Isochorismic acid, also called isochorismate, is an organic dibasic acid synthesized from chorismate.
Synthesis
The enzyme chorismate hydroxymutase (isochorismate synthase, CF 5.4.4.2) reversibly isomerizes chorismate into isochorismate, giving rise to one of the branches of the
shikimate pathway.
Isochorismate is a precursor in the biosynthesis of many natural compounds. Salicylic acid and terpenoid naphthoquinones (menaquinones, phylloquinones) are synthesized from isochorismate, although in some organisms these compounds can be synthesized from chorismate in alternative ways, not through isochorismate (for example, the futalosine pathway of menaquinone biosynthesis in some prokaryotes).
Discovery
The compound was discovered by Australian researchers in 1968 as an intermediate in the biosynthesis of 2,3-dihydroxybenzoate (ortho-pyrocatechate, an
enterobactin precursor) from chorismate in
Aerobacter aerogenes. The reaction presumably proceeds via nucleophilic attack of water at the carbon atom.
The trivial name "isochorismic acid", which has been fixed for the compound, was proposed by these researchers, who described the substance for the first time.
Properties
Isochorismic acid is a thermodynamically unstable compound. In an aqueous solution at room temperature and pH = 7, isochorismate decomposes into a mixture of salicylate and meta-carboxyphenylpyruvate.
The latter is formed from
isoprephenate (also a thermodynamically unstable compound), which arises as a result of the 3,3-sigmatropic rearrangement of isochorismate.
