Threose

Threose is a four-carbon monosaccharide, an aldotetrose with the molecular formula C4H8O4. In its open-chain form it contains an aldehyde group at the first carbon and two stereocenters at the second and third carbons, giving rise to two enantiomers, D-threose and L-threose, and to the diastereomeric pair erythrose and threose. In Fischer projections, the typical skeleton is CHO-CHOH-CHOH-CH2OH, with the specific arrangement of hydroxyl groups determining the isomer.

Like other aldoses with several carbons, threose can exist in cyclic forms. It commonly forms a five-membered ring (a furanose) through intramolecular reaction of the carbonyl group with one of the hydroxyls, and it can undergo mutarotation between different cyclic forms in solution.

Occurrence and uses: Threose is not a major metabolite in most standard biochemical pathways. It serves primarily as a reference compound in carbohydrate chemistry and as a synthetic building block for stereochemical studies and organic synthesis. Related sugars such as erythrose are involved in certain metabolic pathways, but threose itself is typically encountered in laboratory contexts rather than as a central biological metabolite.

Threose also features in research on alternative genetic systems. Threose nucleic acid (TNA) uses a four-carbon threose sugar in its backbone and has been studied as a potential surrogate for RNA or DNA in origins-of-life research and synthetic biology.

See also: aldose, aldotetrose, erythrose, threose nucleic acid.