Direct high-performance liquid chromatographic enantioseparation of secondary amino acids on Cinchona alkaloid-based chiral zwitterionic stationary phases. Unusual temperature behavior

High-performance liquid chromatographic separation of unusual β3-amino acid enantiomers in different chromatographic modes on Cinchona alkaloid-based zwitterionic chiral stationary phases

“…Relatively few papers have been published on chromatographic enantioseparation by zwitterionic phases with water-containing eluents. A small number of examples for the enantioseparation of free α-amino acids (Ala, Asp, Asn, Phe, Pro, α-Me-mTyr and Trp analogs, secondary amino acids) have been described with low or moderate water contents in the mobile phase (Hoffmann et al 2009a, b;Ilisz et al 2014c;Zhang et al 2014a, b). The mobile phases were…”

Enantioresolution of Amino Acids: A Decade’s Perspective, Prospects and Challenges

“…The zwitterionic character of these CSPs as well as appropriate mobile phase offered the selective features of a double ion-pairing resulting in improved retention and resolution. Similarly, two other CSPs containing quinine-, or quinidine-based zwitterionic ion-exchanger as chiral selector were investigated for the enantioseparation of 27 unusual cyclic secondary α-AAs [48]. They have also studied the effect of the parameters such as nature and concentration of the bulk solvent, acid and base additives, the structures of the analytes and temperature on enantioseparation.…”

“…Enantioseparation of several racemic α-AAs (native and derivatized) was obtained using cinchona alkaloids as chiral selectors in mobile phase along with Cu(II) ions in chiral ligandexchange chromatography by HPLC [46]. Cinchona alkaloid-derived zwitterionic chiral stationary phases (CSPs) containing a chiral sulfonic acid motif [namely, CHIRALPAK ZWIX(+) and ZWIX(−)] which serve as negatively charged interaction site for direct enantioseparation of AAs [47,48] have been developed. In zwitterionic CSPs, the chiral selector contains a positive and a negative charge in suitable mobile phase.…”

Investigation of Novel Cinchona Alkaloid-based Zwitterionic Chiral Stationary Phases in Cation- and Zwitterion-Exchange Modes

“…the k1 values increased with increasing temperature. This behavior was earlier registered in nonchiral separations [98][99][100] and for enantiomer separations [37,88] . This phenomenon was observed on ZWIX(-) Since the effect of temperature on the separation was complex, a detailed thermodynamic study may contribute to understand the mechanistic aspects of chiral recognition [97,[101][102][103] .…”

“…To investigate the effect of acid and base additives in an earlier study the acid-to-base ratio was varied between 4:1 to 1:4 (from acid to base excess) [57,88] . electrostatic interaction between SO and SA is balanced, which is important in the view of chiral discrimination and column efficiency [89] .…”