ENANTIOMERIC RESOLUTION METHOD

摘要

A method for the preparation of pioglitazone O,O'-dibenzoyl-L-tartrate wherein the content by weight of pioglitazone consists of at least 95 % by weight of the 5R enantiomer and less than 5 % of the 5S enantiomer, which method comprises: (1a) adding seed crystals of 5R- pioglitazone O,O'-dibenzoyl-l-tartrate to a rnethanol-water solution of racemic pioglitazone hydrochloride and O,O'-dibenzoyI-L-tartaric acid, thereby precipitating pioglitazone O,O'- dibenzoyl-L-tartrate;(1b) recovering said precipitate from step (1a); (1c) forming a solution of the precipitate from step (1b) in a solvent mixture of methanol, acid and water and mixing into to the resultant solution seed crystals of 5R-pioglitazone O,O'-dibenzoyl-L-tartrate, thereby precipitating pioglitazone O,O'-dibenzoyl-L-tartrate; (1d) recovering said precipitate from step (1c); (1e) repeating steps (1c) and (1d), the recovered product being the desired pioglitazone O,O'-dibenzoy! tartrate wherein the content by weight of pioglitazone consists of at least 95 % by weight of the 5R enantiomer and less than 5 % of the 5S enantiomer. Also disclosed is a modification of the method in which step 1(e) is omitted.