EVALUATION OF AN OPTICALLY-ACTIVE CROWN-ETHER FOR THE CHIRAL SEPARATION OF DIPEPTIDES AND TRIPEPTIDES

The direct optical resolution of a number of di- and tripeptides was a chieved by capillary zone electrophoresis using an enantioselective cr own ether as buffer additive. The protonated primary amines form inclu sion complexes with the crown ether. Chiral resolution is based on dif ferent stability constants of the diastereomeric complexes thereby cha nging the electrophoretic mobilities of the enantiomers. Enantioselect ivity is strongly affected by the distance between the amine functiona lity and the chiral carbon atom. This effect was studied using di- and tripeptides especially synthesized for this purpose. In general, base line resolution was obtained for those peptides with the amine group l ocated as far as four bonds from the stereogenic center. Additionally, tripeptides possessing two chiral centers were separated to investiga te the potential of the chiral selector for the analysis of complex an alytes with related structures. Experimental factors such as crown eth er concentration, buffer pH and temperature also show a strong influen ce on the resolution. These factors can be successfully employed for m ethod optimization.