Preparation of the First Bench-Stable Phenyl Selenolate: an Interesting “On Water” Nucleophilic Reagent

Ni(II)-catalyzed nucleophilic substitution for the synthesis of allenylselenide

A method for synthesizing allenylselenides has been developed using readily available propargyl carbonate and phenylselenol. The reaction is catalyzed by Ni(II) and proceeds via a migratory insertion and β-oxygen elimination mechanism. Due to the strong interaction between Se and Ni leading to catalyst deactivation, zinc salt was used to mitigate the deleterious effects of Se anions on the catalyst, thereby facilitating the successful synthesis of the target products.

Benzisoselenazoles as Selenophenolate Anion Surrogates for the Formation of Carbon-Selenium Bonds via the Selena-Kemp Reaction

The in situ base-promoted generation of unstable selenophenolate anions from 1,2-benzisoselenazoles via a variant of the Kemp elimination has been developed. 2-Cyano-substituted selenophenolate anions obtained by this methodology were engaged in nucleophilic substitution, aromatic nucleophilic substitution, and Pd-catalyzed cross-coupling reactions to give functionalized arylalkyl and diaryl selenides in moderate to excellent yields.

Organic Selenium induces ferroptosis in pancreatic cancer cells

Pancreatic ductal adenocarcinoma (PDA) cells reprogram both mitochondrial and lysosomal functions to support growth. At the same time, this causes significant dishomeostasis of free radicals. While this is compensated by the upregulation of detoxification mechanisms, it also represents a potential vulnerability. Here we demonstrate that PDA cells are sensitive to the inhibition of the mevalonate pathway (MVP), which supports the biosynthesis of critical antioxidant intermediates and protect from ferroptosis. We attacked the susceptibility of PDA cells to ferroptotic death with selenorganic compounds, including dibenzyl diselenide (DBDS) that exhibits potent pro-oxidant properties and inhibits tumor growth in vitro and in vivo. DBDS treatment induces the mobilization of iron from mitochondria enabling uncontrolled lipid peroxidation. Finally, we showed that DBDS and statins act synergistically to promote ferroptosis and provide evidence that combined treatment is a viable strategy to combat PDA.

Role of Group 12 Metals in the Reduction of H2O2 by Santi's Reagent: A Computational Mechanistic Investigation

PhSeZnCl, which is also known as Santi's reagent, can catalyze the reduction of hydrogen peroxide by thiols with a GPx-like mechanism. In this work, the first step of this catalytic cycle, i.e., the reduction of H2O2 by PhSeZnCl, is investigated in silico using state-of-the-art density functional theory calculations. Then, the role of the metal is evaluated by replacing Zn with its group 12 siblings (Cd and Hg). The thermodynamic and kinetic factors favoring Zn are elucidated. Furthermore, the role of the halogen is considered by replacing Cl with Br in all three metal compounds, and this turns out to be negligible. Finally, the overall GPx-like mechanism of PhSeZnCl and PhSeZnBr is discussed by evaluating the energetics of the mechanistic path leading to the disulfide product.

In vitro toxicological assessment of PhSeZnCl in human liver cells

Phenylselenenylzinc chloride (PhSeZnCl) is an air-stable selenolate, easily synthesizable through oxidative insertion of elemental zinc into the Se-halogen bond of the commercially available phenylselenyl chloride. PhSeZnCl was shown to possess a marked GPx-like activity both in NMR and in vitro tests, and to effectively react with cellular thiols, and was supposed for a potential use in the chemotherapy of drug-resistant cancers. However, activity of PhSeZnCl in hepatic cells has never been tested before now. In this in vitro approach, we evaluated the cytotoxic, genotoxic, and apoptotic activities, as well as the effects on cell cycle of PhSeZnCl in two preclinical hepatic models, namely HepG2 and HepaRG cells. Results showed that cell viability of HepG2 and HepaRG cells decreased in a dose-dependent manner, with a more marked effect in HepG2 tumour cells. Moreover, treatment with 50 µg/mL PhSeZnCl caused an increase of primary DNA damage (4 h) and a statistically significant increase of HepG2 cells arrested in G₂/M phase. In addition, it altered mitochondrial membrane potential and induced chromosomal DNA fragmentation (24 h). In HepaRG cells, PhSeZnCl was able to determine a cell cycle-independent induction of apoptosis. Particularly, 50 µg/mL induced mitochondrial membrane depolarization after 24 h and apoptosis after 4 h treatment. Futhermore, all PhSeZnCl concentrations tested determined a significant increase of apoptotic cells after 24 h. Apoptosis was also highlighted by the detection of active Caspase-3 by Western Blot analysis after 24 h exposure. In conclusion, this first toxicological assessment provides new insights into the biological activity of PhSeZnCl in preclinical hepatic models that will be useful in future safety assessment investigation of this compound as a potential pharmaceutical.

