The present invention relates to novel and industrially advantageous process for the preparation of syn-isomers of cephem compounds of Formula I, as shown in the accompanied drawings.
The compounds of the present invention represent a known class of valuable cephalosporin antibiotics, more specifically, cefotaxime, cefetamet,. ceftriaxone, cefpodoxime, and ceftazidime. The latter compounds are disclosed, for example, in U.S. Pat. Nos. 4,098,888, 4,327,210 and 4,486,425 as well as in numerous other patents and publications. This class of antibiotics is characterized by the presence of an oximino group and a 2-aminothiazolyl heterocyclic ring in the 7-acylamido side chain attached to the cephalosporin nucleus. This class of compounds is also characterized by suitable substituents at the 3-position of the cephalosporin nucleus. It is also known that the oximino group in the 7-acylamido side chain may have the syn- or anti-configuration, but that the syn-isomers have higher antibiotic activity, as disclosed in US Patents : 4,152,432 and 4,224,371.
Conventionally, this class of compounds is prepared by first introducing the suitable substituent into the 3-position of the cephalosporin nucleus and then acylating the 7-aminocephalosporanic acid derivative with reactive derivatives of 2-aminothiazolyl oxiimino acetic acid. Thus, U.S. Patent No. 4,767,852 discloses a process for the production of known 2-oximinoacetamido-3-cephem-4-carboxylic acid derivatives, including cefotaxime and ceftriaxone, by acylating 7-amino-3-cephem-4-carboxylic acid derivatives already substituted at the 3-position with 2-mercaptobenzothiazolyl-(Z)-2-(2-aminothiazol-4-yl)-2-methoxyimino acetate, the latter often referred to as MAEM.
The present invention provides a novel method involving the acylation of alkylidene ammonio salts of Formula 111, as such without deprotecting their amino group, with activated esters of Formula II, as shown in the accompanied drawings,- to give desired syn-isomers of compounds of Formula I of the present invention in high purity and yield. The present invention makes use of the alkylidene ammonio salts of Formula II, which are stable crystalline compounds and can be easily obtained in quantitative yields.
More particularly, the present invention relates to a process for the preparation of syn-isomers of cephem compounds of Formula I, as shown in the accompanied drawings wherein R is selected from the group consisting of hydrogen, alkyl, phenylalkyl, carbalkoxyalkyl, acyl or carboxyalkyl, preferably R is methyl and 1-carboxy-1-methylethyl, R^

is hydrogen, methyl, chlorine or a group -CH2Y, in which Y represents methoxy, acetoxy, carbamoyloxy, a heterocyclic ring, preferably pyridyl, and a group of formula -CH2-S-Z, in which Z is a heterocyclic ring that may be substituted, preferably Z is 1,2,5,6-tetrahydro-2-methyl-5,6-dioxo-1,2,4-triazinyl, comprising reacting a syn-isomer of reactive esters of Formula II wherein R is as defined above, L is 2-benzothiazolyl- or 2-(5-methyl-1,3,4-thiadiazolyl)-, with alkylidene ammonio salts of lactam of Formula III as shown in the accompanied drawings, wherein Ri is as defined above, R2 and R3 are the same or different and each is a C1-C16 alkyl group or R2 and R3 form a cycloalkylidene ring with upto 8 carbon atoms together with the carbon atom to which they are attached, X is an anion from an acid HX, in a suitable solvent in the presence of an organic base. The compounds of Formulae II and III are known and can be synthesized by the methods described in US 5,359,058 and US 4,767,852.
The reaction of the compounds of Formulae II and 111 can be effected in a suitable solvent that can dissolve both starting materials. The solvents are selected from the group consisting of ketones, chlorinated solvents, esters, ethers, dipolar aprotic solvent, aromatic solvent, acetonitrile, and mixtures thereof. Preferably, the solvents are selected from the group consisting of acetone, chloroform, dichloromethane, ethylacetate, tetrahydrofuran, dioxane, N,N-dimethylformamide, N.N-dimethylacetamide, N-methyipyrrolidone, dimethylsulphoxide, and mixtures thereof.
