ENANTIOMERIC SEPARATION OF DANSYL-AMINO AND DABSYLAMINO ACIDS BY LIGAND-EXCHANGE CHROMATOGRAPHY WITH (S)-PHENYLALANINAMIDE-MODIFIED AND (R)-PHENYLALANINAMIDE-MODIFIED SILICA-GEL

(S)- and (R)-phenylalaninamide [(S)- and (R)-PheA, respectively] were covalently bonded to silica, and the novel chiral stationary phases (C SPs) obtained were used for ligand-exchange chromatographic (LEC) sepa rations with Cu(II) as complexing metal ion. These CSPs perform good s eparations of dansyl-l (Dns)- and dabsyl-I (Dbs) amino acids. The resu lts [enantioselectivity factor (alpha), retention factor (kappa') and elution order] were compared with the data obtained previously using o ne of the selectors as an additive to the mobile phase. Moreover, thes e CSPs were successfully employed in the direct resolution of a five-m embered ring cyclic sulphonamide (gamma-sultam) without any prederivat ization procedure. The chiral recognition process was found to be cons istent with a ligand-exchange mechanism, the geometry of the mixed dia stereomeric complexes being strongly dependent on the structural featu res of the selector covalently bonded to the phase and on the steric b ulk of the Dns- and Dbs-amino acid protecting groups. In order to inve stigate the nature of the interactions involved in the discrimination process, the influence of temperature on the chromatographic parameter s (kappa', alpha) was also evaluated.