Taurolidine is an antibacterial drug and also has antiendotoxic substance, which is used as an antiseptic solution in surgery for washing out the abdominal cavity and it also prevents septic shock. It is commercially sold as Taurolidine (Formula I). The present invention relates to a process for the preparation of Taurolidine which provides significant advantages over the existing processes.

Formula I

SUMMARY OF THE INVENTION

The following patents and applications describe the synthesis of Taurolidine

CH482713 describes the first synthesis of Taurolidine by reacting Taurinamide HC1 with 1 .5 eq of formaldehyde. One of the major drawbacks of this synthesis is the carry over of the chloride ions to the final stage, which has a stringent specification of NMT 500 ppm in the finished product. It is cumbersome to purify the product devoid of any chloride ions.

EP0863133 describes a process for the preparation of Taurinamide from beta- aminoethanesulfonylazide. Handling of organic azides at commercial scale is highly risky as azides are explosive in nature.

US2184279 describes a process for the preparation of taurinamide from phalimide protected Taurine.

The process described in this patent utilizes hydrazine hydrate for the deprotection of the pthalimide group. The deprotection process usually works well at lab scale and it results in poor yields when performed at commercial scale. Moreover product obtained is difficult to separate from the hydrazine residuals.

Apart from the above said disadvantages, synthesis of Taurolidine at industrial level suffers significant drawbacks discussed subsequently. Therefore there is a need in the art for a simple and most efficient procedure for the synthesis of Taurolidine.

Cbz-taurine (II) is a potential intermediate for the synthesis of Taurol idine. It is highly soluble in water posing difficulties in the isolation procedures. The most efficient way for its isolation known in the art involves water distillation. The sodium salt of Cbz-taurine have earlier been isolated by lyophilization as reported in Tetrahedron 52, 15, 5591 or by complete water distillation as reported in Bioorganic Chemistry 2001 , 29, 6, 357. In one embodiment, the current invention suggests an alternate procedure for isolation of Cbz-taurine without distillation or continuous extraction, and which is viable at a large scale.

Cbz-Taurinamide (III), another crucial intermediate is converted to a HC1 salt - Taurinamide hydrochloride and subsequently to Taurolidine as described in CH482713. This prior art process of hydrochloride salt formation and its conversion to Taurolidine, however, resulted in significant amounts of chloride impurities, which involved tedious workups for the purification.

In another aspect of the invention, an organic acid salt formation is employed for the conversion of Taurinamide to Tauloridine, wherein the chloride ions are totally avoided. Interestingly, this process resulted in increased yields compared to other prior art procedures, which do not involve salt formation.

The final product Taurolidine decomposes during recrystallization procedures posing great difficulties in its purification. None of the prior art references suggest purification procedures without the decomposition of the compound and in substantially pure form.

In one aspect of the invention, Taurolidine is purified without decomposition to obtain a highly pure compound, whose purity is not less than 99.5 %.

Detailed description of the invention

The current process for the preparation of Taurolidine is depicted in Scheme 1 Formula II

Formula IV

Formula I

Cbz-taurine is highly soluble in water posing difficulties in the isolation procedures. The present invention provides a simple process to isolate it as a sodium salt from the reaction mixture. The reaction is performed in the presence of sodium hydroxide and once the reaction is completed, the pH of the reaction is adjusted to make it highly basic (pH 12 - 14) to isolate the corresponding sodium salt of Cbz-taurine. Subsequent cooling results in the precipitation of the product thus avoiding the usage of any solvents or continuous extraction. The product precipitated is collected by filtration. The invention also provides a process for the conversion of Cbz-taurine sodium salt to Cbz- Taurinamide in presence of PC1 ₅ , POCI3 or SOCI ₂ followed by the treatment of ammonia; PCI5 being the most preferred reagent.

Cbz-taurinamide formed is subjected to hydrogenation in presence of palladium catalyst to obtain Taurinamide which is subsequently converted to Taurinamide salt.

The prior art procedures for the conversion of Taurinamide to Taurolidine involve the intermittent Taurinamide hydrochloride salt. The Taurinamide hydrochloride salt resulted in high concentration of chloride content in the final product and attempts to purify the product resulted in significant loss in the yield.

In the present invention several organic acid salts of Taurinamide were synthesized. Interestingly it was found that organic acid salts like oxalate, citrate, fumarate, maleate, malate and succinate yielded purer Taurolidine over the inorganic acid salts, succinate being the most suitable salt for the conversion.

