xylosyl

Xylosyl is a chemical term used to denote a substituent or residue derived from xylose, a five-carbon aldose sugar. In glycoscience, xylosyl indicates that a xylose unit is attached to another molecule via a glycosidic bond, usually at the anomeric carbon, resulting in a xyloside or a xylosylated compound. The term is widely used in naming glycosides, oligosaccharides, and glycoproteins.

Xylose exists as two enantiomers, but the naturally occurring form is predominantly D-xylose. In biology, xylosyl residues appear in the biosynthesis of proteoglycans, where a single xylose molecule is attached to serine residues on core proteins and acts as the primer for the assembly of repeating glycosaminoglycan chains. Beyond proteoglycans, xylosyl groups are found in various glycosides and carbohydrate-based natural products.

In nomenclature, the suffix -osyl denotes a sugar-derived substituent. For example, xylosyl transferases are enzymes that transfer xylosyl residues onto acceptors, and xylosylglycosides refer to glycosides where xylose is the sugar moiety. The term xylosyl should not be confused with xylitol, which is a sugar alcohol, or with xylose itself, which is the carbohydrate unit.