PROCESS FOR PREPARING [R-[R*,S*-(Z)]]-7-[(2-AMINO-2-CARBOXYETHYL)THIO]-2-[((2,2-DIMETHYLCYCLOPROPYL) CARBONYL]AMINO-2-HEPTENOIC ACID SALT

Field of the Invention
In general, this invention relates to a process for preparing [r-[r*,s*-(z)]]-7-[(2-amino-2-carboxyethyl)thio]-2-[((2,2-dimethylcyclopropyl) carbonyl]amino-2-heptenoic acid salt (cilastatin salt). More particularly, the present invention provides an improved and cost effective process for preparing pure cilastatin salt employing an intermediate (Z)-7-chloro-((S)-2,2-dimethyl cyclopropanecarboxamido)-2-heptenoic acid salt and process for preparing said intermediate.

Background of the Invention
Cilastatin salt is salt of a derivatized heptenoic acid. Chemically, it is [R-[R*,S*-(Z)]]-7-[(2-amino-2-carboxyethyl)thio]-2-[((2,2-dimethylcyclopropyl) carbonyl]amino-2-heptenoic acid salt and has the structural Formula I’.

Formula I
The prototype carbapenem antibacterial agent imipenem, having structural Formula II,

Formula II
has a very broad spectrum of anti-bacterial activity. It is co-administered with a renal dehydropeptidase inhibitor, cilastatin, in order to prevent its renal metabolism in clinical use. Imipenem/cilastatin sodium combination is a potent broad spectrum antibacterial agent for intramuscular administration. It is an effective monotherapy for septicemia, neutropenic fever and intra abdominal, lower respiratory tract, genitourinary, gynecological, skin and soft tissue, and bone and joint infections. In these indications, imipenem/cilastatin generally exhibits similar efficacy to broad spectrum cephalosporin and other carbapenems.

Cilastatin was first disclosed in U.S. Patent No. 5,147, 868 and obtained in a multi-step synthesis involving condensing cysteine hydrochloride with heptenoic acid derivative of Formula III,

Formula III
wherein X is chloro or bromo, in the presence of sodium hydroxide and aqueous medium. U.S. Patent No. 5,147,868 also teaches a method for isolating cilastatin intermediate in the form of an acid of Formula III as a gummy residue from the reaction mixture, involving acid base purifications. However, this process is not suitable for industrial scale production as it involves handling of gummy residue which is cumbersome, tedious and not feasible on industrial scale.

Further, U.S. Patent Application No. 20050119346 discloses the preparation of cilastatin in which cilastatin intermediate of Formula IV is treated in-situ with cysteine hydrochloride monohydrate to get the desired compound. However, this process is not viable because impurity of intermediate stage is carried forward to final stage and contaminates the final product. Further, the above process to prepare and purify the pure cilastatin intermediate as alkali metal or alkaline earth metal salts of Formula IV lead to a product with less yield and purity.

Formula IV

wherein X is chloro or bromo and Y is alkali metal or alkaline earth metal.

In light of the existing processes there still exists a need to develop an alternate process for large scale production of highly pure cilastatin salt that is economical and high yielding. Further, there is need to develop a simple process for preparing cilastatin salt that involves the isolation of highly pure compound of Formula IV with minimal impurities and then its conversion of cilastatin salt.

Objects and Summary of the Invention
It is an object of the present invention to provide a simple, cost-effective process for preparing highly pure cilastatin salt free from impurities.

It is another object of the present invention to provide a process for preparing pure cilastatin with high purity and yield at large scale industrial production.

The above and other objects of the present invention are attained according to following preferred embodiments of the present invention. However the scope of the invention is not restricted to the particular embodiments discussed herein after.

In accordance with one embodiment of the present invention, there is provided a process for preparing [R-[R*,S*-(Z)]]-7-[(2-amino-2-carboxyethyl)thio]-2-[((2,2-dimethylcyclopropyl) carbonyl]amino-2-heptenoic acid salt of Formula I’ comprising treating the crude compound of Formula III with alkali metal hydroxide, alkaline earth metal hydroxide or alkoxide in presence of an organic solvent followed by isolating the resultant compound of Formula IV and converting the same into the cilastatin salt.

In accordance with another embodiment of the present invention, there is provided a process for preparing compound of Formula I’, wherein the compound is [R-[R*,S*-(Z)]]-7-[(2-amino-2-carboxyethyl)thio]-2-[((2,2-dimethylcyclopropyl) carbonyl]amino-2-heptenoic acid mono sodium salt.

