Theoretical study on mechanism of reactions of triarylphosphines with S-nitrosated proteins

Triarylphosphines are recently found to be effective biomarkers for S-nitrosated proteins (RSNOs). Mechanistic study has been carried out on the reactions of triarylphosphines with S-nitrosated proteins using theoretical calculations. According to which atom of MeSNO (S, N or O) is first attacked by triphenylphosphine, there are three possible pathways. It is found that the pathway in which the triphenylphosphine first attacks the N atom of MeSNO is the most favored. In this pathway, triphenylphosphine first reacts with the MeSNO to form a three-membered ring intermediate. Then the intermediate converts to a phosphine oxide and a new intermediate MeSN. MeSN readily reacts with another triphenylphosphine to form an S-methyl aza-ylide intermediate. Finally, the protonated S-methyl aza-ylide reacts with a triphenylphosphine to yield an S-methylphosphonium ion and a triphenylphosphoranimine. The rate-determining step is the attack of the triphenlyphosphine on the N atom of MeSNO, with the energy barrier of 24.7 kcal/mol.