Aldobiouronic acid

K3. Kuenzle, C. C., Bilirubin conjugates of human bile. The excretion of bilirubin as the acyl glycosides of aldobiouronic acid, pseudoaldobiouronic acid and hex-uronosylhexuronic acid, with a branched-chain hexuronic acid as one of the components of the hexuronosylhexuronide. Biochem. J. 119, 411-435 (1970). 

These are some examples of the use of i.r. spectra in the analysis and identification of carbohydrates in foods and natural products. Very often, these spectroscopic techniques are complementary to others, such as the study of aldobiouronic acids obtained by hydrolysis of peach-gum polysaccharides by their optical rotations and their i.r. spectra.100 However, the i.r. results appear to be sufficiently reliable to be used in the detection of traces of fructose and glucose, and to determine the d.e. (dextrose equivalent) of corn syrups, as well as the quantitative carbohydrate content in different products.101... 

Most of the known oligoglycuronic acids are aldobiouronic acids. Because of the stability of the glycosidic linkage of aldobiouronic acids toward acid hydrolysis, they are readily isolated after vigorous hydrolysis of polysaccharides that contain uronic acid residues. They have been obtained from wood hemicelluloses, plant mucilages, gums, bacterial and animal polysaccharides, and by synthesis. 

Aldobiouronic acids have also been prepared by the Koenigs Rnorr reaction.2 /-J-o-Glneuronic acid-containing disaccharides have been synthesized using derivatives of methyl (l-thio-/l-D-glucopyranosid)uronate with different protective groups as glycosyl donors.183... 

The occurrence in many polyglycosiduronic acids of relatively resistant linkages, usually those between uronic acid residues and adjacent residues, has resulted in the isolation of several aldobiouronic acids on graded hydrolysis of acidic polysaccharides. The isolation of such aldobiouronic acids, and subsequent conversion to their fully methylated derivatives, has become a standard procedure in structural studies on polyglycosiduronic acids, especially those of plant gums and mucilages.1 In other cases, partially methylated aldobiouronic acids have been isolated from the hydrolyzates of methylated polysaccharides. The sources and methods of isolation of the methyl ethers of aldobiouronic acids so far examined are given in Table I. Some properties of derivatives are recorded in Table Y. 

Despite the frequent isolation of the same methylated aldobiouronic acid from more than one source, the direct identification of such a com-... 

A, Hydrolysis of naturally-occurring polysaccharide B, inethylation of aldobiouronio acid isolated after graded hydrolysis of polysaccharide C, hydrolysis of methylated polysaccharide D, methylation of partially methylated aldobiouronic acid isolated by method C. 

Like the parent compounds, the methyl ethers of aldobiouronic acids are resistant to acid hydrolysis, and it is difficult to carry out hydrolysis without some decomposition of the product. This difficulty has recently been overcome by reduction of the uronic acid residue with lithium aluminum hydride66-67 the resulting disaccharide then undergoes hydrolysis without difficulty. The first reduction of the uronic acid residue of a methylated aldobiouronic acid methyl ester was accomplished by Levene, Meyer and Kuna,69 who reduced the methylated aldobiouronic acid from gum arabic with hydrogen in the presence of copper chromite catalyst under the conditions previously used701 for reducing the acety-... 

The following Tables (II, III, and IV) record appropriate data and references relating to the methyl ethers of some hexuronic acids and their derivatives. In the case of methyl ethers of aldobiouronic acids (Table V), data have been recorded only for crystalline derivatives. Where uronic acids have been characterized by reduction to the corresponding hexose, reference should be made to the previous articles in this series dealing with the methyl ethers of D-glucose,71 D-galactose,72 and D-mannose.73... 

Many polysaccharides of the xylan group contain residues of D-glucuronic acid or 4-0-methyl-D-glucuronic acid. Since glycosiduronic acids are particularly resistant to acid hydrolysis, aldobiouronic acids may be isolated... 

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