Hybrid polysaccharides

Applications of sol-gel-processed interphase catalysts. Chemical Reviews, 102, 3543-3578. Pierre, A.C. (2004) The sol-gel encapsulation of enzymes. Biocatalysis and Biotransformation, 22, 145-170. Shchipunov, Yu.A. (2003) Sol-gel derived biomaterials of silica and carrageenans. Journal of Colloid and Interface Science, 268, 68-76. Shchipunov Yu.A. and Karpenko T.Yu. (2004) Hybrid polysaccharide-silica nanocomposites prepared by the sol-gel technique. Langmuir, 20, 3882-3887. 

Shchipunov, Yu.A., Burtseva, Yu.V., Karpenko, T.Yu., Shevchenko, N.M. and Zvyagintseva, T.N. (2006) Highly efficient immobilization of endo-l,3-P-D-glucanases (laminarinases) from marine mollusks in novel hybrid polysaccharide silica nanocomposites with regulated composition. Journal of Molecular Catalysis B-Enzymatic, 40, 16-23. 

R. Takano, Y. Nose, K. Hayashi, S. Hara, and S. Hirase, Agarose-carrageenan hybrid polysaccharide from Lomentaria catenata, Phytochemistry, 37 (1994) 1615-1619. 

The examples reviewed in this chapter prove that enzymatic polymerizations using glycosyltransferases and glycosidases are powerful techniques for synthesizing various well-defined polysaccharides ranging from natural saccharides such as cellulose, amylose, amylopectin etc. to non-natural hybrid polysaccharides. 

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). 

Biocatalysis is a key route to both natural and non-natural polysaccharide structures. Research in this area is particularly rich and generally involves at least one of the following three synthetic approaches 1) isolated enzyme, 2) whole-cell, and 3) some combination of chemical and enzymatic catalysts (i.e. chemoenzymatic methods) (87-90). Two elegant examples that used cell-fi-ee enzymatic catalysts were described by Makino and Kobayashi (25) and van der Vlist and Loos (27). Indeed, for many years, Kobayashi has pioneered the use of glycosidic hydrolases as catalysts for polymerizations to prepare polysaccharides (88,91). In their paper, Makino and Kobayashi (25) made new monomers and synthesized unnatural hybrid polysaccharides with regio- and stereochemical-control. Van der Vlist and Loos (27) made use of tandem reactions catalyzed by two different enzymes in order to prepare branched amylose. One enzyme catalyzed the synthesis of linear structures (amylose) where the second enzyme introduced branches. In this way, artificial starch can be prepared with controlled quantities of branched regions. 

Synthesis of Unnatural Hybrid Polysaccharides via Enzymatic Polymerization... 

Figure 1. Synthes of hybrid polysaccharides via enzymatic polymerization.

After completion of the enzymatic reaction, a white precipitate was separated by centrifugation, and the supernatant was analyzed by MALDI-TOF/MS, and NMR measurements. From the MALDI-TOF/MS spectrum, the peaks appeared at every m z 365, corresponded to the molecular mass of the repeating disaccharide unit of 3. and NMR spectra supported that the resulting product is a cellulose-chitin hybrid polysaccharide. Furthermore, it has been proven by CP/MAS NMR spectrum that the white precipitate is also hybrid polysaccharide 3. 

Characterization data of the resulting cellulose-chitin hybrid polysaccharide 3 are summarized in Table 1. The average molecular wei t value (M ) of the resulting product 3 via cellulase- and chitinase catalyzed polymerization reached to 2840 and 4030, which correspond to 15-16 and 22 saccharide units, respectively. 

The target glycosidic linkages for the synthesis of a chitin-chitosan hybrid polysaccharide are (1—>4)-j8-D-glucosaminide and (1—>4)- 8-iV-acetyl-D-... 

The yields and Mn value of the resulting chitin-chitosan hybrid polysaccharides 8 under various reaction conditions were summarized in Table 2. The yields of 8 were around 60-75% and there were little significant differences in catalysis between these two enzymes except for the reaction time. However, A4 value of 8 reached 1600 and 2020 with using chitinases from Bacillus sp. and Serratia marcescens, respectively, which correspond to 8-10 (n = 4-5) and 10-12 (n = 5-6) saccharide units, respectively. These results Indicated that values of polysaccharides are controllable to some extent by selecting enzymes from different origins. 

Cellulose-Xylan Hybrid Polysaccharide (46) and Chitin-Xylan Hybrid Polysaccharide (47)... 

Here, compounds 10 and 13 were chemically synthesized as monomers for the synthesis of cellulose-xylan hybrid polysaccharide 11, and chitin-xylan hybrid polysaccharide 14, respectively (Figure 8). 

In order to polymerize a fluoride-type monomer 10, cellulase and xylanase were chosen for the catalyst. In an acetonitrile-acetate buffer mixed solution, the consumption of 10 was accelerated by the addition of xylanase from Trichoderma viride, giving rise to a white precipitate as the progress of the reaction in a 58% yield. From the analysis of the resulting products, it is a cellulose-xylan hybrid polysaccharide 11 and polymers with the degree of polymerization up to 12 (24 saccharide units) were detected from the MALDI-TOF/MS. 

Chitinase from Bacillus sp. was added to a solution of Xyl (l— 4)GlcNAc oxazoline 13 dissolved into a phosphate buffer. The consumption rate of 13 was accelerated by the enzyme addition and chitin-xylan hybrid polysaccharide 14 was produced. During the polymerization, the reaction proceeded homogenously throughout the reaction. The yield was 76% and its average molecular weight value of 14 was M = 1500 with MJMa = 1.76, determined by GPC. Furthermore, MALDI-TOF mass spectrum of 14 indicated the peaks at every m/z 335, which corresponds to the molecular mass of the repeating disaccharide unit. 

Figure 8. Chemical structures of cellulose-xylan hybrid polysaccharide 11 chitirHxylan hybrid polysaccharide 14 as well as designed monomers 10 and...

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