1,2-Benzisoselenazol-3(2H)-one Derivatives As a New Class of Bacterial Urease Inhibitors

Construction of 5-Amino-1,2-Selenazole Scaffolds through N-Selenocyanation/Cyclization of Enaminones Using KSeCN

A metal-free and mild approach for constructing 5-amino-1,2-selenazole skeletons by NBS/KSeCN-mediated N-selenocyanation and nucleophilic cyclization of β-enaminones has been developed. Various isoselenazole compounds and the isoselenazolyl derivatives of anti-inflammatory medicines, including isosepac, oxaprozin, and ibuprofen, have been obtained with good yields. This efficient, "one-pot", and atomic economy strategy may represent an alternative route for the construction of a 1,2-selenazole framework via the "+SeCN" pathway and provide new access to heterocycles containing a Se-N bond.

Ebselen: A Promising Repurposing Drug to Treat Infections Caused by Multidrug-Resistant Microorganisms

Bacterial multiresistance to drugs is a rapidly growing global phenomenon. New resistance mechanisms have been described in different bacterial pathogens, threatening the effective treatment of even common infectious diseases. The problem worsens in infections associated with biofilms because, in addition to the pathogen's multiresistance, the biofilm provides a barrier that prevents antimicrobial access. Several "non-antibiotic" drugs have antimicrobial activity, even though it is not their primary therapeutic purpose. However, due to the urgent need to develop effective antimicrobials to treat diseases caused by multidrug-resistant pathogens, there has been an increase in research into "non-antibiotic" drugs to offer an alternative therapy through the so-called drug repositioning or repurposing. The prospect of new uses for existing drugs has the advantage of reducing the time and effort required to develop new compounds. Moreover, many drugs are already well characterized regarding toxicity and pharmacokinetic/pharmacodynamic properties. Ebselen has shown promise for use as a repurposing drug for antimicrobial purposes. It is a synthetic organoselenium with anti-inflammatory, antioxidant, and cytoprotective activity. A very attractive factor for using ebselen is that, in addition to potent antimicrobial activity, its minimum inhibitory concentration is very low for microbial pathogens.

Unveiling Novel Urease Inhibitors for Helicobacter pylori: A Multi-Methodological Approach from Virtual Screening and ADME to Molecular Dynamics Simulations

Helicobacter pylori (Hp) infections pose a global health challenge demanding innovative therapeutic strategies by which to eradicate them. Urease, a key Hp virulence factor hydrolyzes urea, facilitating bacterial survival in the acidic gastric environment. In this study, a multi-methodological approach combining pharmacophore- and structure-based virtual screening, molecular dynamics simulations, and MM-GBSA calculations was employed to identify novel inhibitors for Hp urease (HpU). A refined dataset of 8,271,505 small molecules from the ZINC15 database underwent pharmacokinetic and physicochemical filtering, resulting in 16% of compounds for pharmacophore-based virtual screening. Molecular docking simulations were performed in successive stages, utilizing HTVS, SP, and XP algorithms. Subsequent energetic re-scoring with MM-GBSA identified promising candidates interacting with distinct urease variants. Lys219, a residue critical for urea catalysis at the urease binding site, can manifest in two forms, neutral (LYN) or carbamylated (KCX). Notably, the evaluated molecules demonstrated different interaction and energetic patterns in both protein variants. Further evaluation through ADMET predictions highlighted compounds with favorable pharmacological profiles, leading to the identification of 15 candidates. Molecular dynamics simulations revealed comparable structural stability to the control DJM, with candidates 5, 8 and 12 (CA5, CA8, and CA12, respectively) exhibiting the lowest binding free energies. These inhibitors suggest a chelating capacity that is crucial for urease inhibition. The analysis underscores the potential of CA5, CA8, and CA12 as novel HpU inhibitors. Finally, we compare our candidates with the chemical space of urease inhibitors finding physicochemical similarities with potent agents such as thiourea.

