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Selenium Catalysts and Antioxidants

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A special issue of Molecules (ISSN 1420-3049). This special issue belongs to the section "Organic Chemistry".

Deadline for manuscript submissions: closed (30 April 2015) | Viewed by 116323

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Prof. Dr. Thomas G. Back

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Department of Chemistry, University of Calgary, Calgary, AB T2N 1N4, Canada
Interests: organic synthesis; medicinal chemistry; organosulfur and selenium chemistry; glutathione peroxidase mimetics

Special Issue Information

Dear Colleagues,

Selenium-based catalysts play an important role in organic synthesis and biology. The unique redox properties of the element can be exploited in a variety of synthetically useful transformations and are known to play crucial roles in several biological processes. While traditional laboratory oxidations were carried out in the past with stoichiometric reagents, such as selenium dioxide or benzeneseleninic anhydride, more recent emphasis has focused on catalytic variations, particularly ones employing stoichiometric amounts of inexpensive and environmentally benign co-oxidants, such as hydrogen peroxide. Examples include dehydrogenations of carbonyl compounds, epoxidations, and brominations. Several catalytic electrophilic and nucleophilic selenium reactions have also been reported, along with enantioselective variations. On the other hand, the redox properties of selenium also enable it to catalyze the reduction of harmful peroxides in living organisms, thereby mitigating oxidative stress, which results from the in vivo formation of peroxides and from other reactive oxygen species derived from those peroxides. For example, selenoenzyme glutathione peroxidase reduces peroxides, with glutathione as the sacrificial co-reductant. Small-molecule selenium compounds that mimic this activity are also of current interest as biological antioxidants. Several other selenoenzymes that regulate biologically important processes, along with their mimetics, have also been reported.

This Special Issue welcomes the submission of papers based on original research that describe selenium compounds as catalysts in synthetically valuable organic transformations or in the area of selenium-based antioxidants and related compounds, including both selenoenzymes and small molecules that emulate them.

Prof. Dr. Thomas G. Back
Guest Editor

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Keywords

Synthetic applications
catalytic oxidations
catalytic reductions
enantioselective catalytic processes
selenoenzymes
glutathione peroxidase
small-molecule selenium antioxidants

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Published Papers (12 papers)

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Research

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6 pages, 1375 KiB

Open AccessCommunication

Synthesis of a Stable Primary-Alkyl-Substituted Selenenyl Iodide and Its Hydrolytic Conversion to the Corresponding Selenenic Acid

by Shohei Sase, Ryo Kakimoto, Ryutaro Kimura and Kei Goto

Molecules 2015, 20(12), 21415-21420; https://doi.org/10.3390/molecules201219773 - 2 Dec 2015

Cited by 12 | Viewed by 5878

Abstract

A primary-alkyl-substituted selenenyl iodide was successfully synthesized through oxidative iodination of a selenol with N-iodosuccinimide by taking advantage of a cavity-shaped steric protection group. The selenenyl iodide exhibited high thermal stability and remained unchanged upon heating at 100 °C for 3 h in [D₈]toluene. The selenenyl iodide was reduced to the corresponding selenol by treatment with dithiothreitol. Hydrolysis of the selenenyl iodide under alkaline conditions afforded the corresponding selenenic acid almost quantitatively, corroborating the chemical validity of the recent proposal that hydrolysis of a selenenyl iodide to a selenenic acid is potentially involved in the catalytic mechanism of an iodothyronine deiodinase. Full article

(This article belongs to the Special Issue Selenium Catalysts and Antioxidants)

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19 pages, 1468 KiB

Open AccessArticle

Aspects of a Distinct Cytotoxicity of Selenium Salts and Organic Selenides in Living Cells with Possible Implications for Drug Design

by Ethiene Castellucci Estevam, Karolina Witek, Lisa Faulstich, Muhammad Jawad Nasim, Gniewomir Latacz, Enrique Domínguez-Álvarez, Katarzyna Kieć-Kononowicz, Marilene Demasi, Jadwiga Handzlik and Claus Jacob

