title: Optimization of the antioxidant activity of hydroxy-substituted 4-thiaflavanes: a proof-of-concept study.
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 (k(inh)), and bond dissociation energies (BDE), of the ArO-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 k(inh) up to 4.0×10(6) M(-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.
authors.affiliation: Dipartimento di Chimica Ugo Schiff, Polo Scientifico e Tecnologico Università di Firenze, Via della Lastruccia 3-13, 50019 Sesto Fiorentino, Italy.
authors.forename: Caterina
authors.initials: C
authors.lastname: Viglianisi
authors.forename: Maria Grazia
authors.initials: MG
authors.lastname: Bartolozzi
authors.forename: Gian Franco
authors.initials: GF
authors.lastname: Pedulli
authors.forename: Riccardo
authors.initials: R
authors.lastname: Amorati
authors.forename: Stefano
authors.initials: S
authors.lastname: Menichetti
mesh_terms: D000975:Antioxidants / Q000737:chemistry*; D005419:Flavonoids / Q000737:chemistry*; D006571:Heterocyclic Compounds / Q000737:chemistry*; D006860:Hydrogen Bonding; D007700:Kinetics; D008968:Molecular Conformation; D015394:Molecular Structure; D013455:Sulfur / Q000737:chemistry*; D024505:Tocopherols / Q000737:chemistry*
chemical_list: D000975:Antioxidants; D005419:Flavonoids; D006571:Heterocyclic Compounds; D013455:Sulfur; D024505:Tocopherols