Enantioseparation of chiral aromatic acids by multiple dual mode counter-current chromatography using hydroxypropyl-β-cyclodextrin as chiral selector.

This work concentrates on extending the utilization of multiple dual mode (MDM) counter-current chromatography in chiral separations. Two aromatic acids, 2-(6-methoxy-2-naphthyl)propionic acid (NAP) and 2-phenylpropionic acid (2-PPA), were enantioseparated by MDM counter-current chromatography using hydroxypropyl-β-cyclodextrin (HP-β-CD) as chiral selector. The two-phase solvent systems consisting of n-hexane/ethyl acetate 0.1 mol/L phosphate buffer pH 2.67 containing 0.1 mol/L HP-β-CD (7.5:2.5:10 for NAP and 7:3:10 for 2-PPA, v/v/v) were used. Conventional MDM and modified MDM were compared according to peak resolution under current separation mechanism. The influence of elution time after the first-phase inversion and number of cycles for MDM were investigated. Peak resolution of NAP and 2-PPA increased from 0.62 to 1.05 and 0.72 to 0.84, respectively, using optimized MDM conditions. Being an alternative elution method for counter-current chromatography, MDM elution greatly improved peak resolution in chiral separations.