Metabolism and relative carcinogenic potency of chloroethylenes: a quantum chemical structure-activity study.

Properties of six chloroethylenes which could serve as indicators of their relative metabolic behavior and carcinogenic activity have been calculated using Modified Neglect of Diatomic Overlap (MNDO), a semiempirical, all valence electron, molecular orbital method. Possible pathways of transformation of parent compounds to acylchlorides, chloroaldehydes and epoxides--their putative ultimate carcinogens--were considered, and heats of formation and relative stabilities of intermediates were calculated. Our results indicate that carbonyl compounds could be formed with and without the intermediacy of epoxides, suggesting the possibility of more than one pathway in activation of parent compounds. Electronic properties of carbonyl products and epoxide carbocations, putative ultimate carcinogens which could serve as indicators of their relative electrophilicities, were also calculated. The results obtained indicated that the relative extent of metabolism to carbonyl products, rather than their electrophilicity, is a determinant of the relative carcinogenic activity of the parent compound. Of the various thermodynamic criteria investigated, four were found to be indicators of both relative metabolic behavior and carcinogenic activity.