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In Search of Catalytic Antioxidants-(Alkyltelluro)phenols, (Alkyltelluro)resorcinols, and Bis(alkyltelluro)phenols
Uppsala University, Disciplinary Domain of Science and Technology, Chemistry, Department of Chemistry - BMC, Synthetical Organic Chemistry.
Uppsala University, Disciplinary Domain of Science and Technology, Chemistry, Department of Chemistry - BMC, Biochemistry.
Uppsala University, Disciplinary Domain of Science and Technology, Chemistry, Department of Chemistry - BMC, Synthetical Organic Chemistry.
2013 (English)In: Journal of Organic Chemistry, ISSN 0022-3263, E-ISSN 1520-6904, Vol. 78, no 12, 6008-6015 p.Article in journal (Refereed) Published
Abstract [en]

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-butyllithiutn 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 alpha-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.

Place, publisher, year, edition, pages
2013. Vol. 78, no 12, 6008-6015 p.
National Category
Natural Sciences
URN: urn:nbn:se:uu:diva-205014DOI: 10.1021/jo400703wISI: 000320979500020OAI: oai:DiVA.org:uu-205014DiVA: diva2:640496
Available from: 2013-08-13 Created: 2013-08-13 Last updated: 2016-09-04Bibliographically approved
In thesis
1. Exploring Catalytic Tellurium-Based Antioxidants: Synthesis and Evaluation
Open this publication in new window or tab >>Exploring Catalytic Tellurium-Based Antioxidants: Synthesis and Evaluation
2016 (English)Doctoral thesis, comprehensive summary (Other academic)
Abstract [en]

This thesis is concerned with the synthesis and evaluation of various tellurium-based chain-breaking antioxidants. The purpose is to find novel regenerable compounds with improved radical-trapping capacity.

In the first part of this work, we explore the possibilities to incorporate tellurium into tocopherols and aromatic amines. Overall, tocopherols carrying alkyltelluro groups are better radical-trapping agents than the corresponding sulfur- and selenium analogues. Among them, 7-octyltelluro δ-tocopherol showed a ca. 17-fold higher reactivity than recorded for α-tocopherol and much better regenerability. Even longer inhibition times were recorded for the corresponding bis(tocopheryl) tellurides. In the aromatic amine series, diphenyl amines carrying alkyltelluro groups were shown to function as efficient radical-quenchers capable of inhibiting peroxidation for 460 min in the presence of N-acetylcysteine. Thiol-consumption experiments suggested that the long inhibition times are due to efficient quenching of in-situ formed alkoxyl radicals in a solvent cage.

In the second part of the thesis, we study how the antioxidant properties are affected by variations in the electron density at tellurium and the number of alkyltelluro substituents in the molecule. Evaluation of a series of aryltelluro phenols carrying electron donating and electron withdrawing groups in the para-position of the aryl moiety suggested that a high electron density at the heteroatom prolonged the inhibition time. Among alkyltelluro phenols, alkyltelluro resorcinols and bis(alkyltelluro) phenols, phenols carrying alkyltelluro groups in both ortho positions were superior when it comes to radical-trapping activity and regenerability.

Place, publisher, year, edition, pages
Uppsala: Acta Universitatis Upsaliensis, 2016. 72 p.
Digital Comprehensive Summaries of Uppsala Dissertations from the Faculty of Science and Technology, ISSN 1651-6214 ; 1423
antioxidant, tellurium, selenium, radical-trapping, chain-breaking, ROS, glutathione peroxidase, tocopherol, aromatic amine, oxidative stress
National Category
Organic Chemistry
urn:nbn:se:uu:diva-302475 (URN)978-91-554-9684-5 (ISBN)
Public defence
2016-10-27, B41, BMC, Husargatan 3, Uppsala, 09:30 (English)
Available from: 2016-10-03 Created: 2016-09-04 Last updated: 2016-10-03

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