Model reactions of the quinone metabolites of carcinogenic hydrocarbons with t-butylthiol

Reactions of benzo[a]pyrene 1,6-dione with t-butylthiolate affords two products of conjugate addition and subsequent spontaneous reoxidation, namely, 2-t-butylthio- and 2,4-di-t-butylthiobenzo[a]pyrene 1,6-dione. Analogous reaction of benzo[a]pyrene 3,6-dione furnished only 12-t-butylthiobenzo[a]pyrene 3,6-dione. Structural assignments are based on analysis of the high-resolution 270-MHz Fourier-transform proton nmr spectra. In both products the attachment of the entering nucleophile is on an aromatic ring remote from either of the carbonyl groups, the first examples of such detected. The biological significance of these results with relation to the potential reactions of these quinones, known to be major metabolites of the carcinogen benzo[a]pyrene, with glutathione, cysteine, and proteins in vivo is discussed.