Chitosan-Oxanorbornadiene: A Convenient Chitosan Derivative for Click Chemistry without Metal Catalyst Problem

Click chemistry is considered to be a good pathway to conjugate chitosan with functional molecules due to the ease of the reaction at room temperature. However, as chitosan forms a complex with metal ions, there is a problem with the existence of metal ions in the derivative. The present work demonstrates that chitosan-oxanorbornadiene can provide metal-free Click by showing the optimal condition to introduce oxanorbornadiene, with 80% substitution, and clarifies model reactions of chitosan with azido-modified substrates for the ligation of bioactive molecules.