title: Bioactivation of substituted thiophenes including α-chlorothiophene-containing compounds in human liver microsomes.
abstract: The thiophene moiety has been recognized as a toxicophore because of the potential of oxidative bioactivation leading to electrophilic species. The introduction of bulky or electron-withdrawing groups at the α-carbon to the sulfur atom has the potential to reduce or eliminate bioactivation. In this article, we describe the bioactivation of a variety of substituted thiophenes. These compounds were incubated in NADPH-fortified human liver microsomes with or without the addition of reduced glutathione (GSH) as a trapping agent. The resulting GSH adducts were characterized by high performance liquid chromatography/high resolution mass spectrometry with the aid of a background subtraction methodology. Four of the five α-chlorothiophenes tested formed NADPH-dependent GSH adducts. Most adducts had masses consistent with the nominal substitution of chlorine by GSH. LC/MS/MS and proton NMR of the major GSH adduct of 1-(5-chlorothiophen-2-yl)ethanone (1a) confirmed that GSH displaced chlorine. To further explore the effect of different substitutions on the bioactivation potential, a series of 2-acetylthiophenes substituted at the C4 or C5 positions were tested in a quantitative thiol-trapping assay using dansyl glutathione. Substitutions at the C4 or C5 positions gave adduct levels that decreased in the following order: 4-H, 5-H (no substitution) > 4-Br ∼ 4-Cl > 5-Cl > 5-CN > 4-CH(3) > 5-Br > 5-CH(3) (no adduct detected). In conclusion, bioactivation was detected in a series of substituted thiophenes. Although substitutions on the thiophene ring can reduce the formation of reactive metabolites, the degree of reduction is dependent on the substitution position and substituent.
authors.affiliation: Pharmaceutical Candidate Optimization, Bristol-Myers Squibb Research and Development , Princeton, New Jersey 08543, United States.
authors.forename: Weiqi
authors.initials: W
authors.lastname: Chen
authors.forename: Janet
authors.initials: J
authors.lastname: Caceres-Cortes
authors.forename: Haiying
authors.initials: H
authors.lastname: Zhang
authors.forename: Donglu
authors.initials: D
authors.lastname: Zhang
authors.forename: W Griffith
authors.initials: WG
authors.lastname: Humphreys
authors.forename: Jinping
authors.initials: J
authors.lastname: Gan
mesh_terms: D002851:Chromatography, High Pressure Liquid; D005978:Glutathione / Q000737:chemistry / Q000378:metabolism; D054879:Halogenation; D006801:Humans; D013058:Mass Spectrometry; D008862:Microsomes, Liver / Q000378:metabolism; D013876:Thiophenes / Q000737:chemistry / Q000378:metabolism*
chemical_list: D013876:Thiophenes; D005978:Glutathione