Preparation Of Polysaccharide Phenylcarbamates-based Chiral Stationary Phases And Their Applications In Separation Of Enantiomers

High performance liquid chromatography(HPLC)based on chiral stationary phases(CSPs)is one of the effective methods to obtain optically pure substances,not only for analytical separation but also for preparative purpose.Preparation of CSP is crucial and central part of the method.In recent 30 years,many HPLC CSPs have been developed.Exhibiting high chiral recognition to a wide range of chiral compounds,CSPs based on polysaccharide derivatives are mostly widely used for HPLC enantioseparation at present.In this work,novel polysaccharide-based CSPs were prepared,including positively charged,regioselectively modified,and immobilized polysaccharide derivatives-based CSPs and their chiral recognition were evaluated.In the first part,various HPLC CSPs and their applications in HPLC were reviewed,and the development of polysaccharide CSPs was discussed in detail.In the second part,positively charged cellulose derivatives-based CSPs were prepared by introducing 4-dimethylamino phenylcarbamate residues onto glucose unit.The effect of the amont of 4-dimethylamino group on separation of basic racemates was studyed.The retention of most of the tested basic racemates decreased with the increase of the 4-dimethylamino group and the derivative containing about 5.4%4-dimethylamino exhibited high chiral recognition.In the third part,cellulose phenylcarbamates bearing a small amount of 3-(triethoxysilyl)propyl residues were synthesized and efficiently immobilized onto silica gel by intermolecular polycondensation of triethoxysilyl groups.The chiral recognitions of the obtained CSPs were studied.The derivative having about 2.5%3-(triethoxysilyl)propyl residue was efficiently immobilized and the obtained CSP exhibited high chiral recognition.Also,the obtained CSPs demonstrated good solvent durability,solvents such as chloroform and tetrahydrofuran which were prohibitted for the coated-type CSPs could be used as mobile phase additives for the obtained CSPs,and with these eluents,some of the tested racemates were better resolved.In the fourth part,the classical method for preparation of covalently boned cellulose derivatives-based CSPs utlizing a diisocyanate as crosslinker was improved and three immobilized-type CSPs were prepared.using the improved method.The immobilized cellulose 3,5-dimethylphenylcarbamate CSPs showed high chiral recognition,comparable to that of Chiralpak IB.While the CSP,utilizing immobilized amylose 3-chlorophenylcarbamate as the chiral selector,exhibited low chiral recognition.In the last part,four regioselectively substituted cellulose phenylcarbamates bearing different substituents at 2-,3-positions and 6-position of the glucose unit were prepared,characterized,and their HPLC enantioseparations were evaluated.The derivatives exhibited characteristic chiral recognition and some racemates were better resolved than on the corresponding homogenously substituted derivatives.The nature as well as the position of the substituents located played an importat role on chiral recognition.Most of the tested racemates were best resolved on cellulose 2,3-bis(4-methylphenylcarbamate)-6-(3-chloro-4-methylphenyl carbamate).