Highly N-deacetylated chitosan was chosen as a natural chiral origin for the synthesis of the selectors of chiral stationary phases. Therefore, chitosan was firstly acylated by various alkyl chloroformates yielding chitosan alkoxyformamides, and then these resulting products were further derivatized with 4-methylphenyl isocyanate to afford chitosan bis(4-methylphenylcarbamate)-(alkoxyformamide). A series of chiral stationary phases was prepared by coating these derivatives on 3-aminopropyl silica gel. The content of the derivatives on the chiral stationary phases was nearly 20% by weight. The chiral stationary phases prepared from chitosan bis(4-methylphenylcarbamate)-(ethoxyformamide) and chitosan bis(4-methylphenylcarbamate)-(isopropoxyformamide) comparatively showed better enantioseparation capability than those prepared from chitosan bis(4-methylphenylcarbamate)-(n-pentoxyformamide) and chitosan bis(4-methylphenylcarbamate)-(benzoxyformamide). The tolerance against organic solvents of the chiral stationary phase of chitosan bis(4-methylphenylcarbamate)-(ethoxyformamide) was investigated, and the results revealed that this phase can work in 100% ethyl acetate and 100% chloroform mobile phases. Because as-synthesized chiral selectors did not dissolve in many common organic solvents, the corresponding chiral stationary phases can be utilized in a wider range of mobile phases in comparison with conventional coating type chiral stationary phases of cellulose and amylose derivatives.
Keywords: Chiral stationary phases; Chitosan; Enantioseparation; High-performance liquid chromatography; Organic solvent tolerance.
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