Uronic acids identification

The identification of L-iduronic acid as the major glycuronic acid constituent of heparin proved to be a much slower process than the identification of the amino sugar residue. Although this compound was detected in acid hydrolyzates of heparin116117 and heparin oligosaccharides,118 its yield was usually poor, because of the drastic conditions used for the acid hydrolysis (which are known to lead to extensive destruction of uronic acid).119120 Also, L-iduronic acid escaped detection as L-idose in the hydrolyzates of carboxyl-reduced heparin, probably because L-idose is readily converted into 1,6-anhydro-L-idose under the usual hydrolytic conditions. 

In model experiments,205 it was found that concentration of an aqueous solution of the aldonic acids in the presence of hydrochloric acid gives exclusively the 1,4-lactones, which, on subsequent trimethyl-silylation, give only one peak on the chromatogram. This method was successfully employed for the separation of D-galacturonic, D-glucuronic, and D-mannuronic acids. Of the 1,4-lactones examined, only the trimethylsilyl ether of D-mannono-1,4-lactone was obtained in crystalline form. However, all of the derivatives showed characteristic differences in their infrared spectra in the range of 1500 to 600 cm"1. When this method was applied to the determination of uronic acids in a variety of polysaccharides,205 it was impossible to find any hydrolytic conditions under which the uronic acids were quantitatively released and then reduced, a problem experienced by other workers.20 The method was, however, successful in affording a qualitative, microscale procedure for the identification of hexuronic acids (which otherwise are difficult to detect). 

The characterization and quantitative determination of uronic acid components in polysaccharides faces the problem of complete release of the uronic acids without accompanying decomposition. This is a difficult task because of the acid resistance of the glycosiduronic bond. From a comparison of several methods, it was shown that methanolysis combined with trifluoroacetic acid hydrolysis is the best for the liberation of uronic acids.204 The identification can be performed by gas chromatography of the trimethylsilyl derivatives.205... 

Bromine water, III, 133, 140, 150 p-Bromophenylhydrazine, in identification of uronic acids, I, 339 Brucella melitensis, antigens, II, 166, 200 Brucellosis, III, 339 Brucine D-altronate, I, 73 Brucine L-altronate, I, 73 Brucine salts, III, 143, 144, 164 —, with uronic acids, I, 339 Buffered solutions, carbohydrate oxidation in, III, 151... 

Hyaluronidase, effect on blood group substances, IV, 55 Hydration, of starch, I, 275 Hydratopectin, II, 239 Hydrazine, derivatives, in identification of uronic acids, I, 339 Hydrazine, l,2-bis(a-metbylbenzyl-)-,... 

Non-endospermic xylans have substituent groups of D-glucopyrano-syluronic acid, or its 4-methyl ether, or both. Individual molecules may lack such residues, but, almost certainly, other xylan molecules in the total hemicelluloses from each grass have both groups.137,157 Uronic acid groups may escape detection or identification in hydrolyzates of xylans studied by paper chromatography, and in hydrolyzates and methanolyzates of methylated xylans studied by g. l.c. after conversion of the products into volatile derivatives. 

Stoffyn, P. J., and Jeanloz, R. W., The identification of the uronic acid component of dermatan sulphate (fi-heparin, chondroitin sulfate B). J. Biol. Chem. 235, 2507-2510 (1960). 

The identification of the uronic acid in a polyuronide is somewhat difficult because during hydrolysis a large part of it is destroyed, and the free acid finally obtained is contaminated with decomposition and reversion products as well as with low polymers resulting from incomplete... 

Norman has tabulated the constants for various derivatives of the uronic acids and has summarized previous work on their identification. The free acids or their lactones have been used for the purpose of identification. The quinine, brucine, and cinchonine salts" have also been used for this purpose, although their isolation in pure form is hindered by the presence of the corresponding alkaloidal salts of the low polymers of the acid. Some of the complex hydrazines have been used to identify the acids. p-Bromophenylhydrazine has been frequently used for this purpose. One difficulty in the use of hydrazines is that they may form numerous types of derivatives such as salts, hydrazides, hydrazones and osazones. 

The particular value of acid hydrolysis is that, used in conjunction with paper chromatography, much evidence may be obtained from very small amounts of compound. As the identification of monosaccharides by paper chromatography is well established, the use of this technique in conjunction with total, acid hydrolysis provides a ready means for identifying, both qualitatively and quantitatively, the monosaccharide components of an oligosaccharide. Acid stability of different glycosidic links differs, and total hydrolysis may require from one to four hours at 100° in N acid even more vigorous conditions may be required when amino sugar or uronic acid residues are present. Very rapid hydrolysis in dilute acid,... 

Since no methods exist for analysing discrete seawater polysaccharides directly, their identifications can at best only be inferred by an examination of their constituent monomers, including uronic acids and amino sugars. 

---