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Regenerable Organochalcogen Antioxidants: An Explorative Study
Uppsala University, Disciplinary Domain of Science and Technology, Chemistry, Department of Chemistry - BMC, Organic Chemistry.ORCID iD: 0000-0003-0689-3180
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. , p. 70
Series
Digital Comprehensive Summaries of Uppsala Dissertations from the Faculty of Science and Technology, ISSN 1651-6214 ; 1556
Keyword [en]
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: urn:nbn:se:uu:diva-329217ISBN: 978-91-513-0068-9 (print)OAI: oai:DiVA.org:uu-329217DiVA, id: diva2:1139922
Public defence
2017-10-27, B7:101a, BMC, Husargatan 3, 751 23, Uppsala, 09:30 (English)
Opponent
Supervisors
Available from: 2017-10-05 Created: 2017-09-10 Last updated: 2017-10-18
List of papers
1. Multifunctional Antioxidants: Regenerable Radical-Trapping and Hydroperoxide-Decomposing Ebselenols
Open this publication in new window or tab >>Multifunctional Antioxidants: Regenerable Radical-Trapping and Hydroperoxide-Decomposing Ebselenols
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2016 (English)In: Angewandte Chemie International Edition, ISSN 1433-7851, E-ISSN 1521-3773, Vol. 55, no 11, p. 3729-3733Article in journal (Refereed) Published
Abstract [en]

Regenerable, multifunctional ebselenol antioxidants were prepared that could quench peroxyl radicals more efficiently than -tocopherol. These compounds act as better mimics of the glutathione peroxidase enzymes than ebselen. Production of reactive oxygen species (ROS) and reactive nitrogen species (RNS) in human mononuclear cells was considerably decreased upon exposure to the organoselenium compounds. At a concentration of 25m, the ebselenol derivatives showed minimal toxicity in pre-osteoblast MC3T3cells.

National Category
Natural Sciences Engineering and Technology
Identifiers
urn:nbn:se:uu:diva-280006 (URN)10.1002/anie.201510947 (DOI)000371521000034 ()26879742 (PubMedID)
Funder
Swedish Research CouncilCarl Tryggers foundation , 13:346, 13:120
Available from: 2016-03-07 Created: 2016-03-07 Last updated: 2017-11-30Bibliographically approved
2. Chain-Breaking Phenolic 2,3-Dihydrobenzo[b]selenophene Antioxidants: Proximity Effects and Regeneration Studies
Open this publication in new window or tab >>Chain-Breaking Phenolic 2,3-Dihydrobenzo[b]selenophene Antioxidants: Proximity Effects and Regeneration Studies
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2017 (English)In: Chemistry - A European Journal, ISSN 0947-6539, E-ISSN 1521-3765, Vol. 23, no 60, p. 15080-15088Article in journal (Refereed) Published
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
chain-breaking antioxidants, phenols, dihydrobenzoselenophenes, lipid peroxidation, co-antioxidants
National Category
Organic Chemistry
Research subject
Chemistry with specialization in Organic Chemistry
Identifiers
urn:nbn:se:uu:diva-329201 (URN)10.1002/chem.201702350 (DOI)000413768900018 ()28857289 (PubMedID)
Available from: 2017-09-10 Created: 2017-09-10 Last updated: 2018-02-23Bibliographically approved
3. Regenerable thiophenolic radical-trapping antioxidants
Open this publication in new window or tab >>Regenerable thiophenolic radical-trapping antioxidants
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2015 (English)In: Organic Letters, ISSN 1523-7060, E-ISSN 1523-7052, Vol. 17, no 24, p. 6162-6165Article in journal (Refereed) Published
Abstract [en]

Diphenyl disulfides carrying alkyltelluro groups in the o-, m-, and p-positions were prepared using ortho-lithiation and lithium halogen exchange reactions. The novel antioxidants showed only minimal inhibitory effect on the azo-initiated peroxidation of linoleic acid in chlorobenzene until reduced to the corresponding thiophenols by tris(2-carboxyethyl)phosphine (TCEP). The best in situ generated thiophenol (from 7c) under these conditions quenched peroxyl radicals more efficiently than α-tocopherol with an almost 3-fold increase in inhibition time.

National Category
Organic Chemistry
Identifiers
urn:nbn:se:uu:diva-269896 (URN)10.1021/acs.orglett.5b03169 (DOI)000366878300057 ()
Funder
Swedish Research Council, 621-2011-4006Carl Tryggers foundation , CTS:120
Available from: 2015-12-18 Created: 2015-12-18 Last updated: 2017-12-01Bibliographically approved
4. Substituent Effects in Chain-Breaking Aryltellurophenol Antioxidants
Open this publication in new window or tab >>Substituent Effects in Chain-Breaking Aryltellurophenol Antioxidants
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2018 (English)In: Chemistry - A European Journal, ISSN 0947-6539, E-ISSN 1521-3765, Vol. 24, no 14, p. 3520-3527Article in journal (Refereed) Published
Abstract [en]

2-Aryltellurophenols substituted in the aryltelluro or phenolic part of the molecule were prepared by lithiation of the corresponding O-THP-protected 2-bromophenol, followed by reaction with a suitable diaryl ditelluride and deprotection. In a two-phase system containing N-acetylcysteine as a co-antioxidant in the aqueous phase, all compounds quenched lipid peroxyl radicals more efficiently than α-tocopherol with 3 to 5-fold longer inhibition times. Compounds carrying electron donating para-substituents in the phenolic or aryltelluro part of the molecule showed the best results. The mechanism for quenching of peroxyl radicals was discussed in the light of calculated OH bond dissociation energies, deuterium labeling experiments and studies of thiol-consumption in the aqueous phase. 

National Category
Organic Chemistry
Research subject
Chemistry with specialization in Organic Chemistry
Identifiers
urn:nbn:se:uu:diva-329202 (URN)10.1002/chem.201704811 (DOI)000426764400024 ()29266496 (PubMedID)
Funder
Stiftelsen Olle Engkvist Byggmästare, 1016/159ÅForsk (Ångpanneföreningen's Foundation for Research and Development), 16-364
Note

Poon, J. and Yan, J. are equally contributing.

Available from: 2017-09-10 Created: 2017-09-10 Last updated: 2018-05-22Bibliographically approved

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