Aldohexose

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An aldohexose is a hexose with an aldehyde group on one end.

The aldohexoses have four chiral centres for a total of 16 possible aldohexose stereoisomers (2⁴). Of these, only three commonly occur in nature: D-glucose, D-galactose, and D-mannose. The D/L configuration is based on the orientation of the hydroxyl at position 5, and does not refer to the direction of optical activity.

There are eight D-aldohexoses:

   CH=O           CH=O          CH=O            CH=O
   |              |             |               |
  HC-OH        HO-CH           HC-OH         HO-CH
   |              |             |               |
  HC-OH          HC-OH       HO-CH           HO-CH
   |              |             |               |
  HC-OH          HC-OH         HC-OH           HC-OH
   |              |             |               |
  HC-OH          HC-OH         HC-OH           HC-OH
   |              |             |               |
   CH2-OH         CH2-OH        CH2-OH          CH2-OH
D-Allose      D-Altrose     D-Glucose      D-Mannose

   CH=O        CH=O            CH=O            CH=O
   |           |               |               |
  HC-OH     HO-CH             HC-OH         HO-CH
   |           |               |               |
  HC-OH       HC-OH         HO-CH           HO-CH
   |           |               |               |
HO-CH       HO-CH           HO-CH           HO-CH
   |           |               |               |
  HC-OH       HC-OH           HC-OH           HC-OH
   |           |               |               |
   CH2-OH      CH2-OH          CH2-OH          CH2-OH
D-Gulose    D-Idose       D-Galactose        D-Talose

[edit] Deoxyaldohexoses

Aldohexoses can have one or more of their hydroxyl groups replaced by hydrogens to form deoxyaldohexoses. The following are well known cases of such compounds :

L-Fucose (6-deoxy-L-galactose)
L-Rhamnose (6-deoxy-L-mannose)
D-Quinovose (6-deoxy-D-glucose)
Quinovose is found as part of the sulfolipid SQDG.
L-Pneumose (6-deoxy-L-talose)