Oligosaccharides linkage types

Cyclic oligosaccharides composed of a single type of residue can be named by giving the systematic name of the glycosyl residue, preceded by the linkage type in parentheses, preceded in turn by cyclo- with a multiplicative suffix (i.e. cyclohexakis- etc.)... 

Xylans as true homopolymers occur in seaweeds of the Palmariales and Nemaliales, however, their backbone consists of Xylp residues linked by -(1 3) (Type X3, Fig. la) or mixed -(1 3, 1 -> 4)-glycosidic linkages (Type Xmy Fig. lb). They are assumed mainly to have a structural function in the cell-wall architecture, but a reserve function cannot be ruled out [4]. From the microfibrils of green algae (Siphonales) such as Caulerpa and Bryop-sis sp., X3 was isolated and the structure confirmed by methylation analysis, C-NMR spectroscopy [7], as well as by mass spectrometry of enzymically released linear oligosaccharides up to a degree of polymerization (DP) of... 

The differences in the rates of hydrolysis of various linkage types by a particular glycosidase can be used to provide information about this aspect of structure. Jack-bean a-D-mannosidase cleaves a-(l- 2) and a-(l- 6) linkages much faster than a-(l -> 3). Oligosaccharides, obtained by endo-N-acetyl-/J-D-glucosaminidase hydrolysis of ovalbumin, were subjected to acetolysis, which selectively cleaved the a-(l - 6) bonds. A tetrasaccharide isolated after this treatment was then incubated with jack-bean o-d-... 

The sequence, bond geometry, and linkage type of monosaccharides in an oligosaccharide or polysac-... 

The structural complexity of oligosaccharides goes far beyond that of proteins and nucleotides [1-4], Because with nucleotides or amino acids only hnear chains with just one linkage type are formed, a tetramer of nucleotides or amino acids with four different monomeric subunits can have only 24 different stractures, while in excess of 10,000 different stractures are possible for a tetrasaccharide. The various stereochemical centres, the anomeric centre, the multiple linkage types, and the ability to form branched stractures all contribute to this structural diversity. 

The H-n.m.r. data of 20 oligosaccharides containing a-NeuAc linked (2->3) or (2->6) to a-E>-GajpNAc or P-D-Ga p residues in D2O have been carefully analyzed. It was found that the chemical shift of H-6 of the NeuAc residue is characterisatic for the linkage type."... 

Figure 17.1 Examples of important sialylated oligosaccharide structures illustrating the common linkage types found for natural sialo-conjugates-...

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