Synthesis of Non‐natural Xyloglucans by Polycondensation of 4,6‐Dimethoxy‐1,3,5‐triazin‐2‐yl Oligosaccharide Monomers Catalyzed by Endo‐β‐1,4‐glucanase

Abstract

AbstractSummary: A cellotetraose‐backboned hepta‐saccharide (XXXG) (a capital X represents a glucopyranose residue that is substituted with a xylopyranose through an α‐1,6 glycosidic bond, and a capital G represents a non‐substituted glucopyranose residue) and a nona‐saccharide (XLLG) (a capital L represents a glucopyranose residue that is substituted with a galactopyranoseβ(1‐2)xylopyranose through an α‐1,6 glycosidic bond) have directly been converted to the corresponding 4,6‐dimethoxy‐1,3,5‐triazin‐2‐yl derivatives (DMT‐β‐XXXG 1 and DMT‐β‐XLLG 2, respectively) by the action of 4‐(4,6‐dimethoxy‐1,3,5‐triazin‐2‐yl)‐4‐methyl morpholinium chloride (DMT‐MM). The selective nucleophilic attack of the anomeric hydroxyl group to DMT‐MM has been achieved in water without using any protection of the hydroxyl groups. The resulting activated oligosaccharide derivatives (1 and 2) were found to polymerize catalyzed by an endo‐β‐1,4‐glucanase as catalyst. The polymerization took place in a complete regio‐ and stereo‐selective manner, affording non‐natural polysaccharides having a XXXG‐repeating unit and a XLLG‐repeating unit, respectively, in the main chain. It is extremely difficult to construct such definite repeating structures via the conventional synthetic routes including protection‐deprotection procedures.