Imidazo[1,5-a]pyrimidine and benzo[4,5]imidazo-[1,2-a]pyrimidine derivatives as calcium antagonists

Several bicyclic dihydropyrimidines were synthesized and evaluated for their calcium antagonistic activities by comparison with the usual 1,4-dihydropyridine calcium antagonist reference compound nifedipine. The solid-state structure of the isopropyl 2-methyl-4-(3'-nitrophenyl)-1,4-dihydrobenzo[4,5]imidazo[1,2- a]pyrimido-3-carboxylate shows that these compounds can adopt the most important structural features of the 1,4-dihydropyridine and 1,4-dihydropyrimidine calcium channel blockers. The high-potassium depolarized rat aorta assay was used for testing the compounds as calcium channel blockers. Some compounds showed interesting vasorelaxant activity.