ribopyranose

Ribopyranose is the six-membered ring form (pyranose) of ribose, the aldopentose sugar with five carbon atoms. It is a cyclic hemiacetal formed when the aldehyde group at C1 reacts with the hydroxyl group on C5, yielding a six-membered oxygen-containing ring in which C1 becomes the anomeric carbon. Like other aldopyranoses, ribopyranose exists in two anomeric configurations, α and β, and can interconvert with the linear form and the furanose form via mutarotation.

In the ribopyranose ring, the ring consists of six atoms: five carbons and one ring oxygen. The ring can adopt chair or boat conformations, with substituents on the ring favoring positions that minimize steric strain. The configuration at C1 defines the anomer (α or β). The hydroxymethyl group at C5 remains attached as a substituent on the ring, and the other ring hydroxyl groups follow the stereochemistry inherited from D-ribose.

Ribopyranose is a less common cyclic form of ribose in biological systems; ribose predominantly exists in the furanose form in nucleic acids and many carbohydrate derivatives. Nevertheless, the pyranose form can occur in solution and is part of the anomeric/tautomeric equilibrium between cyclic ribose isomers. The term ribopyranose helps distinguish studies that focus on the six-membered-ring form from the more prevalent ribofuranose form.