In accordance with still other embodiment of the present invention, there is provided a process for producing an intermediate (Z)-7-chloro-((S)-2,2-dimethyl cyclopropanecarboxamido)-2-heptenoic acid salt of Formula IV for preparing [R-[R*,S*-(Z)]]-7-[(2-amino-2-carboxyethyl)thio]-2-[((2,2-dimethylcyclopropyl) carbonyl]amino-2-heptenoic acid salt comprising treating the crude compound of Formula III with alkali metal hydroxide, alkaline earth metal hydroxide or alkoxide in presence of an organic solvent and isolating the resultant compound of Formula IV.
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Detailed Description of the Invention
While this specification concludes with claims particularly pointing out and distinctly claiming that, which is regarded as the invention, it is anticipated that the invention can be more readily understood through reading the following detailed description of the invention and study of the included examples.

The disclosed embodiment of the present invention deals with a process for preparing pure cilastatin salt of Formula I’ employing a highly pure intermediate. The process according to the present invention is advantageous over the prior art due to the isolation of highly pure intermediate compound of Formula IV and then its conversion to cilastatin salt.

According to the invention, the process for preparing [R-[R*,S*-(Z)]]-7-[(2-amino-2-carboxyethyl)thio]-2-[((2,2-dimethylcyclopropyl) carbonyl]amino-2-heptenoic acid salt of Formula I’ comprises;

I’
treating the crude compound of Formula III with alkali metal hydroxide, alkaline earth metal hydroxide or alkoxide in presence of an organic solvent;

III IV
isolating the resultant compound of Formula IV and converting the same into cilastatin salt of Formula I’.

In accordance with the invention X is chloro or bromo and Y is alkali metal or alkaline earth metal.

According to the invention, the salt of compound of Formula I’ is preferably [R-[R*,S*-(Z)]]-7-[(2-amino-2-carboxyethyl)thio]-2-[((2,2-dimethylcyclopropyl) carbonyl]amino-2-heptenoic acid mono sodium salt.

In accordance with the present invention there is provided a process for preparing the intermediate compound of Formula IV employed for preparing [R-[R*,S*-(Z)]]-7-[(2-amino-2-carboxyethyl)thio]-2-[((2,2-dimethylcyclopropyl) carbonyl]amino-2-heptenoic acid salt of Formula I’

Formula IV

wherein X is chloro or bromo and Y is alkali metal or alkaline earth metal, comprising treating a crude compound of Formula III with alkali metal hydroxide, alkaline earth metal hydroxide or alkoxide in presence of an organic solvent, and followed by isolating the resultant compound of Formula IV.

wherein X is chloro or bromo.

According to the invention the process for preparing cilastatin intermediate of Formula IV comprises reacting the mass containing cilastatin intermediate Formula III or crude compound of Formula III obtained by the condensation of S-2,2-dimethylcylopropyl carboxamide (V) with 7-chloro-2-oxo-heptanoate derivative (VI) in the presence of p-toluene sulphonic acid in toluene employing any of the process disclosed in literature , with any suitable alkali metal hydroxide, alkaline earth metal hydroxide or alkoxide in suitable organic solvent.

The alkali metal, alkaline earth metal hydroxide and alkoxide is preferably selected from the group consisting of but not limited to sodium hydroxide, potassium hydroxide, lithium hydroxide, calcium hydroxide, magnesium hydroxide, sodium methoxide, sodium ethoxide, potassium methoxide and potassium ethoxide; and more preferably sodium hydroxide. The reaction is preferably performed at 0 to 50oC and preferably at 10 to 40oC and more preferably at 25 to 30oC.

The suitable organic solvents utilized for this step include and are not limited to alcohol, such as methanol, ethanol, isopropyl alcohol, and n-propanol; halogenated hydrocarbon, such as dichloromethane, 1,2-dichloroethane and chloroform; ketone, such as acetone, ethylmethyl ketone, and methyl isobutyl ketone; ether, such as tetrahydrofuran, and 1 ,4-dioxane; nitrile, such as acetonitrile and propionitrile; dimethylsulfoxide (DMSO); N,N-dimethylformamide (DMF); N,N-dimethylacetamide and mixtures thereof. Preferably, the solvent(s) may be acetone, methanol, tetrahydrofuran, acetonitrile; and mixtures thereof in various proportions. More preferably, the solvent is methanol, ethanol.

