The mechanism of oxidation of NADH analogues 5: Photooxidation of N-methyl substituted 1,4- and 1,2-dihydropyrimidines in the presence of quinones

The photoinduced interaction of the 1-methyl-4-phenyl-5-carbomethoxy-6-methyl-1,4(1,2)-dihydropyrimidines (1,4- and 1,2-DHPm) with quinones has been studied by means of CIDNP method in polar media. It was established that 1-methyl-4-phenyl-5-carboxymethyl-6-methylene-1,6-dihydropyrimidine (1,6-MDHPm) is a main reaction product. It has been found that radical cation of DHPm is more reactive species than earlier studied radical cations of related N-methyl substituted dihydropyridines and is disposed to proton loss resulting in neutral pyrimidinyl radical. The 1,6-MDHPm was formed by hydrogen atom loss from 6-CH3 group of pyrimidinyl radical. Oxidation of the pyrimidinyl radical to pyrimidinium cation was not detected. Formation of pyrimidinium cation was detected in the presence of a high concentration of acetic acid in the reaction mixture.