Supplementary Information

The online version contains supplementary material available at 10.1007/s43188-022-00148-y.

Proton reduction by a bimetallic zinc selenolate electrocatalyst

The development of alternative energy sources is the utmost priority of developing society. Unlike many prior homogeneous electrocatalysts that rely on a change in the oxidation state of the metal center and/or electrochemically active ligand, here we report the synthesis and structural characterization of a bimetallic zinc selenolate complex consisting of a redox silent zinc metal ion and a tridentate ligand that catalyzes the reduction of protons into hydrogen gas electrochemically and displays one of the highest reported TOF for a homogeneous TM-metal free ligand centered HER catalyst, 509 s-1. The current-voltage analysis confirms the onset overpotential of 0.86 V vs. Ag/AgCl for the HER process. Constant potential electrolysis (CPE) has been carried out to study the bulk electrolysis of our developed protocol, which reveals that the bimetallic zinc selenolate catalyst is stable under cathodic as well as anodic potentials and generates hydrogen gas with a faradaic efficiency of 75%. Preliminary studies on the heterogeneous catalyst were conducted by depositing the bimetallic zinc selenolate catalyst on the electrode surface.

Selenosteroids - promising hybrid compounds with pleiotropic biological activity: synthesis and biological aspects

It is established that steroid based agents are an example of compounds obtained from natural patterns and are of great importance due to their application in the prevention and treatment of diseases. Selenosteroids are hybrids formed by attaching Se-moiety to a steroid molecule. In these types of hybrids, selenium can be present as selenide or as a part of selenosemicarbazones, isoselenocyanates, selenourea, etc. Attaching a Se-moiety to a biologically active steroid might enhance the biological properties of both fragments. Available literature indicates that these kinds of hybrids demonstrate significant anticancer activity, which renders them interesting in terms of medical use. In this review, we present various methods of synthesis and demonstrate that seleno-steroid compounds are promising molecules for further pharmaceutical application.

Synthetic Approaches to Selenoesters

Selenoesters are compounds of great synthetic relevance since they can be used in several types of chemical transformations and mainly due to their great capacity in the formation of acyl radicals. Therefore, the scientific community has been developing several methods for the synthesis of this class of molecules. This review will address the synthesis of these compounds from different starting materials, such as carboxylic acids derivatives (acid chlorides and anhydrides), aldehydes, selenoacetylenes and miscellaneous methods.

Polyselenonium salts: synthesis through sequential selenium-epoxy 'click' chemistry and Se-alkylation

With the help of amphiphilic homopolymers, this work explores three new avenues in polymer chemistry: (i) the 'click' nature of the selenium-epoxy reaction, (ii) alkylation of the seleno-ethers as a means to prepare cationic polyelectrolytes, and (iii) the antibacterial activity of polyselenonium salts.

Selenium-Epoxy ‘Click’ Reaction and Se-Alkylation—Efficient Access to Organo-Selenium and Selenonium Compounds

This work establishes the ‘click’ nature of the base-catalyzed oxirane ring opening reaction by the selenolate nucleophile. The ‘click’-generated ß-hydroxy selenide can be alkylated to afford cationic selenium species. Hemolytic studies suggest that selenonium cations do not lyse red blood cells even at high concentrations. Overall, these results indicate the future applicability of the developed organo-selenium chemistry in the preparation of a new class of cationic materials based on the seleno-ether motif.

Unexpected Ethyltellurenylation of Epoxides with Elemental Tellurium under Lithium Triethylborohydride Conditions

The one-pot multistep ethyltellurenylation reaction of epoxides with elemental tellurium and lithium triethylborohydride is described. The reaction mechanism was experimentally investigated. Dilithium ditelluride and triethyl borane, formed from elemental tellurium and lithium triethylborohydride, were shown to be the key species involved in the reaction mechanism. Epoxides undergo ring-opening reaction with dilithium ditelluride to afford β-hydroxy ditellurides, which are sequentially converted into the corresponding β-hydroxy-alkyl ethyl tellurides by transmetalation with triethyl borane, reasonably proceeding through the SH2 mechanism.

