Dxylose

D-xylose is a naturally occurring aldopentose monosaccharide with five carbon atoms and an aldehyde group. Its molecular formula is C5H10O5. In aqueous solution it exists in equilibrium between an open-chain form and cyclic forms, commonly as a five-membered ring (furanose). The naturally occurring configuration is the D enantiomer; L-xylose is the mirror image and is not as prevalent in nature.

It is a constituent of xylan, a major component of plant hemicelluloses. D-xylose is obtained commercially from plant biomass via acid or enzymatic hydrolysis of xylan, followed by purification. In industry it is used as a chemical building block and in the preparation of xylose-containing derivatives, such as xylitol upon reduction, and as a reference compound in carbohydrate analyses.

Biologically, humans do not rely on D-xylose for energy, and it is poorly metabolized. After oral ingestion, it is absorbed from the intestine and is largely excreted unchanged in the urine, with minimal transformation by human enzymes.

Clinical use of D-xylose includes the D-xylose absorption test, historically employed to assess intestinal absorptive capacity and differentiate mucosal disease from pancreatic insufficiency. Following a measured oral dose, urinary excretion is quantified over several hours; reduced excretion suggests mucosal malabsorption, as seen in conditions like celiac disease. The test has largely declined in routine practice but remains referenced in some diagnostic contexts.