AN IMPROVED PROCESS FOR THE PREPARATION OF CEPHALOSPORIN

ANTIBIOTIC

Field of the Invention

The present invention provides an improved process for the preparation of the cephalosporin antibiotic of formula (I) or its salt wherein R represents hydrogen or a protecting group. More particularly, this present invention relates to an improved process for the preparation of Cefcapene of formula (I) or its salt.

Background of the Invention

Cefcapene is chemically known as (6R,7R)-3[[(Aminocarbonyl)oxy]methyl]-7- [[(2Z)-2-(2-amino-4-thiazolyl)-l-oxo-2-pentenyl]amino]-8-oxo -5-thia-l- azabicyclo[4.2.0]oct-2-ene-2-carboxylic acid and widely administered as its ester, particularly (2,2-dimethyl-l-oxopropoxy)methyl ester or (6R,7R)-7-[(Z)-2-(2- Aminothiazol-4-yl)-2-pentenoylamino]-3-(carbamoyloxymethyl)- 3-cephem-4-carboxylic acid pivolyloxymethyl ester (Cefcapene Pivoxil). Cefcapene is a third generation antibiotic and is reported to have exhibited potent antibacterial activities against gram positive and gram-negative bacteria.

US patent No. 4,731,361 claims Cefcapene and discloses the process for the preparation of Cefcapene, which involves condensation of compound of formula (A) with cephem derivative of formula (B) in which the amino group in the amino thiazolyl acetic acid moiety is protected with tertiary butoxy carbonyl group while carrying out the condensation (Example 6)

The process depicted as above involves the protection of amino group of aminothiazolylpentenoic acid prior to the condensation of cephem moiety and subsequent deprotection after condensation.

Example 5 of US 4,731,362 specifically teaches the carbomylation stage. This example utilizes THF solvent for carbomylation of 3-hydroxymethyl-3-cephem-4- carboxylic acid sodium salt.

US 4,775,750 also disclose ethyl acetate for carbomylation stage for the preparation of Cefuroxime sodium. Example 1 of this patent discloses the carbamoylation of (6R,7R)-3-hydroxymethyl-7-[Z-2-(fur-2-yl)-2-methoxyiminoacet amido]ceph-3-em-4- carboxylic acid in methyl acetate using chlorosulphonylisocyanate. Using the aforesaid compound for the carbamoylation leads to the side reactions such as lactonization of the cephem ring.

JP 2960790 discloses crystalline 7-β-[(Z)-2-(2-amino-4-thiazolyl)-2- pentenoylamino]-3-carbamoyloxymethyl-3-cephem-4-carboxylicac id pivaloyloxymethyl ester hydrochloride monohydrate. This patent also discloses the process for the

preparation of said crystalline compound by recrystallisation of crude compound from methanol and water.

In an effort to prepare an industrially viable process, we have identified an improved process for the manufacture of Cefcapene of formula (I), which avoids the side reactions associated with the Carbamoylation stage and yields the final compound in good purity and yield. None of the prior art suggests the invention disclosed in this specification.

Objective of the Invention

Accordingly, the objective of the present invention is to provide an improved process for the manufacture of compound of formula (I) or its salt, which is easy to implement on industrial scale and avoids lactone formation during carbamoylation stage.

Yet another objective of the present invention is to provide an improved process for the preparation of compound of formula (I), which involves less number of unit operations, which is cost effective.

Still another objective of the present invention is to provide an improved process, wherein the preparation of Cefcapene Pivoxil hydrochloride monohydrate of formula (I) is obtained in good yield, and high purity.

Summary of the Invention

Accordingly, the present invention provides a process for the preparation of compound of formula (I) or its salt

which comprises the steps of:

i) condensing compound of formula (II) or its reactive derivative

(II) wherein R is an amine protecting group or hydrogen with compound of formula (III) in its silylated form

7-HACA (Ml) in the presence of a solvent and in the presence or absence of a base to give compound of formula (IV); and

ii) carbamoylating compound of formula (IV) with an isocyante of formula (V)

R'NCO (V) wherein R' is a labile group, in a solvent to give compound of formula (I) or its salt; The process of this invention is disclosed in the Scheme- 1

SCHEME-1

Detailed description of the invention

In an embodiment of the present invention, silylating the 7-amino-3- hydroxymethylcephalosporinic acid (7-HACA) of formula (III) was carried out using a silylating agent followed by reacting with reactive derivative of the compund formula (II). Suitable examples of the reactive derivative of the compound (II) include the corresponding acid halides (e.g., chloride, bromide), active thioesters (e.g., mercaptobenzothiazole ester, 2,4-dinitrophenyl ester, succinimide ester, phthalimide ester, benzotriazole ester, 2-pyrrolidon-l-yl ester), acid azide, acid amides (e.g., imidazole amide, 4-substituetd-imidazole amide, triazole amide) and mixed anhydride (mixed anhydride with pivolyl chloride, ethyl chloroformate, methane sulphonyl chloride and the like). The silylation of 7-HACA was carried out in the presence of solvents such as halogenated hydrocarbons, ethyl acetate, tetrahydrofuran, acetonitrile, N,N- dimethylformamide, N,N-dimethylacetamide (DMAc) and the like or mixtures thereof using silylating agents which include but not limited to N,O-bistrimethylsilylacetamide (BSA), N,N'-bis(trimethylsilyl)urea, hexamethyldisilazane-acetamide and hexamethyldisilazane -trimethylchlorosilane and the like.

