Macrocyclic glycopeptides- and derivatized cyclofructan-based chiral stationary phases for the enantioseparation of fluorinated ß-phenylalanine analogs.

The enantioseparation of five fluorinated β-phenylalanine analogs together with the nonfluorinated α- and β-phenylalanines has been investigated utilizing chiral stationary phases. The employed chiral selectors include macrocyclic antibiotics, such as vancomycin, teicoplanin, and teicoplanin aglycone, isopropyl carbamate functionalized cyclofructan-6, and Cinchona alkaloid-based tert.-butyl carbamate quinine, all covalently bonded to 2.7 µm superficially porous silica particles. The applied conditions included reversed-phase and polar-ionic modes where the vancomycin-, and the cyclofructan-6-based core-shell particles proved to offer suitable efficiency. Under reversed-phase conditions typical hydrophobic chromatographic behavior was observed, especially in the HO/MeOH system. The improved selectivity with increasing MeOH content observed in polar ionic mode suggests that H-bonding may not play a major role in the chiral recognition. The stoichiometric displacement model was probed to gather information on the ionic interactions. The ion-exchange process was found to affect retention, but it has no essential contribution to chiral recognition. Without paying special attention to the optimization of the system volume of the UHPLC instrument plate heights varying in the range of 10-50 µm were obtained. In all cases, retention and selectivity decreased with increasing temperature, and enthalpy-driven enantiorecognition was observed. Elution sequences were determined in all cases.