Enantioseparation using chitosan 2-isopropylthiourea-3,6-dicarbamate derivatives as chiral stationary phases for high-performance liquid chromatography

A new class of chitosan derivatives with an isopropylthiourea at the 2-position and various carbamates at the 3,6-positions of the glucosamine skeleton was synthesized by the selective thiocarbamoylation of the 2-amino group. The chiral stationary phases (CSPs) were then prepared by coating the obtained chitosan 2-isopropylthiourea-3,6-dicarbamate derivatives onto silica gel. The enantioseparation property of the chitosan-based CSPs was assessed with twelve racemates by high-performance liquid chromatography (HPLC). The CSPs displayed a characteristic enantioseparation power, which seemed to be significantly affected by the 3,6-substituents of the glucosamine unit. The chitosan derivatives with the 3,6-diphenylcarbamate, except for 2-methylphenylcarbamate, possessed higher enantioseparation abilities than those with the 3,6-dicyclohexylcarbamate. Compared to other chitosan derivatives with 2-various substituents and commercialized Chiralcel OD, the chitosan 2-isopropylthiourea derivatives revealed a relatively higher enantioselectivity for some racemic compounds.