Quantum chemical studies of polycyclic aromatic hydrocarbons and their metabolites: correlations to carcinogenicity

In the context of the bay region hypothesis for polycyclic aromatic hydrocarbon (PAH) carcinogenesis, molecular properties were calculated for seventeen polycyclic aromatic hydrocarbons related to (1) intrinsic substrate reactivities towards activating and detoxifying metabolism and (2) the stabilities of the putative carbocation ultimate carcinogens. All-valence electron methods were used, avoiding the inherent difficulties found in the pi-electron methods. The calculated substrate reactivities were found to predict major metabolites successfully, supporting the validity of their use in attempted correlations with observed carcinogenic potencies. Positive correlations were found between observed carcinogenic potencies and (1) the reactivities of the parent polycyclic aromatic hydrocarbons towards the initial distal bay region epoxidation and (2) the stabilities of the diol epoxide carbocations. The reactivities of the distal bay region diol epoxides, were high for both carcinogenic and non-carcinogenic compounds, implying that the second epoxidation does not determine relative carcinogenic activity. Support for a possible alternative hypothesis, that polycyclic aromatic hydrocarbons are activated by one electron oxidation, was also found.