Cationic cyclodextrin clicked chiral stationary phase for versatile enantioseparations in high-performance liquid chromatography

Abstract

In this work, a novel cationic cyclodextrin (CD) chiral stationary phase (CSPs) has been developed by clicking 6A-azido-6C-[(3-methoxylpropyl)-1- ammonium]-heptakis[2,3-di-O-(3-chloro-4-methylphenylcarbamate)-6B,6D,6E,6F,6G-pentakis-O-per(3-chloro-4-methylphenylcarbamate)-β-CD chloride onto alkynyl silica support. The enantioselectivies of the as-obtained novel CSP were evaluated using 21 model racemates including flavonoids, aromatic alcohols, acidic drugs, β-blocker and amino acids. Good enantioseparations were achieved in polar-organic phase high performance liquid chromatography (HPLC), with the highest resolution of 8.07 observed for 7-methoxyflavanone. The enantioseparations in normal-phase HPLC were fine-tuned with the polarity of the mobile phase with different alcohols as organic modifiers. Improved chiral resolutions of analytes but longer retention were observed in mobile phases with decreased polarity. On comparison with previously reported clicked CD CSP, the cationic CD clicked CSP exhibited better enenatioseparations for selected racemates even in normal-phase HPLC. The results indicate that 3-methoxypropylammonium and phenylcarbamoylated moieties of the cationic CSP may provide intermolecular interactions such as hydrogen bonding, π–π conjugation and dipole–dipole besides inclusion complexation to drive the enantioseparation.