The present invention relates to an industrially feasible and cost-efficient process for the preparation of isomerically pure S-amlodipine besylate hemipentahydrate (1), a useful calcium antagonist inhibitor. Previous workers reported that R-amlodipine-tartrate was crystallized out preferentially from the reaction mixture when naturally occurring l-tartaric acid and racemic amlodipine base in DMSO are mixed. In order to crystallize S-amlodipine-tartrate, the use of unnatural d-tartaric acid as a resolving agent in DMSO was required. However, the cost of d-tartaric acid was not conducive to overall cost efficiency in the resolution protocol. Subsequent to the above observations, we have developed a novel resolving system in which amlodipine base with natural l-tartaric acid in DMF as a solvent gave preferentially the S-form of amlodipine tartrate directly from the reaction. The optimization of this approach by adjusting the water percentage in DMF ensured consistent purity of S-amlodipine (+99%) and satisfactory resolution efficiency.
Urea derivativesUrea derivatives Q 0640 Total Synthesis of cis and trans-Hydroxyglimepiride: Active Metabolite of Glimepiride. -(GURJAR*, M. K.; JOSHI, R. A.; CHAUDHURI, S. R.; JOSHI, S. V.; BARDE, A. R.; GEDIYA, L. K.; RANADE, P. V.; KADAM, S. M.; NAIK, S. J.; Tetrahedron Lett. 44 (2003) 26, 4853-4855; Natl. Chem. Lab., Pune 411 008, India; Eng.) -Mais 39-078
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