title: In search of catalytic antioxidants--(alkyltelluro)phenols, (alkyltelluro)resorcinols, and bis(alkyltelluro)phenols.
abstract: The quenching of peroxyl radicals by ortho-(alkyltelluro)phenols occurs by a more complex mechanism than formal H-atom transfer. In an effort to improve on this concept, we have prepared (alkyltelluro)resorcinols and bis(alkyltelluro)phenols and evaluated their catalytic chain-breaking and preventive antioxidative properties. The in situ formed trianion produced from 2-bromophenol and 3 equiv of tert-butyllithium was allowed to react with dialkyl ditellurides to provide ortho-(alkyltelluro)phenols in low yields. 2-Bromoresorcinols after treatment with 4 equiv of tert-butyllithium similarly afforded 2-(alkyltelluro)resorcinols. Bis(alkyltelluro)phenols were accessed by allowing the trianion produced from the reaction of 2,6-dibromophenol with 5 equiv of tert-butyllithium to react with dialkyl ditellurides. The novel phenolic compounds were found to inhibit azo-initiated peroxidation of linoleic acid much more efficiently than α-tocopherol in a two-phase peroxidation system containing excess N-acetylcysteine as a stoichiometric thiol reducing agent in the aqueous phase. Whereas most of the (alkyltelluro)phenols and resorcinols could inhibit peroxidation for only 89-228 min, some of the bis(alkyltelluro)phenols were more regenerable and offered protection for >410 min. The novel (alkyltelluro)phenols were also evaluated for their capacity to catalyze reduction of hydrogen peroxide in the presence of thiophenol (glutathione peroxidase-like activity). (Alkyltelluro)resorcinols 7a-c were the most efficient catalysts with activities circa 65 times higher than those recorded for diphenyl diselenide.
authors.affiliation: Uppsala University, Department of Chemistry, BMC, Box 576, SE-751 23 Uppsala, Sweden.
authors.forename: Jia-fei
authors.initials: JF
authors.lastname: Poon
authors.forename: Vijay P
authors.initials: VP
authors.lastname: Singh
authors.forename: Lars
authors.initials: L
authors.lastname: Engman
mesh_terms: D000111:Acetylcysteine / Q000737:chemistry; D000975:Antioxidants / Q000138:chemical synthesis*; D001555:Benzene Derivatives / Q000737:chemistry; D002384:Catalysis; D006861:Hydrogen Peroxide / Q000737:chemistry; D019787:Linoleic Acid / Q000737:chemistry; D015227:Lipid Peroxidation; D009942:Organometallic Compounds / Q000138:chemical synthesis* / Q000737:chemistry; D016566:Organoselenium Compounds / Q000737:chemistry; D010545:Peroxides / Q000037:antagonists & inhibitors / Q000737:chemistry; D010636:Phenols / Q000138:chemical synthesis*; D012118:Resorcinols / Q000138:chemical synthesis*; D013691:Tellurium / Q000737:chemistry*; D024502:alpha-Tocopherol / Q000737:chemistry
chemical_list: D000975:Antioxidants; D001555:Benzene Derivatives; D009942:Organometallic Compounds; D016566:Organoselenium Compounds; D010545:Peroxides; D010636:Phenols; D012118:Resorcinols; C434823:n-butyllithium; C061132:diphenyldiselenide; C049375:perhydroxyl radical; D019787:Linoleic Acid; D006861:Hydrogen Peroxide; D024502:alpha-Tocopherol; D013691:Tellurium; D000111:Acetylcysteine