Preparation of aflatoxin B1 8,9-epoxide using m-chloroperbenzoic acid

Aflatoxin B1 is a potent carcinogen which requires activation in order to react with DNA. The exo-8,9-epoxide is putatively the active form although it has thus far eluded direct detection in biological systems. This laboratory has reported a synthesis of the epoxide using dimethyldioxirane as the oxidant [(1988) J. Am. Chem. Soc. 110, 7929-7931]. A new, very convenient synthesis is described herein in which m-chloroperbenzoic acid is used as the oxidant in a two-phase system. The reaction is carried out in CH2Cl2 in contact with an aqueous phosphate buffer (pH 7.2) to remove the byproduct m-chlorobenzoic acid, which would otherwise react with the epoxide. Excess m-chloroperbenzoic acid is removed with aqueous sodium thiosulfate.