Synthesis and Properties of Bay-Region Episulfides of Benzo[a]Pyrene

Abstract A highly efficient, general method was developed for conversion of epoxides to the corresponding episulfides with dimethylthioformamide in the presence of BF3Et2O at low temperature (-20°C). Thus, the 9,10-epoxide of 7,8,9,10-tetrahydrobenzo[a]pyrene (3) and 4-methoxystyrene oxide (6) were converted to the corresponding episulfides (4) and (7), respectively, in over 90% yield. Highly stereoselective conversions of (±)-7β,8α-dihydroxy-9β, 10β-epoxy-7,8,9, 10-tetrahydrobenzo[a]pyrene (DE-1, 1a) and its diastereomeric 9,10-isomer (DE-2, 2a) to the corresponding diol episulfide-2b (DES-2) and -1b (DES-1), respectively, were also achieved by this method. These episulfides showed remarkable stability towards aqueous acid (>105 less reactive than the corresponding epoxides). Studies in Chinese hamster V-79 cells indicated that 1b and 2b have very low toxicity and mutagenicity compared to 2a.