Patent ID: 7446200

Claim:
A process of preparation of (S)-(+)-α-(o-chlorophenyl)- 6,7 -dihydrothieno [3,2-c] pyridine-5 (4H)-acetate bisulfate, which comprises; a) condensing 4,5,6,7-Tetrahydrothieno [3,2-c] pyridine hydrochloride with α-bromo-2-chloroquine acetic acid methyl ester in an organic solvent at an ambient temperature in presence of an inorganic base to obtain racemic Clopidogrel base; b) resolving the racemic clopidogrel base using levo rotatory camphor-10- sulphonic acid in a mixture of organic solvents under stirring for 6-12 hrs within a temperature of range of 0-70° C; c) purifying the obtained (S)-Clopidogrel camphor sulfonate salt in a ketonic solvent; d) converting the (S)-Clopidogrel camphor sulfonate salt to (S)-Clopidogrel free base by separating the camphor sulfonic acid moiety from the (S)- Clopidogrel camphor sulfonate salt; e) dissolving (S)-Clopidogrel free base in a solubilizing solvent to form a clear solution; f) adding the solution of sulfuric acid in anti-solvent within temperature range 0-25° and stirring the obtained solution for several hours; g) filtering the separated solid to get crystalline (S)-Clopidogrel bisulfate having two crystallographically independent cations of clopidogrel and two independent bisulfate anions, wherein said two independent cations are of similar conformation.