Oligosaccharide configurations

Fig. 1. Proposed ortho-ester configuration for ring C of the oligosaccharide antibiotics.

The c.d. spectra are also available for a few oligosaccharides that contain N-acetylneuraminic acid. " These spectra depend on the intersaccharide linkages and the state of ionization of the carboxyl group, but no systematic scheme has yet been set up to derive configurational information from the c.d. spectra. Of particular interest is the c.d. spectrum of beef ganglioside, which fully differentiates the amide mr, amide tttt, and carboxylate nir c.d. bands. 

This structure was confirmed, and the configurations of all the linkages were determined, in complementary studies.56 Periodate oxida-tion-borohydride reduction of deacetylated S34, followed by dephosphorylation, produced a pentasaccharide (37) in which the L-arabinofuranose and glycerol moieties derive from D-galactofuranosyl and ribitol residues, respectively. Oligosaccharide 37... 

It is noteworthy that D-fructose, which has a pyranose structure in the free crystalline state, assumes a furanose configuration whenever it combines with another sugar to form an oligosaccharide or polysaccharide. Apparently the ketohexose L-sorbose shows the same behavior. 

Hodosi, G. Kovac, P., Glycosylation via locked anomeric configuration stereospecific synthesis of oligosaccharides containing the beta-D-mannopyranosyl and beta-L-rhamnopyranosyl linkage. Carbohydr. Res. 1998, 308, 63-75. 

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