Mutagenicity of the Enantiomers of the Diastereomeric Bay-Region Benzo(c)phenanthrene 3,4-Diol-1,2-epoxides in Bacterial and Mammalian Cells

The mutagenic activities of the enantiomers of the pair of diastereomeric bay-region benzo(c)phenanthrene 3,4-diol-1,2epoxides were evaluated in histidine-dependent strains of Sal monella typhimurium and in an 8-azaguanine-sensitive Chinese hamster œil line. In strains TA 98 and TA 100 of S. typhimurium, the range in mutagenic activity observed for the four optically active isomers was less than 4and 2-fold, respectively. The diol-epoxide with (1S,2fl,3fl,4S) absolute configuration and the benzylic hydroxyl group trans to the epoxide oxygen [(+)-diol epoxide-2] was the most active isomer in both strains. The enantiomeric (-)-diol-epoxide-2 isomer, with (1fî,2S,3S,4fî) ab solute configuration identical to that of the exceptionally tumorigenie (+)-diol-epoxide-2 isomers of benzo(a)pyrene, benz(a)anthracene, and chrysene, was the least active isomer in strain TA 98 (27%) and the second most active isomer in strain TA 100 (90%). In Chinese hamster V79 cells (-)-diol-epoxide-2 was the most active of the four benzo(c)phenanthrene isomers, and a 4to 5-fold range in mutagenic activity was observed. The differ ences in mutagenic activity between the four bay-region diolepoxide isomers of benzo(c)phenanthrene in the three test sys tems are relatively small when compared with results from similar studies with optically active bay-region diol-epoxide isomers of three other polycyclic aromatic hydrocarbons, and may be expli cable, in part, by a tendency of the hydroxyl groups of benzo(c)phenanthrene diol-epoxides to adopt comparable pseudodiequatorial conformations.