A Simple Zinc-Mediated Method for Selenium Addition to Michael Acceptors

In this work, we focused our attention on seleno-Michael type reactions. These were performed using zinc-selenolates generated in situ from diphenyl diselenide 1, 1,2-bis(3-phenylpropyl)diselenide 30, and protected selenocystine 31 via an efficient biphasic Zn/HCl-based reducing system. Alkenes with a variety of electron-withdrawing groups were investigated in order to gauge the scope and limitations of the process. Results demonstrated that the addition to acyclic α,β-unsaturated ketones, aldehydes, esters amides, and acids was effectively achieved and that alkyl substituents at the reactive β-centre can be accommodated. Similarly, cyclic enones undergo efficient Se-addition and the corresponding adducts were isolated in moderate to good yield. Vinyl sulfones, α,β-unsaturated nitriles, and chalcones are not compatible with these reaction conditions. A recycling experiment demonstrated that the unreacted Zn/HCl reducing system can be effectively reused for seven reaction cycles (91% conversion yield at the 7° recycling rounds).

The Thiol-Modifier Effects of Organoselenium Compounds and Their Cytoprotective Actions in Neuronal Cells

Most pharmacological studies concerning the beneficial effects of organoselenium compounds have focused on their ability to mimic glutathione peroxidase (GPx). However, mechanisms other than GPx-like activity might be involved on their biological effects. This study was aimed to investigate and compare the protective effects of two well known [(PhSe)₂ and PhSeZnCl] and two newly developed (MRK Picolyl and MRK Ester) organoselenium compounds against oxidative challenge in cultured neuronal HT22 cells. The thiol peroxidase and oxidase activities were performed using the glutathione reductase (GR)-coupled assay. In order to evaluate protective effects of the organoselenium compounds against oxidative challenge in neuronal HT22 cells, experiments based on glutamate-induced oxytosis and SIN-1-mediated peroxynitrite generation were performed. The thiol peroxidase activities of the studied organoselenium compounds were smaller than bovine erythrocytes GPx enzyme. Besides, (PhSe)₂ and PhSeZnCl showed higher thiol peroxidase and lower thiol oxidase activities compared to the new compounds. MRK Picolyl and MRK Ester, which showed lower thiol peroxidase activity, showed higher thiol oxidase activity. Both pre- or co-treatment with (PhSe)₂, PhSeZnCl, MRK Picolyl and MRK Ester protected HT22 cells against glutamate-induced cytotoxicity. (PhSe)₂ and MRK Picolyl significantly prevented peroxinitrite-induced dihydrorhodamine oxidation, but this effect was observed only when HT22 were pre-treated with these compounds. The treatment with (PhSe)₂ increased the protein expression of antioxidant defences (Prx3, CAT and GCLC) in HT22 cells. Taking together, our results suggest that the biological effects elicited by these compounds are not directly related to their GPx-mimetic and thiol oxidase activities, but might be linked to the up-regulation of endogenous antioxidant defences trough their thiol-modifier effects.

PhSeZnCl in the Synthesis of Steroidal β-Hydroxy-Phenylselenides Having Antibacterial Activity

We report here the reaction of in situ prepared PhSeZnCl with steroid derivatives having an epoxide as an electrophilic functionalization. The corresponding ring-opening reaction resulted to be regio- and stereoselective affording to novel phenylselenium-substituted steroids. Assessment of their antibacterial properties against multidrug-resistant bacteria, such as Pseudomonas aeruginosa Xen 5 strain, indicates an interesting bactericidal activity and their ability to prevent bacterial biofilm formation.

Ring opening reactions of heterocycles with selenium and tellurium nucleophiles

An overview of the preparation and synthetic potentialities of functionalized organoselenium and organotellurium compounds is presented.

Copper complexes and carbon nanotube–copper ferrite-catalyzed benzenoid A-ring selenation of quinones: an efficient method for the synthesis of trypanocidal agents

A-ring selenation of naphthoquinones and anthraquinones is reported. The reaction proceeds in the presence of a copper source, and provides an efficient and general method for preparing selenium-based quinones with trypanocidal activity.

