- Threose is a four-carbon aldotetrose monosaccharide with the chemical formula C₄H₈O₄. Like erythrose, it belongs to the family of simple sugars that contain an aldehyde group at carbon 1 and hydroxyl groups on the remaining carbons.
- The defining feature of threose is the stereochemistry at its two chiral centers (carbons 2 and 3), which distinguishes it from its diastereomer, erythrose. In the Fischer projection, threose has the hydroxyl groups at carbons 2 and 3 on opposite sides, while erythrose has them on the same side. Threose thus exists in two enantiomeric forms, D-threose and L-threose, though it is much less commonly encountered in biological systems compared to erythrose.
- While D-erythrose plays central roles in pathways such as the pentose phosphate pathway and the shikimate pathway, threose does not have a major direct role in central metabolism of most organisms. However, it has attracted scientific interest in specialized contexts. One of the most notable is its role in the development of synthetic genetic systems, particularly L-threose nucleic acid (TNA). In this artificial genetic polymer, the usual five-carbon sugar (ribose in RNA or deoxyribose in DNA) is replaced by threose. TNA has the ability to form stable Watson–Crick base pairing with both RNA and DNA, making it a potential precursor to modern genetic systems in origin-of-life research. Because threose is simpler than ribose and may have been more readily available under prebiotic conditions, TNA has been proposed as a candidate for an early genetic material that could have evolved into RNA.
- From a chemical perspective, threose is highly reactive due to its aldehyde group and hydroxyl functionalities, similar to other small sugars. Although it is not a major metabolite in living systems, threose and its derivatives can form in non-enzymatic sugar reactions and may appear transiently in pathways involving carbohydrate interconversions. Its stereochemistry also makes it an important model compound for studying the principles of carbohydrate chemistry, stereoisomerism, and enzymatic specificity.
- In biological and biomedical contexts, threose has gained attention through its derivative threose nucleic acid (TNA), which has been explored not only in prebiotic chemistry but also in biotechnology. TNA has demonstrated resistance to nuclease degradation and potential as a biostable genetic material, making it promising for therapeutic and diagnostic applications. Beyond this, threose derivatives are studied in experimental chemistry for their ability to form Schiff bases and undergo glycation-like reactions, processes relevant to aging and disease.
