FORM 2
THE PATENTS ACT 1970
(39 of 1970)
AND
The Patents Rules, 2003
COMPLETE SPECIFICATION
(See section 10 and rulel3)
1. TITLE OF THE INVENTION:
"PROCESS FOR THE PREPARATION AND PURIFICATION OF SODIUM-4-CARBOXY-3-HYDROXY-5MERCAPTO-ISOTHIAZOLE"
2. APPLICANT (S):
(a) NAME: WANBURY LIMITED
(b) NATIONALITY: Indian Company incorporated under the Indian
Companies Act, 1956
(c) ADDRESS: B- Wing, 10th Floor, BSEL Tech Park, Sector 30 A,
Plot no.39/5 & 39/5A, Opp. Vashi Railway Station, Navi-Mumbai- 400 703, Maharashtra, India.
3. PREAMBLE TO THE DESCRIPTION:
The following specification particularly describes the invention and the manner in which it is to be performed.

FIELD OF THE INVENTION:
The present invention relates to an improved process for the preparation and purification of compound of formula 1, sodium-4-carboxy-3-hydroxy-5-mercaptoisothiazole (ISONA), an intermediate for the preparation of cephalosporins. More particularly, instant invention provides a feasible process with high reproducibility for the preparation of the title compound which involves employment of a weak acid for the work up of the base hydrolysis step.

BACK GROUND AND PRIOR ART:
Sodium or potassium salt of 4-carboxy-3-hydroxy-5-mercapto isothiazole(ISONA) is used in the production of Cefotetan, a semi synthetic injectable cephamycin antibiotic which shows a strong and wide spectrum of antibacterial activity.
US3230229 describe preparation of disodium salt of 3-hydroxy-5-mercapto-4-isothiazole carbonitrile. It further describes recrystallisation of the product from methanol/ethanol/ether for purification. However, the elemental analysis reported does not match exactly with that of the product and also the product of desired quality and purity was not obtained. Also the purity of the compound, disodium salt of 3-hydroxy-5-mercapto-4-isothiazole carbonitrile, is observed to have a direct bearing on the base hydrolysis step. The said patent further discloses a method for preparation of 3,5-bis(methylthio)-4-isothiazole carbonitrile. The process however employs 11.25 volumes of alcoholic solvent and the sulphur content reported however does not match with that of the product. Also, there are no details regarding purification of the product.
According to the method described in U.S.Pat. No. 4,263,432 and in Chem.Pharm.BuU 28,2629-2636 (1980), Cefotetan is obtained from 7a-(4-carboxy-3-hydroxyisothia- zol-5-


yl)thioacetamido-7a-methoxy-3-(l-methyItetrazo]-5-yl)thiomethyl-A3-cephem-4-carboxylic acid of formula (11)
which is itself prepared by reacting 7a-bromoacetamido-7a-methoxy-3-(l-methyltetrazol-5-yl) thiomethyl 3-cephem-4-carboxylic acid with a trisodium 4-carboxy- 3-hydroxy-5-mercapto-isothiazole of formula III

where Rl=R2=R3=Na
The reaction mixture is adjusted to pH 8.0 with dilute HC1 and a precipitate of the compound of formula (I) is obtained. The trisodium 4-carboxy-3-hydroxy-5-mercapto-isothiazole of formula (III) in which RI=R2=R3=Na is an essential intermediate (according to the known art) in the preparation of Cefotetan.
The aforementioned literature also describes the method used to prepare trisodium 4-carboxy-3-hydroxy-5-mercapto-isothiazo!e of formula III wherein Rl=R2=R3=Na which requires the use of metal sodium and liquid ammonia as detailed on page 2633 of the aforementioned edition of Chem, Pharm. Bull.
US 6583291 discloses hydrolysis of disodium or dipotassium salt of 3-hydroxy-5-mercapto-4-isothiazole carbonitrile with aqueous solution of sodium hydroxide or potassium hydroxide to 1SONA. The said patent employs NaOH (1.29 mol) and KOH (1.62 mol) and high reflux time (16-18 hrs) respectively. Further, the work up process employs concentrated HC1 to precipitate lSONA. The said patent however does not disclose any purification process and moreover analysis of the product prepared by the patented process revealed several decomposition products. An intermediate amide impurity more than 2% is detected. Also large amounts of starting materials were present even after refluxing for more than 20 hours. HPLC reported is only 80 %.

