Dketohexose

D-ketohexose refers to any hexose sugar that contains a ketone functional group at carbon 2 and exists in the D-configuration. Like other hexoses, they have six carbon atoms and the general molecular formula C6H12O6. In Fischer projections, the ketone at C2 distinguishes ketohexoses from aldohexoses, and the D designation indicates the configuration of the chiral center farthest from the carbonyl (C5). In solution, these sugars can cyclize to form both pyranose (six-membered) and furanose (five-membered) rings.

Common examples include D-fructose, the principal naturally occurring ketohexose, found in many fruits and honey. Other D-ketohexoses are less common but are studied as rare sugars or used as sweeteners; notable examples include D-tagatose and D-allulose (also known as D-psicose). These sugars can be metabolized by humans, with fructose entering glycolysis after phosphorylation to fructose-6-phosphate or fructose-1-phosphate, depending on tissue and enzymes involved. Allulose and tagatose are of interest as low-calorie sweeteners because they provide sweetness with fewer calories and may have distinct metabolic effects.

Nomenclature-wise, D-ketohexose denotes the D enantiomeric series of six-carbon sugars with a ketone at C2. L-ketohexoses are the mirror images. The term is mainly used in carbohydrate chemistry and biochemistry to classify a subset of hexoses bearing a ketone function.