Block Copolysaccharides from Methylated and Acetylated Cellulose and Starch.

Abstract

All-glucose block copolysaccharides with alternated α- and β-configured blocks do not exist in nature. Such polysaccharides, and materials made thereof, might exhibit very interesting properties due to the different supramolecular structures of the two α- and β-configured blocks. This would be helical for starch and linear for cellulose in the case of a non-derivatized all-glucose polysaccharide. We propose a synthetic pathway for the preparation of methylated and acetylated building blocks of cellulose and amylose for the regioselective modification at the non-reducing and reducing end to act as glycosyl acceptors and donors, respectively. The glycosyl acceptors with the opposite α- or β-configured blocks were prepared by acid-catalyzed methanolysis of permethylated amylose as well as cellulose. The regioselectively modified glycosyl donors and acceptors were successfully used in the preparation of block copolysaccharides with an α(1 → 4)-configured and a β(1 → 4)-configured oligo- or polysaccharide block, respectively.