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Chain-Breaking Phenolic 2,3-Dihydrobenzo[b]selenophene Antioxidants – Proximity Effects and Regeneration Studies
Uppsala University, Disciplinary Domain of Science and Technology, Chemistry, Department of Chemistry - BMC, Organic Chemistry. Department of Chemistry & Centre of Advanced Studies in Chemistry, Panjab University, India.
Uppsala University, Disciplinary Domain of Science and Technology, Chemistry, Department of Chemistry - BMC, Organic Chemistry. (Lars Engman)ORCID iD: 0000-0003-0689-3180
Uppsala University, Disciplinary Domain of Science and Technology, Chemistry, Department of Chemistry - BMC, Organic Chemistry. (Lars Engman)
School of Chemistry, University of Bristol, United Kingdom.
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(English)In: Chemistry - A European Journal, ISSN 0947-6539, E-ISSN 1521-3765Article in journal (Refereed) Accepted
Abstract [en]

Phenolic 2,3-dihydrobenzo[b]selenophene anti-oxidants carrying the OH-group ortho (9), meta (10, 11) and para (8) to the Se were prepared by seleno-Claisen rearrangement/intramolecular hydroselenation. Meta-isomer (11) was studied by X-ray crystallography. The radical-trapping activity and regenerability of compounds 8-11 were evaluated using a two-phase system where linoleic acid was undergoing peroxidation in the lipid phase while regeneration of the antioxidant by co-antioxidants (N-acetylcysteine, glutathione, dithiothreitol, ascorbic acid, tris(carboxyethyl)phosphine hydrochloride) was ongoing in the aqueous layer. Compound 9 quenched peroxyl radicals

more efficiently than α-tocopherol. It also provided the most long-lasting antioxidant protection. With thiol co-antioxidants it could inhibit peroxidation for more than five-fold longer than the natural product. Regeneration was more efficient when the aqueous phase pH was slightly acidic. Since calculated O-H bond dissociation energies for 8-11 were substantially larger than for α-tocopherol, an antioxidant mechanism involving O-atom transfer from peroxyl to selenium was proposed. The resulting phenolic selenoxide/alkoxyl radical would then exchange a hydrogen atom in a solvent cage before antioxidant regeneration at the aqueous lipid interphase.

Keyword [en]
chain-breaking antioxidants, phenols, dihydrobenzoselenophenes, lipid peroxidation, co-antioxidants
National Category
Organic Chemistry
Research subject
Chemistry with specialization in Organic Chemistry
Identifiers
URN: urn:nbn:se:uu:diva-329201DOI: 10.1002/chem.201702350OAI: oai:DiVA.org:uu-329201DiVA: diva2:1139907
Available from: 2017-09-10 Created: 2017-09-10 Last updated: 2017-09-10
In thesis
1. Regenerable Organochalcogen Antioxidants: An Explorative Study
Open this publication in new window or tab >>Regenerable Organochalcogen Antioxidants: An Explorative Study
2017 (English)Doctoral thesis, comprehensive summary (Other academic)
Abstract [en]

Antioxidants are widely used to protect organic materials from damages caused by autoxidation, an oxidation process that occurs under normal aerobic conditions. In this thesis, novel multifunctional organoselenium and organotellurium antioxidants were designed, synthesized, and evaluated in search for compounds with better radical-trapping capacity, regenerability, and hydroperoxide-decomposing ability.

Selenium was incorporated into ebselenols and hydroxy-2,3-dihydrobenzo[b]selenophenes and tellurium into diaryl disulfides and aryltellurophenols. All newly developed antioxidants were evaluated in a chlorobenzene/water two-phase lipid peroxidation system containing suitable co-antioxidants in the aqueous phase. Ebselenol carrying a hydroxyl group (OH) ortho to selenium showed a two-fold longer inhibition time than the reference α-tocopherol in the presence of aqueous-phase ascorbic acid. 2,3-Dihydrobenzo[b]selenophenes carrying a 5- or 7-OH outperformed α-tocopherol both when it comes to radical-trapping capacity and regenerability. Alkyltellurothiophenols, in situ formed from their corresponding disulfides by tris(2-carboxyethyl)phosphine, were also efficient regenerable radical-trapping antioxidants. The consumption of N-acetylcysteine in the water phase was followed and found to be limiting for the duration of the inhibition. The hydroperoxide-decomposing ability of all organoselenium antioxidants was evaluated. Ebselenols were often better glutathione peroxidase mimics than the parent.

In an effort to find out more about antioxidant mechanisms, aryltellurophenols carrying electron donating and electron withdrawing groups in the phenolic or aryltelluro parts were synthesized and OH bond dissociation enthalpies, BDEO-Hs, were calculated. Compounds carrying electron donating groups in the phenolic or aryltelluro part of the molecule showed the best radical-trapping capacity. Deuterium labelling experiments suggested that hydrogen atom transfer could be the rate-limiting step in the antioxidant mechanism.  

Place, publisher, year, edition, pages
Uppsala: Acta Universitatis Upsaliensis, 2017. 70 p.
Series
Digital Comprehensive Summaries of Uppsala Dissertations from the Faculty of Science and Technology, ISSN 1651-6214 ; 1556
Keyword
autoxidation, antioxidant, selenium, tellurium, regenerable, multifunctional, radical-trapping, hydroperoxide-decomposing, co-antioxidant
National Category
Organic Chemistry
Research subject
Chemistry with specialization in Organic Chemistry
Identifiers
urn:nbn:se:uu:diva-329217 (URN)978-91-513-0068-9 (ISBN)
Public defence
2017-10-27, B7:101a, BMC, Husargatan 3, 751 23, Uppsala, 09:30 (English)
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Available from: 2017-10-05 Created: 2017-09-10 Last updated: 2017-10-18

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