Electrochemical Oxidation of Methyl (±)-4,7-Dihydro-3-isobutyl-6-methyl-4-(3-nitrophenyl)thieno-[2,3-b]pyridine-5-carboxylate, a New Type of Dihydropyridine Calcium Blocker

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Electrochemical oxidation of methyl (±)-4,7-dihydro-3-isobutyl-6-methyl-4-(3-nitrophenyl)thieno[2,3-b]pyridine-5-carboxylate (1), a new dihydropyridine calcium blocker, in both methanol and acetonitrile was investigated by cyclic voltammetry, macroscale controlled potential electrolysis (CPE), in situ electron spin resonance (ESR) and ultraviolet-visible spectral studies. CPE of 1 in methanol at the potential of the first anodic peak on cyclic voltammetry gave four final products, the corresponding pyridine (2,yield, 73.9%), the 2-methoxy-substituted derivative of 2 (3,11.9%), the 2,2'-dimer (4,7.9%) and the 2,5'-dimer (5,5.8%), while in acetonitrile, CPE of 1 gave 2 (12.2%), 4 (85.3%) and 5(1.2%). It is suggested that the initial step is a one-electron oxidation of 1 to give the radical cations based on the results of in situ ESR. A possible mechanism of the electrode reactions of 1,which involves one-electron oxidation followed by deprotonation, radical coupling, substitution and further oxidation, is proposed.
公益社団法人日本薬学会の論文
1992-06-25