wherein R represents hydrogen, a negative charge or together with COO group to which R is attached is an ester; Rj represents hydrogen, trityl, CH3, CRaRbCOORc where Ra and Rb independently represent hydrogen or methyl and Re represents hydrogen or (CrC6)alkyl; R2 represents CH3, CH2OCOCH3, CH=CH2, CH2OCONH2,



X represents methanesulfonyl, p-toluenesulfonyl and trifluoromethanesulfonyl group.
BACKGROUND OF THE INVENTION
Generally, the cephalosporin compounds of Formula I are prepared by acylation of 7-amino-3-substituted-3-cephem compounds with reactive derivative of 2-(2-amino-4-thiazolyl)-2-(substituted imino)acetic acid. These reactive derivatives can be the acid halide, the acid anhydride, mixed anhydride, reactive ester, reactive amide and the like. Several patents such as US 4,406,899, US 5,594,129, and US 5,594,131 disclose this methodology of preparing cephalosporins.
US 4,406,899 describes two methods for the preparation of Cefepime. Both these methods make use of the protecting groups that require additional protection and deprotection steps. Furthermore, chromatographic purification has been used to isolate Cefepime zwitterion.
US 5,594,129 describes preparation of Cefepime wherein acid chloride hydrochloride of the following Formula,


has been used for the N-acylation of 7-amino-3-[(l-methyl-l-pyrrolidinium)methyl]-3-cephem-4-carboxylate under anhydrous conditions. In US Patent 5,594,130, the same acid chloride hydrochloride has also been used for N-acylation in aqueous conditions to prepare Cefepime. In both of these U.S. patents, the preparation of the desired acid chloride hydrochloride involves first the conversion of syn-2-(2-amino-4-thiazolyl)-2-(methoxyimino)acetic acid to the corresponding hydrochloride salt which is then treated with chlorinating agent under specifically defined reaction conditions to obtain the syn-isomer of 2-(2-amino-4-thiazolyl)-2-(methoxyimino)acetyl chloride hydrochloride that contains less than about 5% of the undesirable anti-isomer which affects the subsequent acylation reaction to obtain Cefepime antibiotic.
Alternatively, a different methodology to prepare cephalosporin compounds has been disclosed in British Patent GB 2 012 276, wherein 7-amino-3-substituted-3-cephem compounds have been acylated with 4-halogeno-3-oxo-2-(substituted imino)butyric acid or its reactive derivative and the resultant intermediate has been treated with thiourea to prepare thiazole ring. Subsequently, similar methodology has been used to prepare different Cephalosporin compounds in several patents such as EP 0 030 294, CA 1146165 and US 6,552,186.
US 4,716,158 discloses the preparation of Cefpodoxime proxetil wherein pivaloyloxymethyl 7-amino-3-methoxymethyl-3-cephem-4-carboxylate has been acylated with 2-methoxyimino-3-oxo-4-p-toluenesulphonyloxybutyric acid chloride and the resulting intermediate is cyclized with thiourea to prepare thiazole ring. However, there is no such report yet to date for preparing other cephalosporin compounds through this route.

The present invention describes a process for the manufacture of Cephalosporin compounds through novel intermediate compounds of Formula II. The conversion of intermediate compounds of Formula II to Cephalosporins provides control of the stereochemical configuration of methoxyimino group and the A3-double bond of cephalosporin nucleus without a need to separate undesirable cephalosporin by-products by chromatography. Another advantage of the present invention is the use of stable carboxylic acids of Formula III

wherein X is a good leaving group such as methanesulfonyl, P-toluenesulfonyl and trifluoromethanesulfonyl group.
OBJECTIVE OF INVENTION
The main objective of the present invention is to provide a simple and effective process for the preparation of Cephalosporins of high purity on a commercial scale.

wherein R is hydrogen, a negative charge or together with COO group to which R is attached is an ester; R1 represents hydrogen, trityl, CH3, CRaRbCOORc where

