Allopyranose

Allopyranose is a form of aldose sugar, a monosaccharide containing an aldehyde functional group, with a six-carbon chain. The "allo" prefix indicates a specific stereochemical configuration of the hydroxyl groups on the carbon chain. Specifically, allopyranose is the cyclic hemiacetal form of allose, where the aldehyde group has reacted with a hydroxyl group to form a six-membered ring containing one oxygen atom. This ring structure is a pyranose ring, hence the "-opyranose" suffix.

In aqueous solution, allopyranose exists in equilibrium with its open-chain form, allose, and also with its anomers. The anomers, alpha-allopyranose and beta-allopyranose, differ in the configuration of the hydroxyl group at the anomeric carbon (the carbon that was originally the aldehyde carbon). Alpha-allopyranose has its anomeric hydroxyl group in the axial position, while beta-allopyranose has it in the equatorial position. Allopyranose is a stereoisomer of other common hexopyranoses like glucose, galactose, and mannose, differing in the arrangement of its hydroxyl groups. It is a relatively rare sugar found naturally in some plants and bacteria, but it is not as abundant as glucose or fructose. Its chemical properties are similar to other pyranoses, participating in glycosidic bond formation and undergoing oxidation and reduction reactions.