The reaction is carried out in the presence of a base, such as pyridine, picoline, quinoline, isoquinoline, triethylamine, tributylamine, N-methylpiperidine, N-methylmorpholine, N,N-dimethylaniline, N,N-diethylaniline, etc. and mixture thereof. Triethylamine is preferred, as it is inexpensive and easily commercially available.
Thus, the reactive ester of Formula II, is dissolved in a suitable solvent or a mixed solvent and alkylidene ammonio salt of lactam of Formula 111 is added with stirring at a selected temperature within the range of -20 to 50° C, preferably 0 to 20° C, even more preferably 10 to 20° C. The resulting reaction mixture is then stirred from one to several hours, after which 3NHCI and water are added. The reaction mixture is then washed with a water-immiscible solvent, preferably a chlorinated hydrocarbons, e.g. dichloromethane, chloroform, etc. The aqueous layer is then acidified with hydrochloric acid to pH 1 to 6, preferably pH 3 to 6, even more preferably pH 3. The desired precipitated compound at this pH level is isolated by conventional methods without further purification.
It has been found that if the reaction is carried out under the working conditions defined above, the following advantages are achieved:
1. One pot acylation of alkylidene ammonio salt of Formula III can be carried out , without the necessity of deprotection of the amino group.
2. The process is convenient to handle on a commercial scale
3. Crude 7-amino cephalosporanic acid can be used without purification to manufacture the Cephem compounds of Formula I.
4. The desired product can be obtained in high purity and yield.
Several preferred embodiments to illustrate the process of this invention are described below. However, they are not intended in any way to limit the scope of the present invention.
EXAMPLE 1
Preparation of 3-Acetoxymethyl-7-(Z)-2-(2-aminothiazoi-4-yl)-2-(methoxyimino)-acetamido]-3-chephem-4-carboxylic acid (cefotaxime).
2,2'-Dithiobis-(5-methyl-1,3,4, thiadiazole), (27.52 g, 105 mmoles) and (Z)-2-(2-aminothiazol-4-yl)-2-methoxyiminoacetic acid (16.24 g, 80.8 mmoles) were suspended in tetrahydrofuran (160 ml) and triphenylphosphine (27.52 g, 105 mmoles) was added at 20-25°C. The mixture was stirred for about 2 hrs to give 2-mercapto-5-methyl-1,3,4-thiadiazo!yl-(Z)-2-(2-amino-thiazol-4-yl)-2-methoxyimino acetate in solution. The reaction mixture was cooled to 0 to 5°C and diluted with N, N-dimethylacetamide (35 ml). 3-Acetoxymethyl-4-carboxy-7-isopropylideneammonio-cephem chloride (20 g, 57.39 mmoles) and triethylamine (23.2 g, 229.7 mmoles) were added at 0-5°C and the reaction mixture was stirred for 2-3 hrs. at 5-10°C. Thereafter, 3N HCI (32 ml) and water (200ml) were added and the aqueous layer was washed with methylene chloride (200ml). Isopropyl alcohol (180ml) was then added to the aqueous layer and acidified to pH 2.8 with 3N HCI at 0-5°C. The resulting solid was filtered and washed with water followed by isopropyl alcohol and dried to obtain cefotaxime acid with a purity of more than 98% (By HPLC). Yield 24.5g, (94%).

EXAMPLE 2
3-Acetoxymethyl-7-[(Z)-2-(2-aminothiazol-4-yl)-2-(methoxyimino)-acetamido]-3-cephem-4-carboxylic acid (cefotaxime).
3-Acetoxymethyl-4-carboxy-7-isopropylideneammonio-3-cephem chloride (10 g, 28.69 mmoles) was suspended in methylene chloride (100ml) and cooled to -5°C to 0°C. Triethylamine (11.6 g, 114.8 mmoles) was added at -5°C to 0°C to obtain a clear solution. Thereafter, 2-mercaptobenzothiazolyl-(Z)-2-[2-aminothiazol-4-yl)-2-methoxyiminoacetate (12.05 g, 34.43 mmoles) was added and the mixture was stirred for 3-4 hours at -5 to +5°C. The product was then extracted with water (100ml) and isopropyl alcohol (80ml) was then added. It was acidified with 3N HCI to pH 2.8-3.0. The solid so obtained was filtered, washed with water followed by isopropyl alcohol and dried. Yield 12.4 g (95%) and purity 98.5% (By HPLC).