Selenium Dibromide Click Chemistry: The Efficient Synthesis of Novel Selenabicyclo[3.3.1]nonene-2 and -nonane Derivatives

Highly efficient and convenient methods for the preparation of 35 novel derivatives of 9-selenabicyclo[3.3.1]nonane and 9-selenabicyclo[3.3.1]nonene-2 in high yields based on the adduct of the transannular addition of SeBr2 to 1,5-cyclooctadiene were developed. The methods for the amination of the adduct made it possible to obtain both diamino selenabicyclo[3.3.1]nonane derivatives and their dihydrobromide salts in one step in 88-98% yields. The methods meet the criteria of click chemistry. Compounds with high glutathione peroxidase mimetic activity were found among water-soluble dihydrobromide salts. The selective reaction of 2,6-dibromo-9-selenabicyclo[3.3.1]nonane with acetonitrile to form 6-bromo-9-selenabicyclo[3.3.1]nonene-2 was discovered. The latter compound served as a promising starting material to give rise to the new class of selenabicyclo[3.3.1]nonene-2 derivatives, e.g., 6-alkoxy-9-selenabicyclo[3.3.1]nonenes were obtained in 94-99% yields.

The Influence of Long Carbon Chains on the Antioxidant and Anticancer Properties of N-Substituted Benzisoselenazolones and Corresponding Diselenides

Organoselenium compounds are well-known for their numerous biocapacities, which result from the uniqueness of the selenium atom and the possibility of constructing heterorganic molecules that can mimic the activity of selenoenzymes, crucial for a multitude of important physiological processes. In this paper, we have synthesized a series of N-substituted benzisoselenazolones and corresponding diphenyl diselenides possessing lipophilic long carbon chains, solely or with additional polar insets: phenyl linkers and ester groups. Evaluation of their antioxidant and cytotoxic activity revealed an increased H2O2-reduction potential of diphenyl diselenides bearing N-octyl, ethyl N-(12-dodecanoate)- and N-(8-octanoate) groups, elevated radical scavenging activity of 2,2'-diselenobis(N-dodecylbenzamide) and a promising cytotoxic potential of N-(4-dodecyl)phenylbenzisoselenazol-3(2H)-one.

Organoselenium Compounds: Chemistry and Applications in Organic Synthesis

Selenium, originally described as a toxin, turns out to be a crucial trace element for life that appears as selenocysteine and its dimer, selenocystine. From the point of view of drug developments, selenium-containing drugs are isosteres of sulfur and oxygen with the advantage that the presence of the selenium atom confers antioxidant properties and high lipophilicity, which would increase cell membrane permeation leading to better oral bioavailability. In this article, we have focused on the relevant features of the selenium atom, above all, the corresponding synthetic approaches to access a variety of organoselenium molecules along with the proposed reaction mechanisms. The preparation and biological properties of selenosugars, including selenoglycosides, selenonucleosides, selenopeptides, and other selenium-containing compounds will be treated. We have attempted to condense the most important aspects and interesting examples of the chemistry of selenium into a single article.

First Exclusive Stereo- and Regioselective Preparation of 5-Arylimino-1,3,4-Selenadiazole Derivatives: Synthesis, NMR analysis, and Computational Studies

