Reduction of diphenyl diselenide and analogs by mammalian thioredoxin reductase is independent of their gluthathione peroxidase-like activity: a possible novel pathway for their antioxidant activity

Since the successful use of the organoselenium drug ebselen in clinical trials for the treatment of neuropathological conditions associated with oxidative stress, there have been concerted efforts geared towards understanding the precise mechanism of action of ebselen and other organoselenium compounds, especially the diorganyl diselenides such as diphenyl diselenide, and its analogs. Although the mechanism of action of ebselen and other organoselenium compounds has been shown to be related to their ability to generally mimic native glutathione peroxidase (GPx), only ebselen however has been shown to serve as a substrate for the mammalian thioredoxin reductase (TrxR), demonstrating another component of its pharmacological mechanisms. In fact, there is a dearth of information on the ability of other organoselenium compounds, especially diphenyl diselenide and its analogs, to serve as substrates for the mammalian enzyme thioredoxin reductase. Interestingly, diphenyl diselenide shares several antioxidant and neuroprotective properties with ebselen. Hence in the present study, we tested the hypothesis that diphenyl diselenide and some of its analogs (4,4'-bistrifluoromethyldiphenyl diselenide, 4,4'-bismethoxy-diphenyl diselenide, 4.4'-biscarboxydiphenyl diselenide, 4,4'-bischlorodiphenyl diselenide, 2,4,6,2',4',6'-hexamethyldiphenyl diselenide) could also be substrates for rat hepatic TrxR. Here we show for the first time that diselenides are good substrates for mammalian TrxR, but not necessarily good mimetics of GPx, and vice versa. For instance, bis-methoxydiphenyl diselenide had no GPx activity, whereas it was a good substrate for reduction by TrxR. Our experimental observations indicate a possible dissociation between the two pathways for peroxide degradation (either via substrate for TrxR or as a mimic of GPx). Consequently, the antioxidant activity of diphenyl diselenide and analogs can be attributed to their capacity to be substrates for mammalian TrxR and we therefore conclude that subtle changes in the aryl moiety of diselenides can be used as tool for dissociation of GPx or TrxR pathways as mechanism triggering their antioxidant activities.     

Selenium‐Modified Microgels as Bio‐Inspired Oxidation Catalysts

Active colloidal catalysts inspired by glutathione peroxidase (GPx) were synthesized by integration of catalytically active selenium (Se) moieties into aqueous microgels. A diselenide crosslinker (Se X‐linker) was successfully synthesized and incorporated into microgels through precipitation polymerization, along with the conventional crosslinker N,N′‐methylenebis(acrylamide) (BIS). Diselenide bonds within the microgels were cleaved through oxidation by H₂O₂ and converted to seleninic acid whilst maintaining the intact microgel microstructure. Through this approach catalytically active microgels with variable amounts of seleninic acid were synthesized. Remarkably, the microgels exhibited higher catalytic activity and selectivity at low reaction temperatures than the molecular Se catalyst in a model oxidation reaction of acrolein to acrylic acid and methyl acrylate.     

Biscarbamoyl diselenides as new carbamoylating reagents. Lewis acid promoted carbamoylation of aromatic compounds

The reaction of biscarbamoyl diselenides with aromatic compounds in the presence of Lewis acids resulted in Friedel-Crafts type carbamoylation (Gatterman amide synthesis) to give corresponding aromatic amides in good yields. This methodology was successfully applied to aroylation and benzylation by use of dibenzoyl diselenide and dibenzyl diselenide, respectively.     

Ephedrine-based diselenide: a promiscuous catalyst suitable to mimic the enzyme glutathione peroxidase (GPx) and to promote enantioselective C-C coupling reactions

The ephedrine-based diselenide appears as a new promiscuous catalyst, able to generate optically active alcohols by addition of organozinc to aldehydes (up to 97% ee), and shows powerful GPx like activity, reducing H(2)O(2) to water in only 16.33 min (eleven times faster than PhSeSePh).     

