Ring structures polysaccharides

In 1947, L-rhamnose was first recognized by Stacey as a constituent of Pneumococcus Type II specific polysaccharide. This finding was confirmed, in 1952, by Kabat et al. and in 1955 again by Stacey when 2,4- and 2,5-di-O-methyl-L-rhamnose were synthesized and the former was shown to be identical with a di-O-methylrhamnose, obtained by hydrolysis of the methylated polysaccharide. This result indicated a pyranose ring structure for the rhamnose units in the polysaccharide. Announcement of the identification of D-arabinofuranose as a constituent of a polysaccharide from M. tuberculosis aroused considerable interest. The L-enantiomer had been found extensively in polysaccharides, but reports of the natural occurrence of D-arabinose had been comparatively rare. To have available reference compounds for comparison with degradation products of polysaccharides, syntheses of derivatives (particularly methyl ethers) of both d- and L-arabinose were reported in 1947. 

Monomers and polymers of carbohydrates, (a) The most common carbohydrates are the simple six-carbon (hexose) and five-carbon (pentose) sugars. In aqueous solution, these sugar monomers form ring structures, (b) Polysaccharides are usually composed of hexose monosaccharides covalently linked together by glycosidic bonds to form long straight-chain or branched-chain structures. 

See also Sugar Ring Structures, Derivatives of Monosaccharides, Oligosaccharides, Polysaccharides, Anomers, Ouabain, Amygdalin, Mutarotation... 

The ring structure results from the helical segments of the polysaccharide. 

This type of polysaccharide may be prepared from anhydro disaccharides. Polymerization reactivity of anhydro disaccharide derivatives, however, is lower than that of the corresponding anhydro monosaccharide derivatives. In order to obtain comb-shaped polysaccharides of moderate molecular weight, highly reactive disaccharide anhydrides are required. Hence we gave attention to a dideoxygenated anhydro-ring structure. 

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