Bioactivation of substituted thiophenes including α-chlorothiophene-containing compounds in human liver microsomes.

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 th...