Oxidation process of 1,4-dihydropyridine, 1,4-dihydropyrimidine, and pyrrolo-1,4-dihydropyrimidine: quantum chemical study

Derivatives of 1,4-dihydropyridine, 1,4-dihydropyrimidine, and its azolo analogs possess a wide range of biological activity and are involved in cellular bioenergetics. Dihydrocycles can be oxidized up to corresponding aromatic ones due to two one-electron transfers. Mechanism of the oxidation process was modeled as a stepwise change of the 1,4-dihydropyridine, 1,4-dihydropyrimidine, and pyrrolo-1,4-dihydropyrimidine using different levels of theory (Hartree–Fock, MP2, DFT), basis sets, and models of environment (vacuum approximation, PCM model describing a non-specific influence of polarizing environment, or PCM model with an explicit water molecule describing both non-specific and specific influence of neighboring molecules). It is shown that the potential of the first one-electron transfer I₁ depends on the level of theory and the model of an environment used in calculations. The potential of the second one-electron transfer I₂ depends only on the model of an environment. The analysis of their differences calculated using different approaches has revealed the dependence only from the level of theory. Since DFT methods provide the geometric characteristics of 1,4-dihydroheterocycles closest to the experimental data, it seems reasonable to use these relatively cheap calculations to study the oxidation process.