Nitration of Bio-related Compounds with Peroxynitrite Mechanistic Implications to Biological Nitration

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In order to get insight into the mechanism of biological nitration, the reaction of peroxynitrite with some bio-related model compounds has been investigated in buffered aqueous solutions and acetonitrile. The compounds employed included phenols, N, N- i dimethylanline and activated olefines such as stilbene, 1, 4-diphenylbutadiene and 1, 4- diphenylbutenyne. Peroxynitrite was generated by the oxidation of sodium azide with ozone in aqueous alkaline solution.With phenols, concurrent nitration and hydroxylation took place on aromatic ring and the product distribution pattern showed a typical electrophilic nature. Side products included quinones and cyclohexadienes. A^A^-Dimethylaniline underwent extensive demethylation, which suggested involvement of the nitrosonium ion as active species. Stilbene afforded benzil, stilbene epoxide and benzaldehyde, together with some ring nitration products. The mechanism of oxidative cleavage of the carbon-carbon bond is not clear at present, since stilbene oxide, 1, 2-diphenylethanediol and diphenylhy＆roxyethanone were all found to be inert toward peroxynitrite. Under similar conditions, diphenylacetyle afforded benzil as the main product along with ring nitration products ; strangely enough, the substitution pattern of which was only ortho and meta. The olefinic bond was more reactive than the acetylenic one, but the difference was not so large as expected from the electrophilic process. The difference in relative reactivity between the olefinic and polyenic bonds was not so large, either.