Thus, the processes disclosed in the prior arts for the preparation of ISONA or the intermediates are not reproducible. Moreover, HPLC analysis reveals several decomposition products, affecting the yield and purity. Further, the product ISONA displays resin like behavior in solvents such as ethanol and methanol that are used for recrystallization thus encountering additional problems in the synthesis of cefotetan.
In view of the shortcomings of the base hydrolysis step and purification processes of the prior arts, there still remains a need in the art to develop an effective and efficient method for industrial production of ISONA, a valuable compound for the preparation of Cephalosporin, pharmaceutically important molecules.
OBJECT OF THE INVENTION:
It is therefore an object of the invention to develop an efficient, industrially viable, and highly reproducible process for preparation of ISONA.
Another object of the invention is to employ a weak acid during the work up of the hydrolysis reaction to obtain the product in high purity, yield with good reproducibility.
Yet another objective is to reduce the solvent quantity for the reactions and employ higher homologue alcohol for the purification step.
SUMMARY OF THE INVENTION:

which comprises of the following steps;
In accordance with the above objectives, the present invention provides an improved process for the preparation of ISONA, compound of formula 1,

a) Condensing propane dinitrile with carbon disulfide in the presence of a base and a solvent to obtain disodium 2,2 -dicyanoethene-l,l-bis(thiolate), the compound of formula 2, followed by its precipitation using mixture of alcohols,
b) Intramolecular cyclising the compound of formula 2 with aqueous H202 and a solvent to yield disodium-4-cyano-5-sulfido-l,2-thiazol-3-olate, compound of formula 3, followed by its precipitation using mixture of alcohols,
c) Hydrolysing compound of formula 3 by employing 10 equivalents of the base and refluxing at least for 10 hours followed by neutralization employing weak acid or weak salts (pH to 8.0-8.5), to obtain 1SONA, the compound of formula 1, and
d) Purifying compound of formula 1 by dissolving the product in water followed by salting it out or by precipitation employing higher homologue alcohol.
The intermediates of formula 2 and 3 involved in the process for preparation of compound of formula 1, ISONA, are given below

In an aspect, the process of the present invention provides a method for purification of compounds of formula 2 and 3.Accordingly, compounds of formula 2 and formula 3 are precipitated out from mixture of alcohols wherein comparatively pure products are obtained.
In a preferred aspect of the present invention, the process provides a method for isolation and purification of ISONA, the compound of formula -1. Accordingly, compound of formula 3 is hydrolyzed employing at least 10 equivalents of the base and refluxing at least for 10 hours, followed by adjusting the pH to 8.0 to 8.5 by employing a weak acid. Various acids may be employed such as acetic acid, oxalic acid, formic acid, benzoic acid etc. Neutral work up may be carried out by employing salts such as ammonium chloride and ammonium acetate for adjusting the pH to 8.0 to 8.5. This is followed by dissolving

the product in water and precipitation by adding higher homolog alcohol or salting it out to obtain ISONA in good yield and purity.
The details of one or more embodiments in the practice of the inventions are set forth in the description below. Other features, objects and advantages of the inventions will be apparent from the appended examples and claims.
DETAILED DESRIPTION:
Unless specified otherwise, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art, to which this invention belongs. Although any methods and materials similar or equivalent to those described herein can be used in the practice or testing of the present invention, the preferred methods and materials are described. To describe the invention, certain terms are defined herein specifically as follows.
Unless stated to the contrary, any of the words "having" "including," "includes," "comprising," and "comprises" mean "including without limitation" and shall not be construed to limit any general statement that it follows to the specific or similar items or matters immediately following it. Embodiments of the invention are not mutually exclusive, but may be implemented in various combinations. The described embodiments of the invention and the disclosed examples are given for the purpose of illustration rather than limitation of the invention as set forth the appended claims.
The term "obtaining" is used to indicate formation or isolation or recovery of the compound being obtained, which include in situ conversion of the said compound into a target product.
The term "isolating" is used to indicate separation or collection or recovery of the compound being isolated in a reasonably pure form.
The term "treating" means adding or combining or mixing the stated reagent or materials to the thing being treated.