Molecules 2015, 20(8), 13894-13912; https://doi.org/10.3390/molecules200813894 - 31 Jul 2015

Cited by 22 | Viewed by 7836

Abstract

Selenium is traditionally considered as an antioxidant element and selenium compounds are often discussed in the context of chemoprevention and therapy. Recent studies, however, have revealed a rather more colorful and diverse biological action of selenium-based compounds, including the modulation of the intracellular redox homeostasis and an often selective interference with regulatory cellular pathways. Our basic activity and mode of action studies with simple selenium and tellurium salts in different strains of Staphylococcus aureus (MRSA) and Saccharomyces cerevisiae indicate that such compounds are sometimes not particularly toxic on their own, yet enhance the antibacterial potential of known antibiotics, possibly via the bioreductive formation of insoluble elemental deposits. Whilst the selenium and tellurium compounds tested do not necessarily act via the generation of Reactive Oxygen Species (ROS), they seem to interfere with various cellular pathways, including a possible inhibition of the proteasome and hindrance of DNA repair. Here, organic selenides are considerably more active compared to simple salts. The interference of selenium (and tellurium) compounds with multiple targets could provide new avenues for the development of effective antibiotic and anticancer agents which may go well beyond the traditional notion of selenium as a simple antioxidant. Full article

(This article belongs to the Special Issue Selenium Catalysts and Antioxidants)

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20 pages, 1054 KiB

Open AccessArticle

Substituent Effects on the Stability and Antioxidant Activity of Spirodiazaselenuranes

by Devappa S. Lamani, Debasish Bhowmick and Govindasamy Mugesh

Molecules 2015, 20(7), 12959-12978; https://doi.org/10.3390/molecules200712959 - 17 Jul 2015

Cited by 14 | Viewed by 7508

Abstract

Spirodiazaselenuranes are structurally interesting compounds and the stability of these compounds depends highly on the nature of the substituents attached to the nitrogen atoms. Aromatic substituents are known to play important roles in stabilizing the Se-N bonds in spiro compounds. In this study, several spirodiazaselenuranes are synthesized by introducing benzylic and aliphatic substituents to understand their effect on the stability of the Se-N bonds and the antioxidant activity. Replacement of phenyl substituent by benzyl/alkyl groups significantly reduces the stability of the spirodiazaselenuranes and slows down the oxidative cyclization process. The selenium centre in the spiro compounds undergoes further oxidation to produce the corresponding selenurane oxides, which are stable at room temperature. Comparison of the glutathione peroxidase (GPx) mimetic activity of the compounds showed that the diaryl selenides having heterocyclic rings are significantly more active due to the facile oxidation of the selenium centre. However, the activity is reduced significantly for compounds having aliphatic substituents. In addition to GPx activity, the compounds also inhibit peroxynitrite-mediated nitration and oxidation reaction of protein and small molecules, respectively. The experimental observations suggest that the antioxidant activity is increased considerably upon substitution of the aromatic group with the benzylic/aliphatic substituents on the nitrogen atoms. Full article

(This article belongs to the Special Issue Selenium Catalysts and Antioxidants)

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16 pages, 1689 KiB

Open AccessArticle

Synthesis, Structure and Antioxidant Activity of Cyclohexene-Fused Selenuranes and Related Derivatives

by Poonam Rajesh Prasad, Harkesh B. Singh and Ray J. Butcher

Molecules 2015, 20(7), 12670-12685; https://doi.org/10.3390/molecules200712670 - 13 Jul 2015

Cited by 17 | Viewed by 6996

Abstract

Synthesis, structure and antioxidant activity of new cyclohexene-fused spiroselenuranes and a spirotellurane is reported. Oxidation reactions of bis(o-formylcyclohex- 1-ene)selenide/bis(2-hydroxymethylcyclohex-1-ene)selenide provide the corresponding spiroselenuranes. The glutathione peroxidase-like activity of the newly synthesized compounds has been evaluated. Full article

(This article belongs to the Special Issue Selenium Catalysts and Antioxidants)

