title: Study on the regioselectivity and mechanism of the aromatic hydroxylation of monofluoroanilines.
abstract: The in vitro and in vivo metabolism of monofluoroanilines was investigated. Special attention was focused on the regioselectivity of the aromatic hydroxylation by cytochromes P-450 and the mechanism by which this reaction might proceed. The results clearly demonstrate that the in vitro and in vivo regioselectivity of the aromatic hydroxylation by cytochromes P-450 is dependent on the fluoro-substituent pattern of the aromatic aniline-ring. Results from experiments with liver microsomes from differently pretreated rats demonstrate that the observed regioselectivity for the aromatic hydroxylation is not predominantly determined by the active site of the cytochromes P-450. To investigate the underlying reason for the observed regioselectivity, semi-empirical molecular orbital calculations were performed. Outcomes of these calculations show that neither the frontier orbital densities of the LUMO/LUMO + 1 (lowest unoccupied molecular orbital) of the monofluoroanilines nor the spin-densities in their NH. radicals can explain the observed regioselectivities. The frontier orbital densities of the HOMO/HOMO - 1 (highest occupied molecular orbital) of the monofluoroanilines however, qualitatively correlate with the regioselectivity of the aromatic hydroxylation. Based on these results it is concluded that the cytochrome P-450 dependent aromatic hydroxylation of monofluoroanilines does not proceed by hydrogen or electron abstraction from the aniline substrate to give an aniline-NH. radical. The results rather suggest that cytochrome P-450 catalyzed aromatic hydroxylation of monofluoroanilines proceeds by an electrophilic attack of the (FeO)3+ species of cytochrome P-450 on a specific carbon atom of the aromatic aniline-ring.
authors.affiliation: Department of Biochemistry, Agricultural University, Wageningen, The Netherlands.
authors.forename: N H
authors.initials: NH
authors.lastname: Cnubben
authors.forename: J
authors.initials: J
authors.lastname: Vervoort
authors.forename: C
authors.initials: C
authors.lastname: Veeger
authors.forename: I M
authors.initials: IM
authors.lastname: Rietjens
mesh_terms: D000814:Aniline Compounds / Q000378:metabolism* / Q000493:pharmacokinetics / Q000652:urine; D000818:Animals; D001711:Biotransformation; D003577:Cytochrome P-450 Enzyme System / Q000378:metabolism*; D005461:Fluorine; D005464:Fluorobenzenes / Q000378:metabolism / Q000493:pharmacokinetics / Q000652:urine; D006900:Hydroxylation; D009682:Magnetic Resonance Spectroscopy / Q000379:methods; D008297:Male; D008862:Microsomes, Liver / Q000201:enzymology / Q000378:metabolism; D008956:Models, Chemical; D051381:Rats; D017208:Rats, Wistar; D013237:Stereoisomerism
chemical_list: D000814:Aniline Compounds; D005464:Fluorobenzenes; D005461:Fluorine; C066212:2-fluoroaniline; C079598:3-fluoroaniline; C043455:4-fluoroaniline; D003577:Cytochrome P-450 Enzyme System