Diferulic acids
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Diferulic acids (also known as dehydrodiferulic acids) are dimers of ferulic acid.(1) Just as ferulic acid is not the proper IUPAC name, the diferulic acids also tend to have trivial names that are more commonly used than the correct IUPAC name.

Occurrence

They have been found in the cell walls of most plants, but are present at higher levels in the grasses (Poaceae) and also sugar beet and Chinese water chestnut.(2) It is thought that they have a structural function in plant cell walls, where they form cross-links between polysaccharide chains. They have been extracted attached to a few sugar molecules at both ends, but so far no definitive proof of them linking separate polysaccharide chains has been found. (ref)

Structures

There are currently nine known structures for diferulic acids.(3) They are usually named after the positions on each molecule that form the bond between them. Ferulic acid can aso form trimers and tetramers, known as triferulic and tetrafeulic acids respectively.

Preparation

Most diferulic acids are not commercially available and must be synthesised in house. Synthetic routes have been published, but it is often simpler to extract them from plant material. They can be extracted from plant cell walls (often maize bran) by concentrated solutions of alkali, the resulting solution is then acidified and phase separated into an organic solvent. The resulting solution is evaporated to give a mixture of ferulic acid moieties that can be separated by column chromatography. Identification is often by High performance liquid chromatography with a UV detector or by LC-MS. Alternatively they can be derivatised to make them volatile and therefore suitable for GC-MS. Curcumin can be hydrolyzed (alkaline) to yield two molecules of ferulic acid. (ref) Peroxidases can produce dimers of ferulic acid, in the presence of peroxide and ferulic acid.

Uses

They have antioxidant properties and absorb UV light, making them ideal for use in sun creams.(ref)

History

The first diferulic acid discovered was the 5,5'-diferulic acid, and for a while this was thought to be the only one.

See also

• Sinapic acid
• Coumaric acid

References

1. Physiology and biochemistry of plant cell walls, C.Brett and K.W.Waldron, 2nd Ed. (1996).
2. New discoveries relating to diferulates, J.Ralph, J.H.Grabber, R.D.Hatfield and G.Wende, 1996 USDFRC Research Summary, p70-71.
3. Phenolic compounds as cross-links of plant derived polysaccharides, M.Bunzel, J.Ralph, H.Steinhart, Czech J. Food Sci., 22:64-67.