Isoselenocyanates are valuable coupling partners required for preparing key chemical intermediates and biologically active molecules in an accelerated and effective way. Likewise, (Z)-2-oxo-N-phenylpropanehydrazonoyl chlorides have been employed in numerous one-step heteroannulation reactions to assemble the structural core of several various kinds of heterocyclic compounds. Here, we describe the inverse electron demand 1,3-dipolar cycloaddition reaction of isoselenocyanates with a variety of substituted (Z)-2-oxo-N-phenylpropanehydrazonoyl chlorides to generate, regioselectively and stereoselectively, a series of 5-arylimino-1,3,4-selenadiazole derivatives comprising a multitude of functional groups on both aryl rings. The synthetic method features gentle room-temperature conditions, wide substrate scope, and good to high reaction yields. The selenadiazoles were separated by gravity filtration in all instances and chemical structures were validated by multinuclear NMR spectroscopy and high accuracy mass spectral measurements. First conclusive molecular structure elucidation of the observed 5-arylimino-selenadiazole regioisomer was verified by single-crystal X-ray diffraction analysis. Crystal-structure measurement was successfully carried out on (Z)-1-(4-(4-iodophenyl)-5-(p-tolylimino)-4,5-dihydro-1,3,4-selenadiazol-2-yl)ethan-1-one and (Z)-1-(5-((4-methoxyphenyl)imino)-4-(4-(methylthio)phenyl)-4,5-dihydro-1,3,4-selenadiazol-2-yl)ethan-1-one. Likewise, the (Z)-geometry of the hydrazonoyl chloride reactant was proven by X-ray diffraction studies. As representative examples, crystal-structure determination was carried out on (Z)-2-oxo-N-phenylpropanehydrazonoyl chloride and (Z)-N-(3,5-bis(trifluoromethyl)phenyl)-2-oxopropanehydrazonoyl chloride. Density functional theory calculations at the B3LYP-D4/def2-TZVP level were conducted to support the noted experimental findings and suggested mechanism.

Inhibitory activity of catecholic phosphonic and phosphinic acids against Helicobacter pylori ureolysis

Catechols have been reported to be potent covalent inhibitors of ureases, and they exhibit activity by modifying cysteine residues at the entrance to enzymatic active sites. Following these principles, we designed and synthesized novel catecholic derivatives that contained carboxylate and phosphonic/phosphinic functionalities and assumed expanded specific interactions. When studying the chemical stability of the molecules, we found that their intrinsic acidity catalyzes spontaneous esterification/hydrolysis reactions in methanol or water solutions, respectively. Regarding biological activity, the most promising compound, 2-(3,4-dihydroxyphenyl)-3-phosphonopropionic acid (15), exhibited significant anti-urease potential (K_i = 2.36 μM, Sporosarcinia pasteurii urease), which was reflected in the antiureolytic effect in live Helicobacter pylori cells at a submicromolar concentration (IC₅₀ = 0.75 μM). As illustrated by molecular modeling, this compound was bound in the active site of urease through a set of concerted electrostatic and hydrogen bond interactions. The antiureolytic activity of catecholic phosphonic acids could be specific because these compounds were chemically inert and not cytotoxic to eukaryotic cells.

Electrochemical Selenylation of Sulfoxonium Ylides for the Synthesis of gem-Diselenides as Antimicrobials against Fungi

Organoselenium compounds are important scaffolds in pharmaceutical molecules. Herein, we report metal-free, electrochemical, highly chemo- and regioselective synthesis of gem-diselenides through the coupling of α-keto sulfoxonium ylides with diselenides. The versatility of the electrochemical manifold enabled the selenylation with ample scope and broad functional group tolerance, as well as setting the stage for modification of complex bioactive molecules. Detailed mechanistic studies revealed that the key C-Se bond was constructed using n-Bu₄NI as an electrolyte and catalyst through the electrosynthetic protocol. Finally, the desired α-keto gem-diselenides showed excellent antimicrobial activity against Candida albicans, which can be identified as the lead compounds for further exploration.

CuBr2-Catalyzed Annulation of 2-Bromo-N-Arylbenzimidamide with Se/S8 Powder for the Synthesis of Benzo[d]isoselenazole and Benzo[d]isothiazole

A CuBr₂-catalyzed annulation of 2-bromo-N-arylbenzimidamide with selenium/sulfur powder for the synthesis of benzo[d]isoselenazole and benzo[d]isothiazole in generally good yields was investigated. This synthetic strategy features good substrate scope and functional group tolerance. Furthermore, the corresponding products could be converted into N-aryl indoles via rhodium^III-catalyzed ortho C-H activation of the N-phenyl ring, providing an efficient approach for axial aromatic molecules.

