4-oxadiazole-2-thiol of formula (III). The invention also discloses the use of the new intermediate (1) for the preparation of cephalosporanic antibiotics (V^) in excellent yields and purity

wherein
X represents halogen (CL Br and I)
R1 represents C1-C4 alkyl or phenyl
Background Art
Acid chlorides, anhydrides, esters, amide etc, are reported in the chemical literature for activation of carboxylic acid of formula (IV). Activation in the form of acid chloride required protection and deprotection of NH2 group.

Activation of 2- (2-aminothiazol-4-yI)-2-methoxyiminoacetic acid (IV) by S02C12/DMF is reported in US patent 5,856, 502 and activation of SOCIz/DMF is reported in US patent 5,037, 988. These processes suffers with the limitation of poor by moderate yields along with the use of solvents like benzene and stringent conditions required for carrying out the reactions at commercial scale.

In US patent No.4,576,749 and 4,548,748 the acid of formula (IV) have also been activated by reacting with 1-hydroxybenzotriazole (HOBT) or 2-mercaptobenzothiazole (MBT) in the presence of dicyclohexylcarbodimide (DCC) to produce reactive ester of the acid (TV) which reacted to cephem moiety to prepare cephem antibiotics, but the processes are time consuming and with low yields, hence not suitable.
US patent 4,767,852 discloses a process for production of cephems by acylating 7-ainino-3-cephem-4-carboxylic acid with 2-mercaptoben2othiazolyl-(Z)-2-(2-aminothiazol-4-yl)-2-methoxyiminoacetate (MAEM). Similarly, US PatNo,5,026,843 disclosed a process for preparing ceftriaxone disodium hemiheptahydrate by acylation of 7-amino-3-[[(2,5-dihydio-6-hydroxy-2-methyl-5-oxo-l,2,4-triazin-3yl)thio]methyl]3-cephem-4-carboxyU^ acid (ACT) by using MAEM as acylating agents in good yield and quality. Thus MAEM has become the standard acylating agent for the preparation of cephalosporins having an oximino group and a 2-aminothiazolyl group in 7-position of cephem compounds. However, the synthesis of MAEM from 2-(2-aminothiazol-4-yl)-2-methoxyiminoacetic acid (IV) and 2,2'-dithio-bis-benzothiazole involves use of costly condensing agent triphenylphosphine (TPP). Moreover, during condensation of MAEM with 7-amino-3-cephem-4-caiboxylic acid compound (V) , a toxic compound MBT is also produced as a byproduct, see e.g.. Chemical Abstracts, 111, 19243p (1989) which is difficult to remove completely.
Thus it is evident that the procedures described in the prior art for preparation of these antibiotics are complex, involving protection, deprotection and are associated with toxic byproduct generation. Hence there is a need to develop new acylating agents which are capable of transferring the 2-aminothiazolyl moiety to cephem compounds of formula (V) in good yield but without producing this toxic byproduct. On the similar lines, a new thioester was reported by D.G.Walker, Tet. Lett. 1990, 31,6481 to acylate the cephem moiety to get cefepime sulfate but yields obtained by using this thioester wore in the range of 54-73% which cannot be considered as good yield to operate a process at commercial scale. The use of this thioester was reported in the Tet. Lett. 1990, 31, 6481 only for cefepime and not for other cephalosporins. This thioester was exploited in US patent No. 5,869,649 for making three other important cephem antibiotics.
Synthesis of 4-halogeno - 2 - methoxyimino-3-oxo-butyric acid is reported in patent no. EP 0 030 294 and a large number of references are available in the patent literature disclosing the use of 4-halogeno-2-methoxyimino-3-oxo-butyric acid represented by formula (H) as the starting material. EP 0030294 and WO 00 0063214 discloses the condensation of the 4-

