Ketosen

Ketosen, or ketose in English, is a class of monosaccharides defined by a carbonyl group that is a ketone rather than an aldehyde. In most ketoses the carbonyl is located on carbon 2, though some derivatives have different positions. They share the general formula Cn(H2O)n and are usually soluble in water. Ketoses are one of the two main subtypes of simple sugars, the other being aldoses, which contain an aldehyde group at the terminal carbon.

The simplest ketose is dihydroxyacetone; the most common naturally occurring ketose is fructose, found in fruits and honey and widely used as a sweetener. Other ketoses include ribulose and xylulose (pentose ketoses) and hexoses such as sorbose, psicose, and tagatose. Ketoses can exist in linear form or in cyclic forms, typically five- or six-membered rings called furanose and pyranose.

In metabolism, ketoses participate in pathways such as glycolysis and the pentose phosphate pathway, often after isomerization to aldoses or through phosphorylation steps that generate energy or biosynthetic intermediates. In solution, ketoses can isomerize to aldoses under certain conditions through enediol rearrangements, a process known as the Lobry de Bruyn–Alberda van Ekenstein transformation.

Fructose is notable for its high relative sweetness and is a major dietary sugar, while other ketoses serve as intermediates in carbohydrate metabolism or as starting materials in biotechnological syntheses.