Optimized Ebselen-Based Inhibitors of Bacterial Ureases with Nontypical Mode of Action

Screening of 25 analogs of Ebselen, diversified at the N-aromatic residue, led to the identification of the most potent inhibitors of Sporosarcina pasteurii urease reported to date. The presence of a dihalogenated phenyl ring caused exceptional activity of these 1,2-benzisoselenazol-3(2H)-ones, with K_i value in a low picomolar range (<20 pM). The affinity was attributed to the increased π-π and π-cation interactions of the dihalogenated phenyl ring with αHis323 and αArg339 during the initial step of binding. Complementary biological studies with selected compounds on the inhibition of ureolysis in whole Proteus mirabilis cells showed a very good potency (IC₅₀ < 25 nM in phosphate-buffered saline (PBS) buffer and IC₉₀ < 50 nM in a urine model) for monosubstituted N-phenyl derivatives. The crystal structure of S. pasteurii urease inhibited by one of the most active analogs revealed the recurrent selenation of the Cys322 thiolate, yielding an unprecedented Cys322-S-Se-Se chemical moiety.

Antibacterial Activity of Ebselen

Ebselen is a low-molecular-weight organoselenium compound that has been broadly studied for its antioxidant, anti-inflammatory, and cytoprotective properties. These advantageous properties were initially associated with mimicking the activity of selenoprotein glutathione peroxidase, but the biomedical impact of this compound appear to be far more complex. Ebselen serves as a substrate or inhibitor with multiple protein/enzyme targets, whereas inhibition typically originates from the covalent modification of cysteine residues by opening the benzisoselenazolone ring and S-Se bond formation. The inhibition of enzymes of various classes and origins has been associated with substantial antimicrobial potential among other activities. In this contribution, we summarize the current state of the art regarding the antibacterial activity of ebselen. This activity, alone and in combination with commercial pharmaceuticals, against pathogens, including those resistant to drugs, is presented, together with the molecular mechanism behind the reactivity. The specific inactivation of thioredoxin reductase, bacterial toxins, and other resistance factors is considered to have certain therapeutic implications. Synergistic action and sensitization to common antibiotics assisted with the use of ebselen appear to be promising directions in the treatment of persistent infections.

1,3,4-Thiadiazole and 1,2,4-triazole-5-thione derivatives bearing 2-pentyl-5-phenyl-2,4-dihydro-3H-1,2,4-triazole-3-one ring: Synthesis, molecular docking, urease inhibition, and crystal structure

Two series of 1,3,4-thiadiazole (40a-o) and 1,2,4-triazole-5-thione (41a-l) derivatives bearing a 2-pentyl-5-phenyl-1,2,4-triazole-3-one ring were synthesized and then studied for their urease inhibitory activities using thiourea as a standard drug. Among the two groups, the first group (40a-o) did not show good activity while the second group (41a-l) showed excellent activity. Compound 41j (1091.24 ± 14.02 µM) of the second series of compounds showed lower activity than thiourea, while the remaining 11 compounds (41a-i, k, and l) showed better activity than thiourea (183.92 ± 13.14 µM). Among the 11 compounds, 41b (15.96 ± 2.28 µM) having the 3-F group on the phenyl ring showed the highest inhibitory activity. Urease kinetic studies of 41b, which is the most active compound, determined it to have an un-competitive inhibition potential. Moreover, in silico analysis against urease from jack bean with 27 new heterocyclic compounds and the reference molecule was carried out to see the necessary interactions responsible for urease activity. The docking calculations of all compounds supported stronger binding to the receptor than the reference molecule, with high inhibition constants. In addition, compound 40m was characterized by single-crystal X-ray diffraction analysis. X-ray analysis reveals that the structures of the compound 40m crystallize in the monoclinic P21/c space group with the cell parameters: a = 10.2155(9) Å, b = 22.1709(18) Å, c = 21.4858(17) Å, β = 99.677(8)°, V = 4797.0(7) ų . X-ray diffraction analyses were also performed to gain insights into the role of weak intermolecular interactions and C-H…X (halogen) interactions in compound 40m that influence the crystal packing.

