Glyceraldehyde (glyceral) is a triose monosaccharide with chemical formula C<sub>3</sub>H<sub>6</sub>O<sub>3</sub>. It is the simplest of all common aldoses. It is a sweet, colorless, crystalline solid that is an intermediate compound in carbohydrate metabolism. The word comes from combining glycerol and aldehyde, as glyceraldehyde is glycerol with one alcohol group oxidized to an aldehyde.
Aqueous and concentrated solutions of glyceraldehyde
The description above focuses on classification of isomers, but the glyceraldehyde is subject to a further complications: the tendency of hydroxy-aldehydes to exist as hydrates. NMR measurements indicate that in aqueous solution, glyceraldehyde exists in a hydrate owing to this reaction:
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The same study indicates that concentrated ("syrupy") forms of glyceraldehyde exist as dimers, indicating hemiacetal formation.
Nomenclature
In the system, glyceraldehyde is used as the configurational standard for carbohydrates. Monosaccharides with an absolute configuration identical to (R)-glyceraldehyde at the last stereocentre, for example C5 in glucose, are assigned the stereo-descriptor . Those similar to (S)-glyceraldehyde are assigned an . <!---Both and , should be small capital letters.--->
Synthesis and reactions
Glyceraldehyde can be prepared from acetals of acrolein (CH<sub>2</sub>=CHCHO) in two steps, oxidation followed by hydrolysis of the acetal. Its cyclohexylidene acetal can also be produced by oxidative cleavage of the bis(acetal) of mannitol. Glyceraldehyde can also be synthesized through the partial oxidation of Glycerol, for example with a fenton type reagent.
Glyceraldehyde is a precursor to four-carbon sugars (tetroses) via cyanation followed by hydrolysis of the cyanohydrin:
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Biochemistry
The enzyme glycerol dehydrogenase (NADP<sup>+</sup>) has two substrates, glycerol and NADP<sup>+</sup>, and 3 products, D-glyceraldehyde, NADPH and H+.
The interconversion of the phosphates of glyceraldehyde (glyceraldehyde 3-phosphate) and dihydroxyacetone (dihydroxyacetone phosphate), catalyzed by the enzyme triosephosphate isomerase, is an intermediate step in glycolysis.
See also
- Stereoisomerism