An aldose is a monosaccharide (a simple sugar) that contains only one aldehyde (-CH=O) group per molecule. The chemical formula takes the form Cn(H2O)n. The simplest possible aldose is the diose glycolaldehyde, which only contains two carbon atoms.
Because they have at least one asymmetric carbon center, aldoses with three or more carbon atoms exhibit stereoisomerism. Aldoses which contain stereogenic centers can exist in either a D- form or L- form. The determination is made based on the chirality of the penultimate carbon (the second-furthest from the aldehyde), where alcohol groups on the right of the Fischer projection result in D-aldoses and epimers with alcohols on the left result in L-aldoses. Biological systems tend to recognize D-aldoses more than L-aldoses.
An aldose differs from a ketose in that it has a carbonyl group at the end of the carbon chain instead of in the middle. This allows ketoses and aldoses to be chemically differentiated through Seliwanoff's test. An aldose may isomerize to a ketose through the Lobry-de Bruyn-van Ekenstein transformation.
List of aldoses
- Diose: glycolaldehyde
- Triose: glyceraldehyde
- Tetroses: erythrose, threose
- Pentoses: ribose, arabinose, xylose, lyxose
- Hexoses: allose, altrose, glucose, mannose, gulose, idose, galactose, talose
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