Analysis of 1-Aroyl-3-[3-chloro-2-methylphenyl] Thiourea Hybrids as Potent Urease Inhibitors: Synthesis, Biochemical Evaluation and Computational Approach

Urease is an amidohydrolase enzyme that is responsible for fatal morbidities in the human body, such as catheter encrustation, encephalopathy, peptic ulcers, hepatic coma, kidney stone formation, and many others. In recent years, scientists have devoted considerable efforts to the quest for efficient urease inhibitors. In the pharmaceutical chemistry, the thiourea skeleton plays a vital role. Thus, the present work focused on the development and discovery of novel urease inhibitors and reported the synthesis of a set of 1-aroyl-3-[3-chloro-2-methylphenyl] thiourea hybrids with aliphatic and aromatic side chains 4a-j. The compounds were characterized by different analytical techniques including FT-IR, ¹H-NMR, and ¹³C-NMR, and were evaluated for in-vitro enzyme inhibitory activity against jack bean urease (JBU), where they were found to be potent anti-urease inhibitors and the inhibitory activity IC₅₀ was found in the range of 0.0019 ± 0.0011 to 0.0532 ± 0.9951 μM as compared to the standard thiourea (IC₅₀ = 4.7455 ± 0.0545 μM). Other studies included density functional theory (DFT), antioxidant radical scavenging assay, physicochemical properties (ADMET properties), molecular docking and molecular dynamics simulations. All compounds were found to be more active than the standard, with compound 4i exhibiting the greatest JBU enzyme inhibition (IC₅₀ value of 0.0019 ± 0.0011 µM). The kinetics of enzyme inhibition revealed that compound 4i exhibited non-competitive inhibition with a Ki value of 0.0003 µM. The correlation between DFT experiments with a modest HOMO-LUMO energy gap and biological data was optimal. These recently identified urease enzyme inhibitors may serve as a starting point for future research and development.

2-Selenouridine, a Modified Nucleoside of Bacterial tRNAs, Its Reactivity in the Presence of Oxidizing and Reducing Reagents

The 5-substituted 2-selenouridines are natural components of the bacterial tRNA epitranscriptome. Because selenium-containing biomolecules are redox-active entities, the oxidation susceptibility of 2-selenouridine (Se2U) was studied in the presence of hydrogen peroxide under various conditions and compared with previously reported data for 2-thiouridine (S2U). It was found that Se2U is more susceptible to oxidation and converted in the first step to the corresponding diselenide (Se2U)₂, an unstable intermediate that decomposes to uridine and selenium. The reversibility of the oxidized state of Se2U was demonstrated by the efficient reduction of (Se2U)₂ to Se2U in the presence of common reducing agents. Thus, the 2-selenouridine component of tRNA may have antioxidant potential in cells because of its ability to react with both cellular ROS components and reducing agents. Interestingly, in the course of the reactions studied, we found that (Se2U)₂ reacts with Se2U to form new ‘oligomeric nucleosides′ as linear and cyclic byproducts.

Antibiotics-free nanoparticles eradicate Helicobacter pylori biofilms and intracellular bacteria

Biofilms and intracellular survival tremendously help Helicobacter pylori (H. pylori) escape from antibacterial agents attacking, therefore issuing extreme challenges to clinical therapies. Herein, we constructed fucoidan (FU)-coated nanoparticles (FU/ML-LA/EB NPs) via simple self-assembly of biguanide derivative (metformin-linoleic acid, ML) and linoleic acid (LA), encapsulating urease inhibitor ebselen (EB) instead of antibiotics to take antibacterial effect. Negatively charged FU/ML-LA/EB NPs easily penetrated through the gastric mucus layer to arrive at infection sites, then eradicated extracellular polymeric substances (EPS) to destroy H. pylori biofilms structure. After strengthening bacterial membrane permeability, the nanoparticles could enter H. pylori and kill bacteria by inhibiting the activity of urease. FU/ML-LA/EB NPs also entered H. pylori-infected host cells through receptor-mediated internalization, in which they activated AMPK to recover lysosomal acidification for killing intracellular H. pylori. Additionally, FU/ML-LA/EB NPs alleviated oxidative stress, hence reducing gastric mucosal damage and cutting off the pathways of carcinogenesis. Notably, H. pylori burden after FU/ML-LA/EB NPs treatment was reduced to a great extent in vivo, which was significantly lower than that after treatment with clinical therapy. Antibiotics-free FU/ML-LA/EB NPs improving bacterial eradication and alleviating oxidation stress made it a powerful approach against H. pylori.

