Reversion of Sulfenamide Prodrugs in the Presence of Free Thiol-Containing Proteins

The purpose of this work was to study the reaction kinetics between two model sulfenamide prodrugs of linezolid, N-(phenylthio)linezolid and N-[(2-ethoxycarbonyl)ethylthio]linezolid, with free thiol-containing proteins; commercial human serum albumin (HSA); a constitutively active mutant of the protein tyrosine phosphatase PRL-1 (PRL-1-C170S-C171S), a model protein; and diluted fresh human plasma. The reaction was followed by high-performance liquid chromatography, both for the loss of prodrug and appearance of linezolid, and at different pH values with molar excess of the proteins relative to the prodrugs. Pseudo first-order kinetics was observed. Consistent with earlier findings for the reaction between similar sulfenamides and small-molecule thiols, the reaction kinetics appeared to be consistent with thiolate attack at the sulfenamide bond to release the parent drug. The proteins reacted significantly slower on a molar basis than their small-molecule counterparts. It appears that proteins such as HSA may play a role in the in vivo conversion of sulfenamide prodrugs to their parent drug.