Enzymatic polymerization to novel polysaccharides having a glucose-N-acetylglucosamine repeating unit, a cellulose - Chitin hybrid polysaccharide

A cellulose-chitin hybrid polysaccharide having alternatingly β(1→4)-linked D-glucose (Glc) and N-acetyl-D-glucosamine (GlcNAc) was synthesized via two modes of enzymatic polymerization. First, a sugar oxazoline monomer of Glcβ(1→4)GlcNAc (1) was designed as a transition-state analogue substrate (TSAS) monomer for chitinase catalysis. Monomer 1 was recognized by chitinase from Bacillus sp., giving rise to a cellulose-chitin hybrid polysaccharide (2) via ring-opening polyaddition with perfect regioselectivity and stereochemistry. Molecular weight (M_n) of 2 reached 4030, which corresponds to 22 saccharide units. Second, a sugar fluoride monomer of GlcNAcβ(1→4)Glc (3) was synthesized for the catalysis of cellulase from Trichoderma viride. The enzyme catalyzed polycondensation of 3, providing a cellulose-chitin hybrid polysaccharide (4) in regio- and stereoselective manner. M_n of 4 reached 2840, which corresponds to 16 saccharide units. X-ray diffraction measurements revealed that these hybrid polysaccharides did not form any characteristic crystalline structures. Furthermore, these unnatural hybrids of 2 and 4 were successfully digested by lysozyme from human neutrophils.