Precise 13c Nmr Quantification Method for Selective Acylation of Chitosan Oligomers Using Various Cyclic Anhydrides

The chemistry of chitosan is a promising way to afford biobased and biodegradable complex materials using highly reactive compounds such as anhydrides. However, the potential applications are limited due to the absence of control over the acylation and the lack of precise characterization. After model study on glucosamine, a selective acylation method of amines or alcohols of chitosan oligomers using anhydrides has been developed. The N-acylation of COS has been achieved using several anhydrides and the O-acylation has been realized in three steps: (1) Amine protection using p-anisaldehyde (2) O-acylation (with four anhydrides), and (3) Amine deprotection by removing the protective anisyl groups. Functionalized COS have been characterized by a precise quantification method using 13C Nuclear Magnetic Resonance (NMR) spectroscopy. The resulting degrees of substitution show in most of the case a stochiometric reaction between anhydrides and amines of COS, and around 70% of efficiency for O-acylation, proving the promising potential of such modifications. To the best of our knowledge, we describe here the first example of selective acylation of COS using anhydrides, and most of all the first example of 13C quantitative NMR spectroscopy performed on COS and its derivatives.