Xylopyranose

Xylopyranose is the six-membered ring (pyranose) form of xylose, an aldopentose that occurs widely in plants. In solution, xylose exists in equilibrium with its open-chain form and with ring forms, including both the pyranose and the furanose forms. Xylopyranose can adopt two anomeric configurations at C1: alpha and beta. For the naturally occurring D-xylose, the principal forms are alpha-D-xylopyranose and beta-D-xylopyranose.

Structure and stereochemistry: The pyranose ring is formed by cyclization between the aldehyde group at C1 and the hydroxyl group at C5, generating a six-membered ring with the ring oxygen supplied by the former C5 hydroxyl. The anomeric carbon at C1 bears a hydroxyl that is oriented either above (alpha) or below (beta) the plane of the ring.

Occurrence and biology: Xylopyranose residues are components of xylan, the major hemicellulose in plant cell walls. Hydrolysis of xylan yields free D-xylose, which may be metabolized by certain microorganisms via isomerization to xylulose and entry into the pentose phosphate pathway; in humans, xylose is largely not metabolized and is used in some diagnostic tests of intestinal absorption.

Uses and relevance: Xylopyranose serves as a reference sugar in carbohydrate analysis and as a building block for studying glycosidic bonds and xylo-oligosaccharides. Like other sugar rings, its pyranose and furanose forms interconvert in solution depending on conditions such as solvent and temperature.