Monosaccharides uronic acids

Chromatographic separation of free nucleotides from various sources usually gives the glycosyl esters of uridine 5 -pyrophosphate in three fractions, containing fhe derivatives of neutral monosaccharides, uronic acids, and 2-acetamido-2-deoxyglycoses, respectively. 

Acids related to monosaccharides are also common for the formation of natural polysaccharides. There are three types of acids associated with monosaccharides aldonic acids generated by the oxidation of the aldehyde group of a monosaccharide, uronic acids generated by the replacement of the primary alcohol group of a monosaccharide by a carboxyl group, and saccharic acids generated by simultaneous oxidation and replacement. Aldonic acids have a marked tendency to eliminate water and form lactones. The structural formulas of two common hexuronic acids are... 

Neutral monosaccharides, uronic acids, hexosa-mines, and sialic (neurominic acids) are identified and determined by specific colorimetric reactions. The principle behind the techniques rests on the condensation of the degraded products of the neutral monosaccharides (hexose, pentose and methyl pentose) by sulfuric acid with anthrone, cysteine hydrochloride, orcinol, and phenol reagents. Uronic acids may be determined by colorimetric and manometric procedures. While sialic acids are determined after chemical/enzymatic hydrolysis, gravimetric and Van-Soest detergent based methods are used to determine cellulose, hemicellulose, and fiber. 

Uronic acids are monosaccharides in which the terminal primary alcohol group is oxidized to a carboxyhc acid functional group, eg, D-glucuronic acid [6556-12-3] (11). 

Monosaccharides can be oxidized enzymatically at C-6, yielding uronic acids, such as D-glucuronic and L-iduronic acids (Figure 7.10). L-Iduronic acid is similar to D-glucuronic acid, except for having an opposite configuration at C-5. Oxidation at both C-1 and C-6 produces aldaric acids, such as D-glucaric... 

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. 

Rha, Ara and Gal are the neutral sugar components from all the fractions. Xyl is not present in Fla and is significantly present in the hemicellulose fractions, indicating that this monosaccharide is component of hemicellulosic polymers. Chemical composition of the water fractions were determined (Table V). High protein contents and the presence of O-acetyl-groups were observed in four aqueous fractions. Neutral sugar and uronic acid composition points to inclusion of these polymers in the class of pectic polysaccharides. 

Dermatan sulfate, also termed chondroitin sulfate B, a related glycosaminoglycan constituent of connective tissue, was known to be composed of galactosamine and a uronic acid, originally believed to be glucuronic acid but then claimed to be iduronic acid based largely on color reactions and paper chromatography. However, the d or L-enantiomer status of the latter monosaccharide was not clear. Jeanloz and Stoffyn unequivocally characterized the monosaccharide as L-iduronic acid by consecutive desulfation, reduction, and hydrolysis of the polysaccharide, followed by isolation of the crystalline 2,3,4-tri-0-acetyl-l,6-anhydro-/ -L-idopyranose, which was shown to be identical to an authentic specimen synthesized from 1,2-0-isopropylidene-/ -L-idofuranose.34... 

There are three possible classes of sugar acids which may be produced by the oxidation of monosaccharides (Figure 9.11). The aldonic acids are produced from aldoses when the aldehyde group at carbon 1 is oxidised to a carboxylic acid. If, however, the aldehyde group remains intact and only a primary alcohol group (usually at carbon 6 in the case of hexoses) is oxidised then a uronic acid is formed. Both aldonic and uronic acids occur in nature as intermediates in... 

Methanolysis of standard uronic acids has been studied by Inoue and Miyawaki in regard to the depolymerization of chondroitin sulfate and dermatan sulfate. These workers found the glucosiduronic linkage to ga-lactosamine to be rather resistant to methanolysis, but that it is more efficiently cleaved after deamination of the amino galactoside, with its conversion into 2,5-anhydrotalose. For iduronic, glucuronic, and man-nuronic acids released from a polymer, it was found that the peaks monitored for these acids, relative to an internal standard, increase during the first 8 h of methanolysis (M hydrogen chloride, 100°) and remain constant for up to 20 h of methanolysis. This indicated that 8 h is required for complete methanolysis, and that the monosaccharides liberated are stable to the conditions of methanolysis. 

Chaplin used methanolysis for the analysis of carbohydrates in glycoproteins. His method was a variation of the foregoing procedures, with an improvement of using tert-hvAyX alcohol to remove hydrogen chloride by coevaporation, instead of prolonged trituration with silver carbonate. His method is useful for samples containing uronic acids and lipids. Mononen studied methanolysis, followed by deamination and reduction with borohydride, for determination of the monosaccharide constituents of glycoconjugates. This method was applied to a lipid-free, protein fraction of rat brain. 

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. 

A new PET-based chemosensor for uronic and sialic acids utilizing the cooperative action of boronic acid and metal chelate was reported by Shinkai and co-workers. This group synthesized a novel fluorescent chemosensor molecule bearing both an o-aminomethylphenylboronic acid group for diol binding to a saccharide and a l,10-phenanthroline-Zn(II)chelate moiety for the carboxylate binding, which enables this sensor to discriminate between neutral monosaccharides and acidic compounds [110],... 

For accurate results, correction factors must be established for the decomposition of each monosaccharide under the conditions of hydrolysis used. These corrections are of special importance when reliable values for a particular monosaccharide, present in only small proportion, are desired.24,33,34,83,92 96 When polysaccharides containing uronic acids are hydrolyzed, a further ambiguity is introduced, in that only partial cleavage of the glycosiduronic acid linkages may occur. 

The ion-exchange separation usually affords individual fractions of structurally related glycosyl esters of nucleoside pyrophosphates, containing the same nucleotide residue, but differing in the structure of the glycosyl groups. Separation of the esters of N-acetylhexos-amines, uronic acids, and neutral monosaccharides from one another is also usually achieved. 

Glycosaminoglycans are extracellular heteropolysaccharides in which one of the two monosaccharide units is a uronic acid and the... 

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