Metabolic studies on the potent environmental carcinogens :7,9- and 7,10-dimethylbenz[c]acridine

This thesis focuses on the synthetic and metabolic studies of two highly carcinogenic polycyclic aza-aromatic hydrocarbons, 7,9—dimethylbenz[c]acridine (7,9-DMBAC) and 7,10-dimethylbenz[c]acridine (7,10—DMBAC). For the identification of the metabolites, three possible hydroxymethyl derivatives of 7,9-DMBAC and 7,10-DMBAC were prepared through the hydrolysis of the brominated methyl derivatives and 7,9-DMBAC-5,6-oxide was synthesised by direct oxidation using hypochlorite. To facilitate metabolic studies tritiated 7,9-DMBAC and 7,10-DMBAC were synthesised by catalytic debromination of 9-bromomethyl-7MBAC and 10-bromomethyl-7MBAC in the presence of tritium gas. After purification by HPLC, the specific radioactivity was 1180 mCi/mmol for 7,9-DMBAC and 202 mCi/mmol for 7,10-DMBAC. Rat hepatic microsomal metabolism of 7,9-DMBAC and 7,10-DMBAC was investigated. A radiochemical hexane extraction assay was adapted to measure the overall rate of 7,9-DMBAC and 7,10-DMBAC metabolism and the kinetics in microsomal systems. The metabolites of 7, 9-DMBAC and 7,10-DMBAC were separated by HPLC and the structures were assigned using ultraviolet spectroscopy, mass spectrometry and NMR spectrometry when sufficient metabolites were available. Where possible comparison was made with authentic synthetic standards. The following were identified as the metabolites produced by 3-methylcholanthrene (MC) induced liver microsomes: for 7,9-DMBAC, trans-7,9-DMBAC-3,4-dihydrodiol, trans—7,9-DMBAC-5,6-dihydrodiol, 7,9-DMBAC-5,6-oxide, 7-hydroxymethyl-9MBAC, 9-hydroxymethy1-7MBAC, 7,9-dihydroxymethyl-BAC, 9-formyl-7MBAC, two phenols and a number of secondary metabolites; for 7,10-DMBAC, trans-7,10-DMBAC-3,4-dihydrodiol, trans-7,10-DMBAC-5,6-dihydrodiol, trans-7, 10—DMBAC-8,9-dihydrodiol, 7,10—DMBAC-5,6-oxide, 7,10-DMBAC-8,9-oxide, 7-hydroxymethyl-10MBAC, 10- hydroxymethyl-7MBAC, 7,10-dihydroxymethyl-BAC, four phenols and a number of secondary oxidation products. The absolute configuration of the major enantiomers of the metabolically formed dihydrodiols was determined, and the enantiomeric compositions of these dihydrodiols formed by control, MC- and phenobarbital-induced preparations were found to be independent of pretreatment. All were highly enriched in the R,R-enantiomer. Metabolite distributions with the three liver microsomal enzymes were also obtained for the two aza-arenes. The mutagenic activities of 7,9-DMBAC and 7,10-DMBAC metabolites and some synthetic derivatives were undertaken using Ames test with Salmonella typhimurium TA100 strain. The dihydrodiol metabolites which have a vicinal bayregion double bond were all activated to mutagens to a greater extent than their parent compounds, suggesting that both 7,9-DMBAC and 7,10-DMBAC were activated via the formation of the bay-region diolepoxides for which the 3,4-dihydrodiol with a bay-region double bond was the expected metabolic precursor