Ra and Rb independently represent hydrogen or methyl and Rc represents hydrogen or (Ci-C6)alkyl; R2 represents CH3, CH2OCOCH3, CH=CH2, CH2OCONH2,


wherein R, R1 and R2 are as defined above, which comprises reacting the above ■ intermediates compounds of Formula II with thiourea or silylated thiourea and optionally converting Cephalosporin compounds of Formula I into hydrates or pharmaceutically acceptable salts.
According to another embodiment of the present invention, the intermediate compounds of Formula II are prepared by N-acylation of 7-amino-3-substituted-3-cephem compounds of Formula IV

wherein R and R2 are as defined above or its salt with a reactive derivative of carboxylic acid of Formula III
— 1
wherein X and Ri are as defined above.
DETAILED DESCRIPTION OF THE INVENTION
Carboxylic acids of Formula III are prepared in high purity and good yield by reacting ter/-butyl 4-bromo-3-oxo-2-(substituted imino)butyrate and a metal salt of sulfonic acid selected from P-toluenesulfonic acid, methanesulfonic acid or trifluoromethanesulfonic acid and most preferably silver p-toluenesulfonate in a solvent selected from acetonitrile, tetrahydrofuran, toluene, methylene dichloride etc. and subsequently hydrolyzing in presence of an acid selected from formic acid, trifluoroacetic acid, methanesulfonic acid and most preferably trifluoroacetic

acid. The reactive derivatives of carboxylic acids of Formula III are prepared by reacting with phosphorous oxyhalide, phosphorous pentahalide, oxalyl halide. The reactive derivative thus produced may be isolated prior to acylation of a cephalosporin compound or may be generated in situ. The reactive derivative formation is carried out in an inert organic solvent such as chloroform, methylene dichloride, acetonitrile or the like and most preferably the reaction is carried out in methylene dichloride at a temperature of -25°C to -15°C.
The cephalosporin compounds, 7-amino-3-substituted-3-cephem of Formula IV,
which are mostly available as hydrochloride salt, may advantageously be silylated
in an inert organic solvent to form in situ solution of the soluble silylated
derivative. It is important to add sufficient silylating agent to solubilize the
cephalosporin compounds of Formula IV before treating with reactive derivative
of carboxylic acids of Formula III. Silylating agents which may be used are, for
example, hexamethyldisilazane, trimethylchlorosilane, N,N'-
bis(trimethylsilyl)urea, N-(trimethylsilyl)acetamide, N,0-
bis(trimethylsilyl)acetamide, tert-butyldimethylchlorosilane or the like and most preferably N-(trimethylsilyl)acetamide.
The soluble silylated derivative of cephalosporin compounds of Formula IV are then acylated with one molar equivalent of reactive derivative of carboxylic acids of Formula III and most preferably with a slight excess. Suitable solvents which may be used during acylation are inert organic solvents in which the silylated derivative of cephalosporin compounds of Formula IV are soluble, for example, toluene, tetrahydrofuran, acetone, acetonitrile, methylene dichloride, chloroform or the like and most preferably methylene dichloride. The silylation of cephalosporin compounds of Formula IV is completed at about 15°C to 30°C while the N-acylation is advantageously carried out at -60°C to -50°C.
After N-acylation is complete, as ascertained by the known detection methods reported in the art, water is added to the reaction mixture to precipitate 7-[4-

substituted-3-oxo-2-(substituted imino)butyrylamino]cephalosporin compounds of Formula II, which are isolated by filtration. The intermediates of Formula II and their preparation from Cephalosporin compounds of Formula IV, and further their conversion to Cephalosporin compounds of Formula I constitute the inventive part of the present invention.
In accordance with the present invention, the reaction of intermediate compounds of Formula II with thiourea or silylated thiourea to prepare cephalosporin compounds of Formula I can be carried out in a solvent such as ethanol, acetone, tetrahydrofuran, N,N-dimethylformamide, water and mixture thereof. The reaction is generally carried out at a temperature in the range of 0°C to 50°C. Thereafter, when it is desired to prepare salt, the reaction mass after cyclization with thiourea or silylated thiourea, is treated with sufficient amount of mineral acid. The resulting reaction mixture is then diluted with water miscible appropriate solvent to ensure the crystallization of the desired cephalosporin compound. The resulting compound can be further purified by crystallization with suitable solvent to improve the purity and quality of the product.
The Cephalosporin compounds thus obtained are substantially free from anti-isomer and Δ2-isomer. The present process provides control of the stereochemical configuration of methoxyimino group and the A -double bond of cephalosporin nucleus without the need to separate undesirable cephalosporin by-product by chromatography. Another advantage of the present invention is the use of substituted carboxylic acids of Formula III containing a good leaving group such as methanesulfonyl,P-toluenesulfonyl and trifluoromethanesulfonyl.
The following example to prepare Cefepime dihydrochloride will illustrate the nature of the invention and is provided for illustrative purpose only and should not be construed to limit the scope of the invention:

