GPx-Like Activity of Selenides and Selenoxides: Experimental Evidence for the Involvement of Hydroxy Perhydroxy Selenane as the Active Species

The reaction mechanism of the GPx-like oxidation of PhSH
with H2O2 catalyzed by selenoxides proceeds
via formation
of the hydroxy perhydroxy selenane, which is a stronger oxidizing
agent than selenoxide. A hydroxy perhydroxy selenane intermediate
was observed by electrospray ionization mass spectrometry and 77Se NMR spectroscopy in reactions of selenoxide 8 with H2O2.The initial velocity of oxidation
of PhSH by H2O2 with selenoxide 8 is 4 orders of magnitude higher than that of 8 without
peroxide. Selenoxide 8 is not reduced to selenide 6 by PhSH in the presence of H2O2. While
electronic substituent effects have minimal impact on the catalytic
performance of selenoxides, chelating groups increase the rate of
catalysis.