Preparation of a C₆ quaternary ammonium chitosan derivative through a chitosan schiff base with click chemistry

In this study, we explored a new method for preparing C₆ quaternary ammonium chitosan (CTS) derivatives. The C₂-NH₂ of CTS was first protected by benzaldehyde. The C₆-OH of CTS was then transformed into a sulfonyl ester, which was then reacted with NaN ₃ through nucleophilic substitution to introduce the -N₃ group at the CTS C₆ position. This intermediate was reacted in a click chemistry reaction with a terminal alkynyl quaternary ammonium salt; this was followed by the deprotection of C₂-NH₂ with acid to furnish the C₆ quaternary ammonium CTS derivative. The structures and properties of synthesized products in the reactions were characterized by Fourier transform infrared spectroscopy, NMR, X-ray diffraction, and thermogravimetric analysis, respectively. The effects of the reaction conditions on the degree of Schiff-base CTS quaternization were evaluated by elemental analysis. The largest inhibition zone test and the minimum inhibitory concentration test showed that compared with CTS, the prepared CTS derivative had significantly improved antibacterial activity toward Staphylococcus aureus and Escherichia coli.