Statement of Invention
The present invention provides a 2-mercapto-5-phenyl-l, 3,4-oxadiazolyl- {Z)-4-bromo-2-methoxyimino butyric acid derivative used in the preparation of cephalosporin antibiotics. The present invention also discloses the process of preparing novel thioester derivatives of the general formula (I) by reacting 4-halogeno-2~methoxyiniino-3~oxo-butyric acid (II) with 5- substituted-h 3.4-oxadia7-ole-2-thiol of formula (III). The invention also discloses the use of the new intermediate (1) for the preparation of cephalosporanic antibiotics (VT) in excellent yields and purity

Detailed Description of the Invention
The present invention provides new thioesters of 4-halogeno-2-methoxyimino-3-oxo-butyric acid of general fonnula (I). The synthesis of compound (I) is achieved by preparing activated complex of 4-halogeno-2-methoxyimino-3-oxo-butyric acid (H) with DMF-POCI3 followed by the reaction with thio-oxadiazoles of the general formula (HI) in organic solvent in presence of an organic base at the temperature between -30°C and +20°C- The reactive active ester is obtained quantitative yields (95-99%).

product (Vn) which is formed during this reaction has also been controlled in the process.
Surprisingly this side reaction has never been mentioned in the literature.
In an embodiment, in the compound of formula (I), X is chloro, bromo or iodo.
In another embodiment the organic solvent is selected from the group
comprising dichloromethane, tetrahydrofuran, dioxane, N,N-dimethylformamide,
acctonitrile and mixtures thereof.
In still another embodiment the organic base is selected from the group comprising
triethylamine, diethylamine, tributylamine, pyridine, N-alkylanilines, and mixtures thereof.
The compound (I) so obtained is reacted with 7-amino cephem carboxylic acid of general
foramla (V) in two different methods and both the methods lead to same product with
comparable yields and purity.
Using above mentioned thioester the cephalosporin antibiotics obtained are of high purity

(90-99%), The method gives an excellent yield (70-95%) of cephalosporin without
necessitating the protection of the amino group of the acylating agents, and the toxic
byproduct 2-mercaptoben20thiazole is not produced.
The cephalosporin antibiotic were synthesized by following two methods:
Method-I The reactive thioester (I) was reacted with 7-aminocephem compound (V)

in organic solvent in the presence of base to obtained condensed product, which was not
isolated and is directly cyclised with thiourea in mixture of water and a polar organic
solvent like tetrahydrofuran, dimethylfonnamide, dioxane, alcohol to obtain desired
cephalosporanic antibiotics of very good purity and excellent yields.
Method -II
In this approach, starting from active ester of formula (I) final product was prepared in one

pot reaction. The process comprises cyclization of active ester in the first step and in same
reactor addition of amino cephem compound in mixture of water and a polar organic
solvent like tetrahydrofuran, dimethylformamide, dioxane, alcohols to obtain desired
cephalosporanic antibiotics of equally good purity and yields as compared to first
approach. This approach provides a simple , cheap and commercially viable method
without the necessity of isolating thioester and without producing any toxic byproduct
namely 2-mercaptobenzothiazole.
The substituent R2 in cephem compound (V) and (VI) represents hydrogen, methyl,
acetyloxymethyl, methoxymethyl, 2,5-dihydro-6-hydroxy-2-methyl-5-oxo-l,2,4-triazine-3-
thiol, furanyl-2-carbonyl thiol or a standard cephalosporin substituents.
R3 in cephem compound (V) and (VI) represents hydrogen , salt or a ester group which can
be easily removed e.g. p-methoxybenzyl , p-nitrobenzyl , diphenylmethyl , phenacyl ,
trimethylsilyl etc.
In an embodiment of the present invention the organic base may be selected from the
group consisting of triethylamine, N-methylmorpholine, pyridine, N-methylanilines, 1,5-
diazabicyclo[4.3.0] non-5-ene, l,4-diazabicyclo[2*2.2]octane, 4-dimethylaminopyridine,
and mixtures thereof.
Many other beneficial results can be obtained by applying disclosed invention in a
different manner or by modifying the invention with the scope of disclosure. However,
V
since the major characteristic feature of the present invention resides in the use of novel reactive thioester derivatives of 4-bromo-2-methoxyimino-3-oxo-butyric acid of the general formula (I) in preparing the cephalosporin antibiotics, the technical scope of the present invention should not be limited to the following examples. The following examples are provided to illustrate but not to limit the claimed invention.
EXPERIMENTAL
Example -1
Synthesis of 2- mercapto- 5 - phenyl - 1, 3, 4 - oxadiazolyl - (Z) - 4- bromo - 2-
methoxyimino-3-oxo-butyrate (I).
Phosphorus oxy chloride (25,6g) was added slowly to N, N-dimethyl formamide (12.2g) at 0 to -5°C Stirred for 30 minutes. Acetonitrile (200 ml) was added followed by 4-bromo-2-methoxyimino-3-oxo-butyric acid (25.0g) and 5-phenyl-l,3,4-oxadiazole-2-thiol (19.8g). Pyridine (44.1ml) was slowly added to the flask at -10°C. The progress of the reaction was monitored by HPLC, After the disappearance of the starting material, the reaction mass was poured into ice-water, white colored solid separated out which was filtered and

