Study on the regioselectivity and mechanism of the aromatic hydroxylation of monofluoroanilines

• Published in: Chemico-biological interactions Vol. 85; no. 2-3; p. 151
• Main Authors: Cnubben, N H, Vervoort, J, Veeger, C, Rietjens, I M
• Format: Journal Article
• Language: English
• Published: Ireland 01-12-1992
• Subjects: Aniline Compounds - metabolism; Aniline Compounds - pharmacokinetics; Aniline Compounds - urine; Animals; Biotransformation; Cytochrome P-450 Enzyme System - metabolism; Fluorine; Fluorobenzenes - metabolism; Fluorobenzenes - pharmacokinetics; Fluorobenzenes - urine; Hydroxylation; Magnetic Resonance Spectroscopy - methods; Male; Microsomes, Liver - enzymology; Microsomes, Liver - metabolism; Models, Chemical; Rats; Rats, Wistar; Stereoisomerism
• ISSN: 0009-2797
• DOI: 10.1016/0009-2797(92)90059-T

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.