ENANTIOSELECTIVE SYNTHESIS OF CALCIUM-CHANNEL BLOCKERS OF THE DILTIAZEM GROUP

A lipase-catalyzed kinetic resolution of racemic trans-2-phenylcyclohexanol readily provides the (-)-1R,2S enantiomer. This alcohol is employed as its chloroacetate 10a in a chiral auxiliary-induced asymmetric Darzens glycidic ester condensation with p-anisaldehyde (9). Crystallization of the Darzens product affords enantiomerically pure (1R,2S)-2-phenylcyclohexyl (1R,2S)-2-(p-methoxyphenyl)glycidate (11), the structure of which was established by X-ray crystallography. The use of this glycidic ester in syntheses of diltiazem (1) and naltiazem (8), members of the diltiazem group of calcium channel blockers, provides these drug substances directly in enantiomerically pure form.