The final product Taurolidine decomposes during recrystallization procedures posing great difficulties in its purification. It was found that alcoholic solvents and water are most unsuitable for the recrystallization and significant amount of the compound decomposes in these solvents, thereby reducing the final yield quantitatively. None of the prior art references suggest purification procedures without the decomposition of the compound and in substantially pure form.

The present inventors thus propose an industrially viable procedure for isolation of Taurolidine in substantially pure form.

Taurolidine is dissolved in a suitable solvent to obtain a clear solution. The product starts to precipitate and an anti solvent is added optionally to maximize the precipitation procedure. The solvents employed for the purification are non -aqueous aprotic solvents comprising DMSO, DMAc, DMF, Acetonitirle, DMSO being the most preferred solvent. The antisolvents employed are toluene, ethyl acetate, dichloromethane, ether; toluene being the most preferred.

Taurolidine obtained by the instant procedure has purity greater than or equal to 99.5 %. The process of the invention is illustrated by the following examples to obtain Taurolidine. Example I

Cbz-Taurine sodium salt (Formula II)

To 1000ml of water in the RBF charge 192gm of (3.0 eq) of sodium hydroxide under cooling followed by 200gm of Taurine and dissolve it until clear solution is obtained. Cool to 0°C to 5°C, and Charge 50% CBZ-C1 in toluene at 0°C to 5°C. After completion of addition, maintain at room temperature for 14h. Separate the toluene layer and wash the aqueous layer with 2x200ml of ethyl acetate. Add slowly 27gm of sodium hydroxide in 60ml of water to the aqueous layer and adjust pH to 12- 14. Cool to 0°C to 5°C and a white solid separates from the solution. Filter the solid and dry the solid at 60 -70 °C. Weight of the solid: 320 g

Example 2

Cbz-Taurinamide (Formula III)

To a clean dry flask charge 1500ml of toluene and charge 320gm of Formula II and cool to 0°C to 5°C. Charge 308 gm of PC1 ₅ slowly at 0°C to 5°C for 2hrs. Maintain at 0°C to 5°C up to completion of reaction. Quench the RM into another flask containing 2 ltr of water at 0°C to 5°C. Separate the organic layer, wash and extract the aqueous layer with toluene. Dry the organic layer with sodium sulphate and cool to 0°C to 5°C. Purge ammonia gas into the reaction mass till the reaction is complete. Filter the solid and dissolve the solid in 21tr of water and extract the aqueous layer with 2x600ml of ethyl acetate. Dry the organic layer with sodium sulphate and concentrate it under reduced pressure to obtain a white solid. Weight of the solid: 150 g

Example 3

Taurinamide Succinate (Formula IV)

Take a suspension of 100 g of Cbz-Taurinamide in 1000 ml methanol, and 10% Pd/C (1 .0 g) and subject to hydrogenation at 45-50 psi. Upon completion of the reaction filter the catalyst and add succinic acid (1 .0 eq) to the solvent and distill off the solvent under vacuum to provide the title compound in about 90% yield as a white solid.

Example 4

Taurolidine (Formula I)

To a solution of 100 g Taurinamide succinate in water is added sat sodium bicarbonate solution and pH adjusted to 7-8. To the solution was added formaldehyde (50 ml) and allowed to stir for 4 h. The solid obtained was filtered and washed with water to give Taurolidine. The title compound was obtained in about 70% yield and about 98% purity.

Example 5

Purification of Taurolidine

Taurolidine (100 g) was dissolved in DMSO (400 ml) and a clear solution is obtained and a precipitate is obtained immediately. The solid is filtered and washed with toluene and dried to give a white solid in 40 % yield. The product obtained was >99.5% pure.

Example 6

Purification of Taurolidine

Taurolidine (100 g) was dissolved in DMSO (400 ml) and a clear solution is obtained and a precipitate is obtained immediately. To the solution, toluene (1000 ml) is added. The solid is filtered and washed with toluene and dried to give a white solid in 70 % yield. The product obtained was >99.5% pure by HPLC and passed elemental analysis within 0.4% of the theoretical values.

Example 7

Purification of Taurolidine

Taurolidine (100 g) was dissolved in DMAc (800 ml) and to the solution, toluene (1000 ml) is added. The solid is filtered and washed with toluene and dried to give a white solid in 70% yield.