Hexuronic acid, 0-methyl

Hexuronic acids, methyl ethers of, 9, 131-148 Hibbert, Harold, obituary of, 16, 1-11 History,... 

Hexuronic acids, methyl ethers of, 9, 131-148 Hibbert, Harold, obituary of, 16, 1-11 Hudson, Claude Silbert, obituary of, 9, xiii-xviii Hyaluronic acid, biosynthesis of, 12, 299-319 Hydrazones, of sugars, 3, 23-44 Hydrocolloids,... 

In concentrated sulfuric acid, D-glucuronic acid is dehydrated more slowly than either its 4-O-methyl derivative or D-glucose, probably because of the stability of its lactone. All hexuronic acids, however, eventually produce the same characteristic absorbance that corresponds roughly to a composite of 5-formyl-2-furoic acid, 2-furaldehyde, and reductic acid. It is interesting that a thin-layer chromatographic examination of the reaction products of D-glucuronic acid with 89% sulfuric acid at 70° revealed 5-formyl-2-furoic acid as a major product, but no evidence was obtained for the presence of reductic acid. This result is in distinct contrast to the products obtained in dilute acid solutions, in which 5-formyl-2-furoic acid is produced in very low yield, whereas reductic acid is formed in yields in excess of 10%. 

Seaweed polysaccharides form especially complex structures132,133 with residues of D-xylose, L-fucose, and hexuronic acids, and with sulfate groups, and, apparently, covalently bound protein. The results of methylation studies133 indicated that doubly and, possibly, triply substituted fucopyranosyl residues were present. 

VI. Tables of Properties of Methyl Ethers of Hexuronic Acids and Their... 

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... 

Analyses of the hemicelluloses of woods indicate the presence of a high proportion of D-xylose residues in association with those of a methyl ether of a hexuronic acid.64 The first evidence for the chemical structure of such wood xylans came from the isolation of xylobiose, xylotriose,65 and the aldobiouronic acid 0-(4-0-methyl-a-D-glucosyluronic)-(l —> 2)-D-xylose acid (IX)22 from partial hydrolyzates of aspen wood. The role of such oligosaccharide fragments in wood xylans became more apparent as the result of a study of a xylan from European beechwood,26 in which it was shown... 

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