Peroxynitrite oxidises catechols to o‐quinones

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Abstract
Nitration of phenolic compounds is a well‐established mechanism on interaction with peroxynitrite. However, while nitration is the predominant reaction for monophenolic hydroxycinnamates, this does not take place with the catechol‐containing hydroxycinnamate, caffeic acid. The aim of the present study was to investigate the mechanism of the chemical interaction of caffeic acid with peroxynitrite and to characterise the products formed. A novel compound was detected and characterised as the o‐quinone of caffeic acid based on its reaction with nucleophilic thiol compounds, glutathione and l‐cysteine. The same novel product was identified following the oxidation of caffeic acid in alkaline solutions confirming the identity of this species as a caffeic acid oxidation product.