oxosugar

Oxosugar is a monosaccharide in which the carbonyl group is a ketone rather than an aldehyde. In this context, such sugars are commonly called ketoses or oxoses, with the carbonyl typically located at the second carbon in standard Fischer projections. Notable examples include fructose, a ketohexose; ribulose and xylulose, which are ketopentoses; and erythrulose, a keto-tetrose.

Occurrence and metabolism: Ketoses occur naturally as intermediates in carbohydrate metabolism. In the pentose phosphate pathway, ribulose-5-phosphate and xylulose-5-phosphate are examples of oxosugars that participate in sugar interconversions. Ketoses can interconvert with aldoses through enediol rearrangements, a process that enables many ketoses to act as reducing sugars in certain conditions.

Structure and forms: Ketoses can exist in linear form and in several cyclic forms. Cyclic structures arise when the hydroxyl groups react with the carbonyl to form rings, yielding furanose or pyranose ring systems depending on the sugar.

Notable properties and usage: Fructose is the best-known oxosugar and is widely used as a natural sweetener. Other ketoses such as ribulose, xylulose, and erythrulose occur primarily in biological contexts and research settings. Some ketoses are investigated as rare sugars with potential nutritional or industrial applications.

Nomenclature and classification: The term oxosugar is largely historical; contemporary usage typically uses the name of the sugar (for example, fructose, ribulose, xylulose) or the descriptor ketose. Ketoses differ from aldoses in their carbonyl position and, in solution, can undergo tautomerization to aldose forms under certain conditions.