Design, Synthesis, and X-Ray Structure Analysis of Conformationally Restricted 4-Aryldihydropyrimidine Calcium Channel Modulators

4-Aryldihydropyrimidines (DHPMs) represent inherently chiral aza-analogs of nifedipine-type dihydropyridine (DHP) calcium channel modulators. In the context of the recently proposed new binding-site model for these types of cardiovascular drugs, conformationally rigid DHPM analogs were designed that closely mimic the receptor-bound conformation of DHP/DHPM calcium channel modulators. The synthetic methodology towards these pentacyclic DHPM analogs is based on intramolecular 1,3-dipolar cycloaddition reactions of o-alkenylaryl-tethered dihydropyrimidine-fused isomünchnones. Two homologs of these rigid DHPM derivatives were synthesized in good overall yield and their structure established by X-ray crystallographic analysis. Enantioseparation of these DHPMs was achieved by chiral HPLC.