ketohexoser

Ketohexoser are a subset of monosaccharides characterized by six carbon atoms and a ketone functional group. In structural terms, the carbonyl is located at the second carbon, which distinguishes ketoses from aldoses that carry an aldehyde at the first carbon. As a result, ketohexoses form a variety of stereoisomers depending on the arrangement of hydroxyl groups around the chiral centers. They can exist in linear form as well as cyclic forms, typically as furanoses or, less commonly, pyranoses, with interconversion among forms in solution.

The most widely known member of this group is D-fructose, a natural sweetness contributor found in fruits, honey, and many vegetables. Other ketohexoses include D-sorbose, D-tagatose, and D-psicose (also known as allulose). These sugars differ in their specific stereochemistry, giving rise to distinct chemical and biological properties while sharing the common six-carbon, ketose framework. In nature, ketohexoses may appear in small amounts as free sugars or as components of glycosides.

Metabolism and applications distinguish ketohexoses from other hexoses. For example, fructose is rapidly taken up by the liver and phosphorylated by fructokinase to fructose-1-phosphate, feeding into glycolytic and metabolic pathways with unique regulatory implications. Some ketohexoses, such as psicose, are studied for potential use as low-calorie sweeteners due to partial absorption. Beyond nutrition, ketohexoses serve as analytical standards and versatile substrates in carbohydrate chemistry, biocatalysis, and industrial applications.