Pyrolysis of Dibenzyl Selenides to Bibenzyls

The formation of carbon-carbon bond by sulfur extrusion such as pyrolysis of cyclic sulfones is well known as an important synthetic method, especially for the synthesis of cyclophane framework.¹⁾ Little is known about selenium extrusion as the counterpart, though organoseleniums have been properly appreciated as a useful tool for manipulating a functional group.²⁾ Lardon reported that the thermal decomposition of dibenzyl diselenide led to a mixture of dibenzyl selenide and polyselenides.³⁾ In contrast, recent reports showed that at 210°C, heating bis(diphenylmethyl) diselenide resulted in ready selenium extrusion to 1,1,2,2-tetraphenylethane⁴⁾, and dianthrylmethyl mono- and diselenides to 1,2-dianthrylethane.⁵⁾ Therefore,- it is worthwhile to study the thermal behavior of dibenzyl selenide itself.     

Highly efficient dendrimer-based mimic of glutathione peroxidase

In this communication, we report the synthesis of the three generations of Fréchet-type poly(aryl ether) dendrimers with a diselenide core that demonstrate generation-dependent glutathione peroxidase (GPx) activity with initial reduction rates as high as 2431.20 muM min-1 for the third-generation product, around 1400 times faster than Ebselen. It represents a successful example of using a dendrimer as a model for a GPx mimic.     

合成二苄基二硒醚的新方法

苯骈三氮唑和胺(伯、仲胺: 芳胺、杂环胺或杂环芳胺)、苯甲醛发生Mannich反应, 生成N-取代-1-苯骈三氮唑基苄胺, 它与硒氢化钠反应生成二苄基二硒醚, 反应条件温和, 产率高, 胺和苯骈三氮唑均可回收再利用。     

Self-Assembled Monolayers of Organoselenium Compounds on Gold: Surface-Enhanced Raman Scattering Study

To understand the binding nature of organoselenium compounds on gold, we have examined the adsorption behavior of several representative organoselenium compounds, i.e., benzeneselenol (BSe), diphenyl diselenide, dibenzyl diselenide, dioctyl diselenide, and benzyl phenyl selenide (BPSe) on the Au surface by virtue of surface-enhanced Raman spectroscopy (SERS). BSe chemisorbs on gold as selenolate with a tilted orientation. Upon adsorption, the Se–Se bonds of diselenides are cleaved to form selenolates, analogous to the formation of thiolate monolayers from disulfides. BPSe adsorbs on gold without any C–Se bond scission. The benzyl moiety of BPSe assumes a rather vertical stance while the phenyl moiety is more tilted to the gold surface.     

Anti-thyroid drugs and thyroid hormone synthesis: effect of methimazole derivatives on peroxidase-catalyzed reactions

Syntheses and characterization of the selenium analogue (MSeI) of anti-thyroid drug methimazole and a series of organoselenium compounds bearing N-methylimidazole pharmacophore are described. In contrast to the sulfur compound that exists predominantly in its thione form, the selenium analogue exists in a selenol form, which spontaneously oxidizes in air to produce the corresponding diselenide. The reduction of the diselenide by GSH or NaBH(4) affords the biologically active selenol, which effectively inhibits the lactoperoxidase (LPO) activity in vitro. The monoselenides having N-methylimidazole moiety are found to be much less active than the selenol, suggesting that the presence of a selenol moiety is important for the LPO inhibition. The kinetic and mechanistic studies reveal that MSeI inhibits the LPO activity by reducing the H(2)O(2), providing a novel method to reversibly inhibit the enzyme. Although MSeI strongly inhibits LPO, the enzyme's activity can be completely recovered by increasing the H(2)O(2) concentration. On the other hand, the inhibition by methimazole (MMI), the sulfur analogue, cannot be reversed by increasing the H(2)O(2) concentration, leading to a complete inactivation of the enzyme. The reversible inhibition of LPO by some of the selenium derivatives is correlated with their glutathione peroxidase (GPx) activity, and the high GPx activity of the selenium compounds as compared with their sulfur analogues suggests that the selenium derivatives may protect the thyroid gland from oxidative damage.     

