Controlled functionalization of the polysaccharide chitin

In view of rapidly growing interest in the amino polysaccharide chitin as a functional biopolymer, a recent progress of basic and application studies in chitin chemistry is reviewed as well as some basic aspects of this specialty biomass resource. A special emphasis is placed on the controlled modification reactions to prepare chitin derivatives with well-defined structures and thereby to construct sophisticated molecular architecture having various advanced functions. The reactions discussed here include hydrolysis of main chain, deacetylation, acylation, N-phthaloylation of chitosan, tosylation, alkylation, Schiff base formation, reductive alkylation, O-carboxymethylation, N-carboxyalkylation, silylation, and graft copolymerization. For conducting modification reactions in a facile and controlled manner, some soluble chitin derivatives are convenient. Of soluble precursors reported, N-phthaloyl-chitosan has proved particularly useful and made possible series of regioselective and quantitative substitutions thus far difficult. One of the important achievements based on this organosoluble precursor is the synthesis of nonnatural branched polysaccharides that have sugar branches at a specific site of the linear chitin or chitosan backbone. (C) 2001 Elsevier Science Ltd. All rights reserved.