Effect of acyl chain length and branching on the enantioselectivity of Candida rugosa lipase in the kinetic resolution of 4-(2-difluoromethoxyphenyl)-substituted 1,4-dihydropyridine 3,5-diesters.

Since 2,6-dimethyl-4-aryl-1,4-dihydropyridine 3,5-diesters themselves are not hydrolyzed by commercially available hydrolases, derivatives with spacers containing a hydrolyzable group were prepared. Seven acyloxymethyl esters of 5-methyl- and 5-(2-propoxyethyl) 4-[2-(difluoromethoxy)phenyl]-2,6-dimethyl-1,4-dihydro-3,5-pyridinedicarboxylate were synthesized and subjected to Candida rugosa lipase (CRL) catalyzed hydrolysis in wet diisopropyl ether. A methyl ester at the 5-position and a long or branched acyl chain at C3 gave the highest enantiomeric ratio (E values). The most stereoselective reaction (E = 21) was obtained with 3-[(isobutyryloxy)methyl] 5-methyl 4-(2-difluoromethoxyphenyl)-2,6-dimethyl-1,4-dihydropyridine-3,5-dicarboxylate, and this compound was used to prepare both enantiomers of 3-methyl 5-(2-propoxyethyl) 4-[2-(difluoromethoxy)phenyl]-2,6-dimethyl-1,4-dihydro-3,5-pyridinedicarboxylate. The absolute configuration of the enzymatically produced carboxylic acid was established to be 4R by X-ray crystallographic analysis of its 1-(R)-phenylethyl amide.