High Performance Liquid Chromatographic Enantioresolution of Benzoyl Amino Acid,Dipeptides and Tripeptide on β-Cyclodextrin Bonded Stationary Phase Using Polar-Organic Acetonitrile as the Mobile Phase

The enantiomeric resolution of several dipeptides, amino acid (i.e., isoleucine) and tripeptide (i.e., Leu-Gly-Phe) with two stereogenic centers on β-cyclodextrin bonded chiral stationary phase (β-CD CSP) using polar-organic acetonitrile as the mobile phase is examined through pre-column chemical derivatization with a series of tagging reagents such as benzoyl chloride, benzenesulfonyl chloride and 1-naphthalenesulfonyl chloride. These tagging reagents are similar in structure; however, the enantioselectivity for the same analyte derivatized with these tagging reagents is quite different and found to be the best with benzoyl chloride. In the reversed-phase mode or on the γ-CD CSP under the same chromatographic conditions, the enantioresolution diminishes for all tagged enantiomers that were examined in this study. Dipeptides derivatized by benzoyl chloride appear to be better resolved than by dansyl chloride as reported previously. Interestingly, no enantioresolution for most derivatized amino acids with single stereogenic center was observed. Finally, enantioresolution can be enhanced by replacing the basic additive such as triethylamine with tripropylamine in the polar-organic mobile phase.