Theoretical Investigation of N-Nitrosation Mechanism of Amino Acids Mediated by N2O3

N-nitrosation mechanism of amino acids mediated by N₂O₃ was investigated at the B3LYP/6-311+G(d,p) level. Proline and tryptophan were selected as nitrosating substrates and their reactions with three different N₂O₃ isomers, i.e., asym-N₂O₃, sym-N₂O₃, and trans-cis N₂O₃ were studied respectively. The obtained results demonstrate that proline and tryptophan are able to be effectively nitrosated by all three N₂O₃ isomers, and the nitrosation of proline are somewhat easier than that of tryptophan. Moreover, the N-nitrosation of proline and tryptophan is easier to proceed by two relative unstable isomers sym-N₂O₃ and trans-cis N₂O₃ than asym-N₂O₃. The results obtained in this work will be helpful in better understanding the mechanism of N-nitrosation reactions of amino acids and even the modification of proteins through nitrosation.