Rational Development of Bacterial Ureases Inhibitors

Urease, an enzyme that catalyzes the hydrolysis of urea, is a virulence factor of various pathogenic bacteria. In particular, Helicobacter pylori, that colonizes the digestive tract and Proteus spp., that can infect the urinary tract, are related to urease activity. Therefore, urease inhibitors are considered as potential therapeutics against these infections. This review describes current knowledge of the structures, activity, and biological importance of bacterial ureases. Moreover, the structure-based design of several classes of bacterial urease inhibitors is presented and discussed. Phosphinic and phosphonic acids were applied as transition-state analogues, while Michael acceptors and ebselen derivatives were applied as covalent binders of cysteine residue. This review incorporates bacterial urease inhibitors from literature published between 2008 and 2021.

Electrophilic warheads in covalent drug discovery: an overview

INTRODUCTION

Covalent drugs have been used for more than hundred years, but gathered larger interest in the last two decades. There are currently over a 100 different electrophilic warheads used in covalent ligands, and there are several considerations tailoring their reactivity against the target of interest, which is still a challenging task.

AREAS COVERED

This review aims to give an overview of electrophilic warheads used for protein labeling in chemical biology and medicinal chemistry. The warheads are discussed by targeted residues, mechanism and selectivity, and analyzed through three different datasets including our collection of warheads, the CovPDB database, and the FDA approved covalent drugs. Moreover, the authors summarize general practices that facilitate the selection of the appropriate warhead for the target of interest.

EXPERT OPINION

In spite of the numerous electrophilic warheads, only a fraction of them is used in current drug discovery projects. Recent studies identified new tractable residues by applying a wider array of warhead chemistries. However, versatile, selective warheads are not available for all targetable amino acids, hence discovery of new warheads for these residues is needed. Broadening the toolbox of the warheads could result in novel inhibitors even for challenging targets developing with significant therapeutic potential.

Synthesis and Biological Evaluation of Dithiobisacetamides as Novel Urease Inhibitors

Thirty-eight disulfides containing N-arylacetamide were designed and synthesized in an effort to develop novel urease inhibitors. Biological evaluation revealed that some of the synthetic compounds exhibited strong inhibitory potency against both cell-free urease and urease in intact cell with low cytotoxicity to mammalian cells even at concentration up to 250 μM. Of note, 2,2'-dithiobis(N-(2-fluorophenyl)acetamide) (d7), 2,2'-dithiobis(N-(3,5-difluorophenyl)acetamide) (d24), and 2,2'-dithiobis(N-(3-fluorophenyl)acetamide) (d8) were here identified as the most active inhibitors with IC₅₀ of 0.074, 0.44, and 0.81 μM, showing 32- to 355-fold higher potency than the positive control acetohydroxamic acid. These disulfides were confirmed to bind urease without covalent modification of the cysteine residue and to inhibit urease reversibly with a mixed inhibition mechanism. They also showed very good anti-Helicobacter pylori activities with d8 showing a comparable potency to the clinical used drug amoxicillin. The impressive in vitro biological profile indicated their immense potential as therapeutic agents to tackle H. pylori caused infections.

