Synthesis of fjord region tetraols and their use in hepatic biotransformation studies of dihydrodiols of benzo[c]chrysene, benzo[g]chrysene and dibenzo[a,l]pyrene.

ABSTRACT

Metabolic activation of the racemic benzo[c]chrysene-trans-9,10-, benzo[g]chrysene-trans-11,12- and dibenzo[a,l]pyrene-trans-11,12-dihydrodiols to fjord region syn- and anti-dihydrodiol epoxides by microsomes of Aroclor 1254-treated Sprague-Dawley rats has been examined. Since the fjord region dihydrodiol epoxides were hydrolytically unstable under the experimental conditions, their enzymatic formation was determined by analyzing the tetraols as their products of acidic hydrolysis upon addition of perchloric acid. The various stereoisomeric tetraols formed were separated by HPLC and identified by co-chromatography with authentic tetraols, which had been prepared by acidic hydrolysis of synthetically available syn- and anti-dihydrodiol epoxides and characterized by NMR and UV spectroscopy. Under standardized conditions the acidic hydrolysis of syn-dihydrodiol epoxides of benzo[c]chrysene, benzo[g]chrysene and dibenzo[a,l]pyrene resulted in the formation of two tetraols with cis/trans ratios of 8119, 7723 and 8020, respectively, whereas the anti-dihydrodiol epoxides underwent almost exclusively trans hydrolysis. The proportion of the stereoisomeric tetraols obtained from microsomal incubations indicates that all three dihydrodiols are predominantly oxidized at the adjacent olefinic double bond to the anti-diastereomers of the corresponding fjord region dihydrodiol epoxides accounting for 4-35% of the ethyl acetate-extractable metabolites. To allow quantitative assessment of the metabolites 3H-labeled trans-dihydrodiols were synthesized by reduction of the corresponding o-quinones with sodium borotritide. Metabolic conversion of benzo[c]chrysene-trans-9,10- and dibenzo[a,l]pyrene-trans-11,12-dihydrodiol by rat liver microsomes were in a similar low range during the first 10 min of incubation (6.2 +/- 1.2 and 3.4 +/- 1.0 nmol substrate/nmol cytochrome P450/10 min, respectively), whereas the conversion of benzo[g]chrysene-trans-11,12-dihydrodiol was much higher (20.6 +/- 2.2 nmol substrate/nmol cytochrome P450/10 min). Given the strong intrinsic mutagenic and carcinogenic activity of the fjord region dihydrodiol epoxides, our data indicate that their formation, even at a relatively low level, may contribute significantly to the biological activity of the parent hydrocarbons.