A Glutathione Peroxidase Mimic 6,6′-Ditellurobis (6-Deoxy-β-Cyclodextrin) with High Substrate Specificity

Glutathione peroxidase (GPx) is one of the most important antioxidative selenoenzymes in living organisms. The novel GPx mimic 6,6′-ditellurobis(6-deoxy-β-cyclodextrin) (6-TeCD) was prepared and evaluated for its capacity to catalyze the reduction of H₂O₂, tert-butyl hydroperoxide (t-BuOOH), and cumene hydroperoxide (CuOOH) by glutathione (GSH) or 3-carboxy-4-nitrobenzenethiol (ArSH). Compared the ArSH assay with the coupled reductase assay, we found that 6-TeCD exhibited strong substrate specificity for aromatic thiol substrate. The specificity led to efficient peroxidase activity almost 100,000-fold than that for a well-known GPx mimic diphenyl diselenide (PhSeSePh). Furthermore, reduction of lipophilic CuOOH was proceeded ca. 30 times faster than the more hydrophilic H₂O₂, which cannot bind into the hydrophobic cavity of β-cyclodextrin. Thus, it seemed that catalytic activity of cyclodextrin-derived GPx models strongly depends on the structurally different both substrates hydroperoxides (ROOH) and thiols.     

Convenient Preparation of Benzylseleno‐ and Phenylselenoalkanoic Acids: Reagents for Synthesis of Organoselenium Compounds

An efficient and operationally simple route to benzylseleno‐ and phenylselenoalkanoic acids from ethyl benzyl/phenylselenoalkanoates is described. This involves preparation of ethyl benzyl/phenylselenoalkanoates as substrates by reaction of dibenzyl/diphenyl diselenide and sodium borohydride with ethyl chloroalkanoates in ethanol followed by basic hydrolysis and subsequent acidification.     

Polymer micelles as building blocks for the incorporation of azobenzene: enhancing the photochromic properties in layer-by-layer films

We described the use of block copolymer micelles as building blocks for the incorporation of water-insoluble photochromic species of azobenzene and the fabrication of multilayer films by alternating the deposition of the block copolymer micelles of poly(styrene-b-acrylic acid), incorporating azobenzene and poly(diallyl-dimethylammonium chloride). The azobenzene incorporated into the block copolymer micelles can undergo a reversible photoisomerization under the irradiation of UV and visible light sources. An interesting finding is that the photoisomerization of the azobenzene in the multilayer film is faster than it is in its normal solid film, but very similar to that in its diluted solution. Furthermore, the amount of azobenzene incorporated into the micelles can influence the photoisomerization rates in the films. Therefore, we expect that the block copolymer micelles may provide a proper microenvironment for the photoisomerization of azobenzene and the as-prepared polyelectrolyte/block copolymer micelle thin films will be useful for photoswitching materials.     

MPEG-hexPLA micelles as novel carriers for hypericin, a fluorescent marker for use in cancer diagnostics

Ovarian cancer is the most common gynecological cancer diagnosed in Western countries. Detection of micrometastases at an early stage of the disease could lead to a cure rate of 90% by limiting the spread of the disease outside the ovaries. In this article, hypericin (Hy), a hydrophobic photosensitizer used for the photodynamic diagnosis (PD) of ovarian cancer, was efficiently incorporated into a core of micelles made from methoxy-poly(ethylene glycol) and hexyl-substituted poly(lactides) copolymers. The fate of these micelles following intravenous injection was studied in vivo in two ovarian tumor-bearing animal models. In the chick embryo chorioallantoic membrane model, 17 times more Hy accumulated in tumor nodules when Hy was delivered with micelles than when Hy was delivered as an ethanol solution. Studies of the biodistribution of Hy in Fisher rats revealed escape of these nanosized micelles (<32 nm) from the mononuclear phagocyte system. Hy-loaded micelles showed maximal accumulation in tumors and demonstrated the best tumor/muscle contrast visible 3 h after injection in the rat model. The rapid and highly selective accumulation of Hy in tumors that we demonstrated in this study suggests that these micelle formulations could be used for the PD of ovarian cancer in the future.     