The condensation of silylated 7-amino-3-hydroxymethylcephalosporinic acid (silylated 7-HACA) of formula (III) with reactive derivative of the compound of formula (II) was carried out using solvents selected from ethyl acetate, tertrahydrofuran (THF),

dichloromethane (MDC), acetone, ethyl methyl ketone, diglyme, 2-butanone, dioxane, N,N-dimethylformamide (DMF), N-methy-2-pyrrolidone (NMP), N ₅ N- dimethylacetamide (DMAc), acetonitrile, and the like or mixtures thereof.

In another embodiment of the present invention the base used in step (i) was selected from the group consisting of organic base such as, dicyclohexylamine, tetramethylguanidine (TMG), N,N-diisopropylethylamine, l,5-diazabicyclo[4.3.0]non-5- ene (DBN), l,4-diazabicyclo[2.2.2]octane (DABCO), N-methylmorpholine, 1,8- Diazabicyclo[5.4.0]undec-7-ene (DBU), benzathine, octylamine, triethylamine, N- ethyldiisopropylamine and the like.

In still another embodiment of the present invention, the condensation of silylated 7-amino-3-hydroxymethylcephalosporanic acid (silylated 7-HACA) of formula (III) with the activated derivative of the compound of formula (II) resulted in the formation of compound of formula (IV) and silylated derivative so obtained was subjected to in situ carbamoylation with the compound of formula (V) to give compound of formula (I) at low temperature. Accordingly, the present invention obviates the need of conventional method of isolating the compound of formula (IV) in free form, followed by subjecting the ensuing compound for carbamoylation. Owing to such in situ carbamoylation reaction, the reaction proceeds smoothly and yields the final compound in good purity and yield. In situ carbamoylation avoids undesirable side reactions such as lactonisation of the 3 -hydroxy methyl cephalosporin. Moreover, overall yield of the current process is higher than the prior art process, which involves isolation of compound of formula (IV).

In yet another embodiment of the present invention, the labile group represented by R' in compound of formula (V) was selected from chlorosulphonyl, mono, di or trichloroacetyl, bromosulphonyl, trichloroethoxycarbonyl, trimethylsilyl or chlorobenzenesulphonyl group.

In yet another embodiment of the present invention, the carbamoylation of compound of formula (IV) in step (ii) was carried out with isocyanate of formula (V) in a

solvent selected from ethyl acetate, acetonitrile, THF, dichloromethane and the like or mixtures thereof.

In a yet another embodiment of the present invention the protection of amino group in compound of formula (II) was optionally carried out as per the procedure available in the prior art. Suitable amino protecting groups include lower alkanoyl such as formyl, acetyl and pivaloyl; mono-, di- or trihalogeno-lower alkanoyl such as chloroacetyl and trifluoroacetyl; lower alkoxycarbonyl such as methoxycarbonyl, ethoxycarbonyl and tertiary butoxycarbonyl; substituted or unsubstituted ben2yloxycarbonyl such as benzyloxycarbonyl and p-methoxybenzyloxycarbonyl; substituted or unsubstituted phenyl-lower alkyl such as p-methoxybenzyl and 3,4- dimethoxy-benzyl; and di- or triphenyl lower alkyl such as benzhydryl and trityl.

The present invention facilitates the isolation of the compound of formula (I) from the reaction mass directly as alkali metal salt using a source that is selected from sodium acetate, sodium formate, sodium bicarbonate, sodium hydroxide, sodium 2- ethylhexanoate, sodium carbonate, sodium lactate, potassium hydroxide, potassium carbonate, potassium bicarbonate or mixtures thereof, thereby avoiding the isolation of corresponding acid, and hence has been found to be advantageous from industrial point of view. The compound of formula (VI) was converted in to its corresponding ester of formula (VII) by following the process of the present invention which enables and envisages two different synthetic routes whereby (1) in situ carbamoylation of silylated inteπnediate of formula (IV) to give amine protected-Cefcapene acid of formula (VI) and its in situ conversion into ester of formula (VII) followed by deprotection to yield compound of formula (VIII); (2) in situ carbomylation of silylated intermediate and its isolation as a alkali metal salt of amine protected-Cefcapene acid and its further conversion into its ester of formula (VII) followed by deprotection to yield compound of formula (VIII); The scheme being followed is shown in Scheme-2.

