Aldose

Fischer projection of D-glyceraldehyde

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.[1]

Because they have at least one asymmetric carbon center, aldoses with three or more carbon atoms exhibit stereoisomerism. Aldoses containing 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.[2] An aldose may isomerize to a ketose through the Lobry-de Bruyn-van Ekenstein transformation.

List of aldoses

Family tree of aldoses: (1) D-(+)-glyceraldehyde; (2a) D-(−)-erythrose; (2b) D-(−)-threose; (3a) D-(−)-ribose; (3b) D-(−)-arabinose; (3c) D-(+)-xylose; (3d) D-(−)-lyxose; (4a) D-(+)-allose; (4b) D-(+)-altrose; (4c) D-(+)-glucose; (4d) D-(+)-mannose; (4e) D-(−)-gulose; (4f) D-(−)-idose; (4g) D-(+)-galactose; (4h) D-(+)-talose

See also

References

  1. ↑ Berg, J.M. (2006). Biochemistry (6th ed.). New York: W. H. Freeman and Company.
  2. ↑ "Seliwanoff's Test". Harper College. Retrieved 2011-07-10.


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