Improved preparation of chiral stationary phases via immobilization of polysaccharide derivative-based selectors using diisocyanates



The classical method for the preparation of immobilized polysaccharide-based chiral stationary phases (CSPs) with a diisocyanate was improved. Cellulose or amylose was directly coated onto 3-aminopropyl silica gel after it was dissolved in a mixture of N,N-dimethylacetamide, LiCl, and pyridine, then immobilized onto silica gel with a diisocyanate, and finally allowed to react with an excess of corresponding isocyanate. Four polysaccharide derivatives, 3,5-dimethylphenylcarbamate and 3,5-dichlorophenylcarbamate of cellulose, and 3,5-dimethylphenylcarbamate and 5-chloro-2-methylphenylcarbamate of amylose, were immobilized onto silica gel utilizing this method. Compared with the classical diisocyanate method, the improved procedure avoided the derivatization and regeneration of 6-hydroxyl groups of cellulose and amylose, and thus showed an advantage for simple and economical preparation. The relationships among the amount of diisocyanate used, immobilization efficiency, and enantioseparation on the cellulose-based CSPs were investigated. Also, the solvent durability of the obtained CSPs was examined with eluents containing chloroform or THF. By utilizing these eluents, the chiral recognition abilities of the obtained CSPs for some of the tested racemates were improved.