FIELD OF INVENTION

The present invention relates to a novel ecofriendly and industrially advantageous process for the preparation of cilastatin acid and its sodium salt.

BACKGROUND OF THE INVENTION

Cilastatin is known for its ability to prevent nephrotoxicity associated with the use of p-lactam antibiotics such as imipenem. It is chemically represented by name [R-[R*, S*-(Z)]]-7-[(2-amino-2-carboxyethyl)thio]-2-[[(2,2-dimethylcyclo propyl)carbonyl]amino]-2-heptenoic acid and formula I.

It is a renal dehydropeptidase inhibitor and is co-administered as the sodium salt with imipenem in order to prevent its renal metabolism. Imipenem and cilastatin combination marketed as PRIMAXIN is used as a potent broad-spectrum antibacterial agent.
Cilastatin was first reported in US patent 5,147,868. This patent describes various processes for the preparation of cilastatin. One of the examples describes the preparation of cilastatin by the condensation of 7-chloro-2-oxoheptanoic acid ethyl ester with (S)-2,2-dimethylcyclopropanecarboxamide by means of p-toluene sulphonic acid in refluxing toluene to give (S)-7-chloro-2-(2,2-dimethylcyclopropanecarboxamido)-2-heptenoic acid ethyl ester, which is hydrolyzed in aq. NaOH to yield the corresponding carboxylic acid and finally the obtained compound is condensed with (R)-cysteine by means of NaOH in water to afford the target cilastatin, followed by isomerisation at 3.0 pH. It has been observed that the isomerisation process results in the formation of impurities due to degradation of cilastatin which render cilastatin produced by this process unsuitable for human consumption.

US patent 5,147,868 also teaches a method for isolating from the reaction mixture involving two purifications viz. chromatography using a cation exchange resin followed by solvent purification using ethanol and diethylether.

J. Med. Chem. 1987; 30 1083 discloses a process for the preparation of cilastatin involving the condensation of cysteine with the haloheptenoic acid in sodium metal/liquid ammonia and the resultant mixture is isomerized to obtain cilastatin using methyl iodide in methanol. Cilastatin is isolated by using a cation exchange resin followed by the treatment with an anion exchange resin to remove the inorganic salts. However, this process is not suitable on industrial scale as it involves the use of sodium metal/liquid ammonia which are hazardous and also the use of methyl iodide for isomerisation is expensive and requires special storage conditions. Moreover, loading the ion exchange column requires repeated circulation of cilastatin solution. Also, ion exchange column operates on the principle of ionic bonding/acid base reaction. Such reaction being exothermic causes considerable degradation of cilastatin. The use of ion exchange chromatography is cumbersome, tedious and not practicable on an industrial scale.
EP1423360 Bl claims a process for the purification of cilastatin, which comprises contacting a solution of crude cilastatin with a non-ionic adsorbent resin and recovering pure cilastatin from a solution thereof. This patent also claims a process for the isomerisation of cilastatin by heating a solution of cilastatin containing the corresponding E isomer at a pH of about 0.5 to 1.5. This process is not suitable from commercial point of view as it involves column chromatography.

US20040152780 describes a process for the preparation of pure cilastatin sodium in an amorphous form which comprises recovering cilastatin sodium from an organic solvent, homogeneous mixture of organic solvents, or homogeneous mixture of organic solvents and water, by solvent precipitation and recovering the pure cilastatin sodium in amorphous form from the solution of cilastatin sodium in a solvent by adding an anti-solvent.

US20090143614 describes a process for the preparation of cilastatin or its sodium salt by condensing 7-chloro-2-[[(lS)-2,2-dimethylcyclopropane] carboxamide]-2-heptenoic acid with L-cysteine in the presence of base in water and/or an alcoholic solvent, adjusting pH of the resultant solution to 2.0 to 4.0, and isolating the cilastatin acid and further dissolving it in a solvent using a base, adding sodium salt of week acid and isolating cilastatin sodium.