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12 pages, 783 KiB

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Mimicking the Lipid Peroxidation Inhibitory Activity of Phospholipid Hydroperoxide Glutathione Peroxidase (GPx4) by Using Fatty Acid Conjugates of a Water-Soluble Selenolane

by Michio Iwaoka, Arisa Katakura, Jun Mishima, Yoshimi Ishihara, Amit Kunwar and Kavirayani Indira Priyadarsini

Molecules 2015, 20(7), 12364-12375; https://doi.org/10.3390/molecules200712364 - 7 Jul 2015

Cited by 15 | Viewed by 11165

Abstract

A series of fatty acid conjugates of trans-3,4-dihydroxy-1-selenolane (DHS) were synthesized by reacting DHS with appropriate acid chlorides. The obtained monoesters were evaluated for their antioxidant capacities by the lipid peroxidation assay using a lecithin/cholesterol liposome as a model system. The observed antioxidant capacities against accumulation of the lipid hydroperoxide (LOOH) increased with increasing the alkyl chain length and became saturated for dodecanoic acid (C₁₂) or higher fatty acid monoesters, for which the capacities were much greater than those of DHS, its tridecanoic acid (C₁₃) diester, and PhSeSePh. On the other hand, the bacteriostatic activity of myristic acid (C₁₄) monoester, evaluated through the colony formation assay using Bacillus subtilis, indicated that it has higher affinity to bacterial cell membranes than parent DHS. Since DHS-fatty acid conjugates would inhibit lipid peroxidation through glutathione peroxidase (GPx)-like 2e⁻ mechanism, higher fatty acid monoesters of DHS can mimic the function of GPx4, which interacts with LOOH to reduce it to harmless alcohol (LOH). Importance of the balance between hydrophilicity and lipophilicity for the design of effective GPx4 mimics was suggested. Full article

(This article belongs to the Special Issue Selenium Catalysts and Antioxidants)

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7 pages, 750 KiB

Open AccessCommunication

Selenium-Mediated Synthesis of Tetrasubstituted Naphthalenes through Rearrangement

by James Tancock and Thomas Wirth

Molecules 2015, 20(6), 10866-10872; https://doi.org/10.3390/molecules200610866 - 12 Jun 2015

Cited by 6 | Viewed by 6337

Abstract

New β-keto ester substituted stilbene derivatives have been synthesized and cyclized with selenium electrophiles in the presence of Lewis acids. This now allows access to 1,2,3,4-tetrasubstituted naphthalene derivatives as cyclization and rearrangement products. Full article

(This article belongs to the Special Issue Selenium Catalysts and Antioxidants)

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15 pages, 810 KiB

Open AccessArticle

Oxidation of Disulfides to Thiolsulfinates with Hydrogen Peroxide and a Cyclic Seleninate Ester Catalyst

by Nicole M. R. McNeil, Ciara McDonnell, Miranda Hambrook and Thomas G. Back

Molecules 2015, 20(6), 10748-10762; https://doi.org/10.3390/molecules200610748 - 11 Jun 2015

Cited by 27 | Viewed by 11185

Abstract

Cyclic seleninate esters function as mimetics of the antioxidant selenoenzyme glutathione peroxidase. They catalyze the reduction of harmful peroxides with thiols, which are converted to disulfides in the process. The possibility that the seleninate esters could also catalyze the further oxidation of disulfides to thiolsulfinates and other overoxidation products under these conditions was investigated. This has ramifications in potential medicinal applications of seleninate esters because of the possibility of catalyzing the unwanted oxidation of disulfide-containing spectator peptides and proteins. A variety of aryl and alkyl disulfides underwent facile oxidation with hydrogen peroxide in the presence of catalytic benzo-1,2-oxaselenolane Se-oxide affording the corresponding thiolsulfinates as the principal products. Unsymmetrical disulfides typically afforded mixtures of regioisomers. Lipoic acid and N,N′-dibenzoylcystine dimethyl ester were oxidized readily under similar conditions. Although isolated yields of the product thiolsulfinates were generally modest, these experiments demonstrate that the method nevertheless has preparative value because of its mild conditions. The results also confirm the possibility that cyclic seleninate esters could catalyze the further undesired oxidation of disulfides in vivo. Full article

