Glyceraldehyde

Structure

Glyceraldehyde has one chiral center and therefore exists as two different enantiomers with opposite optical rotation:

• In the nomenclature, either from Latin Dexter meaning "right", or from Latin Laevo meaning "left"
• In the R/S nomenclature, either R from Latin Rectus meaning "right", or S from Latin Sinister meaning "left"

While the optical rotation of glyceraldehyde is (+) for R and (−) for S, this is not true for all monosaccharides. The stereochemical configuration can only be determined from the chemical structure, whereas the optical rotation can only be determined empirically (by experiment).

It was by a lucky guess that the molecular geometry was assigned to (+)-glyceraldehyde in the late 19th century, as confirmed by X-ray crystallography in 1951.

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: : 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 .

Synthesis and reactions

Glyceraldehyde can be prepared from acetals of acrolein (CH2=CHCHO) in two steps, oxidation{{cite journal |doi=10.15227/orgsyn.011.0052 |title=dl-Glyceraldehyde Ethyl Acetal |journal=Organic Syntheses |date=1931 |volume=11 |page=52|first1=E. J. |last1=Witzemann|first2=Wm. |last2=Llloyd Evans|first3=Henry|last3=Hass|first4=E. F.|last4=Schroeder

Glyceraldehyde is a precursor to four-carbon sugars (tetroses) via cyanation followed by hydrolysis of the cyanohydrin: : :

Biochemistry

The enzyme glycerol dehydrogenase (NADP+) has two substrates, glycerol and NADP+, 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.

References

References

1. ''Merck Index'', 11th Edition, '''4376'''
2. (1951). "Determination of the Absolute Configuration of Optically Active Compounds by Means of X-Rays". Nature.
3. (1980). "The Composition of Reducing Sugars in Aqueous Solution : Glyceraldehyde, Erythrose, Threose". Australian Journal of Chemistry.
4. (2015-03-19). "22.03: The D and L Notation".
5. (2022). "Preparation of 1,2:5,6-Di-O-cyclohexylidene-D-mannitol and 2,3-Cyclohexylidene-D-glyceraldehyde". Organic Syntheses.
6. Zoltán, Köntös. (2024-01-24). "Fenton oxidation of glycerin: A sustainable approach for byproduct treatment". Journal of Chemical Research.
7. (2023). "Molecule of the Week: D-Glyceraldehyde". C&E News.
8. (1972). "Purification and properties of an NADP+-dependent glycerol dehydrogenase from rabbit skeletal muscle". Biochimica et Biophysica Acta (BBA) - Enzymology.