As referred to herein 'substantially pure ISONA' is ISONA of purity greater than 99 %.
Preferably, substantially pure ISONA (formula 1) has a purity greater than 99.5 % and has no individual impurity that is more than 0.5% by HPLC.
The present invention relates to an improved process for the preparation of ISONA, compound of formula 1,

which comprises of the following steps;
a) Condensation of propane dinitrile with carbon disulfide in the presence of a base and a solvent, to obtain disodium 2,2 -dicyanoethene-1,1-bis(thiolate), the compound of formula 2 followed by its precipitation using mixture of alcohols,
b) Intramolecular cyclisation of the compound of formula 2 with aqueous H2O2 and a solvent to yield disodium-4-cyano-5-sulfido-l,2-thiazol-3-olate, compound of formula 3 followed by its precipitation using mixture of alcohols,
c) Hydrolysis of compound of formula 3 by employing 10 equivalents of the base and refluxing at least for 10 hours followed by neutralization employing weak acid or weak salts(pH to 8,0-8.5), to obtain ISONA, the compound of formula 1, and
d) Purification of compound of formula I by dissolving the product in water followed by salting it out or by precipitation employing higher homologue alcohol.
The compounds of formula 2 and 3 involved in the process for preparation of compound of formula 1, ISONA, are given below


Further, Stage I, II and III for the preparation of ISONA is depicted beiow:

The base used for preparation of compound of formula 2 in Stage I is selected from inorganic base such as alkali metal hydroxide or alkali metal alkoxide or alkali carbonate or alkali bicarbonate. Preferably, alkali metal hydroxide, either sodium or potassium hydroxide is preferred.
In an embodiment, the solvents employed in Stage I and Stage II is selected from aliphatic C1-C5 alcohols. The volume of alcohol employed is preferably in 4-5 volumes only so as to provide for easy scale up of the process and also the product obtained contains less impurity.

In a further embodiment, the process of the present invention provides purification of compounds of formula 2 and formula 3 .The quality and purity of these intermediate compounds has a direct bearing on the base hydrolysis step of Stage III which in turn affects the quality and yield of the final product, 1SONA, a valuable compound for the preparation of cephalosporin, pharmaceutically important molecule. Accordingly, the work up procedure involves precipitation of compounds of formula 2 and formula 3 from mixture of alcohols to obtain comparatively pure products.
In a preferred embodiment, the effectiveness of the process of the present invention lies in base hydrolysis of compound of formula 3 and in the employment of a weak acid, wherein formation of impurities, degradation products and the conversion rate can be efficiently controlled to achieve optimum yield and purity.
Basic hydrolysis of compound of formula 3 proceeds via formation of an amide intermediate of formula 4;

Formula 4 which on further hydrolysis leads to formation of alkali salt of 4-carboxy-3-hydroxy-5-mercaptoisothiazole(ISONA).The said intermediate of Formula 4 exhibits similar solubility and crystallization behavior as the product ISONA itself. Accordingly, by optimizing the stoichiometry of the base employed, reaction time, complete conversion of compound of formula 3 including the intermediate 4 to obtain ISONA with greater purity is achieved. Further, use of a weak acid in the work up procedure of the instant invention does not lead to decomposition of the final product (which is acid sensitve)and also does not affect its quality, thus leading to obtain the product in good yield and purity. Also, ammonia gas formed during base hydrolysis is driven out by continuously bubbling nitrogen in the reaction mixture.
Accordingly, in the preferred embodiment, compound of formula 3 is refluxed with an inorganic base selected from alkali metal hydroxide, in at least 8-10 equivalents,