washed with water. Dried under vacuum to obtain 40.8 gm of thioester with HPLC purity (96.0 - 98.0%)
Melting point : 139-140 °C
^HNMR (DMS0-d6) : 8 4.1 (3H,s4Sr-Oa;y, 4.3(2H,s3iQiCO) 7.6-7.9(5H, m, - C^s) ^°C-NMR(CDCl3) : 5 30.2,65.8,121.3,127.7,129.7,134.1,147.5,147.8,156.3,160.2
186.1.
Example 2
3-Acetyloxymethyl-7-[(ZH2-aminothiazolyl-4-yl)-2-(methoxyimino)acetam cephem-4-carboxylic acid (Cefotaxime acid).
Method-I
A mixture of THF (250ml) and water (150ml) and N,N-dimethylacetamide (25.0ml) was stirred under inert atmosphere. At 0° - 5°C, 7-aminocephalosporanic acid (25.0g) and 2-mercapto-5-phenyl-l,3,4-oxadiazolyl-(20-4-bromo-2-methoxyinuno-3oxo-butyrate(46.0^^ were added. Triethylamine (20.4g) was slowly added to reaction by maintaining pH 7.0 to 8.0. The reaction was checked by HPLC. After 6-8 hrs., the reaction mixture was extracted by methylene chloride(200x3). The aqueous layer is subjected for charcoal treatment Thiourea (18.4g) and sodium acetate (4.2g) were added to the filtered aqueous layer and stirred for 1.0 hr to get the cefotaxime which was isolated with subsequent acidification of the aqueous layer with dil. HCl at 10°C to pH 3.0. The solid separated was filtered, washed with water and ethylacetate and then dried under vacuum at 40-45°C to get Cefotaxime, 40.9g (yield 98%).
' HPLC (purity) = 98-99%
Method-n
2-Mercapto-5-phenyl-l,3,4-oxadiazolyl-(Z)-4-bromo-2-methoxyimino-3-oxo-butyrate (46.0g.) was taken in a mixture of tetrahydrofuran (250ml) and water (150ml). The solution was cooled to lO°C and the thiourea (20.47g) and sodium acetate (4.32g) were added. The reaction mixture was stirred for 1.0 hr. 7-amino cephalosporanic acid (25.0g) was added followed by slow addition of triethylamine (20.4g) the progress of the reaction was monitored by HPLC. The reaction was completed in 6-8 hr. The reaction mixture was extracted with dichloromethane (3 X 200 ml). The aqueous layer was acidified with dil. HCl to obtain cefotaxime, 38,0g.

