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.

Keywords: amylose; cellulose; chiral selector; chiral stationary phase; chromatography; cyclodextrin; enantiomer separation; polysaccharide.

Figure 1

Chemical structures of asparagine and carvone enantiomers.

Figure 2

Chemical structure of cellulose 6-O-benzoyl-2,3-O-(3,5-dimethylphenyl carbamate)-based CSs synthesized by Yin et al. [15].

Figure 3

Chemical structures of common chiral analytes used for evaluation of CSPs.

Figure 4

Chemical structures of linear amylose 3,5-dimethylphenyl carbamate for coating (1), cyclic amylose 3,5-dimethylphenyl carbamate for coating (2), linear amylose 3,5-dimethylphenyl carbamate for immobilization (3), and cyclic amylose 3,5-dimethylphenyl carbamate for immobilization (4), compared in the study of Ryoki et al. [44].

Figure 5

Chemical structures of different chitosan 3,6-bis-(aryl carbamate)-2-(N-cyclopentylcarbonyl) derivative-based CSs synthesized by Fu et al. [63].

Figure 6

Chemical structure of a triazole-bridged bis-(β-cyclodextrin) bonded on silica gel as CSP as used in the study of Shuang et al. [68].