Enzymatic Polymerization to Novel Polysaccharides Having a Glucose-N-acetylglucosamine Repeating Unit,a Cellulose- Chitin Hybrid Polysaccharide

摘要

A cellulose-chitin hybrid polysaccharide having alternatingly beta(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 Glc beta(l->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 GlcNAc beta(l->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.