CHEMOSPECIFIC MANIPULATIONS OF A RIGID POLYSACCHARIDE - SYNTHESES OF NOVEL CHITOSAN DERIVATIVES WITH EXCELLENT SOLUBILITY IN COMMON ORGANIC-SOLVENTS BY REGIOSELECTIVE CHEMICAL MODIFICATIONS

Efficient procedures for the preparations of soluble chitosan derivatives have been established on the basis of the regioselective chemical modifications. Selective and quantitative N-phthaloylation of chitosan proceeds smoothly by the reaction of chitosan with phthalic anhydride in N,N-dimethylformamide (DMF) at 130-degrees-C. The resulting phthaloylchitosan exhibits much improved solubility in common organic solvents such as DMF, N,N-dimethylacetamide, dimethyl sulfoxide, and pyridine. The enhanced solubility of new types of chitosan derivatives under homogeneous reaction conditions. Facile conversions of phthaloylchitosan, a key starting material, into several 6-O-substituted derivatives are carried out by the reactions with bulky substituents such as triphenylmethyl (trityl) and (p-tolysulfonyl)oxy (tosyloxy) groups. These reactions also proceed in homogeneous solution under mild conditions, and the degrees of substitution are estimated to be 1.0. Subsequent 3-O-acetylation of the secondary hydroxyl groups of 6-O-substituted materials gives rise to regioselectively modified chitosan derivatives showing much better solubility. Specific N-dephthaloylation or O-detritylation of 6-O-trityl derivatives affords versatile intermediates, which permit the introduction of additional functional groups regioselectively.