Benzofurazanyl- and benzofuroxanyl-1,4-dihydropyridines: Synthesis, structure and calcium entry blocker activity

The synthesis, structural characterization and calcium blocking activity of a series of benzofurazanyl-1,4-dihydropyridines (18 and 19) and benzofuroxanyl analogues (20 and 21) are reported. H-1-NMR showed that all the benzofuroxan derivatives exist in solution as tautomeric mixtures. The predominant tautomeric form in solution of the derivative 20 (dimethyl 1,4-dihydro-2,6-dimethyl-4-(4-benzofuroxanyl)-3,5-pyridinedicarboxylate) is also the one preferred in the solid state as shown by X-ray analysis. The conformation in the solid state of the benzofurazanyl analogue is also reported. Calcium entry blocker activity of the dihydropyridine derivatives 18-21 has been evaluated in isolated rabbit basilar artery as relaxation of calcium-induced contractions in high K+-depolarizing solution. All the compounds displayed high potency. The activity of benzofurazan derivatives was not changed by the N-oxidation. The two most active compounds 18 and 20 were as potent as Nifedipine.