Synergetic mechanism and enantioseparation of aromatic β-amino acids by biphasic chiral high-speed counter-current chromatography

A biphasic chiral recognition system based on chiral ligand exchange with Cu(II)-N-n-dodecyl-L-proline and hydroxypropyl-beta-cyclodextrin as an additive was developed to enantioseparate aromatic beta-amino acids by high-speed counter-current chromatography. The biphasic chiral recognition system was established with an n-butanol/water (1:1, v/v) solvent system by adding N-n-dodecyl-L-proline and Cu(II) ions to the organic phase and hydroxypropyl-beta-cyclodextrin to the aqueous phase. Several separation parameters, such as temperature, pH value, and chiral selector concentration, were systematically investigated by enantioselective liquid-liquid extraction. Under the optimal separation conditions, 54.5 mg of (R,S)-beta-phenylalanine and 74.3 mg of (R,S)-beta-3,4-dimethoxyphenylalanine were baseline enantioseparated. More importantly, the synergistic enantiorecognition mechanism, based on the Cu(II)-N-n-dodecyl-L-proline and hydroxypropyl-beta-cyclodextrin, was discussed for the first time.