General Scope for Enzymatic Tools in Engineering of Polysaccharide Materials

Figure 2.4 Hydrolase-catalyzed polymerization of glycosyl fluorides to synthetic cellulose (a), amylose (b), and xylan (c). In vitro synthesis of chitin was first reported by utilizing chitinase

as a catalyst [26]. The chitinase-catalyzed enzymatic polymerization of a N,N’-diacetylchitobiose oxazoline monomer proceeded via ring-opening polyaddition under weak alkaline conditions, giving a synthetic chitin (Fig. 2.5a). The process of the higher ordered self-assembly of the synthetic chitin during the enzymatic polymerization was directly observed by phase-contrast and polarization microscopes with SEM and TEM [27]. Hyaluronidase has shown a wide spectrum of catalysis for the ring-opening polyaddition of a variety of sugar oxazoline monomers, controlling stereochemistry and regioselectivity perfectly to provide many natural and nonnatural glycosaminoglycans [19]. For example, hyaluronan, which is a linear polysaccharide having a repeating unit of β-(13)-GlcNAc-β-(14)- GlcA (GlcA, glucuronic acid) was produced by the hyaluronidasecatalyzed polymerization of a GlcA-β-(13)-GlcNAc oxazoline monomer (Fig. 2.5b) [28]. Chondroitin, other glycosaminoglycan, whose structure difference from hyaluronan is the difference in stereochemistry of C-4 in hexosamine unit. Therefore, GlcA-β-(13)- GalNAc oxazoline monomer (GalNAc, N-acetyl-d-galactosamine) was designed for the synthesis of chondroitin via the hyaluronidasecatalyzed ring-opening polyaddition (Fig. 2.5c) [29].