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Vitamin E Chemistry. Studies into Initial Oxidation Intermediates of α-Tocopherol: Disproving the Involvement of 5a-C-Centered “Chromanol Methide” Radicals

Supporting Info

Thomas Rosenau,*^† Elisabeth Kloser,^† Lars Gille,*^‡ Francesco Mazzini,^§ and Thomas Netscher;

Department of Chemistry, University of Natural Resources and Applied Life Sciences, Muthgasse 18, A-1190 Vienna, Austria, Research Institute for Biochemical Pharmacology and Toxicology, University of Veterinary Medicine Vienna, Veterinrpl. 1, A-1210 Vienna, Austria, Dipartimento di Chimica e Chimica Industriale, Universit di Pisa, Via Risorgimento 35, 56126 Pisa, Italy, and Research and Development, DSM Nutritional Products, P.O. Box 3255, CH-4002 Basel, Switzerland

J. Org. Chem., 2007, 72 (9), pp 3268–3281

DOI: 10.1021/jo062553j

Publication Date (Web): March 29, 2007

In papers with more than one author, the asterisk indicates the name of the author to whom inquiries about the paper should be addressed.

†

University of Natural Resources and Applied Life Sciences.

‡

University of Veterinary Medicine.

Università di Pisa.

DSM Nutritional Products.

, thomas.rosenau@boku.ac.at, ; , lars.gille@vu-wien.ac.at

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 α-tocopherol (α-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 α-tocopherol derivatives.

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