was extracted with dichloromethane (3 x 100ml). The aq. layer was separated and treated
with charcoal (0,2g), Thiourea (10.9g) is added to the solution and stirred for LO hr. till
cyclisation is over . A solution of sodium-2-ethylhexanoate (30,5g) in acetone was added
at 10-15°C and stirred for L5 hours (400ml) of acetone was added in 1 hour at 10-15°C to
complete the crystallization. The product was filtered under N2 atmosphere and wet cake
was dissolved in mixture of water and acetone (1:2), and cooled to -lO°C. Colored
impurities were separated. The solution was decanted and diluted with acetone (600ml) at
18-20°C. Precipitated solid was filtered under N2 and washed with acetone (20ml). Dried
under vacuum at 40-45°C to get pure Ceftriaxone sodium 25.5g.
HPLC (purity): 98.0%

for 2-3 hours at a pH of 7.0-8,5 mamtained by triethylamine to get clear solution. The reaction mixture was monitored by HPLC. After completion of reaction, 200ml water was added and pH was adjusted to 7.0. The aqueous layer was separated, charcoalizied and treated with sodium-2-ethylhexanoate (30.5g) in acetone, reaction was proceeded by same method as mentioned in method-I to get crude ceftriaxone sodium (24.0g).

mercapto-5-phenyl-13,4-oxadiazolyHZ)-4-bromo-2-methoxyimmo-3-oxo-butyr^ were
added to a mixture of THF (35ml) and watcir (35ml) at temperature 5^C. The pH of
reaction was maintained at 7,5 to 8.5 by addition of TEA during the reaction- After
completion of reaction, the reaction was extracted with methylene chloride (25ml x 3).
The aqueous layer was diluted with 15ml THF and thiourea was added to the aqueous and
stirring was continued for 30 to 45 min. to complete the cyclisation. After that pH was
lowered to 3 by addition of IN HCL The solution is saturated by salt. The organic layer
was separated and pH was further adjusted to 0.5 by concentrated HCL IPE (250ml) was
added to precipitate the hydrochloride salt of Ceftiofur, 4.3g (yield 75.0%).
HPLC (purity) : 98.0%

WE CLAIM:
1. A 2-mercapto-5-phenyl-l, 3,4-oxadiazolyl- (Z)-4-bromo-2-methoxyimino butyric
acid derivative used in the preparation of cephalosporin antibiotics, and represented by
formula(I)

2. A process for preparing active thioester derivatives 2-mercapto-5-phenyl-l, 3,4
oxadiazolyl- (Z)-4-bromo-2-methoxyimino butyric acid represented by formula (I) as
claimed in claim 1, said process comprising the step of reacting 4-halogeno-2-
methoxyimino-3-oxo- butyric acid represented by formula(II)

wherein X represents halogen(Cl, Br, I)
wherein Rl represents C1-C4 alkyl or phenyl with thio-oxadiazole of formula(III) in the presence of DMF, phosphorous oxychloride, an organic base and an organic solvent at a temperature being maintained in the range of-30°C to +20°C.

3. A process as claimed in claim 2 wherein the organic solvent is selected from the group consisting of dichloromethane, tetrahydrofuran, dioxane, N,N-dimethylformamide, acetonitrile or mixtures thereof.
4. A process as claimed in claim 2 wherein the organic base is selected from the group consisting of triethylamine, diethylamine,tributylamine, pyridine,N-alkylanilines, or mixtures thereof.
5. A process for preparing a cephalosporin compound of formula (VI)

wherein R2 represents H, CH3,CH2OCH3, CH2OCOCH3,

or a conventional cephalosporin moiety, R3 is hydrogen, salt or carboxyl protecting group, said process comprising the step of reacting a compound of formula (V)

wherein R2 and R3 are defined as above,
R4 is hydrogen or silyl group, with a compound of formula (I) and thiourea

