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Regenerable Antioxidants - Introduction of Chalcogen Substituents into Tocopherols
Uppsala University, Disciplinary Domain of Science and Technology, Chemistry, Department of Chemistry - BMC.
Uppsala University, Disciplinary Domain of Science and Technology, Chemistry, Department of Chemistry - BMC.
Uppsala University, Disciplinary Domain of Science and Technology, Chemistry, Department of Chemistry - BMC.
Uppsala University, Disciplinary Domain of Science and Technology, Chemistry, Department of Chemistry - BMC.
2015 (English)In: Chemistry - A European Journal, ISSN 0947-6539, E-ISSN 1521-3765, Vol. 21, no 6, 2447-2457 p.Article in journal (Refereed) Published
Abstract [en]

To improve the radical-trapping capacity of the natural antioxidants, alkylthio-, alkylseleno-, and alkyltelluro groups were introduced into all vacant aromatic positions in β-, γ- and δ-tocopherol. Reaction of the tocopherols with electrophilic chalcogen reagents generated by persulfate oxidation of dialkyl dichalcogenides provided convenient but low-yielding access to many sulfur and selenium derivatives, but failed in the case of tellurium. An approach based on lithiation of the appropriate bromo-tocopherol, insertion of chalcogen into the carbon-lithium bond, air-oxidation to a dichalcogenide, and final borohydride reduction/alkylation turned out to be generally applicable to the synthesis of all chalcogen derivatives. Whereas alkylthio- and alkylseleno analogues were generally poorer quenchers of lipid peroxyl radicals than the corresponding parents, all tellurium compounds showed a substantially improved radical-trapping activity. Introduction of alkyltelluro groups into the tocopherol scaffold also caused a dramatic increase in the regenerability of the antioxidant. In a two-phase lipid peroxidation system containing N-acetylcysteine as a water-soluble co-antioxidant the inhibition time was up to six-fold higher than that recorded for the natural antioxidants.

Place, publisher, year, edition, pages
2015. Vol. 21, no 6, 2447-2457 p.
National Category
Chemical Sciences
Identifiers
URN: urn:nbn:se:uu:diva-243231DOI: 10.1002/chem.201405895ISI: 000348510400023OAI: oai:DiVA.org:uu-243231DiVA: diva2:786459
Note

De två första författarna delar förstaförfattarskapet.

Available from: 2015-02-05 Created: 2015-02-05 Last updated: 2017-12-05Bibliographically 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.
Series
Digital Comprehensive Summaries of Uppsala Dissertations from the Faculty of Science and Technology, ISSN 1651-6214 ; 1423
Keyword
antioxidant, tellurium, selenium, radical-trapping, chain-breaking, ROS, glutathione peroxidase, tocopherol, aromatic amine, oxidative stress
National Category
Organic Chemistry
Identifiers
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)
Opponent
Supervisors
Available from: 2016-10-03 Created: 2016-09-04 Last updated: 2016-10-03

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Poon, Jia-feiSingh, Vijay PYan, JiajieEngman, Lars

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