Enzymatic and chromatographic chiral discrimination of racemic (thio)glycidyl esters: Part I. A chemoenzymatic approach to both enantiomers of thioglycidyl esters

Abstract

AbstractBoth hitherto unknown (+)‐(R)‐ and (−)‐(S)‐thioglycidyl esters, (R)‐(2) and (S)‐(2), have been synthesized with different high enantiomeric excesses (ee) by two routes from the corresponding rac‐glycidyl esters rac‐(1). The first includes a porcine pancreatic lipase (PPL)‐mediated kinetic resolution of these esters followed by sulfuration with practically complete inversion to the (+)‐(R)‐enantiomer (+)‐(R)‐(2) (36–86% ee). (−)‐(S)‐Thioglycidyl esters (−)‐(S)‐(2) are obtained by the reverse reaction sequence (43–80% ee). In the latter case the hydrolysis rate is lower than that of analogous glycidyl esters. Moreover, the dependence of enantiomeric excess on the size of the acyl‐group is of the opposite tendency. Therefore, in both cases suitable selection of the acid residue gives rise to maximum enantioselectivity. The irreversible lipase‐catalyzed acylation of rac‐glycidol and rac‐thioglycidol, however, was found to be a less suitable alternative. The enantiomeric excess of recovered homochiral esters was determined by chiral chromatography using modified cellulose stationary phases (OB, OD). © 1993 Wiley‐Liss, Inc.