In view of the above drawbacks in the prior art processes, there is a need for the development of a simple, convenient and efficient process for the preparation of pure cilastatin and its pharmaceutically acceptable salt. The present inventors after continuous effort have developed a process which is more practical at large scale, efficient, cost effective.

SUMMARY OF THE INVENTION

Accordingly, the present invention provides a process for preparation cilastatin acid comprising:

a) condensing 7-chloro-2-[[(lS)-2,2-dimethylcyclopropane] carboxamide]-2-heptenoic acid with L-cysteine in the presence of an amine and a solvent;

b) adjusting the pH;

c) optionally extracting cilastatin acid in an organic solvent; and

d) isolating cilastatin acid.

DETAIL DESCRIPTION OF THE INVENTION

In an embodiment of the present invention, the amine is selected from the group comprising l,8-diazabicyclo[4.3.0]undec-7-ene (DBU), 1,4-diazabicyclo [2.2.2]octane (DABCO), and Tetramethylguanidine (TMG) for the condensation of 7-chloro-2-[[(lS)-2,2-dimethylcyclopropane]carboxamide]-2-heptenoic acid with L-cysteine is N-ethyldiisopropylamine and the solvent is selected from the group comprising water, a lower alcohol such as methanol, ethanol etc., N-methyl pyrrolidinone, N,N-dimethylFormamide, N,N-dimethyl Acetamide, 2,3-dimethyl Imidazolidinone, tetrahydrofuran (THF) from N-methylpyrrolidinone, Methylenedichloride, N,N-dimethylformamide, 2,3-dimethylimidazolidinone. It has been observed that the condensation of 7-chloro-2-[[(lS)-2,2-dimethylcyclopropane]carboxamide]-2-heptenoic acid with L-cysteine in the above selected solvent and base results into better quality and good yield of the cilastatin acid.

In another embodiment of the present invention, the L- Cysteine used in step (a) is in the form of L- Cysteine hydrochloride monohydrate or R-Cysteine hydrochloride or L-Cysteine hydrobromide monohydrate.

In another embodiment of the present invention the pH is adjusted to 3 to 4 using formic acid, acetic acid or phosphoric acid.

In still another embodiment of the invention, cilastatin acid can be isolated from the reaction mass after pH adjustment by using acetone and optionally it can be purified using an alcoholic solvent preferably using methanol, or acetonitrile or methylenedichloride (MDC) or mixture thereof.

In still another embodiment of the present invention, the Cilastatin obtained according to the present invention can be optionally subjected to isomerisation process by the technique known in prior art.

In still another embodiment of the present invention, the starting material 7-chloro-2-[[(lS)-232-dimethylcyclopropane]carboxamide]-2-heptenoic acid of formula (II) is prepared by utilizing the technique known in the art.

In still another embodiment of the present invention, cilastatin acid obtained by the present invention can be further converted to its sodium salt by the process known in the art.
Advantage of the process of the present invention:

a) The workup of the process has been minimised resulting in the reduction in the loss of yield and cost of production.

b) The product was isolated without inorganic impurities and avoids use of chromatography and provides direct isolation and purification can be done using lower alcohol or MDC or acetonitrile.

The present invention is illustrated with the following non-limiting examples.

Example 1:

(Z)-(S)-7-Chloro-2-(2, 2-dimethyl-cyclopropane carboxamide)-2-heptenoic acid (50gm) was charged in to the flask containing water (350ml) 1,8-diazabicyclo[4.3.0.]undec-7-ene (DBU) (40gm) mixture. Then L-cystine Hydro Chloride Monohydrate (44gm) was added to the same flask and heated to 60°C -75 C, after completion of reaction the mass was cooled to RT. The mass were acidified with the help of formic acid (pH 3 to 4). Product was crystallized out from the medium and optionally by addition of Acetone, the solid was filtered & washed, the solid was dried under vacuum.