Example:
Stage I: Preparation of 4-p-toIuenesulfonyloxy-3-oxo-2-methoxyiminobutyric acid
A) Preparation of t-butyl 4-p-toluenesulfonyloxy-3-oxo-2-methoxyimino-
butyrate
t-Butyl 4-bromo-3-oxo-2-methoxyiminobutyrate (60 g; 0.214 mole) and silver p-toluenesulfonate (67.5 g, 0.243 mole) were added to acetonitrile (600 ml) and stirred for 72 hours at 25-30°C under nitrogen atmosphere. The progress of the reaction was monitored by TLC. After completion of the reaction, the reaction mass was filtered and concentrated the filtrate under reduced pressure. To the concentrated residue, n-hexane (550 ml) was added and heated to 35-40°C for 10 min. The product was separated by filtration, washed and vacuum dried, yield 66 g.
B) Preparation of 4-p-toluenesuIfonyloxy-3-oxo-2-methoxyiminobutyric
acid
t-Butyl 4--p-toluenesulfonyloxy-3-oxo-2-methoxyiminobutyrate (50 g, 0.135 mole) was suspended in methylene dichloride (100 ml). Trifluoroacetic acid (200 ml) was added and stirred the reaction mixture at 20-25 °C for 3 hrs. The progress of the reaction was monitored by TLC. After completion of reaction, solvent was evaporated under reduced pressure and diisopropyl ether (50 ml) was added to the residue followed by dropwise addition of n-hexane (250 ml). The precipitate was stirred for 1 hr at 0-5 °C. The product was collected by filtration and vacuum dried, yield 41 g.

Stage II: Preparation of Cefepime hydrochloride monohydrate
A) Silylation of (6R,7R)-7-aniino-3-[(l-methy1-1-pyrrolidinum)methyl]-3-
cephem-4-carboxylate hydrochloride (NMPCA.HC1):
NMPCA.HC1 (lOg, 0.03 mole) was suspended in methylene dichloride (200 ml). The reaction mixture was cooled to 15°C. N-trimethylsilylacetamide (31.4g, 0.24 mole) was added and the reaction mixture was stirred for 90 min at 15-20°C to obtain a clear solution.
B) Preparation of 4-p-toluenesulfonyloxy-3-oxo-2-methoxyiminobutyryl
chloride:
p-Toluenesulfonyloxy-3-oxo-2-methoxyiminobutyric acid (11.4 g, 0.036 mole) was suspended in methylene dichloride (250 ml). Triethylamine (3.64 g, 0.036 mole) and oxalyl chloride (6 g, 0.047 g) were added at -5° to -10°C followed by a few drops of dimethylformamide. The reaction mixture was stirred at -5°C to -10°C and the progress of the reaction was monitored by TLC. After completion of the reaction, the reaction mass was used as such for acylation.
C) Preparation of (6R,7R)-7-[4-p-toluenesulfonyloxy-2-(methoxyimino)-3-
oxobutyrylamino]-3-[(l-methyl-l-pyrrolidinium)methyl]-3-cephem-4-
carboxylate (TNMPCA)
Silylated solution of NMPCA.HC1 was cooled to -55°C and 4-p-toluenesulfonyloxy-3-oxo-2-methoxyiminobutyryl chloride was added at -50°C to -55°C. Stirring was continued at -50°C to -55°C until NMPCA unreacted was < 1% by qualitative HPLC analysis. Thereafter, DM water (60 ml) was added to the reaction mass and stirring was continued for 15 min

at 25-30°C. The aqueous layer was separated. The aqueous layer containing the TNMPCA was used further for Cefepime preparation.
D) Preparation of (6R,7R)-7-[(Z)-2-(2-amino-4-thiazolyl).2-
(methoxyimino) acetamido]-3- [(l-methyl-l-pyrroIidinium)methyI]-3-cephem-4-carboxylate dihydrochloride monohydrate (Cefepime hydrochloride monohydrate)
Acetone (25 ml) was added to the aqueous layer and solution was cooled to 5°C. The pH was adjusted to 5-5.5 with triethylamine and thiourea (4.56 g, 0.06 mole) was added. Stirring was continued at 0-5°C by maintaining the pH between 5 to 5.5 with triethylamine until TNMPCA left unreacted was < 1% by qualitative HPLC analysis. Thereafter, concentrated hydrochloric acid (12.5 ml) was added at 0-5°C followed by dropwise addition of acetone (1000 ml). The slurry was stirred for 30 min at 0-5°C. The product was isolated by filtration and Cefepime hydrochloride (12 g) was obtained after drying. This was purified from methanol-acetone to obtain Cefepime hydrochloride monohydrate (8.50 g), HPLC purity: 99.35%.