Electrophilic Cyclization Involving Carbon-Selenium/Carbon-Halide Bond Formation: Synthesis of 3-Substituted Selenophenes

The butylselanyl propargyl alcohols reacted with iodine to afford 3-iodoselenophenes. The change of nucleophile position from propargyl to homopropargyl was crucial for the aromatization and formation of selenophene rings. The experiments revealed that bromine and N-bromosuccinimide were not able to cyclize the butylselanyl propargyl alcohols; however, when the bromine source was copper(II) bromide the corresponding 3-bromoselenophenes were obtained in good yields. In addition, the reaction of butylselanyl propargyl alcohols with diorganyl diselenides catalyzed by copper(I) iodide gave the 3-(organoselanyl)selenophenes. The reaction took place with aromatic rings substituted by either electron-donating or -withdrawing groups in the alkynes and propargyl positions. The steric effects of substituents were dominant in determining the yields, whereas electronic effects had only a minor influence. Furthermore, by monitoring the reaction by ¹H NMR, we were able to identify the key intermediate, which supported the elaboration of a proposed reaction mechanism. The 3-iodoselenophenes prepared allowed the synthesis of multifunctional selenophenes via application in metal-catalyzed coupling reactions, such as Sonogashira, Ullmann and Suzuki type reactions.

Induction of reactive oxygen species by diphenyl diselenide is preceded by changes in cell morphology and permeability in Saccharomyces cerevisiae

Organoselenium compounds, such as diphenyl diselenide (PhSe)₂ and phenylselenium zinc chloride (PhSeZnCl), show protective activities related to their thiol peroxidase activity. However, depending on experimental conditions, organoselenium compounds can cause toxicity by oxidising thiol groups of proteins and induce the production of reactive oxygen species (ROS). Here, we analysed the toxicity of (PhSe)₂ and PhSeZnCl in yeast Saccharomyces cerevisiae. Cell growth of S. cerevisiae after 1, 2, 3, 4, 6, and 16 h of treatment with 2, 4, 6, and 10 μM of (PhSe)₂ was evaluated. For comparative purpose, PhSeZnCl was analysed only at 16 h of incubation at equivalent concentrations of selenium (i.e. 4, 8, 12, and 20 μM). ROS production (DCFH-DA), size, granularity, and cell membrane permeability (propidium iodide) were determined by flow cytometry. (PhSe)₂ inhibited cell growth at 2 h (10 μM) of incubation, followed by increase in cell size. The increase of cell membrane permeability and granularity (10 μM) was observed after 3 h of incubation, however, ROS production occurs only at 16 h of incubation (10 μM) with (PhSe)₂, indicating that ROS overproduction is a more likely consequence of (PhSe)₂ toxicity and not its determinant. All tested parameters showed that only concentration of 20 μM induced toxicity in samples incubated with PhSeZnCl. In summary, the results suggest that (PhSe)₂ toxicity in S. cerevisiae is time and concentration dependent, presenting more toxicity when compared with PhSeZnCl.

Ring-opening selenation of cyclobutanols: synthesis of γ-selenylated alkyl ketones through C–C bond cleavage

An efficient, practical, and operationally simple manganese-mediated ring-opening selenation of cyclobutanols is disclosed.

Iodine-mediated regioselective 5-endo-dig electrophilic cyclization reaction of selenoenynes: synthesis of selenophene derivatives

Selenoenynes underwent electrophilic cyclization reactions with iodine in the presence of an appropriate nucleophile to give 3-iodo-selenophenes and 3-organoselenyl-selenophenes.

Water and Aqueous Mixtures as Convenient Alternative Media for Organoselenium Chemistry

Even if water is the natural environment for bioorganic reactions, its use in organic chemistry is often severely limited by the high insolubility of the organic derivatives. In this review, we introduce some examples of the use of water to perform organoselenium chemistry. We mainly discuss the advantages of this medium when the recyclability is demonstrated and when the water can control the selectivity of a reaction or enhance the reaction rate.

A new vinyl selenone-based domino approach to spirocyclopropyl oxindoles endowed with anti-HIV RT activity

Herein, we disclose a general and flexible access to spirocyclopropyl oxindoles by a domino Michael/intramolecular nucleophilic substitution pathway with variously substituted vinyl selenones and enolizable oxindoles in aqueous sodium hydroxide solution. The spirocyclopropyl oxindole being a privileged scaffold, some of the synthesized compounds were selected for biological evaluation. Compound showed selective anti-HIV-1 activity thanks to its ability to inhibit the reverse transcriptase.

