(+)-Benzo(a)pyrene-7,8-dihydrodiol-9,10-epoxide

(+)-Benzo[a]pyrene-7,8-dihydrodiol-9,10-epoxide is an organic compound with molecular formula C_20H_14O_3. It is a metabolite and derivative of benzo[a]pyrene (found in tobacco smoke) as a result of oxidation to include hydroxyl and epoxide functionalities. (+)-Benzo[a]pyrene-7,8-dihydrodiol-9,10-epoxide binds to the N2 atom of a guanine nucleobase in DNA, distorting the double helix structure by intercalation of the pyrene moiety between base pairs through π-stacking. The carcinogenic properties of tobacco smoking are attributed in part to this compound binding and inactivating the tumor suppression ability of certain genes, leading to genetic mutations and potentially to cancer. Pyrene is a polycyclic aromatic hydrocarbon consisting of four benzene rings fused together in a planar aromatic arrangement which approximates a rhombus in shape. Benzo[a]pyrene is a derivative in which a fifth benzene ring has been fused to the pyrene system, and is a component of tobacco smoke which is a procarcinogen partly responsible for the carcinogenic and mutagenic effects of smoking. Benzo[a]pyrene-7,8-dihydrodiol-9,10-epoxide is a metabolite of benzo[a]pyrene formed by the introduction of vicinal hydroxyl and epoxide functional groups to the fifth benzene ring. These oxidations are stereoselective, producing the pair of enantiomers with the hydroxyl groups on opposite sides of the pyrene plane and with the epoxide on the same side as its adjacent hydroxyl group. (+)-Benzo[a]pyrene-7,8-dihydrodiol-9,10-epoxide is specifically the (7R,8S,8aR,9aS) stereoisomer. The metabolism of the tobacco smoke procarcinogen benzo[a]pyrene involves three distinct steps – the introduction of an epoxide group in the 7,8-position, its hydration to a vicinal diol and the introduction of an epoxide in the 9,10-position. In the first step, a cytochrome P450 1A1 (CYP1A1) catalysed oxidation produces several products including (+)-benzo[a]pyrene-7,8-epoxide.