Stereoselective metabolism of 7-nitrobenz(a)anthracene to 3,4- and 8,9- trans-dihydrodiols

Metabolism of 7-nitrobenz(a)anthracene (7-NO2-BA) by rat liver microsomes yielded 7-NO2-BA trans-3,4-dihydrodiol and 7-NO2-BA trans-8,9-dihydrodiol as major metabolites. Proton NMR spectral analyses indicate that 7-NO2-BA trans-3,4-dihydrodiol preferentially adopts a quasidiequatorial conformation and that 7-NO2-BA trans-8,9-dihydrodiol adopts a mixture of quasidiequatorial and quasidiaxial conformations. Circular dichroism spectral analyses of these compounds and their diacetoxy derivatives indicated that the major enantiomers of both dihydrodiols have R,R absolute stereochemistries. The identification of 7-NO2-BA trans-8,9-dihydrodiol as a metabolite of 7-NO2-BA indicates that oxidative metabolism can occur at position peri to the nitro substituent.