Glycuronic Glyconic and Glycaric Acids

The uronic acids are weak sugar acids that have a carboxyl group (—COOH) instead of the terminal — CH2OH (Fig. 1-9). d-G1ucu-ronic acid is an important constituent of gly-cosaminoglycans in mammalian systems, and its C-5 epimer, l-iduronic acid, is present to a lesser extent. Glucuronic acid (and its 4-0-methyl ether), d-galacturonic acid, d-mannu-ronic acid, and the less common l-guluronic

HCOH

HOCH

HCOH

HCOH

CH2OH d-Gluconic Acid

Iduronic Acid

H OH d-Glucono-8-Lactone

Figure 1-9. Carboxylic acid derivatives of d-giucose and l-idose. d-Gluconic acid is shown along with its 1,5-lactone, an intramolecular ester. D-Glucuronic and l-iduronic acids are shown as their ¡3 anomers; uronic acids are important constituents of glycosaminoglycans. The acids are shown in their anionic forms (gluconate, glucuronate, and iduronate).

H HO

H OH d-Glucono-8-Lactone

H HO

|3-d-Glucuronic Acid (GIcA)

p-L-lduronic Acid (IdoA)

Figure 1-9. Carboxylic acid derivatives of d-giucose and l-idose. d-Gluconic acid is shown along with its 1,5-lactone, an intramolecular ester. D-Glucuronic and l-iduronic acids are shown as their ¡3 anomers; uronic acids are important constituents of glycosaminoglycans. The acids are shown in their anionic forms (gluconate, glucuronate, and iduronate).

acid are constituents of the nondigestible polysaccharides of plants and algae, which contribute to dietary fiber. Glycaric acids are dicarboxylic acids in which both terminal groups of the aldose have been oxidized to carboxyls. They are much less common than the glycuronic acids. Glyconic acids are oxidation products of the aldoses in which C-l has been oxidized to a carboxyl group. Glyconic acids lactonize easily to the neutral cyclic lactones.

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