Thiolactone Sulfoxides as New Reactive Metabolites Acting as Bis-Electrophiles: Implication in Clopidogrel and Prasugrel Bioactivation

The antithrombotics of the tetrahydrothienopyridine series, clopidogrel and prasugrel, are prodrugs that must be metabolized in two steps to become pharmacologically active. The first step is the formation of a thiolactone metabolite. The second step is a cytochrome P450 (P450)-dependent oxidation of this thiolactone resulting in the formation of a sulfenic acid that is eventually reduced into the corresponding active thiol. It has been postulated that the sulfenic acid metabolite resulted from a nucleophilic attack of water on a highly reactive thiolactone sulfoxide derived from P450-dependent oxidation of the thiolactone primary metabolite. The data described in the present article are in complete agreement with this proposition as they show that it was possible to trap these thiolactone sulfoxides by a series of nucleophiles such as amines, thiols, or cyclopentane-1,3-dione (CPDH), an equivalent of dimedone that is used as a sulfenic acid trapping agent. HPLC-MS studies showed that various bis-adducts having incorporated two nucleophile molecules were formed in these reactions. One of them that resulted from the oxidation of 2-oxo-prasugrel by human liver microsomes in the presence of ethanolamine and CPDH was isolated and completely characterized by ¹H and ¹³C NMR spectroscopy in addition to MS and MS² spectrometry. All metabolites derived from an attack of H₂O or an amine at the CO carbon of the intermediate thiolactone sulfoxide existed as a mixture of two diastereomers having a <i>cis</i> configuration of the double bond, whereas those formed in the presence of thiols appeared as a mixture of four diastereomers with a <i>cis</i> or <i>trans</i> configuration of the double bond. This led us to propose tentative mechanisms for the previously reported formation of <i>trans</i> isomers of the active thiol metabolite of clopidogrel upon microsomal metabolism of this antithrombotic in the presence of thiols. The results described in this article showed that thiolactone sulfoxides are formed as reactive metabolites during the metabolism of clopidogrel and prasugrel and are able to react as bis-electrophiles with a variety of nucleophiles. The possible implications of the formation of these reactive metabolites in the pharmacological and/or secondary toxic effects of these drugs remain to be studied