Synthesis and calcium antagonist activity of new 1,4-dihydropyridines containing nitrobenzylimidazolyl substituent in guinea-pig ileal smooth muscle.

New alkyl ester analogues of nifedipine, in which the ortho-nitrophenyl group of position 4 is replaced by 1-(4-nitrobenzyl)-5-imidazolyl or 2-methylthio-1-(4-nitrobenzyl)-5-imidazolyl substituent, were synthesized and evaluated as calcium-channel antagonists using the electrically induced contraction of guinea-pig ileal longitudinal smooth muscle. Our results demonstrate that all compounds inhibited the contractile response of guinea-pig ileum to electrical stimulation and the IC50 value of the most potent compounds 6a and 6f were significantly lower than that of nifedipine. Therefore, they are more potent than nifedipine.