Esterification of reduced glutathione

GSH monoethyl ester [gamma-L-glutamyl-L-cysteinyl(ethyl glycinate)] may be used to supplement cellular pools of GSH in vitro and in vivo. The compound was prepared by esterification of GSH in anhydrous ethanol with HCl as the catalyst. However, a full analysis of products from the esterification of GSH revealed the formation of minor products: gamma-L-(ethyl glutamyl)-L-cysteinylglycine, i.e. an isomeric monoester, gamma-L-(ethyl glutamyl)-L-cysteinyl(ethyl glycinate), i.e. GSH diethyl ester, and N-(3-amino-2,6-dioxopiperazino)-L-cysteinyl(ethyl glycinate), i.e. an acid-catalysed cyclization product. These compounds were separated and purified by reverse-phase h.p.l.c. Esterification of GSH produces mainly the glycyl monoester with minor products of gamma-glutamyl ester, diester and the cyclization product. Only analytical reverse-phase h.p.l.c. of the compounds was found to resolve these products.