EXAMPLE 3
7-[Z]-2-(2-Aminothiazol-4-yl)-2-(methoxyimino)acetamido]-3-methyl-3-cephem-4-carboxylic acid (cefetamet)
A mixture of tetrahydrofuran (80ml) and N, N-dimethylacetamide (10ml) was cooled to -5°C. 2-mercapto-5-methyl-1,3,4,thiadiazolyl-(Z)-2-(2-aminothiazol-4-yl)-2-methoxyiminoacetate (13.0 g, 41.27 mmoles), 4-carboxy-7-isopropylideneammonio-3-methyl-3-cephem chloride (10 g, 34.4 mmoles) and triethylamine (14.0 g, 138.6 mmoles) were added to it at -5 to 0°C. The reaction was stirred for 1-2 hours at 0-10°C. Water was added and washed the reaction mixture with methylene chloride. The aqueous phase was separated, acidified to pH-3.0 with 3N HCI and the solid obtained was filtered and dried. Yield 11.6 g (85%) and purity 98.5% (By HPLC).
EXAMPLE 4
7-[Z)-2-(2-Aminothiazol-4-yl)-2-(methoxyimino)acetamido]-3-methyl-3-cephem-4-carboxylic acid (cefetamet).
4-carboxy-7-isopropylideneammonio-3-methyl-3-cephem chloride (5.0g, 17.2 mmoles) was suspended in methylene chloride (50ml) and triethylamine (6.0g, 59.4 mmoles) was added at -5 to 0°C to get a clear solution. Thereafter, 2-mercaptobenzothiazolyl-(Z)-2-(2-aminothiazol-4-yl)-2-methoxyiminoacetate (7.25 g, 20.72 mmoles) was added and stirred for 2-3 hours at 15-20°C. The reaction mixture was then worked up as described in example 3. Yield 5.4g (80%) purity 98% (By HPLC).
EXAMPLE 5
7-[(Z)-2-(2-Aminothiazol-4-yl)-2-(methoxyimino)acetamido]-3-chloro-3-cephem-4-carboxylic acid.
To a suspension of 4-carboxy-7-isoproylideneammonio-3-chloro-3-cephem-chloride (5.0 g, 16.0 mmoles) in methylene chloride (50 ml) at -5 to 0°C, was added triethylamine (5.7g, 56.44 mmoles) to obtain a clear solution. 2-Mercaptobenzothiazolyl (Z)-2-(2-amino-thiazol-4-yl)-2-methoxyiminoacetate (6.7 g, 19.15 mmoles) was then added and the reaction mixture was stirred at 5-10°C for 2-3 hours. The product was extracted with water (50 ml) and aqueous layer was worked up in the same manner as described in example 3. Yield 5.7 g (85%) and purity 97% (By HPLC).
EXAMPLE 6
7-[(Z)-2-(2-aminothiazol-4-yl)-2-(methoxyimino)acetamido]-3-chloro-3-cephem-4-carboxylic acid.
2, 2'-Dithiobis-(5-methyl-1,3,4 thiadiazole) (7.6g, 29 mmoles) and (Z)-2-(2-aminothiazol-4-yl) -2-methoxyiminoacetic acid (4.5g, 22.38 mmoles) were suspended in tetrahydrafuran (40ml). To it was added, triphenylphosphine (7.6g, 29 mmoles ) and the mixture was stirred for 2.5 hours to get 2-mercapto-5-methyl-1,3,4-thiadiazolyl-(Z)-2-(2-aminothiazol-4-yl)-2-methoxy-
iminoacetate in solution. The mixture was then cooled to -5°C to 0°C, and 4- carboxy-3-chloro-7-isopropylideneammonio cephem chloride (5.0g, 16.0 mmoles) was added followed by the addition of triethylamine (5.7g, 56.2 mmoles). It was stirred for 2-3 hours and worked up as described in example 3 to yield 5.5g (82%) of the title compound with a purity of 98% (By HPLC).
EXAMPLE 7
7-[(Z)-2-(2-aminothiazol-4-yl)-2-syn-(methoxyimino)acetamido]-3[(2,5-dihydro-6-hydroxy-2-methyl-5-oxo-1,2,4-triazin-3-yl)methyl]-3-cephem-4-carboxylic acid (ceftriaxone).
