Studies on Preparation and Chiral Recognition of 2-N-phthaloyl Chitosan-based Chiral Stationary Phases

To develop novel polysaccharide-based chiral stationary phases with high chiral recognition, five novel chitosan derivatives, bearing N-phthaloyl at 2-position of a glucose ring and four different phenylcarbamate substituents including 2-chloro, 3-chloro, 4-chloro and 3,5-dichloro, and one chitosan derivative bearing unsubstituted phenylcarbamate at 3- and 6-positions were synthesized by combination of a procedure on the regioselective acylation of 2-position. The structures of the obtained chitosan derivatives were characterized by FTIR and 1 H-NMR. They were then coated on the macroporous silica gel to be used as chiral stationary phases for high-performance liquid chromatography (HPLC). Their chiral recognition abilities were evaluated using ten racemates by HPLC. The results indicated that these coated-type chitosan CSPs exhibited characteristic chiral recognition ability, mainly depending on the position, number and steric hindrance of the substituents introduced on the aromatic moieties of the chitosan derivatives. Meanwhile, the eluent content in chromatographic tests had a great influence on the chiral recognition abilities of the chitosan-based CSPs. The racemates 1,3,6,7,8,10 were better resolved using a hexane/2-propanol (99/1) mixture as the eluent in comparison with the results obtained using hexane/2-propanol (90/10) mixture as the eluent on chitosan 2phthaloyl-3,6-di(3,5-dichlorophenylcarbamate derivative (CSP-3e). The correlations between the chiral recognition abilities and the chemical shifts of the N H protons in the 'H-NMR spectra and the N H frequencies in the IR spectra of the carbamate moieties of these derivatives were also discussed further. Among the CSPs based on the chitosan derivatives bearing different substituents at 2 and 3, 6-postions of the glucose unit, those based on the chitosan derivatives (CSP-3e) bearing 3,5-dichlorophenylcarbamates at 3,6-positions showed higher chiral recognition abilities while those based on the derivatives bearing 2chlorophenylcarbamates at 3, 6-positions showed relatively lower recognition ability. Compared to chitosan 2(3,5-dichlophenylurea)-3, 6-di (3, 5-dichlorophenylcarbamate) (CSP-ref) and chitosan 2-phthaloy1-3, 6(3,5-dichlorophenylcarbamate) (CSP-3e-ref),the chitosan derivative (CSP-3e) showed complementary and similar chiral recognition abilities for some racemates.