(This article belongs to the Special Issue Selenium Catalysts and Antioxidants)

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15 pages, 930 KiB

Open AccessArticle

Selenium Catalyzed Oxidation of Aldehydes: Green Synthesis of Carboxylic Acids and Esters

by Luca Sancineto, Caterina Tidei, Luana Bagnoli, Francesca Marini, Eder J. Lenardão and Claudio Santi

Molecules 2015, 20(6), 10496-10510; https://doi.org/10.3390/molecules200610496 - 8 Jun 2015

Cited by 86 | Viewed by 13262

Abstract

The stoichiometric use of hydrogen peroxide in the presence of a selenium-containing catalyst in water is here reported as a new ecofriendly protocol for the synthesis of variously functionalized carboxylic acids and esters. The method affords the desired products in good to excellent yields under very mild conditions starting directly from commercially available aldehydes. Using benzaldehyde as a prototype the gram scale synthesis of benzoic acid is described, in which the aqueous medium and the catalyst could be recycled at last five times while achieving an 87% overall yield. Full article

(This article belongs to the Special Issue Selenium Catalysts and Antioxidants)

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9 pages, 901 KiB

Open AccessArticle

Effect of Methoxy Substituents on the Activation Barriers of the Glutathione Peroxidase-Like Mechanism of an Aromatic Cyclic Seleninate

by Craig A. Bayse and Ashley L. Shoaf

Molecules 2015, 20(6), 10244-10252; https://doi.org/10.3390/molecules200610244 - 3 Jun 2015

Cited by 7 | Viewed by 6420

Abstract

Density functional theory (DFT) models including explicit water molecules have been used to model the redox scavenging mechanism of aromatic cyclic seleninates. Experimental studies have shown that methoxy substitutions affect the rate of scavenging of reactive oxygen species differently depending upon the position. Activities are enhanced in the para position, unaffected in the meta, and decreased in the ortho. DFT calculations show that the activation barrier for the oxidation of the selenenyl sulfide, a proposed key intermediate, is higher for the ortho methoxy derivative than for other positions, consistent with the low experimental conversion rate. Full article

(This article belongs to the Special Issue Selenium Catalysts and Antioxidants)

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15 pages, 999 KiB

Open AccessArticle

Synthesis and Biological Evaluation of 2-Picolylamide-Based Diselenides with Non-Bonded Interactions

by Jamal Rafique, Sumbal Saba, Rômulo Faria Santos Canto, Tiago Elias Allievi Frizon, Waseem Hassan, Emily Pansera Waczuk, Maryam Jan, Davi Fernando Back, João Batista Teixeira Da Rocha and Antonio Luiz Braga

Molecules 2015, 20(6), 10095-10109; https://doi.org/10.3390/molecules200610095 - 1 Jun 2015

Cited by 42 | Viewed by 9222

Abstract

In this paper, we report the synthesis and biological evaluation of picolylamide-based diselenides with the aim of developing a new series of diselenides with O···Se non-bonded interactions. The synthesis of diselenides was performed by a simple and efficient synthetic route. All the products were obtained in good yields and their structures were determined by ¹H-NMR, ¹³C-NMR and HRMS. All these new compounds showed promising activities when tested in different antioxidant assays. These amides exhibited strong thiol peroxidase-like (TPx) activity. In fact one of the compounds showed 4.66 times higher potential than the classical standard i.e., diphenyl diselenide. The same compound significantly inhibited iron (Fe)-induced thiobarbituric acid reactive species (TBARS) production in rat’s brain homogenate. In addition, the X-ray structure of the most active compound showed non-bonded interaction between the selenium and the oxygen atom that are in close proximity and may be responsible for the increased antioxidant activity. The present study provides evidence about the possible biochemical influence of nonbonding interactions on organochalcogens potency. Full article