Aryl thiol substrate 3-carboxy-4-nitrobenzenethiol strongly stimulating thiol peroxidase activity of glutathione peroxidase mimic 2, 2'-ditellurobis(2-deoxy-beta-cyclodextrin)

Artificial glutathione peroxidase (GPx) model 2, 2'-ditellurobis(2-deoxy-beta-cyclodextrin) (2-TeCD) which has the desirable properties exhibited high substrate specificity and remarkably catalytic efficiency when 3-carboxy-4-nitrobenzenethiol (ArSH) was used as a preferential thiol substrate. The complexation of ArSH with beta-cyclodextrin was investigated through UV spectral titrations, fluorescence spectroscopy, 1H NMR and molecular simulation, and these results indicated that ArSH fits well to the size of the cavity of beta-cyclodextrin. Furthermore, 2-TeCD was found to catalyze the reduction of cumene peroxide (CuOOH) by ArSH 200,000-fold more efficiently than diphenyl diselenide (PhSeSePh). Its steady-state kinetics was studied and the second rate constant kmax/KArSH was found to be 1.05 x 10(7) M(-1) min(-1) and similar to that of natural GPx. Moreover, the kinetic data revealed that the catalytic efficiency of 2-TeCD depended strongly upon the competitive recognition of both substrates for 2-TeCD. The catalytic mechanism of 2-TeCD catalysis agreed well with a ping-pong mechanism, in analogy with natural GPx, and might exert its thiol peroxidase activity via tellurol, tellurenic acid, and tellurosulfide.     

Modeling the reduction of hydrogen peroxide by glutathione peroxidase mimics

Theoretical calculations have been performed on three model reactions representing the reduction of hydrogen peroxide by ebselen, ebselen selenol, and ebselen diselenide. The reaction surfaces have been investigated at the B3PW91/6-311G(2df,p) level, and single-point energies were calculated using the 6-311++G(3df,3pd) basis set. Solvent effects were included implicitly with the conductor-like polarizable continuum model and in one case with explicit inclusion of three water molecules. Mechanistic information is gained from investigating the critical points using the quantum theory of atoms in molecules. The barriers for the reduction of hydrogen peroxide with the ebselen, ebselen selenol, and ebselen diselenide models are 56.7, 53.4, and 35.3 kcal/mol, respectively, suggesting that ebselen diselenide may be the most active antioxidant in the ebselen GPx redox pathway. Results are also compared to that of the sulfur analogues of the model compounds.     

Synthesis and characterization of poly(ε-caprolactone)-block-poly[N-(2-hydroxypropyl)methacrylamide] micelles for drug delivery

Amphiphilic block copolymers based on HPMA and ε-CL were synthesized by ring-opening polymerization of ε-CL followed by RAFT polymerization of HPMA. A copolymer composed of 34 kDa PHPMA and 8.5 kDa PCL associated into micelles with CMC of 5.4 μg · mL(-1) . A novel retinoid, 3-Cl-AHPC-OMe, was incorporated into micelles with 25 wt.-% loading by dialysis method. The effective diameter of drug loading micelles was 117 nm. Incubation of micelles in PBS at 37 °C indicated 86 wt.-% of the drug was released after 96 h. Cytotoxicity studies performed with C4-2 prostate cancer cells showed the IC(50) dose was 1.96 μM after 72 h of incubation, whereas the micelles without drug showed no cytotoxicity.     

A Diselenide Turn‐On Fluorescent Probe for the Detection of Thioredoxin Reductase

We report the first diselenide‐based probe for the selective detection of thioredoxin reductase (TrxR), an enzyme commonly overexpressed in melanomas. The probe design involves conjugation of a seminaphthorhodafluor dye with a diselenide moiety. TrxR reduces the diselenide bond, triggering a fluorescence turn‐on response of the probe. Kinetic studies reveal favorable binding of the probe with TrxR with a Michaelis–Menten constant (K_m) of 15.89 μm . Computational docking simulations predict a greater binding affinity to the TrxR active site in comparison to its disulfide analogue. In vitro imaging studies further confirmed the diselenide probe exhibited improved signaling of TrxR activity compared to the disulfide analogue.     

