Polysaccharides stereoregular, synthesis

Synthesis of natural-type aminopolysaccharide having dibenzylchitin structure was achieved by the polymerization of a sugar oxazoline monomer, 1 having one hydroxy group at position 4 (Scheme 4) [9]. The polymerization was carried out with an acid catalyst in 1,2-dichloroethane solvent at reflux temperature. All the H-NMR, C-NMR, and IR spectra as well as elemental analysis data of the isolated polysaccharide supported that the polymerization proceeded by the stereoregular glycosylation to give (1 4)-... 

N. K. Kochetkov, N. N. Malysheva, E. M. Klimov, and A. V. Demchenko, Synthesis of polysaccharides with 1,2-c -glycosidic linkages by tritylthiocyanate polycondensation. Stereoregular a-(l-6)-D-glucan, Tetrahedron Lett., 33 (1992) 381-384. 

Nowadays, anhydro sugars constitute very versatile starting materials not only in carbohydrate chemistry but also for the synthesis of noncarbohydrate and nonnatural compounds. In the past two decades, interest in anhydro sugars has increased because they have been shown to be suitable monomers for preparing stereoregular polysaccharides and their specifically substituted derivatives. 

K. Kobayashi, K. Nomura, and M. Okada, Chemical synthesis of a comb-shaped, branched stereoregular polysaccharide, 4-0-a-D-mannopyranosyl-( 1 - 6)-a-D-manno-pyranan, Carbohydr. Res., 242 (1993) 161-166. 

T. Uryu, Y. Sakamoto, K. Hatanaka, and K. Matsuzaki, Chemical synthesis of a new polysaccharide ring-opening polymerization of l,6-anhydro-2,3,4-tn-0-benzyl-/S-D-allo-pyranose and preparation of stereoregular (1 - 6)-a-D-allopyranan, Macromolecules, 17 (1984) 1307-1312. 

T. Uryu, K. Hatanaka, K. Matsuzaki, and H. Kuzuhara, Synthesis of stereoregular polysaccharides having amino-groups by ring-opening copolymerization of 1,6-anhydro-azido-sugar derivatives, J. Polym. Sci., Part A Polym. Chem., 21 (1983) 2203-2214. 

In the carbohydrate area, two important uses of the reagent have appeared one uses NBS-MesSiOTf as the promoter for the glycosidic bond formation and simultaneous bromination of an activated aryl aglycon. In the second, the synthesis of branched polysaccharides by polymerization of 6-0-f-butyldimethylsilyl-D-glucal through stereoregular bromoglycosylation was achieved by the use of NBS. 

Understanding the structure-function relations is important to applying polysaccharides more extensively. Synthesis of structurally well-defined polysaccharides, coupled with elucidation of their properties, is indispensable for these purposes. We have been interested in regiospeci-fically modified, stereoregular polysaccharides. We believe that new types of polysaccharides with novel properties will be developed through these processes. 

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