Structural Investigation of Ca2+ Antagonist Benzofurazanyl and Benzofuroxanyl 1,4-Dihydropyridines

The structure of Ca2+ channel blockers benzofurazanyl- and benzofuroxanyl-1,4-dihydropyridines (1,4-DHPs) was investigated by an integrated NMR, X-ray diffraction and molecular graphics study. 1H- and 13C-NMR showed that all the benzofuroxan derivatives exist in solution as tautomeric mixtures. ΔG° and ΔG* for 4′7′ and 5′7′ benzofuroxanyl tautomeric equilibria were determined for the benzofuroxan derivatives VI and VII. These figures are close to those observed for other substituted benzofuroxans known from literature including DHP derivatives.