Derivatives of Monosaccharides

Monosaccharides can be chemically altered in several ways to provide new classes of compounds. These include:

> Phosphorylated derivatives - made by esterifying a phosphate group to one of the hydroxyls. Several examples are shown in Table 9.3. Numerous other examples exist. Phosphoylated sugars have standard state free energies of hydrolysis less negative than that of ATP, but sufficiently negative to act in some cases as "activated compounds" in metabolic reactions. The acid phosphate group gives these molecules a negative charge at neutral pH (see also here).

> Acids and Lactones - made by mild oxidation of an aldose, for example, to form an aldonic acid (see here). Free aldonic acids are in equilibrium with lactones (see here). In metabolic pathways, oxidation at carbon 6 of glucose yields glucuronic acid.

> Alditols - made by reducing the carbonyl group of a sugar. The resulting polyhydroxy compounds are called alditols. Important ones include erythritol, D-mannitol, and D-glucitol (also called sorbitol).

> Amino Sugars - made by replacing a hydroxyl of a sugar with an amine group. Two common examples are -D-glucosamine and -D-galactosamine. Common molecules derived from these include -D-N-acetylglucosamine, muramic acid, N-acetylmuramic acid, -D-N-acetylgalactosamine, and N-acetylneuraminic acid (also called sialic acid). Amino sugars are often found in oligosaccharides and polysaccharides.

> Glycosides - formed by elimination of water between the anomeric hydroxyl of a cyclic monosaccharide and the hydroxyl group of another compound. Glycosides do not undergo mutarotation in the absence of an acid catalyst, so they remain locked in the or configuration. Many glycosides are known. Some, such as ouabain or amygdalin (Figure 9.15) are very poisonous.

See also: Sugar Ring Structures, Monosaccharide Nomenclature, Glycosides and Glycosidic Bonds, Biosynthesis of Amino Sugars (from Chapter 16)