Patent ID: 8198316

Claim:
A process for the preparation of 5,6-dihydro-4H-4(S)-ethylamino-6(S) methylthieno [2,3-b]thiopyran-2-sulfonamide-7,7-dioxide hydrochloride comprising: a. contacting (cis,trans)5,6-dihydro-4H-4-ethylamino-6-methylthieno [2,3-b]thiopyran-2-sulfonamide-7,7-dioxide with a form of di-O-substituted-L-tartaric acid in an organic solvent to obtain intermediate hemitartarate salt of formula IV, wherein R is C 6 H 5 CO— or p—CH 3 C 6 H 4 CO—, and wherein the form of di-O-substituted L-tartaric acid is selected from a di-O-benzoyl-L-tartaric acid monohydrate and a di-O-p-toluoyl-L-tartaric acid monohydrate, b. refluxing the hemitartarate salt with methanol to obtain pure hemitartarate salt, c. treating the purified hemitartarate salt with ethylacetate and an aqueous alkali carbonate solution, separating ethylacetate and aqueous layer, d. extracting the aqueous layer with ethylacetate, separating the ethylacetate layer, e. combining ethylacetate layers of (c) and (d), washing with water, collecting water washed ethylacetate layer to obtain 5,6-dihydro-4H-4(S)-ethylamino-6(S)methylthieno [2,3-b]thiopyran-2-sulfonamide-7,7-dioxide, f. adjusting pH of ethylacetate layer between 1.0 and 2.0 with isopropanol-hydrochloric acid solution, and g. separating the precipitated solid and crystallizing from isopropanol.