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Optimization of the Antioxidant Activity of Hydroxy-Substituted 4-Thiaflavanes: A Proof-of-Concept Study

Authors

  • Dr. Caterina Viglianisi,

    1. Dipartimento di Chimica “Ugo Schiff”, Polo Scientifico e Tecnologico Università di Firenze, Via della Lastruccia 3–13, 50019 Sesto Fiorentino (Italy), Fax: (+39) 055-4573531
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  • Dr. Maria Grazia Bartolozzi,

    1. Dipartimento di Chimica “Ugo Schiff”, Polo Scientifico e Tecnologico Università di Firenze, Via della Lastruccia 3–13, 50019 Sesto Fiorentino (Italy), Fax: (+39) 055-4573531
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  • Prof. Gian Franco Pedulli,

    1. Dipartimento di Chimica Organica “A. Mangini”, Università di Bologna, Via S. Giacomo 11, 40126 Bologna (Italy), Fax: (+39) 051-2095688
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  • Dr. Riccardo Amorati,

    Corresponding author
    1. Dipartimento di Chimica Organica “A. Mangini”, Università di Bologna, Via S. Giacomo 11, 40126 Bologna (Italy), Fax: (+39) 051-2095688
    • Dipartimento di Chimica Organica “A. Mangini”, Università di Bologna, Via S. Giacomo 11, 40126 Bologna (Italy), Fax: (+39) 051-2095688
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  • Prof. Stefano Menichetti

    Corresponding author
    1. Dipartimento di Chimica “Ugo Schiff”, Polo Scientifico e Tecnologico Università di Firenze, Via della Lastruccia 3–13, 50019 Sesto Fiorentino (Italy), Fax: (+39) 055-4573531
    • Dipartimento di Chimica “Ugo Schiff”, Polo Scientifico e Tecnologico Università di Firenze, Via della Lastruccia 3–13, 50019 Sesto Fiorentino (Italy), Fax: (+39) 055-4573531
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Abstract

The design and the synthesis of a new family of hydroxy-4-thiaflavanes, in which the reactive phenolic OH is ortho to the sulfur atom of the benzofused oxathiin ring, allowed to prepare antioxidants that show rate constants for the reaction with peroxyl radicals (kinh), and bond dissociation energies (BDE), of the ArO[BOND]H group identical to those of α-tocopherol, the main component of vitamin E and the most effective lipophilic antioxidant known in nature. The peculiar conformation of the six-membered heterocyclic ring prevents the formation of an intramolecular hydrogen bond between the OH group and the S atom, while ensuring a good stabilization by electron donation of the phenoxyl radical formed after the reaction with peroxyl radicals. The preparation of these compounds was achieved through an inverse electron demand hetero Diels–Alder reaction of styrenes with o-thioquinones, in turn prepared from accurately designed 1,3-dihydroxy arenes. Properly arranging the substitution pattern on the aromatic ring, as in derivatives 9 and 11, allowed to reach values of kinh up to 4.0×106M−1 s−1 and BDE(OH) of 77.2 kcal mol−1. This approach represents an innovative way to obtain highly active antioxidants without using strongly electron donating alkylamino groups which are associated with adverse toxicological profiles.

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