Damage of aromatic amino acids by the atmospheric free radical oxidant NO3˙ in the presence of NO2˙, N2O4, O3 and O2

Abstract

Analysis of the products formed in the reaction of NO₃˙ with the N- and C-protected aromatic amino acids 1–5, which was performed under conditions that simulate exposure of biosurfaces to environmental pollutants, revealed insight how this important atmospheric free-radical oxidant can cause irreversible damage. In general, NO₃˙ induced electron transfer at the aromatic ring is the exclusive initial pathway in a multi-step sequence, which ultimately leads to nitroaromatic compounds. In the reaction of NO₃˙ with tryptophan 5 tricyclic products 12 and 13 are formed through an intramolecular, oxidative cyclization involving the amide moiety. In addition to this, strong indication for formation of N-nitrosamides was obtained, which likely result from reaction with N₂O₄ through an independent non-radical pathway.