Uronic acids degradation

Uronic acid degradation of the fully methylated Klebsiella type 47 capsular polysaccharide120 results in a partially methylated polysaccharide having a disaccharide repeating-unit (see Section IV,2, p. 218), in which the hydroxyl groups at C-3 in the L-rhamnose residues are free. Oxidation with ruthenium tetraoxide consequently gave the product 82, which, on treatment with base, followed by... 

Further examples of modified Smith degradation, in which the polyalcohol is methylated prior to hydrolysis under mild conditions, uronic acid degradation, and /3-elimination preceded by oxidation have been reported in connection with structural studies on the Klebsiella type 28 (Ref. 182), 57 (Ref. 183), 59 (Ref. 142), and 81 (Ref. 184) capsular polysaccharides. 

Much of the chemistry of monosaccharides is the familiar chemistry of alcohols and aldehydes/ketones. Thus, the hydroxyl groups of carbohydrates form esters and ethers. The carbonyl group of a monosaccharide can be reduced with NaBH4 to form an alditol, oxidized with aqueous Br2 to form an aldonic acid, oxidized with HNO3 to form an aldaric acid, oxidized enzymatically to form a uronic acid, or treated with an alcohol in the presence of acid to form a glycoside. Monosaccharides can also be chain-lengthened by the multistep Kiliani-Fischer synthesis and can be chain-shortened by the Wohl degradation. 

The first paper on the bioactive polysaccharides from Glycyrrhiza uralensis roots was published in 1996 by Kiyohara et al. [57]. They isolated a pectic type polymer with anti-complementary and mitogenic activity that was an acidic pectin, possibly containing rhamnogalacturonan type I as part of the total structure. Degradation of the uronic acid part of the molecule decreased both types of bio activities. The neutral oligosaccharide chains were shown to retain some of the activities of the native polymer, but it was suggested that they should be attached to the acidic core to retain maximum activity. 

Figure 2 - Size-exclusion chromatography on Sephacryl S200 of MHR population A after degradation with RGase ------------, uronic acids —, neutral sugars [39].

Honda and coworkers used 4 M hydrochloric acid for 6 h at 100° for the hydrolysis of nondialyzable glycoconjugates when determining amino monosaccharides, but preferred 2 M CF3CO2H for 6 h at 100° when determining the neutral monosaccharides and uronic acids, as these compounds are subject to more-severe degradation by 4 M hydrochloric acid. They obtained complete hydrolysis (with >90% recovery of monosaccharides added prior to hydrolysis) by using these two sets of hydrolytic conditions. 

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