Acid-catalyzed esterification and biotin/fluorescent labeling of glutathione polysulfides based on stability under heating and pH change

Abstract

Glutathione polysulfides GSSSG and GSSSSG are stable in water up to 80 °C and below pH 9. Their carboxyl groups can be efficiently esterified with TMSCl in alcohols, reacting first at glycine, then glutamic acid. The resulting 3-butyne-1-yl esters allow Cu-catalyzed labeling (e.g., biotin, fluorophore) and can be hydrolyzed by esterases.