ENZYMATIC AND CHROMATOGRAPHIC CHIRAL DISCRIMINATION OF RACEMIC (THIO)GLYCIDYL ESTERS .1. A CHEMOENZYMATIC APPROACH TO BOTH ENANTIOMERS OF THIOGLYCIDYL ESTERS

Both 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)-mediate d kinetic resolution of these esters followed by sulfuration with prac tically complete inversion to the (+)-(R)-enantiomer (+)-(R)-(2) (36-8 6% ee). (-)-(S)-Thioglycidyl esters (-)-(S)-(2) are obtained by the re verse reaction sequence (43-80% ee). In the latter case the hydrolysis rate is lower than that of analogous glycidyl esters. Moreover, the d ependence of enantiomeric excess on the size of the acyl-group is of t he opposite tendency. Therefore, in both cases suitable selection of t he acid residue gives rise to maximum enantioselectivity. The irrevers ible 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 chroma tography using modified cellulose stationary phases (OB, OD). (C) 1993 Wiley-Liss, Inc.