Enantioseparation of 4-Nitrophenylalanine using (S)-SDP-metal complex as chiral extractant

Abstract

The development of new and efficient chiral extractant is of great concern in the field of chiral extraction. Axial chiral diphosphine, such as (S)-BINAP, has been proved to be effective chiral extractant. However, the stereoselectivity of chiral diphosphine with novel structure has been rarely investigated in chiral extraction. (S)-SDP, a famous spiro diphosphine used in asymmetric synthesis, was firstly employed to separate 4-Nitrophenylalanine enantiomers in this study. The influences of metal precursors, pH, extractant concentration and temperature on extraction were investigated. Separation factor (α), enantiomeric excess (ee) and performance factor (pf) were adopted to evaluate the efficiency of enantioseparation. (S)-SDP-Pd was suitable for separation of 4-Nitrophenylalanine enantiomers with the highest α of 3.32. L-4-Nitrophenylalanine was preferentially recognized by (S)-SDP-Pd in extraction. The extraction process was systematically optimized by response surface method. The optimum extraction condition was pH of 7.1, (S)-SDP-Pd concentration of 2.2 mmol/L and temperature of 14.0 °C. At this optimum condition, the maximum pf was 0.08536. In addition, the possible chiral recognition mechanism was discussed.