riboside

A riboside is a chemical compound in which a ribose sugar is attached to a base or other aglycone via a glycosidic bond. In biochemistry, the term is most often used for ribonucleosides, which consist of a ribose sugar linked to a nitrogenous base and form the building blocks of RNA. The concept also encompasses other ribose-containing glycosides, including certain drug molecules and metabolic intermediates where ribose is the sugar component.

Structural details define the glycosidic linkage: the bond forms between the anomeric carbon (C1') of the ribose and a nitrogen atom on the base. For purines such as adenine and guanine, the linkage is to N9; for pyrimidines such as cytosine and uracil, it is to N1. In natural ribonucleosides, the sugar adopts the beta configuration. When the sugar is deoxyribose instead of ribose, the corresponding compounds are deoxyribonucleosides.

Canonical examples include the ribonucleosides adenosine, guanosine, cytidine, and uridine, which pair with their respective nucleotides in RNA synthesis. The term also appears in the broader sense of ribosylated molecules, such as nicotinamide riboside, a ribose-conjugated form of nicotinamide that serves as a precursor to NAD+. Ribosides can be hydrolyzed by nucleosidases to release the base and ribose, and in cells they are phosphorylated by kinases to form nucleotides as part of salvage pathways.

In pharmacology and biochemistry, the concept of a riboside is used to describe molecules bearing a ribose moiety, distinguishing them from deoxyribosides and other sugar conjugates.

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