aldotetrose

Aldotetrose is any aldose sugar containing four carbon atoms. Its linear form has an aldehyde group at carbon 1 and three hydroxyl groups on carbons 2, 3, and 4, giving the molecular formula C4H8O4. In Fischer projection, the chain is written as CHO-CHOH-CHOH-CH2OH.

There are two chiral centers in aldotetroses (at C2 and C3), which yields four stereoisomers: D-erythrose, D-threose, and their enantiomers L-erythrose and L-threose. The two diastereomers commonly discussed are erythrose and threose, with their D- forms most frequently encountered in chemistry literature. The L forms are the mirror images and less common in biological contexts.

In solution, aldotetroses exist in equilibrium between linear and cyclic forms. The cyclic form can arise as a five-membered ring (a furanose-type structure) through intramolecular hemiacetal formation between the C1 aldehyde and the C4 hydroxyl group, producing alpha and beta anomers.

Natural occurrence and uses are limited compared with longer sugars, but aldotetroses are important as reference compounds in carbohydrate chemistry and metabolism. Erythrose participates in various biosynthetic pathways, and phosphorylated derivatives such as erythrose-4-phosphate are intermediates in the shikimate pathway in plants and microbes. Aldotetroses are reducing sugars and are soluble in water, properties that make them useful as standards in analytical methods and in studies of enzyme specificity and carbohydrate metabolism.