Crystal structures of calcium channel antagonists: 2,6-dimethyl-3,5-dicarbomethoxy-4-[2-nitro-, 3-cyano-, 4-(dimethylamino)-, and 2,3,4,5,6-pentafluorophenyl]-1,4-dihydropyridine.

The crystal structures of 2,6-dimethyl-3,5-dicarbomethoxy-4-(2-nitrophenyl)-1,4-dihydropyridine (Nifedipine) and the 3-cyano-, 4-(dimethylamino)- and 2,3,4,5,6-pentafluorophenyl derivatives were determined. The 1,4-dihydropyridine ring in all four compounds has a boat-type conformation with varying degrees of puckering at the C4 position. Increasing distortion from planarity at this position shows a limited correlation with decreasing biological activity, determined as the ability to inhibit the Ca2+-dependent muscarinic-induced mechanical responses of guinea pig ileal longitudinal smooth muscle.