Intramolecular Addition of Cysteine Thiyl Radical to Phenylalanine and Tyrosine in Model Peptides, Phe (CysS) and Tyr(CysS): A Computational Study

2009-04-16T00:00:00Z (GMT) by Sergej Naumov Christian Schöneich
Density Functional Theory (DFT) calculations were carried out to evaluate the potential for intramolecular addition of peptide cysteine (Cys) thiyl radicals (CysS) to aromatic amino acids (Phe and Tyr) in water. These calculations yielded cyclic conformations, in which π-complexes were more stable than cyclohexadienyl radicals in water. In these π-complexes, the C2−S distances were significantly shorter compared to the C1−S and C3−S distances. Comparable results on the relative stabilities were obtained for model calculations for the addition of HS/CH3S to toluene and p-hydroxytoluene. The adduct of thiyl radicals with Phe was more stable than that with Tyr, and the stabilization energies depended on the C-terminal substituents.