preferably 10 equivalents, for 10-12 hours. This is followed by employing a weak acid or weak salt to adjust the pH to 8.0-8;5.
The alkali metal hydroxide is selected form sodium or potassium hydroxide and the weak acid employed is selected from acetic acid, oxalic acid, formic acid, benzoic acid etc. for neutral work up. Salts such as ammonium chloride and ammonium acetate are also suitable for adjusting the pH to 8.0-8.5.
In an alternate process, amide intermediate of formula 4 is obtained by hydrolyzing compound of formula 3 with a base and an oxidizing agent followed by purification from solvents such as acetonitrile-water, methanol and water etc. The base is selected from sodium bicarbonate, sodium carbonate, sodium methoxide, potassium methoxide etc. The oxidizing agent is hydrogen peroxide.
In another preferred embodiment, the process of the present invention employs purification of ISONA. The process involves dissolving the product in water followed by its precipitation from a suitable alcoholic solvent. The alcohol employed is selected from isopropanol, butanol or its higher homologues, preferably isopropanol.
Alternately, purification of ISONA can be carried out by dissolving the product in water and further salting out by addition of salts such as sodium chloride, sodium acetate, ammonium chloride, sodium sulphate, ammonium sulphate etc;
In another embodiment, the optimized process of the present invention has been found to be advantageous in that the reactions involved are highly reproducible and the desired product, viz. ISONA (formula 1) can be obtained in high yields and in substantially pure form.
The stepwise preparation of ISONA according to the current invention is described herein
below:
Preparation of disodium 2,2 -dicyanoethene-l,l-bis(thiolate) (Formula 2):
The condensation product was prepared according to the process described in US1966/3230229 with several modifications.

According to the process of the present invention, the condensation product is prepared by adding carbondisulfide solution to propanedinitrile pretreated with a base by employing methanol as a solvent. The volume of alcohol employed is 4- 5 volumes only. During the work up most of the methanol is distilled off and isopropanol is added to precipitate the product. This method can be repeated several times to obtain the pure product.
Preparation of disodium-4-cyano-5-sulfido-l,2-thiazol-3-olate(Formula 3):
The cyclisation product was prepared according to the process reported in US1966/3230229 with several modifications.
The condensation product is subjected to intramolecular cyclisation by oxidizing it with aqueous hydrogen peroxide in the presence of a protic, solvent such as methanol. The volume of alcohol employed is 4- 5 volumes only. During the work up most of the methanol is distilled off and isopropanol is added to precipitate the product. This method can be repeated several times to obtain the pure product.
Preparation of ISONA (Formula 1):
The nitrile (compound of formula 3) was subjected to base hydrolysis by employing 10 equivalents of aqueous base and refluxing the resultant solution for 10-12 hours. Bases such as NaOH, KOH etc may be employed for the reaction. Each mole of nitrile generates a mole of NH3 gas which is driven away by continuously bubbling in nitrogen during the course of the reaction.
Further details of the process of the present invention will be apparent from the examples presented below. The examples presented are purely illustrative and are not limited to the particular embodiments illustrated herein but include the permutations, which are obvious as set forth in the description.
Examples:
Example 1:
Preparation of disodium 2,2 -dicyanoethene-l,l-bis(thiolate)
(condensation)(compound of Formula 2)
NaOH (30.2 grams) was charged into the methanol solution (125.0 ml). The reaction
mixture was stirred for 15.0 minutes and propanedinitrile (25.0 grams) was then added

into the flask. The resultant solution was cooled to 15°C and 29.2 grams of carbondisulphide was added dropwise over a period of 2 hours. The reaction mixture was concentrated to 2/3 of its volume followed by addition of 100 ml Isopropanol. The precipitate obtained was filtered and further dried under vacuum. Yield: 80 % Purity: 96 %
Example 2
Preparation of disodium-4-cyano-5-sulfido-l,2-thiazol-3-olate (compound of formula
3)
To 300.0 grams of the compound 2 was added 3 liters of methanol and cooled to 0 °C. 55
grams of hydrogen peroxide (- 35 % aqueous solution) is then added dropwise over a period of 2 hours. The reaction mixture was stirred for 2 hours at room temperature. The reaction mixture was concentrated to 2/3 of its volume followed by addition of 100 ml Isopropanol. The precipitate obtained was filtered and further dried under vacuum. Yield = 85 % Purity: 98 %
Example 3
Preparation of ISONA (compound of formula 1)
100 grams of the nitrile (compound 3) and 198.0 grams of NaOH were dissolved in 350.0 ml of water and the resultant solution was refluxed for 12 hours. The reaction mixture was cooled to 10 - 15 °C and quenched with acetic acid (250.0 ml) by adding dropwise till a pH of 8.25 is reached. The solid obtained was filtered and dissolved in 150.0 ml water. The reaction mixture was cooled to 10°C followed by dropwise addition of 500.0 ml isopropanol. The solid obtained was filtered and dried at 60 °C for 10 - 12 hours. Yield = 60 % Purity: 99.7 %
Example 4
Preparation of the amide (compound of formula 4)
5 grams of the nitrile (compound 3) was dissolved in 25.0 ml methanol and stirred. 1.4 grams sodium methoxide was added followed by dropwise addition of 4.2 grams of aqueous hydrogen peroxide solution. The reaction mixture is stirred for 24 hours. The

