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  • Title: Vitamin E chemistry. Studies into initial oxidation intermediates of alpha-tocopherol: disproving the involvement of 5a-C-centered "chromanol methide" radicals.
    Author: Rosenau T, Kloser E, Gille L, Mazzini F, Netscher T.
    Journal: J Org Chem; 2007 Apr 27; 72(9):3268-81. PubMed ID: 17391045.
    Abstract:
    Contrary to concepts handed down in the literature from the early days of vitamin E research, one-electron oxidation of vitamin E does not involve 5a-C-centered radicals. A combined approach of analytical techniques, in particular electron paramagnetic resonance spectroscopy (EPR), organic synthesis of special derivatives, isotopic labeling, kinetic studies, and computational chemistry was used to re-evaluate the one-electron and two-electron oxidation chemistry of alpha-tocopherol (alpha-toc). EPR in combination with 5a-13C-labeled compounds provided no indication of the involvement of 5a-C-centered radicals. Oxidation of special tocopherol derivatives were used to disprove the occurrence of 5a-C-centered one-electron intermediates. Additionally it was shown that those vitamin E reactions that were commonly evoked to plead for the involvement of C-centered tocopheryl radicals actually proceeded via heterolytic, i.e., non-radical, intermediates. The results will help to clear widely spread misunderstandings about the chemistry of vitamin E and will have mechanistic implications for the synthesis of tocopherol-based supramolecular structures and 5a-substituted alpha-tocopherol derivatives.
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