Oxidative damage of aromatic dipeptides by the environmental oxidants NO<sub>2</sub>˙ and O<sub>3</sub>
作者:L. F. Gamon、J. M. White、U. Wille
DOI:10.1039/c4ob01577k
日期:——
Irreversible oxidative damage at both aromatic side chains and dipeptide linkage occurs in the aromatic N- and C-protected dipeptides 7â11 upon exposure to the environmental pollutants NO2Ë and O3. The reaction proceeds through initial oxidation of the aromatic ring by in situ generated NO3Ë, or by NO2Ë, respectively, which leads to formation of nitroaromatic products. The indole ring in Phe-Trp undergoes oxidative cyclization to a pyrroloindoline. An important reaction pathway for dipeptides with less oxidisable aromatic side chains proceeds through fragmentation of the peptide bond with concomitant acyl migration. This process is likely initiated by an ionic reaction of the amide nitrogen with the NO2Ë dimer, N2O4.
Damage of aromatic amino acids by the atmospheric free radical oxidant NO3˙ in the presence of NO2˙, N2O4, O3 and O2
作者:Catrin Goeschen、Natalia Wibowo、Jonathan M. White、Uta Wille
DOI:10.1039/c0ob01186j
日期:——
Analysis of the products formed in the reaction of NO3Ë with the N- and C-protected aromatic amino acids 1â5, 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, NO3Ë 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 NO3Ë 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.