The role of intramolecular self-destruction of reactive metabolic intermediates in determining toxicity.

When reactive centers are formed in chemical conversions, intermolecular reactions tend to dominate over intramolecular alternatives whenever both alternatives are possible. Hence, when reactive metabolites are formed from xenobiotics, intramolecular quenching by moieties adjacent to a toxicophore may play an important role in reducing toxicity related to reactive intermediates. The phenomenon is likely to be particularly noticeable for toxicophores that are readily associated with a type of toxicity that is rarely caused by other structural motives. In two demonstrative investigations, it is concluded that nitrobenzenes for which the expected nitrosyl metabolite is likely to react with adjacent groups are less toxic than what is rationally expected, and that among aryl amine drugs allowing for the immediate quenching of the corresponding N-aryl hydroxylamine metabolite, the typical erythrocyte toxicity often seen with aryl amines is absent. The deliberate introduction of effective quenching groups nearby a toxicophoric moiety may present a potential strategy for reducing toxicity in the design of drugs and other man-made xenobiotics.