Gentisic acid is a dihydroxybenzoic acid. It is a derivative of benzoic acid and a minor (1%) product of the metabolic break down of aspirin, excreted by the kidneys.
It is also found in the African tree Alchornea cordifolia and in wine.
Gentisic acid is produced by carboxylation of hydroquinone.
This conversion is an example of a KolbeâÂÂSchmitt reaction.
Alternatively the compound can be synthesized from salicylic acid via Elbs persulfate oxidation.
In the presence of the enzyme gentisate 1,2-dioxygenase and oxygen, gentisic acid undergoes a ring-opening reaction to give 3-maleylpyruvic acid:
This reaction has been used to detect gentisic acid with a whole-cell biosensor developed from a 3-maleylpyruvic acid-inducible gene expression system and the gentisate 1,2-dioxygenase gene from chemolithoautotrophic bacterium Cupriavidus necator.
As a hydroquinone, gentisic acid is readily oxidised and is used as an antioxidant excipient in some pharmaceutical preparations.
In the laboratory, it is used as a sample matrix in matrix-assisted laser desorption/ionization (MALDI) mass spectrometry, and has been shown to conveniently detect peptides incorporating the boronic acid moiety by MALDI.