Influence of microstructure at 2-position of chitosan derivatives on enantioseparation

In order to study the influence of minor variation of the substituent at 2-position of chitosan derivatives upon enantioseparation of corresponding chiral stationary phases (CSPs), a series of chitosan 3,6-bis(phenylcarbamate)-2-(benzamide) were synthesized. The CSPs (Bz-type CSPs) were prepared with the chitosan derivatives. The π-π interactions of the phenyl group (Ph) at the 2-position and aryl group in analytes were confirmed. The enantioseparations of the CSPs in this study and the ones (cHF-type CSPs) prepared with chitosan 3,5-bis(phenylcarbamate)-2-(cyclohexylformamide)s were compared. In each type of the CSPs, chlorosubstituted CSPs demonstrated better enantioseparations than methylsubstituted ones and moreover, cHF-type CSPs exhibited higher chiral recognition capability than the Bz-type ones, when the number and position of the chloro and methyl groups were the same. Based on the enantioseparation results and circular dichroism spectra, the Ph at 2-position was not found to be superior to the cyclohexyl group at the same position, in enantioseparation. In addition, the suprastructure of cHF-type derivatives with a cyclohexyl group at 2-position should be more regular than that of Bz-type derivatives with a Ph at the same position. These observations seemingly were contrary to the conventional idea. • Biphenylcarbamates of N -benzoyl (Bz) or N -cyclohexylformyl (cHF) chitosan were shown. • Cl-substituted derivatives were better than Me-substituted ones in enantioseparation. • cHF-type chiral stationary phases (CSPs) had better performance than Bz-type ones. • π-π interactions at C 2 were confirmed to occur between analytes and CSPs. • The interactions did not improve suprastructural regularity and enantioseparation.