High-throughput tandem-microwell assay for ammonia repositions FDA-Approved drugs to inhibit Helicobacter pylori urease

To date, little attempt has been made to develop new treatments for Helicobacter pylori (H. pylori), although the community is aware of the shortage of treatments for H. pylori. In this study, we developed a 192-tandem-microwell-based high-throughput assay for ammonia that is a known virulence factor of H. pylori and a product of urease. We could identify few drugs, that is, panobinostat, dacinostat, ebselen, captan, and disulfiram, to potently inhibit the activity of ureases from bacterial or plant species. These inhibitors suppress the activity of urease via substrate-competitive or covalent-allosteric mechanism, but all except captan prevent the antibiotic-resistant H. pylori strain from killing human gastric cells, with a more pronounced effect than acetohydroxamic acid, a well-known urease inhibitor and clinically used drug for the treatment of bacterial infection. This study offers several bases for the development of new treatments for urease-containing pathogens and to study the mechanism responsible for the regulation of urease activity.

A review on the structures and biological activities of anti-Helicobacter pylori agents

Helicobacter pylori is one of the main causal risk factor in the generation of chronic gastritis, gastroduodenal ulcers and gastric carcinoma. Thus, the eradication of H. pylori infection is an important way for preventing and managing the gastric diseases. Multiple-therapy with several antibacterial agents is used for the eradication of H. pylori infections; however the increase of resistance to H. pylori strains has resulted in unsatisfactory eradication and unsuccessful treatment. Furthermore, the combination therapy with high dosing leads to the disruption of intestinal microbial flora and undesired side effects. Therefore, the search for new therapeutic agents with high selectivity against H. pylori is a field of current interest. In recent years, diverse compounds originating from natural sources or synthetic drug design programs were evaluated and tried to optimize for applying against H. pylori. In this review, we have described various classes of anti-H. pylori compounds, their structure-activity relationship studies, and mechanism of actions, which could be useful for the development of new drugs for the treatment of H. pylori infections.

Small molecule selenium-containing compounds: Recent development and therapeutic applications

Selenium (Se) is an essential micronutrient of organism and has important function. It participates in the functions of selenoprotein in several manners. In recent years, Se has attracted much attention because of its therapeutic potential against several diseases. Many natural and synthetic organic Se-containing compounds were studied and explored for the treatment of cancer and other diseases. Studies have showed that incorporation of Se atom into small molecules significantly enhanced their bioactivities. In this paper, according to different applications and structural characteristics, the research progress and therapeutic application of Se-containing compounds are reviewed, and more than 110 Se-containing compounds were selected as representatives which showed potent activities such as anticancer, antioxidant, antifibrolytic, antiparasitic, antibacterial, antiviral, antifungal and central nervous system related effects. This review is expected to provide a basis for further study of new promising Se-containing compounds.

Toxicology and pharmacology of synthetic organoselenium compounds: an update

Here, we addressed the pharmacology and toxicology of synthetic organoselenium compounds and some naturally occurring organoselenium amino acids. The use of selenium as a tool in organic synthesis and as a pharmacological agent goes back to the middle of the nineteenth and the beginning of the twentieth centuries. The rediscovery of ebselen and its investigation in clinical trials have motivated the search for new organoselenium molecules with pharmacological properties. Although ebselen and diselenides have some overlapping pharmacological properties, their molecular targets are not identical. However, they have similar anti-inflammatory and antioxidant activities, possibly, via activation of transcription factors, regulating the expression of antioxidant genes. In short, our knowledge about the pharmacological properties of simple organoselenium compounds is still elusive. However, contrary to our early expectations that they could imitate selenoproteins, organoselenium compounds seem to have non-specific modulatory activation of antioxidant pathways and specific inhibitory effects in some thiol-containing proteins. The thiol-oxidizing properties of organoselenium compounds are considered the molecular basis of their chronic toxicity; however, the acute use of organoselenium compounds as inhibitors of specific thiol-containing enzymes can be of therapeutic significance. In summary, the outcomes of the clinical trials of ebselen as a mimetic of lithium or as an inhibitor of SARS-CoV-2 proteases will be important to the field of organoselenium synthesis. The development of computational techniques that could predict rational modifications in the structure of organoselenium compounds to increase their specificity is required to construct a library of thiol-modifying agents with selectivity toward specific target proteins.

