title: Stereochemical aspects in the 4-vinylcyclohexene biotransformation with rat liver microsomes and purified cytochrome P450s: diepoxide formation and hydrolysis.
abstract: The stereochemical course of the biotransformation of 1,2-monoepoxides of 4-vinylcyclohexene (2 and 3) by liver microsomes from control and induced rats and by purified P4502B1 and P4502E1 has been determined. The epoxidation of monoexpodies cis-4-vinylcyclohexene 1,2-epoxide (2) and trans-4-vinylcyclohexene 1,2-epoxide (3) gives the corresponding eight isomeric diepoxides cis-4-vinylcyclohexene diepoxide (9) and trans-4-vinylcyclohexene diepoxide (10). The stereoselectivity of this process is affected by P450 induction. Phenobarbital is able to enhance the yield of epoxidation to give preferentially diepoxide (1R, 2S, 4R, 7R)-trans-10b. This enantiomer is also formed as nearly the sole product by P450-catalyzed epoxidation of (1R,2S,4R)-trans-3b, the monoepoxide that, as a consequence of the selective formation from 4-vinylcyclohexene and/or reduced elimination by epoxide hydrolase, tends to accumulate in rat. Also, the P4502B1 but not 2E1, in a reconstituted system, is able to perform the epoxidation of (1R,2S,4R)-trans-3b to produce selectively the same diepoxide. Diepoxides cis-9 and trans-10 are biotransformed by mEH catalyzed hydrolysis. Although the hydrolysis of diepoxides 9 is characterized by a lower substrate enantioselection, the reaction of diepoxides 10 occurs with a good substrate enantioselectivity favoring the hydrolysis of the epoxides (1R,2S,4R,7S)-trans-10b and (1S,2R,4S,7S)-trans-10a. Diepoxide (1R,2S,4R,7R)-trans-10b is therefore the isomer primarily formed by P450-catalyzed oxidation of monoepoxide trans-3, and it is also the compound showing the lower propensity to undergo mEH-catalyzed hydrolysis. On the basis of this result, the ovotoxicity of 4-vinylcyclohexene is expected to be due to the stereoisomer diepoxide (1R,2S,4R,7R)-trans-10b, whose biological reactivity, via cross-linking, may be strongly different to the other isomer diepoxides, being dependent by its specific conformation.
authors.affiliation: Dipartimento di Chimica Bioorganica e Biofarmacia, Università di Pisa, via Bonanno 33, 56126 Pisa, Italy. cinziac@farm.unipi.it
authors.forename: Cinzia
authors.initials: C
authors.lastname: Chiappe
authors.forename: Antonietta
authors.initials: A
authors.lastname: De Rubertis
authors.forename: Giandomenico
authors.initials: G
authors.lastname: Piegari
authors.forename: Giada
authors.initials: G
authors.lastname: Amato
authors.forename: Pier Giovanni
authors.initials: PG
authors.lastname: Gervasi
mesh_terms: D000818:Animals; D001711:Biotransformation; D002849:Chromatography, Gas; D003510:Cyclohexanes / Q000378:metabolism*; D053138:Cyclohexenes; D003577:Cytochrome P-450 Enzyme System / Q000096:biosynthesis*; D003907:Dexamethasone / Q000494:pharmacology; D004790:Enzyme Induction; D004852:Epoxy Compounds / Q000032:analysis / Q000378:metabolism*; D006868:Hydrolysis; D007527:Isoenzymes; D008297:Male; D008862:Microsomes, Liver / Q000187:drug effects / Q000378:metabolism*; D008968:Molecular Conformation; D010634:Phenobarbital / Q000494:pharmacology; D011720:Pyrazoles / Q000494:pharmacology; D051381:Rats; D017207:Rats, Sprague-Dawley
chemical_list: D003510:Cyclohexanes; D053138:Cyclohexenes; D004852:Epoxy Compounds; D007527:Isoenzymes; D011720:Pyrazoles; C013733:4-vinylcyclohexene; C031280:pyrazole; D003907:Dexamethasone; D003577:Cytochrome P-450 Enzyme System; D010634:Phenobarbital