Polysaccharides cleavage

A. Polysaccharide Cleavage and Synthesis. B. Disaccharide, Hcxoside, and Glucuronide Metabolism. C. Metabolism of Hexoses. D. Metabolism of Pentoses. E. Metabolism of Three-Carbon Compounds. F. Reactions of Two-Carbon Compounds. G. Reactions of P ormate. 

To gain an insight into the likely hydrolytic behavior of sulfated simple sugars and polysaccharides, Brimacombe, Foster, Hancock, Overend, and Stacey carried out a rigorous set of experiments with the cyclic sulfates of cyclohexane cis-and trims-1,2-diol as model compounds. The results were interpreted on the reasonable assumption that, in all cases, the cyclic sulfates initially afford a diol monosulfate. Examples of both S-0 and C-0 bond cleavage were encountered. A qualitative reaction mechanism was proposed for use as a working hypothesis for the hydrolysis of sugar sulfates. 

The oxidative cleavage of v/c-diols to give two carbonyl functions (Eq. 5.3) by periodates was first observed by Malaprade and has since been widely applied to the carbohydrate area.50 Since both the reagent sodium periodate and the carbohydrate substrate are water soluble, the reaction is usually carried out in aqueous media.51 The reaction has been applied to polysaccharides such as starch.52 The periodate oxidations of sodium alginate in water as well as a dispersion in 1 1 ethanol-water mixture have been compared.53 Because sodium alginate forms a highly viscous solution, the oxidation was observed to be more extensive in ethanol-water. 

Extracts of Flavobacterium heparinum that had been induced to grow on heparin-like polysaccharides contain a number of enzymes that may ultimately degrade heparin and heparan sulfate to monosaccharides.137,145 240 The enzymes that cause the primary cleavage of heparinlike chains are heparinase (EC 4.2.2.7) and heparanase (EC 4.2.2.8, formerly called heparitinase241,242). 

Oxidation of polysaccharides using 10 mM or greater concentrations of sodium periodate at room temperature results in the cleavage of adjacent hydroxyl-containing carbon-carbon bonds on other sugars besides just sialic acid residues (Lotan et al., 1975). High concentrations... 

On treatment with periodatd ion, straw and beechwood xylan oxidize rapidly.104 As with other polysaccharides, the oxidation comes to a more definite end point in solutions which are buffered to pH 4-5. While somewhat more than the theoretical amount of periodate ion is consumed, the reaction apparently proceeds uniformly with oxidative cleavage of the 2,3 carbon bond to produce the structure indicated in Figure 4. In the course of the reaction the xylan passes into solution. The optical rotation of the oxidized product is surprisingly high (co. 100°). 

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