High-performance liquid chromatographic enantioseparation of beta(2)-amino acids using a long-tethered (+)-(18-crown-6)-2,3,11,12-tetracarboxylic acid-based chiral stationary phase.

Reversed-phase high-performance liquid chromatographic methods were developed for the separation of enantiomers of eleven unnatural beta(2)-amino acids on a new chiral stationary phase, using the 11-methylene-unit spacer of aminoundecylsilica gel for the bonding of (+)-(18-crown-6)-2,3,11,12-tetracarboxylic acid as selector. The nature and concentration of the acidic and organic modifiers, the pH, the mobile phase composition, and the structures of the analytes substantially influenced the retention and resolution. Separations were carried out at constant mobile phase compositions in the temperature range 7-40 degrees C and the changes in enthalpy, Delta(DeltaH degrees ), entropy, Delta(DeltaS degrees ), and free energy, Delta(DeltaG degrees ) were calculated. The elution sequence was determined in some cases: the S enantiomers eluted before the R enantiomers.