Stereoselective metabolism of chrysene by rat liver microsomes. Direct separation of diol enantiomers by chiral stationary phase h.p.l.c.

Abstract

The direct enantiomeric resolution of non-K region trans-1, 2-dihydrodiol, l, 2, 3, 4-tetrahydro-trans-1,2-diol, trans-3, 4-dihydrodiol and l, 2, 3, 4-tetrahydro-trans-3, 4-diol, K region trans- and cis-5, 6-dihydrodiols and their monomethyl ethers of chrysene was studied by chiral stationary phase high-performance liquid chromatography (CSP-h.p.l.c). The chiral stationary phase columns were packed with γ-aminopropyl-silanized silica to which either (R)-N-(3,5-dinitrobenzoyl)-phenyiglycine or (S)-AK3, 5-dinitrobenzoyDleucine was bonded either ionically or covalently. Enantiomers of all dihydrodiol derivatives were resolved by one or more, but not all, of the chiral stationary phases utilized. Enantiomeric resolutions were substantially improved when the non-K region dihydrodiols were converted to tetrahydrodiols. The absolute configurations of the K region trans- and cis-5, 6-dihydrodiols were established by the exciton chirality circular dichroism method. The (R, R): (S, S) enantiomer ratios, determined by CSP-h.p.l.c, of the 1, 2-, 3, 4- and 5, 6-trans-dihydrodiols formed in the metabolism of chrysene by liver microsomes from untreated male rats of the Sprague-Dawley strain were found to be 51: 49, 99: 1 and 86: 14, respectively; from phenobarbital-treated rats, 41: 59, 99: 1 and 87: 13, respectively; from 3-methylcholanthrene-treated rats, 96: 4, 99: 1 and 92: 8, respectively. The absolute configurations of chrysene 5, 6-epoxide enantiomers, resolved by CSP-h.p.l.c, were elucidated by the determination of the structures and absolute configurations of their methoxylation products. Both enantiomers of chrysene 5, 6-epoxide were hydrated by micro-somal epoxide hydrolase to chrysene trans-5, 6-dihydrodiol enriched (67–92%) in the 5R, 6R enantiomer. Chrysene 5R, 6S-epoxide was hydrated to trans-5, 6-dihydrodiol at a rate approximately 6-fold faster than chrysene 55, 6R-epoxide.