The compound of Formula IV can be further purified optionally by treating it with organic solvent using any suitable techniques. The solvents that may be utilized for this step include and are not limited to ketone, such as acetone, ethylmethyl ketone, and methyl isobutyl ketone; ether, such as diethyl ether, dimethylether, diisopropyl ether and methyl tert-butyl ether; hydrocarbon, such as n-heptane, cyclohexane, and n-hexane; nitrile, such as acetonitrile and propionitrile and mixtures thereof. Preferably, the solvent(s) may be acetone, methanol, tetrahydrofuran, acetonitrile, propionitrile and mixtures thereof in various proportions. More preferably, the solvent is acetonitrile.

According to the invention, the purification is preferably performed at -20 to 40oC and preferably at -10 to 25oC and more preferably at -5 to 5oC. Additionally, it may be advantageous to conduct this step under an inert atmosphere, such as oxygen-free argon or nitrogen gas. Isolation of the product thus obtained includes collection of the material by any techniques, such as, for example, decantation, filtration by gravity or suction, centrifugation, and the like and optional washing with solvent. If required, the reaction mass may be cooled before product isolation. The solid material obtained by any of the techniques described above may be further dried. Drying may be suitably carried out by any methods, such as, for example, use a tray dryer, vacuum oven, air oven, fluidized bed drier, spin flash dryer, flash dryer, and the like. The drying may be carried out under reduced pressures and at various temperatures. The temperatures may range from about ambient temperature to about 100oC, for a time period that produces the desired result.

The obtained pure compound of Formula IV can be further converted to cilastatin by the any process disclosed in prior art or literature.

In the following section preferred embodiments are described by way of examples to illustrate the process of the invention. However, these are not intended in any way to limit the scope of the present invention.

Example 1
Sodium salt of Z-7-chloro-2-(2,2-dimethylcyclopropanecarboxamido)-2-heptenoic acid
A. Condensation and Hydrolysis
To the solution of (S)-2,2-dimethylcylopropylcarboxamide (113 gm) in toluene (500), ethyl-7-chloro-2-oxo-heptanoate (50 gm) and p-toluene sulphonic acid (0.5 gm) was added. The resulting solution was refluxed for 20 hrs followed by cooling to 20-30oC. To the reaction mixture 4% aqueous solution of hydrochloric acid (100 ml) was added and the resultant layers were separated. Organic layer was collected and washed with water followed by distillation under reduce pressure. Methanol and aqueous solution of sodium hydroxide was charged to reaction mass and stirred for 12 hrs at room temperature. After the completion of the reaction, pH was adjusted to 3.0 to 3.5 by using hydrochloric acid solution followed by extraction with toluene. Organic layer was distilled out and to the residue methanol was charged and pH adjusted to 8.0 to 8.5 using methanolic sodium hydroxide solution. The solvent was distilled out from the reaction mass completely under reduce pressure and used as such for the next step.

B. Purification
Acetonitrile (250 ml) was charged in above concentrated reaction mass and distilled out completely under reduce pressure. Again acetonitrile (250 ml) was charged to the reaction mass and the mass chilled at -5 to 0oC. The solid was filtered under nitrogen atmosphere and washed with pre-cooled acetonitrile. The resultant was then dried under vacuum at 40 to 45oC to obtain 98% pure sodium salt of Z-7-chloro-2-(2,2-dimethyl cyclopropanecarboxamido)-2-heptenoic acid (45 gm) as white solid.

Example 2
Preparation of Cilastatin Acid
To the mixture of L-Cysteine hydrochloride monohydrate (21 gm), sodium dithionite (0.25 gm) and sodium salt of Z-7-chloro-2-(2,2-dimethylcyclopropanecarboxamido)-2-heptenoic acid (25 gm), solution of sodium hydroxide (16 gm) in water (250 ml) was added and stirred. After completion of reaction, the pH of the solution was adjusted to 0.5 to 0.8 with conc. HCl, and the reaction mass heated to 95oC. After 30 minutes, reaction mass was washed with dichloromethane. To the aqueous layer, carbon was added followed by stirring and filtration. The reaction mass pH was adjusted to 1.5 to 2.0 using 10% NaOH solution followed by purification using Diaion HP-20 resin. The fractions which contain desire purity of cilastatin acid were collected and distilled off under reduce pressure. The resultant residue was charged with acetone (250 ml) to make slurry and stirred. The solid was filtered and washed with acetone (250 ml) followed by drying under vacuum at 40 to 45oC to obtain Cilastatin acid (18 gm) as white solid.

Example 3
Preparation of Cilastatin sodium
The cilastatin acid (25 gm) was dissolved in the mixture of ethanol (250 ml) and adds solution of sodium hydroxide (2.8 gm) in water at room temperature. To the resultant clear solution, carbon (2.5 gm) was added and stirred followed by filtration. The filtrate was filtered again through sterile micron (0.2µ) filter. To the resultant clear solution, acetone (1250 ml) was added under inert atmosphere and stirred for 3 hrs at RT. The precipitated cilastatin sodium was filtered and washed with acetone (25ml x 2) followed by drying under vacuum to obtain 24 gm cilastatin sodium as amorphous white solid.