Generation of oligonucleotide conjugates via one-pot diselenide-selenoester ligation–deselenization/alkylation

A breadth of strategies are needed to efficiently modify oligonucleotides with peptides or lipids to capitalize on their therapeutic and diagnostic potential, including the modulation of in vivo chemical stability and for applications in cell-targeting and cell-permeability. The chemical linkages typically used in peptide oligonucleotide conjugates (POCs) have limitations in terms of stability and/or ease of synthesis. Herein, we report an efficient method for POC synthesis using a diselenide-selenoester ligation (DSL)-deselenization strategy that rapidly generates a stable amide linkage between the two biomolecules. This conjugation strategy is underpinned by a novel selenide phosphoramidite building block that can be incorporated into an oligonucleotide by solid-phase synthesis to generate diselenide dimer molecules. These can be rapidly ligated with peptide selenoesters and, following in situ deselenization, lead to the efficient generation of POCs. The diselenide within the oligonucleotide also serves as a flexible functionalisation handle that can be leveraged for fluorescent labelling, as well as for alkylation to generate micelles.

An efficient and versatile approach for the late-stage generation of oligonucleotide conjugates by diselenide-selenoester ligation (DSL)–deselenization/alkylation was developed.     

Antioxidant activity of the anti-inflammatory compound ebselen: a reversible cyclization pathway via selenenic and seleninic acid intermediates

A revised mechanism that accounts for the glutathione peroxidase (GPx)-like catalytic activity of the organoselenium compound ebselen is described. It is shown that the reaction of ebselen with H(2)O(2) yields seleninic acid as the only oxidized product. The X-ray crystal structure of the seleninic acid shows that the selenium atom is involved in a noncovalent interaction with the carbonyl oxygen atom. In the presence of excess thiol, the Se--N bond in ebselen is readily cleaved by the thiol to produce the corresponding selenenyl sulfide. The selenenyl sulfide thus produced undergoes a disproportionation in the presence of H(2)O(2) to produce the diselenide, which upon reaction with H(2)O(2), produces a mixture of selenenic and seleninic acids. The addition of thiol to the mixture containing selenenic and seleninic acids leads to the formation of the selenenyl sulfide. When the concentration of the thiol is relatively low in the reaction mixture, the selenenic acid undergoes a rapid cyclization to produce ebselen. The seleninic acid, on the other hand, reacts with the diselenide to produce ebselen as the final product. DFT calculations show that the cyclization of selenenic acids to the corresponding selenenyl amides is more favored than that of sulfenic acids to the corresponding sulfenyl amides. This indicates that the regeneration of ebselen under a variety of conditions protects the selenium moiety from irreversible inactivation, which may be responsible for the biological activities of ebselen.     

Diselenides and allyl selenides as glutathione peroxidase mimetics. Remarkable activity of cyclic seleninates produced in situ by the oxidation of allyl omega-hydroxyalkyl selenides

A series of aliphatic diselenides and selenides containing coordinating substituents was tested for glutathione peroxidase (GPx)-like catalytic activity in a model system in which the reduction of tert-butyl hydroperoxide with benzyl thiol to afford dibenzyl disulfide and tert-butyl alcohol was performed under standard conditions and monitored by HPLC. Although the diselenides showed generally poor catalytic activity, allyl selenides proved more effective. In particular, allyl 3-hydroxypropyl selenide (25) rapidly generated 1,2-oxaselenolane Se-oxide (31) in situ by a series of oxidation and [2,3]sigmatropic rearrangement steps. The remarkably active cyclic seleninate 31 proved to be the true catalyst, reacting with the thiol via a postulated mechanism in which the thioseleninate 32 is first produced, followed by further thiolysis to selenenic acid 33 and oxidation-dehydration to regenerate 31. In contrast to catalysis with GPx, formation of the corresponding selenenyl sulfide 34 comprises a competing deactivation pathway in the catalytic cycle of 31, as a separate experiment revealed that authentic 34 was a much less effective catalyst than 31. 1,2-Oxaselenane Se-oxide (37), the six-membered homologue of 31, was formed similarly from allyl 4-hydroxybutyl selenide (26), but proved a less effective catalyst than 31. Compounds 31 and 37 are the first examples of unsubstituted monocyclic seleninate esters.