Polysaccharide and Glycoconjugate Structure

Cellobiose repeating unit of cellulose D-Glucose joined in p-1,4-linkages 

Maltose repeating unit of starch (amylose) D-Glucose joined in a-1,4-linkages 

Similarly, ketose sugars participate in polysaccharide formation by reaction of their ano-meric carbon with a hydroxyl of another monosaccharide to create a ketal linkage. The acetal and ketal bonds within polysaccharides are termed o-glycosidic linkages. 

Hemiacetal hydroxyl groups of carbohydrate molecules also may be coupled to amine-containing molecules to form N-glycosidic linkages, such as those in nucleic acids and oligonucleotides. 

Polysaccharide synthesis is under enzymatic control, but does not occur from a template as in protein synthesis. For this reason, each molecule of a particular polysaccharide will have its own unique molecular weight. The molecular weight of a carbohydrate polymer is usually expressed as an average. Starch or cellulose chains, for example, may vary by several hundred thousand in their molecular weights between individual molecules. For an excellent review of carbohydrate chemistry, see Binkley (1988). 

Polysaccharide synthesis is under enzymatic control, but does not occur from a 

Polysaccharide solubility in aqueous solutions usually is dependent on polymer size and its allied three-dimensional structure. Even water-insoluble carbohydrates may be solubilized by controlled hydrolysis of O-glycosidic linkages to create smaller polysaccharide molecules Thus, cellulose may be solubilized by heating in an alkaline solution until the polymers are broken up sufficiently to reduce their average molecular weight. Many such soluble forms of common polysaccharides are available commercially. 

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A more recent international journal. Journal of Carbohydrate Chemistry, was introduced in 1982. It requires camera-ready copy and is devoted primarily to the organic and physical chemistry of carbohydrates, such as novel synthetic methods mechanisms involved in carbohydrate reactions uses of carbohydrates in the synthesis of natural products, drugs, and antibiotics use of carbohydrates as synthetic reagents separation methods as applied to carbohydrate reactions and synthesis spectroscopic and crystallographic structure studies of carbohydrates molecular modeling studies and the chemistry of carbohydrate polymers, oligosaccharides, polysaccharides, and glycoconjugates. 

The elucidation of the structure of polysaccharides and of the carbohydrate portion of glycoconjugates involves sugar analysis, linkage analysis, and the determination of anomeric configurations and the sequences of the sugar residues. When non-sugar substituents are present, these should also be identified and located. 

The direct introduction of active groups on the polysaccharide and the protein could seriously affect the efficiency of the coupling by steric hindrance [114]. By direct attachment, the saccharide epitopes could be shielded by the secondary structure of the protein. To avoid this problem, a spacer arm is frequently introduced either on the modified CPS or on the protein carrier during the design of a glycoconjugate. The conjugates represented in Scheme 4 have been shown to be highly stable. They contained aliphatic amines [115], amides [116,117], or thioethers [118]. 

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