MOLECULAR-STRUCTURES OF THE DIHYDRODIOLS AND DIOL EPOXIDES OF CARCINOGENIC POLYCYCLIC AROMATIC-HYDROCARBONS - X-RAY CRYSTALLOGRAPHIC AND NMR ANALYSIS

The molecular dimensions and conformations of the trans-1,2- and 10,11-dihydrodiols of benz[a]anthracene have been determined from X-ray crystal structure analyses. The cell dimensions are a = 14.399 (3) Å, b = 7.942 (2) Å, c = 11.579 (3) Å, β = 100.93 (2)°, space group P21/c for the 1,2-dihydrodiol, and a = b = 18.905 (3), c = 7.529 (1) Å, space group P42/n for the 10,11-dihydrodiol. The trans hydroxyl groups are axial in the 1,2-dihydrodiol; the bulk of H(12) would be presumed to hinder the formation of the diequatorial conformer of the diol. This steric problem does not exist for the 10,11 -dihy-drodiol and the hydroxyl groups in the molecule in the crystalline state are diequatorial. NMR analyses in solutions of deuterated chloroform, acetone, or dimethyl sulfoxide give results which indicate that the diaxial conformation also predominates for the 1,2-dihydrodiol in solution. In the case of the less hindered 10,11-dihydrodiol there is an equilibrium of approximately 30% diaxial and 70% diequatorial conformers in solution. The experimentally determined dimensions for these two trans diols, together with previously determined dimensions of arene oxides, have given sufficient data for the calculation of approximate dimensions for the diol epoxides of benz[a]anthracene and of benzo[a]pyrene which have been implicated as the ultimate carcinogenic metabolites of these hydrocarbons. A characteristic of the covalent bond formed to a biological macromolecule from an atom in the bay region of an activated polycyclic aromatic hydrocarbon is that it is axial as a result of steric hindrance. © 1979, American Chemical Society. All rights reserved.