Yield: 37gm (dry)

Example 2:

(Z)-(S)-7-Chloro-2-(2, 2-dimethyl-cyclopropane carboxamide)-2-heptenoic acid (50gm) was charged in to the flask containing water (350ml) 1,8-diazabicyclo[4.3.0.]undec-7-ene (DBU) (40gm) mixture. Then L-cystine Hydro Chloride Monohydrate (44gm) was added to the same flask and heated to 60 C -75°C, after completion of reaction the mass was cooled to RT. The mass were acidified with the help of formic acid. Product was crystallized out from the medium and optionally by addition of acetonitrile, the solid was filtered & washed, the solid was dried under vacuum.

Yield: 35gm (dry)

Example 3:

(Z)-(S)-7-Chloro-2-(2, 2-dimethyl-cyclopropane carboxamide)-2-heptenoic acid (50gm) was charged in to the flask containing methanol (300ml) 1,8-diazabicyclo[4.3.0.]undec-7-ene (DBU) (37gm) mixture. Then L-cystine Hydro Chloride Monohydrate (44gm) was added to the same flask and heated to 60 C -65°C, after completion of reaction the mass was distilled and add water 250ml cooled to RT. The mass were acidified with the help of phosphoric acid. Product was crystallized out from the medium and the solid was filtered & washed, the solid was dried under vacuum.

Yield: 42gm (dry)

Example 4:

(Z)-(S)-7-Chloro-2-(2, 2-dimethyl-cyclopropane carboxamide)-2-heptenoic acid (50gm) was charged in to the flask containing methanol (300ml) 1,8-diazabicyclo[4.3.0.]undec-7-ene (DBU) (37gm) mixture. Then L-cystine Hydro Chloride Monohydrate (44gm) was added to the same flask and heated to 60°C -65°C, after completion of reaction the mass was distilled and add water 250ml cooled to RT. The mass were acidified with the help of phosphoric acid ( pH 3-4). Product was crystallized out from the medium and the solid was filtered & washed, the solid was dried under vacuum.

Yield: 35gm (dry)

Example-5

(Z)-(S)-7-Chloro-2-(2, 2-dimethyl-cyclopropane carboxamide)-2-heptenoic acid (50gm) was charged in to the flask containing N-Methyl Pyrrolidinone (250ml) 1,8-diazabicyc!o[4.3.0.]undec-7-ene (DBU) (37gm) mixture. Then L-cystine Hydro Chloride Monohydrate (44gm) was added to the same flask, The RM was heated to 70°C, after completion of reaction the mass was cooled to RT, pH was adjusted to 3-4 by using Acetic Acid. And crystallized out by using MDC at 40°C, the solid was filtered & washed; the solid was dried under vacuum.

Yield: 30gm (dry)

Example-6

(Z)-(S)-7-Chloro-2-(2, 2-dimethyl-cyclopropane carboxamide)-2-heptenoic acid (50gm) was charged in to the flask containing N,N-DimethylFormamide (250ml) l,8-diazabicyclo[4.3.0.]undec-7-ene (DBU) (37gm) mixture. Then L-cystine hydrochloride mnohydrate (44gm) was added to the same flask, The RM was heated to 70°C, after completion of reaction the mass was cooled to RT, pH was adjusted to 3-4 by using Acetic Acid. And crystallized out by using MDC at 40°C, the solid was filtered & washed; the solid was dried under vacuum.

Yield: 30gm (dry)

Example 7;

(Z)-(S)-7-Chloro-2-(2, 2-dimethyl-cyclopropane carboxamide)-2-heptenoic acid (50gm) was charged in to the flask containing N,N-Dimethyl Acetamide (350ml) l,8-diazabicyclo[4.3.0.]undec-7-ene (DBU) (37gm) mixture. Then L-cystine Hydro Chloride Monohydrate (44gm) was added to the same flask, The RM was heated to 70°C, after completion of reaction the mass was cooled to RT, pH was adjusted to 3-4 by using Acetic Acid. And crystallized out by using MDC at 40°C, the solid was filtered & washed; the solid was dried under vacuum.
Yield: 28gm (dry)