While this invention has been described in detail with reference to certain preferred embodiments, it should be appreciated that the present invention is not limited to those precise embodiments. Rather, in view of the present disclosure, which describes the current best mode for practicing the invention, many modifications and variations would present themselves to those skilled in the art without departing from the scope and spirit of this invention.

We claim:
1. A process for preparing [R-[R*,S*-(Z)]]-7-[(2-amino-2-carboxyethyl)thio]-2-[((2,2-dimethylcyclopropyl) carbonyl]amino-2-heptenoic acid salt of Formula I’;

I’

comprising:
treating the crude compound of Formula III with alkali metal hydroxide, alkaline earth metal hydroxide or alkoxide in presence of an organic solvent;

III IV
wherein X is chloro or bromo and Y is alkali metal or alkaline earth metal,
isolating the resultant compound of Formula IV; and
converting the same into cilastatin salt of Formula I’.

2. The process according to claim 1, wherein the alkali metal hydroxide, alkaline earth metal hydroxide or alkoxide is selected from sodium hydroxide, potassium hydroxide, lithium hydroxide, calcium hydroxide, magnesium hydroxide, sodium methoxide, sodium ethoxide, potassium methoxide and potassium ethoxide.

3. The process according to claim 1, wherein the compound of Formula I’ is [R-[R*,S*-(Z)]]-7-[(2-amino-2-carboxyethyl)thio]-2-[((2,2-dimethylcyclopropyl) carbonyl]amino-2-heptenoic acid mono sodium salt.

4. The process according to claim 1, wherein the organic solvent is selected from alcohol, such as methanol, ethanol, isopropyl alcohol, and n-propanol; halogenated hydrocarbon, such as dichloromethane, 1,2-dichloroethane and chloroform; ketone, such as acetone, methylethyl ketone, and methyl isobutyl ketone; ether, such as tetrahydrofuran, and 1 ,4-dioxane; nitrile, such as acetonitrile and propionitrile; dimethylsulfoxide (DMSO); N,N-dimethylformamide (DMF); N,N-dimethylacetamide and mixtures thereof.

5. A process for producing an intermediate (Z)-7-chloro-((S)-2,2-dimethyl cyclopropanecarboxamido)-2-heptenoic acid salt of Formula IV for preparing [R-[R*,S*-(Z)]]-7-[(2-amino-2-carboxyethyl)thio]-2-[((2,2-dimethylcyclopropyl) carbonyl]amino-2-heptenoic acid salt of Formula I’.

Formula IV

wherein X is chloro or bromo and Y is alkali metal or alkaline earth metal,
the process comprising:
treating the crude compound of Formula III with alkali metal hydroxide, alkaline earth metal hydroxide or alkoxide in presence of an organic solvent, and

wherein X is chloro or bromo,
isolating the resultant compound of Formula IV.

6. The process according to claim 5, wherein the organic solvent is selected from alcohol, such as methanol, ethanol, isopropyl alcohol, and n-propanol; halogenated hydrocarbon, such as dichloromethane, 1,2-dichloroethane and chloroform; ketone, such as acetone, methylethyl ketone, and methyl isobutyl ketone; ether, such as tetrahydrofuran, and 1 ,4-dioxane, nitrile, such as acetonitrile and propionitrile; dimethylsulfoxide (DMSO); N,N-dimethylformamide (DMF); N,N-dimethylacetamide and mixtures thereof.

Dated this 19th day of February, 2011.
MANISHA SINGH NAIR
Agent for the Applicant [IN/PA –740]
LEX ORBIS IP PRACTICE

PROCESS FOR PREPARING[R-[R*,S*-(Z)]]-7-[(2-AMINO-2-CARBOXYETHYL)THIO]-2-[((2,2-DIMETHYLCYCLOPROPYL) CARBONYL]AMINO-2-HEPTENOIC ACID SALT

Abstract of the Invention
Disclosed herein is a process for preparing [R-[R*,S*-(Z)]]-7-[(2-amino-2-carboxyethyl)thio]-2-[((2,2-dimethylcyclopropyl) carbonyl]amino-2-heptenoic acid salt of Formula I’. Further, the invention also provides a process for preparing an intermediate (Z)-7-chloro-((S)-2,2-dimethyl cyclopropanecarboxamido)-2-heptenoic acid salt of Formula IV to prepare the compound of Formula I’.