SCHEME-2

Accordingly the present invention provides an improved process for the preparation of compound of formula (A) and its salt and its ester, the said process comprising the steps of:

(A)

or hydrogen

R1 is hydrogen or -OMe group and R2 is hydrogen or amine protecting group

i) acylating the compound of formula of formula (III) in its silylated form

in the presence of solvent and in the presence or absence of base to give compound of formula (B); and

^(B) ii) carbamoylating compound of formula (B) with isocyante of formula (V)

R'NCO (V) wherein R' is labile group, in a solvent to yield compound of formula (A) or its salt or its ester; wherein the improvement consists of: i) using silylated compound of formula (III) in step (i) to give silylated intermediate (B) and/or ii) in situ carbamoylation of silylated intermediate (B) in step (ii) to give compound of formula (A).

The starting material of the compound of formula (II) is prepared according to the procedure available in our granted Indian Patent No. IN 194929 filed on 17.09.2002. (Application Number: 689/MAS/2002)

Apart from the aforesaid advantages, the present invention enables isolation of the compound of formula (I) in good purity (99.5%). Thus, this invention provided a method for the improved quality of crystalline material of Cefcapene Pivoxil hydrochloride monohydrate.

The present invention is illustrated with the following examples, which should not be construed as limiting to the scope of the invention.

Example-1 Preparation of Boc-Ccfcapene acid sodium salt

To (Z)-2-(2-t-butoxycarbonylaminothiazol-4-yl)-2-pentenoic acid (BOC-ATPAA, 100 g) in ethyl acetate (100 mL) containing triethyl amine (90 g) was added methanesulphonyl chloride (90 g) at -20 ⁰ C to -30°C. 7-amino-3 -hydroxy methylcephalosporanic acid (7-HACA, 100 g) was silylated using BSA (176.5 g) in ethyl acetate (500 mL) and N,N-dimethylformamide (10 mL). The silylated 7-HACA solution was mixed with BOC-ATPAA mixed anhydride solution at -30°C to -2O ⁰ C and stirred. To this was added chlorosulphonyl isocyanate (128 g) in acetonitrile (200 mL). After completion of the reaction, the reaction mixture was quenched in water and stirred. The pH of the aqueous solution was adjusted with aqueous ammonia solution to -2.5 at 10 ⁰ C and the organic layer was separated. To the ethyl acetate layer was added sodium 2- ethylhexanoate solution (144 g dissolved in 500 mL of Acetone). The solid obtained was filtered, washed with acetone and dried under reduced pressure to get Boc-Cefcapene sodium salt with a HPLC purity of 94-96%. Examplc-2

Preparation of Cefuroxime acid

To (fur-2-yl)-2-methoxyimino acetic acid ammonium salt in ethyl acetate containing triethylamine was added methanesulphonyl chloride at -20°C to -3O ⁰ C for 30- 45 min. 7-HACA was silylated using N,O-bistrimethylsilylacetamide (BSA) in ethyl acetate and N,N-dimethylformamide The silylated 7-amino-3- hydroxymethylcephalosporanic acid (7-HACA) solution was mixed with (fur-2-yl)-2- methoxyimino acetic acid ammonium salt mixed anhydride solution at -30 ⁰ C to -20 ⁰ C and stirred for 2 h. To this was added chlorosulphonyl isocyanate in acetonitrile. After stirring, the reaction mixture was quenched in water and stirred. The pH was adjusted with aqueous ammonia solution to -2.5 at 10 ⁰ C and the organic layer was separated. To the ethyl acetate layer was added sodium 2-ethylhexanoate solution. After stirring for 1 h,

solid obtained was filtered, washed with acetone and dried under reduced pressure to get

Cefuroxime sodium salt.

ExampIe-3

Preparation of Boc-Cefcapene Pivoxil To Boc-Cefcapene acid sodium salt (100 g) in a mixture of ethyl acetate and water was added iodomethyl pivalate (75 g) and tetra-n-butylammonium bromide (10 g) at 25°C to 30°C. After completion of reaction, the organic layer was separated and concentrated under reduced pressure followed by the addition of diisopropyl ether. The solid obtained was filtered and dried under reduced pressure to get BOC-Cefcapene Pivoxil as an off-white solid (90-95 g).

Example-4

Preparation of Cefcapene pivoxil hydrochloride monohydrate

To a stirred slurry of Boc-Cefcapene Pivoxil (100 g) in anisole (250 mL), was added BF ₃ in acetonitrile solution at -30 ⁰ C to 30°C. After completion of reaction, reaction mixture was mixed with MIBK and aqueous NaHCO ₃ solution. MIBK layer was separated. To the separated MIBK layer was added a solution of Cone. HCl in acetic acid at 25 ⁰ C to 3O ⁰ C. The solid obtained was filtered, washed with MIBK to get Cefcapene pivoxil hydrochloride monohydrate (70-75g) with purity greater than 99.0%.