wherein, X and Rl are defined as claimed in claim 1.
6. A process as claimed in claim5, wherein the compound of formula (I) is reacted with compound of formula (V) in a mixture of an organic solvent and water, in the presence of an organic base at a temperature in the range of 0°-30°C preferably at 15°C and the intermediate formed is treated in situ with thiourea to obtain cephalosporin antibiotic of formula (VI).
7. A process as claimed in claim 5, wherein the compound of formula (1) is reacted with thiourea in mixture of an organic solvent and water in the presence of an organic base at a temperature in the range of-5°C to 30°C, preferably atl5°C, followed by addition of cephalosporin compound of formula (VI) in situ, maintaining the pH between 7.0 to 8.5 by addition of a base to obtain the cephalosporin antibiotic of formula (VI).
8. A process as claimed in claim 5 wherein R2 is hydrogen, methyl, methoxymethyl, acetyloxymethyl, (2,5-dihydro-6-hydroxy-2-methyl-5-'oxo-l, 2,4-triazin-3-yl) thiomethyl, furylcarbonyl thiomethyl or a conventional cephalosporin moiety.
9. A process as claimed in claim 5 wherein R3 is hydrogen or alkali metal salt.
10. A process as claimed in claims 6 and 7 wherein the organic solvent used is selected from the group consisting of tetrahydrofuran, N,N-dimethylacetamide, N, N dimethylformamide, dioxane, alcohol, acetonitrile or mixtures thereof

11. A process as claimed in claims 6 and 7 wherein the organic base used is selected
from the group consisting of triethylamine, N-methylmorpholine, pyridine, N
methylanilines, 1, 5-diazabicyclo [4.3. 0]non-5-ene, 1,4-diazabicyclo [2.2. 2] octane, 4
dimethylaminopyridine or mixtures thereof.
12. A process as claimed in claims 6 and 7 v'herein said compound of formula (VI) is a syn isomer.
13. A 2-mercapto-5-phenyl-l, 3,4-oxadiazolyl- (Z)-4-bromo-2-methoxyimino butyric acid derivative used in the preparation of cephalosporin antibiotics, substantially as herein described with reference to the foregoing examples.
14. A process for preparing active thioester derivatives 2-mercapto-5-phenyl-l, 3,4
oxadiazolyl- (Z)-4-bromo-2-methoxyimino butyric acid, substantially as herein described
with reference to the foregoing examples.

Documents:

1766-chenp-2003-abstract.pdf

1766-chenp-2003-claims filed.pdf

1766-chenp-2003-claims granted.pdf

1766-chenp-2003-correspondnece-others.pdf

1766-chenp-2003-correspondnece-po.pdf

1766-chenp-2003-description(complete)filed.pdf

1766-chenp-2003-description(complete)granted.pdf

1766-chenp-2003-form 1.pdf

1766-chenp-2003-form 18.pdf

1766-chenp-2003-form 26.pdf

1766-chenp-2003-form 3.pdf

1766-chenp-2003-form 5.pdf

1766-chenp-2003-other documents.pdf

1766-chenp-2003-pct.pdf

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Patent Number

212050

Indian Patent Application Number

1766/CHENP/2003

PG Journal Number

02/2008

Publication Date

11-Jan-2008

Grant Date

13-Nov-2007

Date of Filing

10-Nov-2003

Name of Patentee

ORCHID CHEMICALS & PHARMACEUTICALS LTD

Applicant Address

ORCHID TOWERS', VILLAGE ROAD, NUNGAMBAKKAM, CHENNAI - 600 034

Inventors:

#	Inventor's Name	Inventor's Address
1	DESHPANDE, PANDURANG, BALWANT	T-1, NAVIN'S VASUNDHARA, 12TH CROSS ROAD, DOOR NO.5, INDIRA NAGAR, CHENNAI - 600 020,
2	LUTHRA, PARVEN, KUMAR	H-85, S-1, TNHB FLATS, VALMIKI NAGAR, THIRUVANMIYUR, CHENNAI 600 - 041,

PCT International Classification Number

C07D 271/113

PCT International Application Number

PCT/IN2001/000113

PCT International Filing date

2001-06-14

PCT Conventions:

#	PCT Application Number	Date of Convention	Priority Country
1			NA