Separation of Amlodipine Enantiomers by Diastereomeric Salt Formation

Abstract

Despite the dramatic development of enantioselective synthesis and chromatographic separation methods, optical resolution still remains the most cost effective and operationally simplest method for producing pure enantiomers on an outsized scale. No extreme conditions or expensive reagents are required, and resolving agents are often recovered. The present invention relates to method of resolving racemic amlodipine into enantiomerically enriched composition with good yield and high optical purity by precipitation with tartaric acid derivative in the presence of non-aqueous solvent. Optically active O, O'-Di-ptoluoyl-D-tartaric acid and O, O'-Di-p-toluoyl-L-tartaric acid is used as chiral reagent. The process can be performed by first reacting racemic amlodipine and O, O'-Di-p-toluoyl-tartaric acid in the presence of solvent mixture including acetonitrile/isopropanol in the ratio of 1/9v/v to produce (R) or (S) amlodipine di-p-toluoyl tartrate diastereomer. Further treating the prepared (R) or (S) amlodipine diastereomeric salt with a base and gentisic acid obtaining enantiomerically pure (R) or (S) amlodipine gentisate.