Example-5 Preparation of Cefcapene pivoxil hydrochloride monohvdrate

To a stirred slurry of Boc-Cefcapene Pivoxil (100 g) in acetonitrile was added

BF ₃ in acetonitrile solution (2.5 mole equivalent) at -30 ⁰ C to 30 ⁰ C. After completion of reaction, reaction mixture was mixed with MIBK and aqueous NaHCO ₃ solution. MIBK layer was separated. To the separated MIBK layer was added methanolic hydrochloric acid. The solid obtained was filtered, washed with MIBK to get Cefcapene pivoxil hydrochloride monohydrate (70-75 g).

Example-6

Preparation of Cefcapene pivoxil hydrochloride monohvdrate

To a stirred slurry of Boc-Cefcapene Pivoxil (100 g) in MDC was added TiCl ₄ (1 14 g) at 0 ⁰ C to 5 ⁰ C. After being completion of reaction, cold IPA was added followed by sodium hydroxide solution. Organic layer was separated and washed with sodium

bicarbonate solution. The organic layer was concentrated and mixed with MIBK followed by addition of methanolic HCl solution to get fine crystalline Cefcapene Pivoxil hydrochloride monohydrate (65-70 g) in good purity (99.5%). Example-7 Preparation of Cefcapene pivoxil hydrochloride monohydrate

To a stirred slurry of Boc-Cefcapene Pivoxil (100 g) in MDC was added AlCl ₃ (114 g) at O ⁰ C to 5°C over a period of 30 min. After completion of reaction, cold IPA was added followed by sodium hydroxide solution. Organic layer was separated and washed with sodium bicarbonate solution. The organic layer was concentrated and mixed with MIBK followed by the addition of methanolic HCl solution to get fine crystalline Cefcapene Pivoxil hydrochloride monohydrate (65-70 g) in good purity (99.5%).

Example-8 Preparation of Cefuroxime acid

To (fur-2-yl)-2-methoxyimino acetic acid ammonium salt in ethyl acetate containing triethylamine was added methanesulphonyl chloride at -20°C to -3O ⁰ C for 30- 45 min. 7-HACA was silylated using BSA in ethyl acetate and N,N-dimethylformamide The silylated 7-HACA solution was mixed with activated (fur-2-yl)-2-methoxyimino acetic acid solution at -30 ⁰ C to -20°C and stirred. To this was added chlorosulphonyl isocyanate in acetonitrile or tetrahydrofuran. After completion of the reaction, the reaction mixture was quenched in water and layers separated. The pH was adjusted to -2.5 at 10 ⁰ C, the solid obtained was filtered and washed with water to yield Cefuroxime acid. The Cefuroxime acid thus obtained was converted to Cefuroxime sodium by dissolution of Cefuroxime acid in aqueous acetone or mixture of acetone and methanol followed by addition of sodium acetate/sodium lactate or sodium 2-ethylhexonate in methanol. Example-9

Preparation of Iodomethyl pivolate from chloromethyl pivolate

To a stirred suspension of chloromethyl pivolate (33 g) in acetonitrile (66 mL) was added sodium iodide (59.4 g) at 25°C and stirred for 4-6 h at 30-32 ⁰ C, the reaction

mixture was quenched over a mixture of ethyl acetate and water at 25-30°C. Layers were separated and ethyl acetate layer was washed sodium thiosulphate solution to de-colorise the ethyl acetate layer. The obtained ethyl acetate layer containing iodomethyl pivolate was directly used for esterification of BOC-Cefcapene sodium.

Example-10

Preparation of BOC-Cefcapene Pivoxil through in-situ esterification of BOC- Cefcapene acid To the ethyl acetate layer obtained from example- 1 was added sodium bicarbonate solution (5 L) at 10-20°C and stirred for 60-120 min. at the same temperature. Layers were separated and to the aqueous layer was added fresh ethyl acetate tetra butyl ammonium bromide (TBAB) and iodomethyl pivolate solution (Prepared as per example-9). After stirring at 25-30°C, layers were separated and ethyl acetate layer was concentrated under reduced pressure followed by subsequent addition of isopropyl ether or heptane or hexane gave BOC-Cefcapene Pivoxil as an off-white solid (95 g).

Abbreviations: Boc : tertiary-butoxycarbonyl

7-HACA : T-amino-S-hydroxymethylcephalosporanic acid

Boc-ATPAA : (z)-2-(2-t-butoxycarbonylaminothiazol-4-yl)-2-pentenoic acid