Preparation of highly regioselective amphiprotic chitosan derivative via "click chemistry".

Synthesis of a highly regioselective amphiprotic chitosan derivative was achieved by click chemistry. The Huisgen cycloaddition between 6-azido-6-deoxy-N-pthaloyl-chitosan and methyl propiolate was successfully carried out in the presence of Cu(I) catalyst. After the reaction, both the phthaloyl protecting group and methyl group were completely removed by hydrazine. FT-IR and NMR spectroscopy as well as elemental analysis strongly support the structural uniformity of the desired amphiprotic chitosan derivative, which has both a carboxylic group with a 1,4-triazole linker at the C-6 position and an amino group at the C-2 position per repeating unit. The amphiprotic chitosan derivative was soluble under both acidic and basic aqueous conditions. In contrast, it formed nanoparticle under neutral condition due to the interaction between the positive (-NH(3)(+)) and negative (-COO(-)) ions on the chitosan derivative.