SYNTHESIS OF FJORD REGION TETRAOLS AND THEIR USE IN HEPATIC BIOTRANSFORMATION STUDIES OF DIHYDRODIOLS OF BENZO[C]CHRYSENE, BENZO[G]CHRYSENEAND DIBENZO[A,L]PYRENE

Metabolic activation of the racemic benzo[e]chrysene-trans-9,10-, benz o[g]chrysene-trans-11,12- and dibenzo[a,I]pyrene-trans-11,12-dihydrodi ols 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 forme d were separated by HPLC and identified by co-chromatography with auth entic tetraols, which had been prepared by acidic hydrolysis of synthe tically 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]ch rysene and dibenzo[a,I]pyrene resulted in the formation of two tetraol s with cis/trans ratios of 81:19, 77:23 and 80:20, respectively, where as the anti-dihydrodiol epoxides underwent almost exclusively trans hy drolysis. The proportion of the stereoisomeric tetraols obtained from microsomal incubations indicates that all three dihydrodiols are predo minantly oxidized at the adjacent olefinic double bond to the anti-dia stereomers of the corresponding fjord region dihydrodiol epoxides acco unting for 4-35% of the ethyl acetate-extractable metabolites. To allo w quantitative assessment of the metabolites H-3-labeled trans-dihydro diols were synthesized by reduction of the corresponding o-quinones wi th sodium borotritide. Metabolic conversion of benzo[c]chrysene-trans- 9,10- and dibenzo[n,I]pyrene-trans-11,12-dihydrodiol by rat liver micr osomes were in a similar low range during the first 10 min of incubati on (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 cy tochrome P450/10 min). Given the strong intrinsic mutagenic and carcin ogenic activity of the fjord region dihydrodiol epoxides, our data ind icate that their formation, even at a relatively low level, may contri bute significantly to the biological activity of the parent hydrocarbo ns.