Intramolecular 1,2‐ and 1,3‐Hydrogen Transfer Reactions of Thiyl Radicals

Abstract

AbstractThis review article summarizes recent experiments on 1,2‐ and 1,3‐hydrogen transfer reactions in thiyl radicals from cysteine and related compounds. Pulse radiolysis in combination with time‐resolved UV spectroscopy was applied to monitor the equilibration of initial thiyl radicals with carbon‐centered radicals at both the Cα and Cβ positions of cysteine. Experiments with thiyl radicals from penicillamine and cysteamine confirmed the formation of carbon‐centered radicals at these positions. Complementary evidence for the intermediary formation of carbon‐centered radicals was obtained from mass spectrometry and 1H NMR spectroscopy experiments, both of which indicated covalent H/D exchange at original CH bonds when thiyl radicals were generated in D2O. The 1,2‐ and 1,3‐hydrogen transfer reactions can have profound consequences for the integrity of proteins when Cys residues are oxidized to Cys thiyl radicals, which subsequently equilibrate with carbon‐centered radicals.