ketoser

Ketoser, or ketoses, are a class of monosaccharides that contain a ketone functional group on the carbon backbone. The carbonyl is typically located at carbon 2, which distinguishes ketoses from aldoses that carry an aldehyde at carbon 1. Ketoses span a range of carbon numbers from three onward; well-known examples include dihydroxyacetone (C3) and fructose (C6), as well as ribulose and xylulose (C5) and sedoheptulose (C7).

In aqueous solution, ketoses can interconvert between linear and cyclic forms. They often adopt five-membered ring structures known as furanoses, and less commonly six-membered rings called pyranoses, depending on the sugar and conditions. Like other sugars, they exist as enantiomeric pairs (D- and L- forms) determined by the configuration at the chiral centers, most notably the penultimate carbon.

Biological relevance: fructose is a common dietary sugar and a metabolic intermediate. In glycolysis, fructose is eventually split into glyceraldehyde-3-phosphate and dihydroxyacetone phosphate, while in the pentose phosphate pathway, ketoses such as xylulose-5-phosphate participate in carbon rearrangements essential for nucleotide biosynthesis and reductive metabolism.

Nomenclature and distribution: ketose names derive from the combination of “keto” and “-ose.” The term ketoser is used in some languages as the plural form of ketose. Ketoses occur in fruits, honey, plants, and microbial metabolites, and they are studied for their stereochemistry, metabolism, and potential applications in food chemistry and biochemistry.