(This article belongs to the Special Issue Selenium Catalysts and Antioxidants)

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24 pages, 1282 KiB

Open AccessArticle

Xerogel-Sequestered Silanated Organochalcogenide Catalysts for Bromination with Hydrogen Peroxide and Sodium Bromide

by Caitlyn M. Gatley, Lisa M. Muller, Meredith A. Lang, Eduardo E. Alberto and Michael R. Detty

Molecules 2015, 20(6), 9616-9639; https://doi.org/10.3390/molecules20069616 - 26 May 2015

Cited by 23 | Viewed by 8208

Abstract

While H₂O₂ is a powerful oxidant, decomposing into environmentally benign H₂O and O₂, a catalyst is often required for reactions with H₂O₂ to proceed at synthetically useful rates. Organotellurium and organoselenium compounds catalyze the oxidation of halide salts to hypohalous acids using H₂O₂. When sequestered into xerogel monoliths, the xerogel-chalcogenide combinations have demonstrated increased catalytic activity relative to the organochalcogen compound alone in solution for the oxidation of halide salts to hypohalous acids with H₂O₂. Diorganotellurides, diorganoselenides, and diorganodiselenides bearing triethoxysilane functionalities were sequestered into xerogel monoliths and their catalytic activity and longevity were investigated. The longevity of the catalyst-xerogel combinations was examined by isolating and recycling the catalyst-xerogel combination. It was found tellurium-containing catalyst 3 and selenium-containing catalyst 8 maintained their catalytic activity through three recycling trials and adding electron-donating substituents to catalyst 3 also increased the catalytic rate. The presence of organotellurium and organoselenium groups in the +4 oxidation state was determined by X-ray photoelectron spectroscopy. Full article

(This article belongs to the Special Issue Selenium Catalysts and Antioxidants)

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Review

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39 pages, 891 KiB

Open AccessReview

Developments in Synthetic Application of Selenium(IV) Oxide and Organoselenium Compounds as Oxygen Donors and Oxygen-Transfer Agents

by Jacek Młochowski and Halina Wójtowicz-Młochowska

Molecules 2015, 20(6), 10205-10243; https://doi.org/10.3390/molecules200610205 - 3 Jun 2015

Cited by 127 | Viewed by 20215

Abstract

A variety of selenium compounds were proven to be useful reagents and catalysts for organic synthesis over the past several decades. The most interesting aspect, which emerged in recent years, concerns application of hydroperoxide/selenium(IV) oxide and hydroperoxide/organoselenium catalyst systems, as “green reagents” for the oxidation of different organic functional groups. The topic of oxidations catalyzed by organoselenium derivatives has rapidly expanded in the last fifteen years This paper is devoted to the synthetic applications of the oxidation reactions mediated by selenium compounds such as selenium(IV) oxide, areneseleninic acids, their anhydrides, selenides, diselenides, benzisoselenazol-3(2H)-ones and other less often used other organoselenium compounds. All these compounds have been successfully applied for various oxidations useful in practical organic syntheses such as epoxidation, 1,2-dihydroxylation, and α-oxyfunctionalization of alkenes, as well as for ring contraction of cycloalkanones, conversion of halomethyl, hydroxymethyl or active methylene groups into formyl groups, oxidation of carbonyl compounds into carboxylic acids and/or lactones, sulfides into sulfoxides, and secondary amines into nitrones and regeneration of parent carbonyl compounds from their azomethine derivatives. Other reactions such as dehydrogenation and aromatization, active carbon-carbon bond cleavage, oxidative amidation, bromolactonization and oxidation of bromide for subsequent reactions with alkenes are also successfully mediated by selenium (IV) oxide or organoselenium compounds. The oxidation mechanisms of ionic or free radical character depending on the substrate and oxidant are discussed. Coverage of the literature up to early 2015 is provided. Links have been made to reviews that summarize earlier literature and to the methods of preparation of organoselenium reagents and catalysts. Full article

(This article belongs to the Special Issue Selenium Catalysts and Antioxidants)

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