Preparation of chiral oxazolinyl-functionalized β-cyclodextrin-bonded stationary phases and their enantioseparation performance in high-performance liquid chromatography

Abstract

Preparation of chiral oxazolinyl-functionalized ␤-cyclodextrin-bonded stationary phases and their enantioseparation performance in high-performance liquid chromatography A simple procedure for the synthesis of three new oxazolinyl-substituted ␤-cyclodextrins (6-deoxy-6-R-(-)-4-phenyl-4,5-dihydrooxazolinyl-␤-cyclodextrin, 6-deoxy-6-S-(-)-4-phenyl-4,5-dihydrooxazolinyl-␤-cyclodextrin, and 6-deoxy-6-S-(-)-(4-pyridin-1-ium-4-methyl-benzenesulphonate)-4,5-dihy-drooxazolinyl-␤-cyclodextrin) and their covalent bonding to silica are reported. The ability of these chiral stationary phase columns for separating compounds is also presented and discussed. Twenty-eight compounds were examined in the polar-organic mobile phase mode, and 11 ␤-nitroethanols were tested in the reversed-phase mode. Excellent enantioseparations were achieved for most of the analytes, even for several challenging compounds. The rigid and flexible structures of mono-substituted chiral groups and the fragments around the rim of the ␤-cyclodextrin cavity played an important role in the separation process. Factors such as -stacking, dipole-dipole interactions, ion-pairing, and steric hindrance effects were found to affect the chromatographic performance. Moreover, the buffer composition, and percentages of organic modifiers in the mobile phase, were investigated and compared. The mechanisms involved in the separation were postulated based on the chromatographic data.

Chiral Stationary Phases for Liquid Chromatography: Recent Developments

“…Li et al [150] arrived at similar conclusions after preparing oxazolinyl-functionalized β-cyclodextrins covalently bonded to silica support (CSP86–88) (Figure 3). They described that analytes with electron-donating or hydrogen-bonding groups were easily enantioseparated due to a higher number of π-π and hydrogen-bonding interactions [150]. CSP88 was more suitable for enantioseparation of polar compounds since it promoted electrostatic interactions due to the presence of an ionic group [150].…”

“…It was found that the majority of the new cyclodextrin-based CSPs were prepared based on the most widely used cyclodextrin as CSP, i.e., the β-cyclodextrin [148,149,150,151]. Moreover, the immobilization strategy of the chiral selector on the chromatographic support was, mainly, by click chemistry [149,150,151,152]. The main advantages of this approach are the mild reaction conditions and the enhanced tolerance of the CSPs to solvents and the range of pH values [153].…”

Thiol‐ene click derived structurally well‐defined per(3,5‐dimethyl)phenylcarbamoylated cationic cyclodextrin separation material for achiral and chiral chromatography

“…Since the shape of truncated hollow cone favor their ability to form stable inclusion with guest molecules [6], cyclodextrins (CDs) are widely used for enantioseparation, especially as CSPs in HPLC [7][8][9][10]. Besides its inclusion features, CDs can be chemically modified to build hydrogen bonding, π-π, steric repulsion interactions, which are all beneficial for chiral recognition process [11].…”

Investigation of the chromatographic regulation properties of benzyl groups attached to bridging nitrogen atoms in a calixtriazine‐bonded stationary phase

“…Recently, organic silanes with reactive groups have been used to enrich the family of HPLC stationary phases by further derivatization using ligands of suitable size . In some of the new stationary phases, ligands with a synthetic macrocyclic receptor, such as crown ether , cyclodextrin , calixaromatics , sapphyrin , pillararene , and cucurbituril have been tethered with silica. With these new phases, separation of desired solutes can be achieved based on a multiple host–guest recognition interactions.…”