N-phthaloylated chitosan as an essential precursor for controlled chemical modifications of chitosan: Synthesis and evaluation

Abstract

In view of the importance of phthaloylated chitosan as a key intermediate that allows controlled modification reactions of chitosan, phthaloylation of chitosan was studied in detail to elucidate the substitution behavior and to establish a reliable method for preparing structurally well-defined N-phthaloyl-chitosan. The reaction of chitosan with phthalic anhydride in N,N-dimethylformamide resulted in N,O-phthaloylation, and the O-phthaloyl groups had to be removed through tritylation-detritylation, hydrolysis, or alcoholysis to afford N-phthaloyl-chitosan. In the presence of some water, however, perfect discrimination of the functional groups became possible, and selectively and quantitatively N-phthaloylated chitosan could be synthesized in a simple one-step reaction. The resulting N-phthaloyl-chitosan exhibited higher reactivity than N,O-phthaloylated chitosan as confirmed by tritylation and is promising as a precursor for C-6 substitution. © 2007 The Society of Polymer Science.