Tetrose

Tetrose refers to a monosaccharide that contains four carbon atoms. Tetroses can be aldoses (aldotetroses) or ketoses (ketotetroses), and their general molecular formula is C4H8O4. The aldose family includes two common stereoisomeric forms, erythrose and threose, each existing as D- and L-enantiomers. In Fischer projections, erythrose has the middle two hydroxyls on opposite sides, while threose has them on the same side. A ketotetrose example is erythrulose, which has a ketone at carbon 2 and also exists as enantiomeric pairs.

In nature and biology, tetroses mostly occur as intermediates rather than as free sugars. Erythrose-4-phosphate is a well-known intermediate in the shikimate pathway, contributing to the biosynthesis of aromatic amino acids in plants and microorganisms. Erythrulose is a ketotetrose that can appear in small amounts and is used commercially in cosmetic tanning products; as with other sugars, it can be prepared or manipulated in chemical synthesis and research contexts.

Chemical properties of tetroses reflect their highly hydroxylated, small carbon skeletons. They can exist in open-chain (linear) forms with a carbonyl group and in cyclic forms derived from intramolecular reactions with a hydroxyl group, typically forming five-membered rings in some conditions. Like other reducing sugars, tetroses may participate in redox reactions in solution, and they exhibit optical activity corresponding to their chiral centers. Overall, tetroses are primarily of interest in carbohydrate chemistry and biochemistry as simple models and as metabolic intermediates.