wherein R is hydrogen, a negative charge or together with COO group to
which R is attached is an ester; R\ represents hydrogen, trityl, CH3,
CRaRbCOORc where Ra and Rb independently represent hydrogen or methyl
and Rc represents hydrogen or (Ci-C6)alkyl; R2 represents CH3,
CH2OCOCH3, CH=CH2, CH2OCONH2,



wherein X represents methanesulfonyl, p-toluenesulfonyl and trifluoromethanesulfonyl group and R, Ri, R2 are as defined above with thiourea or silylated thiourea in an organic solvent and in the presence of a base.
2. A process according to claim 1, wherein the organic solvent is selected
from ethanol, acetone, tetrahydrofuran, N,N-dimethylformamide, water
and mixture thereof.
3. A process according to claim 1 wherein the base is selected from
triethylamine, diethylamine, diisopropylamine.
4. A process according to claim 1 wherein the reaction is carried out at a
temperature in the range of 0°C to 50°C.
5. A process according to claim 1, wherein a compound of Formula II is
prepared by a process comprising:
- reacting tert-butyl 4-bromo-3-oxo-2»(substituted imino)butyrate and a metal salt of sulfonic acid selected from P-toluenesulfonic acid, methanesulfonic acid or trifluoromethanesulfonic acid in a solvent selected from acetonitrile, tetrahydrofuran, toluene, methylene dichloride,

- hydrolyzing the resulting compound in presence of an acid selected
from formic acid, trifluoroacetic acid, methanesulfonic acid to produce
carboxylic acid of Formula III

wherein X and R\ are same as described above,
- N-acylation of 7-amino-3-substituted-3-cephem compound of Formula
IV

wherein R and R2 are as defined above or its salt, with reactive derivative of carboxylic acid of Formula III in an inert organic solvent.
6. A process according to claim 5, wherein the metal salt of sulfonic acid is
silver p-toluenesulfonate.
7. A process according to claim 5, wherein 7-amino-3-substituted-3-cephem
carboxylic acid of Formula IV is silylated prior to acylation with a reactive
derivate of carboxylic acid of Formula III.
8. A process according to claim 5, wherein the inert organic solvent is
selected from toluene, tetrahydrofuran, acetone, acetonitrile, methylene
dichloride, chloroform.
9. A process according to claim 5, wherein N-acylation is carried out at a
temperature in the range of -10°C to about -70°C.

wherein R is hydrogen, a negative charge or together with COO group to
which R is attached is an ester; R\ represents hydrogen, trityl, CH3,
CRaRbCOORc where Ra and Rb independently represent hydrogen or methyl
and Rc represents hydrogen or (Ci-C6)alkyl; R2 represents CH3,
CH2OCOCH3, CH=CH2, CH2OCONH2,



wherein X represents methanesulfonyl, p-toluenesulfonyl and trifluoromethanesulfonyl group and R, Ri, R2 are as defined above with thiourea or silylated thiourea in an organic solvent and in the presence of a base.
2. A process according to claim 1, wherein the organic solvent is selected
from ethanol, acetone, tetrahydrofuran, N,N-dimethylformamide, water
and mixture thereof.
3. A process according to claim 1 wherein the base is selected from
triethylamine, diethylamine, diisopropylamine.
4. A process according to claim 1 wherein the reaction is carried out at a
temperature in the range of 0°C to 50°C.
5. A process according to claim 1, wherein a compound of Formula II is
prepared by a process comprising:
- reacting tert-butyl 4-bromo-3-oxo-2»(substituted imino)butyrate and a metal salt of sulfonic acid selected from P-toluenesulfonic acid, methanesulfonic acid or trifluoromethanesulfonic acid in a solvent selected from acetonitrile, tetrahydrofuran, toluene, methylene dichloride,

- hydrolyzing the resulting compound in presence of an acid selected
from formic acid, trifluoroacetic acid, methanesulfonic acid to produce
carboxylic acid of Formula III

wherein X and R\ are same as described above,
- N-acylation of 7-amino-3-substituted-3-cephem compound of Formula
IV

wherein R and R2 are as defined above or its salt, with reactive derivative of carboxylic acid of Formula III in an inert organic solvent.
6. A process according to claim 5, wherein the metal salt of sulfonic acid is
silver p-toluenesulfonate.
7. A process according to claim 5, wherein 7-amino-3-substituted-3-cephem
carboxylic acid of Formula IV is silylated prior to acylation with a reactive
derivate of carboxylic acid of Formula III.
8. A process according to claim 5, wherein the inert organic solvent is
selected from toluene, tetrahydrofuran, acetone, acetonitrile, methylene
dichloride, chloroform.
9. A process according to claim 5, wherein N-acylation is carried out at a
temperature in the range of -10°C to about -70°C.