Polysaccharide- and β-Cyclodextrin-Based Chiral Selectors for Enantiomer Resolution: Recent Developments and Applications

Abstract

Polysaccharides, oligosaccharides, and their derivatives, particularly of amylose, cellulose, chitosan, and β-cyclodextrin, are well-known chiral selectors (CSs) of chiral stationary phases (CSPs) in chromatography, because they can separate a wide range of enantiomers. Typically, such CSPs are prepared by physically coating, or chemically immobilizing the polysaccharide and β-cyclodextrin derivatives onto inert silica gel carriers as chromatographic support. Over the past few years, new chiral selectors have been introduced, and progressive methods to prepare CSPs have been exploited. Also, chiral recognition mechanisms, which play a crucial role in the investigation of chiral separations, have been better elucidated. Further insights into the broad functional performance of commercially available chiral column materials and/or the respective newly developed chiral phase materials on enantiomeric separation (ES) have been gained. This review summarizes the recent developments in CSs, CSP preparation, chiral recognition mechanisms, and enantiomeric separation methods, based on polysaccharides and β-cyclodextrins as CSs, with a focus on the years 2019–2020 of this rapidly developing field.

Synthesis by carbonate aminolysis and chiral recognition ability of cellulose 2,3-bis(3,5-dimethylphenyl carbamate)-6-(α-phenylethyl carbamate) selectors

“…Besides the chemical structure of the CS, the enantioseparation performance of a coated chiral stationary phase is significantly dependent on the polysaccharide raw material, its molecular weight (Ichida et al 1984;Chassaing et al 1997;Okada et al 2016;Zhang et al 2020), the coating amount, the coating procedure and solvent used (Yashima et al 1996;Wei et al 2019), as well as silica gel characteristics, such as particle size, dispersity, or pore size (Yashima et al 1996;Qin et al 2010;Bezhitashvili et al 2017;Kohout et al 2019), and of course the respective analytes, the mobile phase and HPLC conditions (Yashima et al 1996;Bui et al 2021). To ensure an objective comparison and proper evaluation of the enantioseparation performance of novel CSs, all parameters except the actual chemical structures of these CSs should of course be kept constant.…”

Analytical Separation of Closantel Enantiomers by HPLC

“…Moreover, the position of the substituents fused with the phenyl moiety also had a significant influence on chiral recognition. Therefore, the stereo-electronic, dipole–dipole, π–π bonding, and hydrogen bonding interactions can form evanescent, transient diastereomer complexes through interactive forces, thus leading to differences in the migration between the enantiomers inside the column causing enantioseparation [ 25 ]. The ADMPC (amylose tris 3, 5 dimethyl phenyl carbamates) enantioselectivity results not only from D-glucopyranose residues of amylose but also from helical grooves existing in the polymeric backbone, of which the difference in their molecular environment is considered to have a strong impact on the chiral recognition [ 26 ].…”

Prediction of Enantioseparation of Econazole on the Cyclodextrin Derivatives as Chiral Selectors by Molecular Docking Approach

“…From the docking test, the RMSD value was less than 3 Å, so the prediction was quite accurate. The complexing ability of cyclodextrin was modified by the presence of hydroxypropyl (HP) substituent, therefore, the interaction and complexation energies for S-β-CD are higher than other cyclodextrin derivatives [27][28]. Based on the research that has been done, the use of S-β-CD as a chiral selector for chiral separation of econazole obtained the lowest ΔG value with high affinity and stable complex.…”