Nonnatural Branched Polysaccharides:  Synthesis and Properties of Chitin and Chitosan Having α-Mannoside Branches

Abstract

Regioselective introduction of alpha-mannoside branches at C-6 of chitin and chitosan has been accomplished by a series of regioselective modification reactions starting from N-phthaloyl-chitosan as a key precursor. Glycosylation of the derived acceptor with reactive groups only at C-6 with an ortho ester of d-mannose proceeded smoothly in dichloromethane in the presence of trimethylsilyl trifluoromethanesulfonate, and the degree of branching was up to 0.6. Full deprotection gave chitosans with alpha-mannoside branches, which were subsequently transformed into the corresponding branched chitins by N-acetylation. The resulting branched polysaccharides showed a remarkable solubility in neutral water in sharp contrast to the insoluble linear chitin and chitosan. Concanavalin A exhibited a specific affinity for these products, which was ascribable to the presence of alpha-mannoside groups. Though nonnatural, the branched chitins were susceptible to lysozyme, and the enzymatic degradation was heavily dependent on the extent of branching. Furthermore, the branched chitosan exhibited considerable antimicrobial activity.

Nanoparticles and whiskers-based chitosan films for Cr complexation

“…When the degree of deacetylation reaches higher than 50 %, chitosan becomes soluble in acidic aqueous solutions and it behaves as a cationic polyelectrolyte. Chemical modification of chitosan is a means that can be used to improve water solubility (Kurita et al 1998). As a consequence, the use of chitosan in the form of a colloidal suspension is an attractive choice, since chitosan still retains its solid nanocrystalline state so as to avoid the use of an expensive solvent.…”

Development of an Amphiphilic Chitin Derivative with Lipid/Peptide-Type Side Chains Having Skin Protective Ability

“…[10][11][12][13][14][15] Various modifications of chitin and chitosan have been investigated for their practical applicability and in light of the intractable bulk structure of chitin. [16][17][18] Water-soluble chitin (WSC), which is 50% randomly deacetylated, is known to be soluble in water at room temperature. 19 WSC has a novel crystal structure that lacks the highly ordered crystalline structure of raw a-chitin formed by hydrogen bonds between hydroxyl groups and amide groups in the repeating unit.…”

Quantitative protection of chitin by one-step tritylation and benzylation to synthesize precursors for chemical modifications

“…As protective and solubilizing groups, trimethylsilyl [11][12][13] and phthaloyl [14][15][16][17][18][19][20][21][22] are especially practical for chitin and chitosan to give derivatives with required molecular structures. For instance, sugar branches could be incorporated into chitin and chitosan through a series of site-specific reactions starting from 2-N-phthaloylchitosan; the resulting nonnatural branched chitins and chitosans were water-soluble and exhibited significant medicinal functions such as antimicrobial [16,17,19] and antitumor activities [22].…”

“…For instance, sugar branches could be incorporated into chitin and chitosan through a series of site-specific reactions starting from 2-N-phthaloylchitosan; the resulting nonnatural branched chitins and chitosans were water-soluble and exhibited significant medicinal functions such as antimicrobial [16,17,19] and antitumor activities [22].…”