Intersaccharide

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. 

Another, industrially relevant foUow-up reaction of isomaltulose comprises its ready conversion into 5-(a-D-glucosyloxymethyl)-furfural ( a-GMF ) by acidic dehydration of its fructose portion under conditions (acidic resin in DMSO, 120°C ) that retain the intersaccharidic linkage (Scheme 2.17). As this process can also be performed in a continuous-flow reactor,a most versatile building block is available from sucrose in two steps, of which the first is already industrially realized, and the second simple enough to be performed on a large scale. 

Figure 5. Intersaccharide hydrogen bonds (dotted lines) and the glycosidic angle 0 (05-01-04 -04 ) between site A and B. These hydrogen bonds and 0 (= -86 ) are similar to those found for cellulose.

H. Kunz and C. Unverzagt, Protecting group-dependent stability of intersaccharide bonds— synthesis of a fucosyl-chitobiose glycopeptide, Angew. Chem. lnt. Ed. Engl. 27 1697 (1988). 

Kunz, H. and Unverzagt, C. (1988) Protecting-group-dependant stability of intersaccharide bonds-Synthesis of a fucosyl-chitobiose glycopeptide. Angew. Chem. Int. Ed. 27, 1697-1699. 

Polysaccharides. The most important member of this class of polysaccharides is alginate, a polysaccharide produced by seaweed and bacteria and widely used in the food industry. It is biosynthesised initially as a p-(1 4)-linked poly-mannuronic acid, by sequential transfer from GDP mannuronate. Some of the individual mannuronate residues are then epimerised at C5 to yield a-L-guluronate residues. The conformation of these guluronate residues is disfavoured by the axial OH on C2, the anomeric effect at Cl and above all by the now-axial carboxylate at C5 the C4 conformation, with the intersaccharide linkages now 1,4-diaxial, is adopted by the guluronate residues. 

CD provides a powerful mean to determine the intersaccharide linkages in di- and trisaccharides. Voelter et al. (46,47) demonstrated that 6-0-pyranosyl sugars can be differentiated from 4-O-pyranosyl sugars by CD. The essential requirement for di- and trisaccharides to show Cotton effects is the same as for monosaccharides, namely that complex formation requires free hydroxyl groups at C-1, C-2 and C-3. However, although lactose(26), cello-biose(27), maltose(28) and maltotriose(29) possess free hydroxyl... 

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