To a mixture of tetrahydrofuran (40ml) and dimethylacetamide (10ml) at 0-5°C, was added 3-[(2,5-dihydro-6-hydroxy-2-methyl-5-oxo-1,2,4-triazin-3-yl)thio]methyl]-7-isopropylidene ammonio-3-cephem-chloride (5.0g, 11.17 mmoles) followed by 2-mercapto-5-methyl-1,3,4-thiadiazolyl-(Z)-2-(2-amiothiazol-4-yl)-2-methoxyiminoacetate (4.22 g, 13.40 mmoles) and triethylamine (4.5g, 44.5mmoles). The mixture was stirred at 10-12°C for 2 hrs. Water (25ml) is added to the reaction mixture followed by washing with methylene chloride. The aqueous layer is separated and sodium-2-ethylhexanoate (5.56g) dissolved in acetone (20ml) is added. Ceftriaxone disodium is precipitated by adding acetone. The separated solid is filtered , washed with acetone and dried to give 6.28 g (85%) of the title compound of purity 99% (By HPLC).
While the present invention has been described in terms of its specific embodiments, certain modifications and equivalents will be apparent to those skilled in the art and are intended to be included within the scope of the present invention, which is to be limited only by scope of the appended claims.

CLAIMS
1. A process for the preparation of syn-isomers of cephem compounds of Formula I as shown in the accompanied drawings, wherein R is selected from the group consisting of hydrogen, alkyl, phenylalkyl, carbalkoxyalkyl, acyl or carboxyalkyl, preferably R is methyl and 1-carboxy-1-methylethyl, R1 is hydrogen, methyl, chlorine or a group -CH2Y, in which Y represents methoxy, acetoxy, carbamoyloxy, a heterocyclic ring, preferably pyridyl, and a group of formula -CH2-S-Z, in which Z is a heterocyclic ring that may be substituted, preferably Z is 1,2,5,6-tetrahydro-2-methyl5,6-dioxo 1,2,4 -triazinyl, comprising reacting a syn-isomer of reactive esters of Formula II wherein R is as defined above, L is benzothiazolyl-or 2-(5-methyl-1,3,4-thiadiazolyl)-with alkylidene ammonio salts of lactam of Formula III as shown in the accomapnied drawings, wherein R1is as defined herein, and R2 and R3 are the same or different and each is a C1-C16 alkyl group or R2 and R3 form a cycloalkylidene ring with up to 8 carbon atoms together with the carbon atom to which they are attached, X is an anion from an acid HX , in a suitable solvent in the presence of an organic base.
2. The process of claim 1 wherein R is methyl or 1-carboxy-1-methyl-ethyl.
3. The process of claim 1 wherein R1 is -CH2Y, in which Y is methoxy, acetoxy or pyridyl.
4. The process of claim 1 wherein R1 is a group of formula -CH2-S-Z, in which Z is 1,2,5,6-tetrahydro-2-methyl-5,6-dioxo-1,2,4-triazinyl.
5. The process of claim 1 wherein the reaction of compounds of Formulae II and III is effected in suitable solvent, which includes a class of solvents selected from the group consisting of ketones, chlorinated solvents, esters, ethers, dipolar aprotic solvent, aromatic solvent, acetonitrile, and mixtures thereof.
6. The process of claim 5 wherein said suitable solvent is selected from the group consisting of acetone, chloroform, dichloromethane, ethylacetate, tetrahydrofuran, dioxane, N,N-dimethylformamide, N,N-dimethylacetamide, N-methylpyrrolidone, dimethylsulphoxide and mixtures thereof.

7. The process of claim 6 wherein said suitable solvent is selected from the group consisting of acetone, N,N-dimethylacetamide, dichloromethane, and mixtures thereof.
8. The process of claim 1 wherein the organic base is selected from the group consisting of pyridine, picoline, quinoline, isoquinoline, triethylamine, tributylamine, N-methyl-piperidine, N-methylmorpholine, N,N-dimethylaniline, N,N-diethylaniline, and mixtures thereof.
9. The process of claim 1 wherein the preferred organic base is triethylamine.
10. The process for the preparation of cephem compounds of Formula I as shown in the accompanied drawings substantially as herein described and exemplified by the examples.