High-performance chiral stationary phases based on chitosan derivatives with a branched-chain alkyl urea.

In this study, two series of chitosan 3,6-bis(arylcarbamate)-2-(isobutylurea)s and corresponding coated-type chiral stationary phases (CSPs) were prepared from two kinds of chitosans with different molecular weights. Most of the prepared CSPs demonstrated better enantioseparation performance than the homemade CSP of cellulose tris(3,5-dimethylphenylcarbamate). The CSPs of chitosan 3,6-bis(4-methylphenylcarbamate)-2-(isobutylurea) with higher molecular weight and chitosan 3,6-bis(3-chloro-4-methylphenylcarbamate)-2-(isobutylurea) with lower molecular weight possessed outstanding chiral recognition abilities which were at least as good as that of the commercialized CSP of Chiralcel OD-H towards the tested chiral analytes. Except for the two CSPs derived from chitosan 3,6-bis(4-methylphenylcarbamate)-2-(isobutylurea)s, the CSPs (the first class) with the chiral selectors of lower molecular weight provided better enantioseparations than the ones (the second class) with the chiral selectors of higher molecular weight. On the other hand, the chiral selectors of the first class CSPs showed higher swelling capacities in organic solvents than the ones of the second class. All prepared CSPs could be analyzed with a wider range of mobile phases, in which some "unusual organic solvents" such as ethyl acetate, chloroform and THF etc. could be used as additives. According to separation performance and tolerance against organic solvents, we concluded that the chitosan derivatives with branched-chain alkyl urea at 2-C of glucosamine residue were preferable to be used as chiral selectors for enantiomeric separation.