Selective acylation of chitosan oligomers by several cyclic anhydrides as a 13C NMR quantification method

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 a model study on glucosamine, a selective acylation method of amines or alcohols of chitosan oligomers using anhydrides has been developed. The N-acylation of chitooligosaccharides has been achieved using several anhydrides and the O-acylation has been achieved 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 chitooligosaccharides have been characterized by a precise quantification method using 13C nuclear magnetic resonance spectroscopy. The resulting degrees of substitution show in most of the cases a stochiometric reaction between anhydrides and amines of chitooligosaccharides, 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 chitooligosaccharides using anhydrides, and most of all the first example of 13C quantitative NMR spectroscopy performed on chitooligosaccharides and its derivatives. These innovative structures are the gateway to the creation of new biosourced and/or biodegradable surfactants.