Reduction of xylose by catalytic hydrogenation produces the sugar substitute xylitol

Xylose (cf. Ancient Greek: ξύλον, xylon, “wood”) is a sugar first isolated from wood, and named for it. Xylose is classified as a monosaccharide of the aldopentose type, which means that it contains five carbon atoms and includes an aldehyde functional group. It is derived from hemicellulose, one of the main constituents of biomass. Like most sugars, it can adopt several structures depending on conditions. With its free aldehyde group, it is a reducing sugar.

The acyclic form of xylose has chemical formula HOCH₂(CH(OH))3CHO. The cyclic hemiacetal isomers are more prevalent in solution and are of two types: the pyranoses, which feature six-membered C₅O rings, and the furanoses, which feature five-membered C₄O rings (with a pendant CH₂OH group). Each of these rings is subject to further isomerism, depending on the relative orientation of the anomeric hydroxy group.

The dextrorotary form, d-xylose, is the one that usually occurs endogenously in living things. A levorotary form, l-xylose, can be synthesized.

• https://en.wikipedia.org/wiki/Xylose