Role of the carbohydrate moieties in chiral recognition on teicoplanin-based LC stationary phases

For this study, we used the macrocyclic antibiotic teicoplanin, a molecule consisting of an aglycone peptide "basket" with three attached carbohydrate (sugar) moieties. The sugar units were removed and the aglycone was purifi ed. Two chiral stationary phases (CSPs) were prepared in a similar way, one with the native teicoplanin molecule and the other with the aglycone. Twen ty-six compounds were evaluated on the two CSPs with seven RPLC mobile phas es and two polar organic mobile phases. The compounds were 13 amino acids o r structurally related compounds (including DOPA, folinic acid, etc.) and 1 3 other compounds (such as carnitine, bromacil, etc.). The chromatographic results are given as the retention, selectivity, and resolution factors alo ng with the peak efficiency and the enantioselective free energy difference corresponding to the separation of the two enantiomers. The polarities of the two CSPs are similar. It is clearly established that the aglycone is re sponsible for the enantioseparation of amino acids. The difference in enant ioselective free energy between the aglycone CSP and the teicoplanin CSP wa s between 0.3 and 1 kcal/mol for amino acid enantioseparations. This produc ed resolution factors 2-5 times higher with the aglycone CSP, Four non amin o acid compounds were separated only on the teicoplanin CSP. Six and five c ompounds were better separated on the teicoplanin and aglycone CSPs, respec tively. Although the sugar units decrease the resolution of alpha-amino aci d enantiomers, they can contribute significantly to the resolution of a num ber of non amino acid enantiomeric pairs.