Exceptional time response, stability and selectivity in doubly-activated phenyl selenium-based glutathione-selective platform

A phenyl-selenium-substituted coumarin probe was synthesized for the purpose of achieving highly selective and extremely rapid detection of glutathione (GSH) over cysteine (Cys)/homocysteine (Hcy) without background fluorescence. The fluorescence intensity of the probe with GSH shows a ∼100-fold fluorescent enhancement compared with the signal generated for other closely related amino acids, including Cys and Hcy. Importantly, the substitution reaction with the sulfhydryl group of GSH at the 4-position of the probe, which is doubly-activated by two carbonyl groups, occurs extremely fast, showing subsecond maximum fluorescence intensity attainment; equilibrium was reached within 100 ms (UV-vis). The probe selectivity for GSH was confirmed in Hep3B cells by confocal microscopy imaging.

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

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.

Reaction kinetics and targeting to cellular glutathione S-transferase of the glutathione peroxidase mimetic PhSeZnCl and its D,L-polylactide microparticle formulation

Catalytic properties and cellular effects of the glutathione peroxidase (GPx)-mimetic compound PhSeZnCl or its d,l-lactide polymer microencapsulation form (M-PhSeZnCl) were investigated and compared with the prototypical Se-organic compounds ebselen and diselenide (PhSe)2. PhSeZnCl was confirmed to catalyze the ping-pong reaction of GPx with higher Vmax than ebselen and (PhSe)2, but the catalytic efficiency calculated for the cosubstrates glutathione (GSH) and H2O2, and particularly the high reactivity against thiols (lowest KM for GSH in the series of test molecules), suggested poor biological applicability of PhSeZnCl as a GPx mimetic. Cytotoxicity of PhSeZnCl was demonstrated in various cancer cell lines via increased reactive oxygen species (ROS) generation, depletion of intracellular thiols, and induction of apoptosis. Experiments carried out in GSH S-transferase P (GSTP)-overexpressing K562 human erythroleukemia cells and in GSTP1-1-knockout murine embryonic fibroblasts (MEFs) demonstrated that this cytosolic enzyme represents a preferential target of the redox disturbances produced by this Se-compound with a key role in controlling H2O2 generation and the perturbation of stress/survival kinase signaling. Microencapsulation was adopted as a strategy to control the thiol reactivity and oxidative stress effects of PhSeZnCl, then assessing applications alternative to anticancer. The uptake of this "depowered" GPx-mimetic formulation, which occurred through an endocytosis-like mechanism, resulted in a marked reduction of cytotoxicity. In MCF-7 cells transfected with different allelic variants of GSTP, M-PhSeZnCl lowered the burst of cellular ROS induced by the exposure to extracellular H2O2, and the extent of this effect changed between the GSTP variants. Microencapsulation is a straightforward strategy to mitigate the toxicity of thiol-reactive Se-organic drugs that enhanced the antioxidant and cellular protective effects of PhSeZnCl. A mechanistic linkage of these effects with the expression pattern and signaling properties of GSTP . This has overcome the GPx-mimetic paradigm proposed for Se-organic drugs with a more pragmatic concept of GSTP signaling modulators.

Interaction profile of diphenyl diselenide with pharmacologically significant thiols

Diphenyl diselenide has shown interesting biological activities in various free-radical-induced damage models and can be considered as a potential candidate drug against oxidative stress. Apart from its anti-oxidant activity, this compound can oxidize various thiols. However there are no detailed studies in the literature about the thiol oxidase-like activity of this compound against biologically significant mono and di-thiols with respect to various pH conditions. Keeping in mind the scarcity of data in this area of organochalcogen chemistry, we report for the first time the kinetics of thiol oxidation by diphenyl diselenide, which was carried out in a commonly used phosphate buffer, not only at physiological pH, but also at a number of acidic values. The relative reactivities of the different thiols with diphenyl diselenide were independent of the pKa of the thiol group, such that at pH 7.4, cysteine and dithiothreitol were the most reactive, while 2,3-dimercapto-1-propanesulfonic acid and glutathione were weakly reactive and extremely low reactivity was observed with dimercaptosuccinic acid. Rate of oxidation was dependent on the pH of the incubation medium. The results obtained will help us in the design of rational strategies for the safe pharmacological use of diphenyl diselenide.