Single Heteroatom Substitutions in the Efavirenz Oxazinone Ring Impact Metabolism by CYP2B6

ChemMedChem. 2016 Dec 6;11(23):2630-2637. doi: 10.1002/cmdc.201600519. Epub 2016 Nov 10.


Previously, we observed that the oxazinone ring is important for cytochrome P450 2B6 (CYP2B6) activity toward efavirenz ((4S)-6-chloro-4-(2-cyclopropylethynyl)-1,4-dihydro-4-(trifluoromethyl)-2H-3,1-benzoxazin-2-one), a CYP2B6 substrate used to treat HIV. To further understand the structural characteristics of efavirenz that render it a CYP2B6 substrate, we tested the importance of each heteroatom of the oxazinone ring. We assembled a panel of five analogues: 6-chloro-4-(2-cyclopropylethynyl)-1,4-dihydro-2-methyl-4-(trifluoromethyl)-2H-3,1-benzoxazine (1), (4S)-6-chloro-4-[(1E)-2-cyclopropylethenyl]-3,4-dihydro-4-(trifluoromethyl)-2(1H)-quinazolinone (2), (4S)-6-chloro-4-(2-cyclopropylethynyl)-3,4-dihydro-4-(trifluoromethyl)-2(1H)-quinazolinone (3), 6-chloro-4-(cyclopropylethynyl)-3,4-dihydro-4-(trifluoromethyl)-2(1H)-quinolinone (4), and 6-chloro-4-(cyclopropylethynyl)-4-(trifluoromethyl)-4H-benzo[d][1,3]dioxin-2-one (5). The metabolism of compounds 1-5 was investigated using human liver microsomes, individual P450s, and mass spectrometry or UV/Vis absorbance detection. Steady-state analysis of CYP2B6 metabolism of 1-5 showed KM values ranging from 0.3- to 3.9-fold different from that observed for efavirenz (KM : 3.6±1.7 μm). The lowest KM values, approximating 1 μm, were observed for the metabolism of 1, whereas the greatest KM value, 14±6.4 μm, was found for 4. Our work reveals that analogues with heteroatom changes in the oxazinone ring are still CYP2B6 substrates, although the changes in KM suggest altered substrate binding.

Keywords: cytochromes P450; drug metabolism; efavirenz; structure-activity relationships.

MeSH terms

  • Alkynes
  • Benzoxazines / analysis
  • Benzoxazines / chemistry
  • Benzoxazines / metabolism*
  • Chromatography, High Pressure Liquid
  • Cyclopropanes
  • Cytochrome P-450 CYP2B6 / chemistry
  • Cytochrome P-450 CYP2B6 / metabolism*
  • Humans
  • Kinetics
  • Mass Spectrometry
  • Microsomes, Liver / metabolism
  • Spectrophotometry, Ultraviolet
  • Structure-Activity Relationship
  • Substrate Specificity


  • Alkynes
  • Benzoxazines
  • Cyclopropanes
  • Cytochrome P-450 CYP2B6
  • efavirenz