Liquid chromatographic resolution of secondary amino alcohols on a chiral stationary phase based on (+)-(18-crown-6)-2,3,11,12-tetracarboxylic acid

HPLC enantioseparation of β2‐homoamino acids using crown ether‐based chiral stationary phase

“…The separation factors usually decrease as the temperature is raised, but a for 2, 3, 4, and 5 increased as the temperature was increased. This quite unusual temperature effect on chiral recognition was also observed for b-blockers [32] and for secondary amino alcohols [33] on this type of CSP.…”

Chiral Recognition Mechanism: Practical Considerations for Pharmaceutical Analysis of Chiral Compounds

“…10) are highly effective in the resolution of natural and unnatural α-amino acids (except for proline) [131][132][133], primary and secondary amino alcohols [134][135][136], β-amino acids [137], aryl α-amino ketone [138], and α-amino acid derivatives [20,131]. A number of pharmaceutically important compounds such as β-blockers [134,135], fluoroquinolone antibacterial agents [139], amphetamine, phenylethanolamine, octopamine, and norepinephrine [132] were separated quite well on this crown ether CSP.…”

“…Multiple hydrogen bonds were formed between analytes and the crown ether selector: the protonated secondary amine moiety of the analytes formed two hydrogen bonds with crown oxygens and the asymmetric hydroxyl group formed an additional hydrogen bond with carboxylate side chains of 18C 6 TA. Ionic interaction between the positively charged secondary ammonium and negatively charged carboxylate groups also made significant contribution to the retention and chiral recognition of β-blockers on 18C 6 TA CSP [134][135][136]. In this instance, the enantioseparation is an entropically controlled process.…”

“…Consequently, enantiomers without a primary amine group are less likely to be resolved in acidic aqueous-organic mobile phase. Instead, polar organic mobile-phase and/or normal-phase modes are more suitable for the resolution of enantiomers with secondary amine or other chiral compounds with primary amine where H-bonding interaction is more important for chiral recognition [130,[134][135][136].…”

Temperature effects on a doubly tethered diproline chiral stationary phase: Hold‐up volume, enantioselectivity and robustness

“…Since the surface of CSP1 is heterogeneous, the nonenantioselective hydrogen-bonding interaction between the residual silanol and hydroxyl group of the analytes could be one of the forces in the three-point interaction in chiral separation. Comparison of enantioselectivity before and after end-capping for analytes [1][2][3][4] suggested that the interaction model between enantiomer and CSP1 was probably different before and after end-capping [30]. Before end-capping, hydrogen-bonding or other weak interactions between the residual silanol and the enantiomer presented significant involvement in chiral recognition process.…”