Study on the oxidation of C4-phenolic-1,4-dihydropyridines and its reactivity towards superoxide radical anion in dimethylsulfoxide

Electrochemical characterization on glassy carbon electrode (GCE) and reactivity with superoxide radical anion in aprotic medium of three new synthesized C4-phenolic-1, 4-dihydropyridines is reported.Voltammetry, coulometry, controlled-potential electrolysis (CPE), UV-vis spectroscopy, ¹H NMR techniques were employed for the characterization of title compounds.The oxidation mechanism involves initially an oxidation process on the phenol moiety with the formation of the corresponding quinone followed by a second one affecting the dihydropyridine ring to give the pyridine derivative. Both processes appeared irreversible in character.Cyclic voltammetry was used to generate O₂⁻ by reduction on GCE of molecular oxygen in DMSO. The reactivity of DHPs towards O₂⁻ was directly measured by the anodic current decay of the radical in the presence of increasing concentration of tested 1,4-dihydropyridines and compared with the reaction of the reference antioxidant, Trolox. The linear correlations obtained between the anodic current of O₂⁻ and compound concentrations in the range between 0.01 mM and 1.00 mM allowed the determination of both the DHP antioxidant index (AI) and the concentrations needed to consume 50% of O₂⁻. Synthesized C4-phenolic 1,4-dihydropyridines exhibited significant scavenging capacity towards superoxide radical anion higher than Trolox and tested commercial 1,4-dihydropyridines.