Example 8;

(Z)-(S)-7-Chloro-2-(2, 2-dimethyl-cyclopropane carboxamide)-2-heptenoic acid (50gm) was charged in to the flask containing 2,3-Dimethyl Imidazolidinone (350ml) l,8-diazabicyclo[4.3.0.]undec-7-ene (DBU) (37gm) mixture. Then L-cystine Hydro Chloride Monohydrate (44gm) was added to the same flask, The RM was heated to 70°C, after completion of reaction the mass was cooled to RT, pH was adjusted to 3-4 by using Acetic Acid. And crystallized out by using MDC at 40°C, the solid was filtered & washed; the solid was dried under vacuum.
Yield: 31gm(dry)

Example 9;

(Z)-(S)-7-Chloro-2-(2, 2-dimethyl-cyclopropane carboxamide)-2-heptenoic acid (50gm) was charged in to the flask containing MOPS Buffer (25gm), THF (250ml) l,8-diazabicyclo[4.3.0.]undec-7-ene (DBU) (44gm) mixture. Then L-cystine Hydro Chloride Monohydrate (44gm) was added to the same flask, The RM was heated to 70°C to 80°C, after completion of reaction the mass was cooled to RT, pH was adjusted to 3-4 by using Acetic Acid. Distilled the mass and refluxed using MDC in presence of acetic acid at 40°C, distilled the mass. The solid was isolated by adding acetone /MDC filtered & washed; the solid was dried under vacuum.

Yield: 27gm (dry)

Example 10;

(Z)-(S)-7-Chloro-2-(2, 2-dimethyl-cyclopropane carboxamide)-2-heptenoic acid (50gm) was charged in to the flask containing 2,3-Dimethyl Imidazolidinone (350ml) l,8-diazabicyclo[4.3.0.]undec-7-ene (DBU) (37gm) mixture. Then L-cystine Hydro Chloride Monohydrate (44gm) was added to the same flask, The RM was heated to 70°C, after completion of reaction the mass was cooled to RT, pH was adjusted to 3-4 by using formic acid. And crystallized out by using Acetonitrile the solid was filtered & washed; the solid was warmed in presence of acetic acid, cooled added acetone and filtered the solid. The solid was washed with acetone and dried u/v.
Yield: 24gm (dry)

We Claim:

1. A process for preparation cilastatin acid comprising:

a) condensing 7-chloro-2-[[(lS)-2,2-dimethylcyclopropane] carboxamide]-2-heptenoic acid with L-cysteine in the presence of an amine and a solvent;

b) adjusting the pH;

c) optionally extracting cilastatin acid in an organic solvent; and

d) isolating cilastatin acid.

2. A process according to claim 1, wherein the amine is selected from the group comprising l,8-diazabicyclo[4.3.0]undec-7-ene (DBU), 1,4-diazabicyclo [2.2.2]octane (DABCO), and Tetramethylguanidine (TMG).

3. A process according to claim 1, wherein the amine is 1,8-diazabicyclo[4.3.0]undec-7-ene(DBU).

4. A process according to claim 1, wherein the solvent in step (a) is selected from the group comprising water, a lower alcohol such as methanol, ethanol etc., N-methyl pyrrolidinone, N,N-dimethylFormamide, N,N-dimethyl Acetamide, 2,3-dimethyl Imidazolidinone, tetrahydrofuran (THF) from N-methylpyrrolidinone, Methylenedichloride, N,N-dimethylformamide, 2,3-dimethylimidazolidinone.

5. A process according to claim 1, wherein the pH is adjusted in the range of 3 to 4 using formic acid, acetic acid or phosphoric acid.

6. A process according to claim 1, wherein cilastatin acid is isolated from the reaction mass after pH adjustment by using acetone.

7. A process according to claim 1, wherein the isolated cilastatin acid is purified using an alcoholic solvent preferably using methanol, or acetonitrile or methylenedichloride (MDC) or mixture thereof.