Synthesis, characterization and biological activity of C6-Schiff bases derivatives of chitosan.

C6-Schiff bases derivatives of chitosan were synthesized for the first time. C2-amino groups and C3-hydroxy groups were firstly protected by CuSO4·5H2O, and the C6-hydroxy was then transformed into aldehyde, which then reacted with anilines through nucleophilic addition to introduce the CN group at C6-position in chitosan chain. Finally, C6-Schiff bases derivatives of chitosan were got by the deprotection of C2-NH2 with cation exchange resin. The structures and properties of the new synthesized products were characterized by Fourier transform infrared spectroscopy, 13C NMR, SEM image, and elemental analysis. The antibacterial activities of derivatives were tested in the experiment, and the results showed that the prepared chitosan derivatives had significantly improved antibacterial activity toward Staphylococcus aureus and Escherichia coli. The Cytotoxicity test showed that the prepared chitosan derivatives had low Cytotoxicity, compared with chitosan and C2-benzaldehyde Schiff bases of chitosan. This paper allowed a new method for the synthesis of Schiff bases of chitosan, which was enlightening.