precipitate obtained is filtered and washed with methanol. The solid obtained was purified by employing acetonitrile water mixture. Yield = 85 %. Purity: 99 %
Example 5:
Purification of ISONA (compound of formula 1)
100 grams of the crude product was dissolved in 250 ml H2O and cooled to a temperature of0-5°C. 70.0gofNaCl was added portion wise with stirring of the reaction mixture. The precipitated product was filtered and dried in the oven at 65 - 70 °C for 12 hours. Yield = 90 % Purity = 99.5 %.

We claim:
1. A process for the preparation of Sodium-4-carboxy-3-hydroxy-5-
mercaptoisothiazole, ISONA (formula 1) comprising;

a) Condensing propane dinitrile with carbondisulphide in the presence of base and 4- 5 volumes of alcoholic solvent to obtain compound of formula 2 followed by its precipitation from mixture of alcohols;
b) Intramolecular cyclisation (oxidation) of formula 2 with aqueous H202 in alcoholic solvent and to yield compound of formula 3 followed by its precipitation from mixture of alcohols;
c) Hydrolysis of formula 3 by employing 8-10 equivalents of the base and refluxing for 10-12 hours followed by neutralization employing weak acid or weak salts (pH to 8.0-8.5), to obtain ISONA, the compound of formula 1, and;
d) Purifying compound of formula 1 by dissolving the product in water followed by
its salting out by common ion effect or by precipitation employing higher
homolog alcohol.
2. The process as claimed in claim 1, wherein the hydrolysis reaction proceeds via formation of amide of compound of formula 4.
3. The process as claimed in claim 1, wherein the weak acid is selected from acetic acid, formic acid, oxalic acid, benzoic acid etc..
4. The process as claimed in claim 1, wherein weak salt is selected from ammonium chloride, ammonium acetate etc.
5. The process as claimed in claim 1, wherein the products of stepl(a) and step 1(b) are precipitated employing mixture of methanol and its higher homolog.
6. The process as claimed in claim 1, wherein ISONA (formula 1) obtained in step 1(c) is purified by dissolving the product in water and precipitation employing higher homolog alcohols.

7. The process as claimed in claim 5 or 6, wherein the higher homolog alcohol is selected from isopropanol, butanol etc preferably isopropanol.
8. The process as claimed in claim 1, wherein ISONA (formula 1) obtained in step 1(c) is purified by dissolving the product in water and salting out by addition of salts.
9. The process as claimed in claim 8, wherein the salt employed can be sodium chloride, sodium acetate, ammonium chloride, sodium sulphate, ammonium sulphate etc
10. The process as claimed in claim 1, wherein ISONA (formula 1) is obtained in substantially pure form and has a purity greater than 99 % with no individual impurity greater than 0.5 % by HPLC.
11. The process as claimed in claim 1, optionally comprising a step of hydrolysing compound of formula 3 with a base and an oxidizing agent followed by purification from the solvent, to obtain amide of formula 4.
12. The process as claimed in claim 11, wherein the base employed is selected from sodium bicarbonate, sodium carbonate, sodium methoxide, potassium methoxide etc.
13. The process as claimed in claim 1, wherein the solvent used for the purification is selected from combinations such as acetonitrile -water, methanol-water etc.