Peptide enantiomer separations: Influence of sequential isomerism and the introduction of achiral glycine moieties on chiral recognition

The influence of sequential isomerism and the introduction of achiral, conformationally flexible glycine moieties into a peptide chain on the chiral recognition mechanism of a cinchona alkaloid based chiral selector has been evaluated. For this purpose, enantiomers of N-terminally protected alanine-glycine di- and tripeptides were separated by liquid chromatography-mass spectrometry on a corresponding chiral stationary phase (CSP). To obtain complementary information, the reversed phase retention behaviour of the various peptides was also evaluated and subsequently used to further elucidate the chromatographic characteristics of the CSP. For peptides that contained glycines in the N-terminal region chiral recognition was compromised, while glycines located at the C-terminus had no or little negative effect.