Multi‐faceted Reactivity of Alkyltellurophenols Towards Peroxyl Radicals: Catalytic Antioxidant Versus Thiol‐Depletion Effect

Abstract

Hydroxyaryl alkyl tellurides are effective antioxidants both in organic solution and aqueous biphasic systems. They react by an unconventional mechanism with ROO(·) radicals with rate constants as high as 10(7) M(-1) s(-1) at 303 K, outperforming common phenols. The reactions proceed by oxygen atom transfer to tellurium followed by hydrogen atom transfer to the resulting RO(·) radical from the phenolic OH. The reaction rates do not reflect the electronic properties of the ring substituents and, because the reactions occur in a solvent cage, quenching is more efficient when the OH and TeR groups have an ortho arrangement. In the presence of thiols, hydroxyaryl alkyl tellurides act as catalytic antioxidants towards both hydroperoxides (mimicking the glutathione peroxidases) and peroxyl radicals. The high efficiency of the quenching of the peroxyl radicals and hydroperoxides could be advantageous under normal cellular conditions, but pro-oxidative (thiol depletion) when thiol concentrations are low.

Substituent Effects in Chain‐Breaking Aryltellurophenol Antioxidants

“…We have found a conceptually different way to improve the radical‐trapping activity of phenols. The seminal observation we made some time ago was that alkyltellurophenols could quench lipid peroxyl radicals with k inh >10 7 m −1 s −1 . Because the rate constant for the reaction of phenol itself with peroxyl radicals is only in the order of 10 3 m −1 s −1 , we proposed an unconventional mechanism for the reaction, that involved oxygen‐atom transfer from the peroxyl radical to tellurium, followed by hydrogen‐atom transfer from phenol to the resulting alkoxyl radical (Scheme ).…”

Resveratrol-based benzoselenophenes with an enhanced antioxidant and chain breaking capacity

“…9 Several studies support the introduction of 3 rd period and higher chalcogen atoms as another effective means of enhancing the antioxidant capacity of phenolic compounds. 10,11 Selenium-substitution was found to enhance the chain breaking activity via a decrease in the BDE values of the phenolic groups. 12,13 Similarly, the introduction of an octyltelluro group into the β-or δ-tocopherol system resulted in more efficient quenching of peroxyl radicals via an unusual oxygen transfer process to the chalcogen in the presence of N-acetylcysteine.…”

Regenerable Thiophenolic Radical-Trapping Antioxidants

“…17,18 In this work, we found that alkyltelluro groups have a remarkable effect. For example, introducing an octyltelluro group next to the OH in phenol caused a ca.…”