Chitin enzymatic polymerization

Keywords Cellulose Chitin Enzymatic polymerization Glycosaminoglycan Polysaccharide... 

The polymerization of 1 mentioned above should be compared with the enzymatic synthesis of chitin reported by Kobayashi and coworkers, in which an oxazoline derivative of A, A -diacetylchitobiose, the repeating unit of chitin was polymerized in the presence of chitinase enzyme via ring-opening addition process to give an artihcial chitin (Scheme 6) [5]. The method using an enzyme, however, may not enable synthesis of nonnatural-type aminopolysaccharide because the reaction catalyzed by chitinase enzyme is limited to the formation of (1 4)-P-glycosidic linkage. 

Chitin is the most abundant biomacromolecule in the animal field, which is found normally in invertebrates as a structural component. This important polysaccharide was synthesized for the first time by the enzymatic polymerization using chitinase and a chitobiose oxazoline derivative (Scheme 14).131 The latter activated monomer has a distorted structure with an a configuration at Cl, which resembles a transition-state structure of substrate chitin at the active site during a hydrolysis process (Scheme 15).3b 131132 The ring-opening polyaddition of the chitobiose oxazoline derivative was exclusively promoted by chitinase at pH 10.6, where the hydrolytic activity of chitinase was very much lowered. 

Upon enzymatic polymerization to produce the artificial chitin, spherulites of 20—50 fim in diameter were also obtained (Figure 3).133 Platelike single crystals were gradually shaped into ribbons, followed by formation of bundlelike assemblies to grow into spherulites in the polymerization solution. 

Scheme 8 Enzymatic polymerizations to a cellulose-chitin hybrid polysaccharide.

Kobayashi et have also investigated other modes of enzymatic polymerization to produce a novel cellulose-chitin hybrid polysaccharide. A sugar fluoride monomer of GlcNAc/3(l 4)Glc (17) was designed as a TSAS monomer for polymerization catalyzed by cellulase from Trichoderma viride. In the polymerization, monomer 17 was recognized by cellulase from T. viride, leading to a cellulose-chitin hybrid polysaccharide 18 with perfect regioselectivity and stereochemistry (Scheme 17). 

Sakamoto, J., Sugiyama, J., Kimura, S., Imai, T., Itoh, T., Watanabe, T., Kobayashi, S. Artificial Chitin Spherulites Composed of Single Crystalline Ribbons of alpha-Chitin via Enzymatic Polymerization. Macromolecules. 33, 4155-4160 (2000)... 

Kobyashi S., Makino A., Matsumoto H., Kunii S., Ohmae M., Kiyosada T., Makiguchi K., Matsumoto A., Horie M., Shoda S.I., Enzymatic polymerization to novel polysaccharides having a glucose-JV-acetylglucosamine repeating unit, a ceUulose-chitin hybrid polysaccharide. Biomacromolecules, 7, 2006,1644-1656. 

A very active research is lead by the Kobayashi group in Japan in a recent review, cellulose, chitin, and xylan syntheses were described using Enzymatic Polymerization (qv) (322). 

We have achieved the synthesis of structurally well-defined natural and unnatural oligo- and polysaccharides via enzymatic polymerization utilizing natural glycosyl hydrolases as catalysts (26-57) cellulose and xylan prepared by cellulase (52-54), an amylose oligomer by amylase (55), chitin by chitinase (56, 57), altematingly 6-(9-methylated cellulose by cellulase (55), and a cellulose-... 

Fig. 16 Hierarchy structures in vitro formed by synthetic chitin via enzymatic polymerization...

For the polysaccharide synthesis, enzymatic polymerization has been developed as a new in vitro synthesis method of natural and unnatural polysaccharides having complicated structures.The method utilizes a hydrolysis enzyme to catalyze the bond formation for the polymer construction, a reverse direction of the hydrolysis to cleave the bond. This catalysis is due to the enzymatic characteristics, where enzymes catalyze the reverse reaction involving a common intermediate in both forward and backward reactions. In nature, there are many polysaccharides having N-acetyl groups called mucopolysaccharides such as chitin, hyaluronic acid (HA), and chondroitin (Ch). 

Sakamoto J, Sugiyama J, Kimuia S, Imai T, Itoh T, Watanabe T, Kobayashi S (2(X)0) Artificial chitin spherulites composed of single crystalline ribbons of a-chitin via enzymatic polymerization. Mcromolecules 33 4155-4160... 

Synthetic approaches for these materials are shown in Scheme 13. Introduction of maltoheptaose primer to chitosan by reductive amination was firstly carried out using NaBHaCN in a mixed solvent of aqueous acetic acid and methanol to produce maltoheptaose-grafted chitosan (39) [9]. The functionality of maltoheptaose to chitosan in 39 depended on reaction time. Maltoheptaose-grafted chitin (40) was synthesized by A-acetylation of 39 using acetic anhydride in a mixed solvent of aqueous acetic acid and methanol. Phosphorylase-catalyzed enzymatic polymerization of G-l-P from maltoheptaose in 39 and 40 was then performed to obtain amylose-grafted chitosan (41) and chitin (42), respectively. 

The enzymatic hydrolysis of chitin and chitosan might occur because of the action of chitinases, chitosanases, lysozymes, and cellulases (Shahidi et al., 1999). The products of chitin hydrolysis are of high degree of polymerization... 

Chitin is the most abimdant organic macromolecules in the animal field found in invertebrates (12). The in vitro ssmthesis of this important biomacromolecule has been achieved for the first time by enzymatic ring-opening polyaddition of a chitobiose oxazoline monomer (Fig. 3). Chitinase, a hydrolysis enzyme of chitin, regio- and stereoselectively induced the polymerization of the monomer in a basic buffer (38—41). It is postulated that the monomer is preferable as a... 

---