title: Regio- and stereo-selective metabolism of 4-methylbenz[a]anthracene by the fungus Cunninghamella elegans.
abstract: Metabolism of 4-methylbenz[a]anthracene by the fungus Cunninghamella elegans was studied. C. elegans metabolized 4-methylbenz[a]anthracene primarily at the methyl group, this being followed by further metabolism at the 8,9- and 10,11-positions to form trans-8,9-dihydro-8,9-dihydroxy-4-hydroxymethylbenz[a]anthracene and trans-10,11-dihydro-10,11-dihydroxy-4-hydroxymethylbenz[a]anthracene. There was no detectable trans-dihydrodiol formed at the methyl-substituted double bond (3,4-positions) or at the 'K' region (5,6-positions). The metabolites were isolated by reversed-phase high-pressure liquid chromatography and characterized by the application of u.v.-visible-absorption-, 1H-n.m.r.- and mass-spectral techniques. The 4-hydroxymethylbenz[a]anthracene trans-8,9- and -10,11-dihydrodiols were optically active. Comparison of the c.d. spectra of the trans-dihydrodiols formed from 4-methylbenz[a]anthracene by C. elegans with those of the corresponding benz[a]anthracene trans-dihydrodiols formed by rat liver microsomal fraction indicated that the major enantiomers of the 4-hydroxymethylbenz[a]anthracene trans-8,9-dihydrodiol and trans- 10,11-dihydrodiol formed by C. elegans have S,S absolute stereochemistries, which are opposite to those of the predominantly 8R,9R- and 10R,11R-dihydrodiols formed by the microsomal fraction. Incubation of C. elegans with 4-methylbenz[a]anthracene under 18O2 and subsequent mass-spectral analysis of the metabolites indicated that hydroxylation of the methyl group and the formation of trans-dihydrodiols are catalysed by cytochrome P-450 mono-oxygenase and epoxide hydrolase enzyme systems. The results indicate that the fungal mono-oxygenase-epoxide hydrolase enzyme systems are highly stereo- and regio-selective in the metabolism of 4-methylbenz[a]anthracene.
mesh_terms: D001551:Benz(a)Anthracenes / Q000378:metabolism*; D001711:Biotransformation; D002851:Chromatography, High Pressure Liquid; D002942:Circular Dichroism; D013058:Mass Spectrometry; D008968:Molecular Conformation; D009090:Mucorales / Q000378:metabolism*; D010084:Oxidation-Reduction; D013056:Spectrophotometry, Ultraviolet
chemical_list: D001551:Benz(a)Anthracenes; C040143:4-methylbenz(a)anthracene; C040140:4-hydroxymethylbenz(a)anthracene-8,9-dihydrodiol; C040141:4-hydroxymethylbenz(a)anthracene-10,11-dihydrodiol