title: Single Heteroatom Substitutions in the Efavirenz Oxazinone Ring Impact Metabolism by CYP2B6.
abstract: 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 KMvalues ranging from 0.3- to 3.9-fold different from that observed for efavirenz (KM: 3.6±1.7 μm). The lowest KMvalues, approximating 1 μm, were observed for the metabolism of 1, whereas the greatest KMvalue, 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 KMsuggest altered substrate binding.
authors.affiliation: Department of Medicine, Division of Clinical Pharmacology, Johns Hopkins University School of Medicine, 725 North Wolfe Street, Biophysics 307, Baltimore, MD, 21205, USA.
authors.forename: Philip M
authors.initials: PM
authors.lastname: Cox
authors.affiliation: Department of Medicine, Division of Clinical Pharmacology, Johns Hopkins University School of Medicine, 725 North Wolfe Street, Biophysics 307, Baltimore, MD, 21205, USA.
authors.forename: Namandjé N
authors.initials: NN
authors.lastname: Bumpus
mesh_terms: D000480:Alkynes; D048588:Benzoxazines / Q000032:analysis / Q000737:chemistry / Q000378:metabolism*; D002851:Chromatography, High Pressure Liquid; D003521:Cyclopropanes; D065702:Cytochrome P-450 CYP2B6 / Q000737:chemistry / Q000378:metabolism*; D006801:Humans; D007700:Kinetics; D013058:Mass Spectrometry; D008862:Microsomes, Liver / Q000378:metabolism; D013056:Spectrophotometry, Ultraviolet; D013329:Structure-Activity Relationship; D013379:Substrate Specificity
chemical_list: D000480:Alkynes; D048588:Benzoxazines; D003521:Cyclopropanes; D065702:Cytochrome P-450 CYP2B6; C098320:efavirenz
keywords: cytochromes P450; drug metabolism; efavirenz; structure-activity relationships