ENANTIOMERIC AND DIASTEREOMERIC SEPARATION OF DIPEPTIDES AND TRIPEPTIDES BY CAPILLARY ELECTROPHORESIS

Chiral resolution of a series of di- and tripeptides has been attempte d by indirect and direct methods. For the indirect method, the analyte s were derivatized with a reagent of high chiral purity, (-)-1-(9-fluo renyl)ethyl chloroformate, and the diastereomers produced were subsequ ently separated in a micellar electrokinetic capillary chromatography (MEKC) system. For the direct method, the analytes were derivatized wi th 9-fluorenylmethyl chloroformate and separated by MEKC using gamma-c yclodextrin (CD) or beta-CD as chiral selectors. After optimization, 9 peptides were separated when using the indirect method. Using the dir ect method, 9 peptides were separated with gamma-CD as the chiral sele ctor, and two other peptides were separated with beta-CD. Complete sep aration of two peptides having two chiral centers, Leu-Ala and Leu-Leu , was obtained by the indirect method and Ala-Leu was separated by the direct method. The benefits of using organic modifiers to enhance ena ntioselectivity and separation efficiencies in the direct and indirect method were demonstrated and discussed. High separation efficiencies were obtained for both methods, plate numbers were in the range of 10( 6) plates/m. Separation times were ca. 10 min using the indirect metho d and ca. 17 min using the direct method. It seems that the two method s are complementary.