Synthesis of expected metabolites of benidipine hydrochloride

(+/-)-(R*)-2,6-Dimethyl-4-(m-nitrophenyl)-1,4-dihydropyridine-3, 5-dicarboxylic acid (R*)-1-benzyl-3-piperidinyl ester, methyl ester hydrochloride (benidipine hydrochloride, KW-3049, 1), a highly potent and long-acting calcium antagonistic 1,4-dihydropyridine derivative, is now under clinical study as an antihypertensive and as an antianginal agent. In order to confirm the structures of the metabolites of KW-3049, 19 compounds were prepared. Among them 11 compounds were found to be metabolites (the compounds 2, 3, 6, 8, 14, 15, 16, 28, 31, 32 and 34) of KW-3049 in rats and/or dogs.