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

Chem Biol Interact. 1992 Dec;85(2-3):151-72. 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.

Publication types

  • Comparative Study
  • Research Support, Non-U.S. Gov't

MeSH terms

  • 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


  • Aniline Compounds
  • Fluorobenzenes
  • Fluorine
  • 2-fluoroaniline
  • 3-fluoroaniline
  • 4-fluoroaniline
  • Cytochrome P-450 Enzyme System