Surface‐up click access to allylimidazolium bridged cyclodextrin dimer phase for efficient enantioseparation

Abstract

In this work, a novel allylimidazolium‐bridged bis(β‐cyclodextrin) chiral stationary phase was fabricated via a surface‐up thiol‐ene click chemistry reaction between 7‐SH‐β‐cyclodextrin and 1‐allylimidazole‐β‐cyclodextrin bonded on a silica surface. The structure of the allylimidazolium‐bridged bis(β‐cyclodextrin) chiral stationary phase was characterized by Fourier transform infrared spectra, 13C nuclear magnetic resonance, thermogravimetric analysis, and elemental analysis. Its chiral chromatographic performances were systematically evaluated by separating 35 racemic analytes including isoxazolines, dansyl‐amino acids, and flavanones under reversed‐phase high‐performance liquid chromatography. Compared with the corresponding bottom and top layer of the β‐cyclodextrin stationary phase, the allylimidazolium‐bridged bis(β‐cyclodextrin) chiral stationary phase afforded significantly accentuated chiral recognition ability due to its abundant hydrogen bond sites, electrostatic interactions, and synergistic inclusion. Furthermore, the allylimidazolium‐bridged bis(β‐cyclodextrin) chiral stationary phase showed better enantioseparation ability compared to other reported bridged cyclodextrin stationary phases. In particular, Ar‐Phs and dansyl‐amino acid could be completely separated by allylimidazolium‐bridged bis(β‐mono‐6A‐deoxy‐6‐allylimidazolium‐β‐cyclodextrin chiral stationary phase) chiral stationary phase with high resolutions of 1.14–7.20 and 3.16–5.82, respectively. Molecular docking reveals that good enantioseparation ability arises from the different interaction modes and the synergistic effect of allylimidazolium‐bridged bis(β‐cyclodextrin) chiral stationary phase.