Intramolecularly coordinated diorganyl ditellurides: Thiol peroxidase-like antioxidants

A series of diaryl ditellurides with and without coordinating amino/imino groups are synthesized by using either the Grignard route or the heteroatom-directed aromatic lithiation route. The chiral ditelluride (R),(R)-bis[2-(4-ethyl-2-oxazolinyl)phenyl] ditelluride is synthesized in an enantiomerically pure form by stereoselective ortho-lithiation. The thiol peroxidase activity of the ditellurides is studied by using H2O2 as a substrate and PhSH as a cosubstrate. The initial rates for the reduction of H2O2 catalyzed by diaryl ditellurides are much higher than those catalyzed by the corresponding diselenides. A comparison of the activities between various diorganyl ditellurides and diselenides shows that the presence of basic amino groups in the close proximity of tellurium enhances the reduction rates and the effect of amino groups on the activity is more pronounced in the case of ditellurides as compared to the corresponding diselenides. On the other hand, a correlation between the strength of Te...N intramolecular interactions and thiol peroxidase activity reveals that the strong Te...N interactions reduce the thiol peroxidase activity of amino/imino-substituted ditellurides. A plot of Te...N distances against Te-125 NMR chemical shifts shows a linear correlation.