Transannular dioxygenation of 9,10-dimethyl-1,2-benzanthracene by cytochrome P-450 oxygenase of rat liver

Biotransformation and bioactivation of 7, 12-dimethylbenz[a]anthracene (7, 12-DMBA)

As the result of rapidly developing technological advances, our understanding of the biotransformation and bioactivation of 7, 12-DMBA has increased markedly in recent years. In terms of the metabolic conversion of this polynuclear aromatic hydrocarbon to reactive mutagen/carcinogens, the "bay region" generalization appears to apply, although the candidacy of a number of other intermediary metabolites as ultimate biologically-active forms still remains viable. Large gaps remain in knowledge concerning the nonoxidative metabolic transformations of 7, 12-DMBA, and these require closing in order to further our understanding of the regulation of mechanics controlling steady-state levels of reactive intermediates. Studies on the photooxidation of the hydrocarbon have allowed a stronger appreciation of its chemical reactivity and instability and promise to help resolve many of the apparently conflicting observations of the past. 7, 12-DMBA remains a highly interesting and valuable tool in investigations of bioactivation processes as they relate to the etiology of several important pathologic conditions, including chemically induced tissue necrosis, mutagenesis, carcinogenesis, teratogenesis, atherogenesis, and, possibly, other pathogenic phenomena as well. It is hoped that this review will serve to benefit research in these areas and hasten the reduction of such pathologic phenomena in our society.

Combined reversed-phase and normal-phase high-performance liquid chromatography in the purification and identification of 7,12-dimethylbenz[a]anthracene metabolites

A total of 37 compounds have been identified as rat liver microsomal metabolites of the potent carcinogen 7,12-dimethylbenz[a]anthracene and its hydroxymethyl derivatives 7-methyl-12-hydroxymethylbenz[a]anthracene, 7-hydroxymethyl-12-methylben[a]anthracene and 7,12-dihydroxymethylbenz[a]anthracene. The metabolites were characterized by: (i) retention times on reversed-phase (with a C18 column) and normal-phase (with a silica gel column) high-performance liquid chromatography (HPLC); (ii) ultraviolet absorption and fluorescence spectra; (iii) mass spectral analysis; (iv) optical activity; and (v) comparison of the physicochemical properties of the metabolites with those of some available synthetic standards. The 37 identified metabolites include four trans-3,4-dihydrodiols, four trans-5,6-dihydrodiols, four trans-8,9-dihydrodiols, four trans-10,11-dihydrodiols, two methyl carboxylic acids, two methyl aldehydes, two hydroxymethyl aldehydes, four 2-phenols, four 3-phenols, four 4-phenols and three hydroxymethyl derivatives. The trans configuration of the dihydrodiols was determined by their inability to form vicinal cisacetonides. Seven dihydrodiol metabolites were found to be optically active. Detailed physicochemical properties, such as ultraviolet absorption spectra, fluorescence spectra measured in methanol and in 0.1 N NaOH, major mass ions from mass spectral analysis and the retention times on two HPLC systems, are presented in support of the structural assignments.

Photooxidation products of 7,12-dimethylbenz[a]anthracene

The principal products of the photooxidation of 7,12-dimethylbenz[a]-anthracene (DMBA) in aqueous solutions by photooxidation induced by laboratory lighting have been characterized by high performance liquid chromatograms (HPLC), ultraviolet and mass spectrograms and by comparisons with authentic samples. The products identified were the 7,12-epidioxy-7,12-dihydro-7-12-dimethyl-, 7,12-dione, 7-hydroxymethyl-12-methyl-, 12-hydroxymethyl-7-methyl-, 7-formyl-12-methyl-, 12-formyl-7-methyl-, and 12-hydroxy-12-methyl-7-one derivatives of benz[a]-anthracene. The HPLC profile of products is similar to that obtained from oxidation of DMBA by 'one-electron' reagents, singlet oxygen, or liver microsomal metabolism. The first points of attack are the 7- and 12- positions. The mechanism of photooxidation appears to be generation of singlet oxygen by photodynamic effect of DMBA. None of the products is photosensitizing, however.