Covalent Inhibition of Bacterial Urease by Bifunctional Catechol-Based Phosphonates and Phosphinates

In this study, a new class of bifunctional inhibitors of bacterial ureases, important molecular targets for antimicrobial therapies, was developed. The structures of the inhibitors consist of a combination of a phosphonate or (2-carboxyethyl)phosphinate functionality with a catechol-based fragment, which are designed for complexation of the catalytic nickel ions and covalent bonding with the thiol group of Cys322, respectively. Compounds with three types of frameworks, including β-3,4-dihydroxyphenyl-, α-3,4-dihydroxybenzyl-, and α-3,4-dihydroxybenzylidene-substituted derivatives, exhibited complex and varying structure-dependent kinetics of inhibition. Among irreversible binders, methyl β-(3,4-dihydroxyphenyl)-β-(2-carboxyethyl)phosphorylpropionate was observed to be a remarkably reactive inhibitor of Sporosarcina pasteurii urease (k_inact/K_I = 10 420 s^-1 M^-1). The high potential of this group of compounds was also confirmed in Proteus mirabilis whole-cell-based inhibition assays. Some compounds followed slow-binding and reversible kinetics, e.g., methyl β-(3,4-dihydroxyphenyl)-β-phosphonopropionate, with K_i* = 0.13 μM, and an atypical low dissociation rate (residence time τ = 205 min).

3,3'-Diselenodipropionic acid (DSePA): A redox active multifunctional molecule of biological relevance

BACKGROUND

Extensive research is being carried out globally to design and develop new selenium compounds for various biological applications such as antioxidants, radio-protectors, anti-carcinogenic agents, biocides, etc. In this pursuit, 3,3'-diselenodipropionic acid (DSePA), a synthetic organoselenium compound, has received considerable attention for its biological activities.

SCOPE OF REVIEW

This review intends to give a comprehensive account of research on DSePA so as to facilitate further research activities on this organoselenium compound and to realize its full potential in different areas of biological and pharmacological sciences.

MAJOR CONCLUSIONS

It is an interesting diselenide structurally related to selenocystine. It shows moderate glutathione peroxidase (GPx)-like activity and is an excellent scavenger of reactive oxygen species (ROS). Exposure to radiation, as envisaged during radiation therapy, has been associated with normal tissue side effects and also with the decrease in selenium levels in the body. In vitro and in vivo evaluation of DSePA has confirmed its ability to reduce radiation induced side effects into normal tissues. Administration of DSePA through intraperitoneal (IP) or oral route to mice in a dose range of 2 to 2.5 mg/kg body weight has shown survival advantage against whole body irradiation and a significant protection to lung tissue against thoracic irradiation. Pharmacokinetic profiling of DSePA suggests its maximum absorption in the lung.

GENERAL SIGNIFICANCE

Research work on DSePA reported in fifteen years or so indicates that it is a promising multifunctional organoselenium compound exhibiting many important activities of biological relevance apart from radioprotection.

Anti-tubercular profile of new selenium-menadione conjugates against Mycobacterium tuberculosis H37Rv (ATCC 27294) strain and multidrug-resistant clinical isolates

Tuberculosis (TB) is one of the most fatal diseases and is responsible for the infection of millions of people around the world. Most recently, scientific frontiers have been engaged to develop new drugs that can overcome drug-resistant TB. Following this direction, using a designed scaffold based on the combination of two separate pharmacophoric groups, a series of menadione-derived selenoesters was developed with good yields. All products were evaluated for their in vitro activity against Mycobacterium tuberculosis H37Rv and attractive results were observed, especially for the compounds 8a, 8c and 8f (MICs 2.1, 8.0 and 8.1 μM, respectively). In addition, 8a, 8c and 8f demonstrated potent in vitro activity against multidrug-resistant clinical isolates (CDCT-16 and CDCT-27) with promising MIC values ranging from 0.8 to 3.1 μM. Importantly, compounds 8a and 8c were found to be non-toxic against the Vero cell line. The SI value of 8a (>23.8) was found to be comparable to that of isoniazid (>22.7), which suggests the possibility of carrying out advanced studies on this derivative. Therefore, these menadione-derived selenoesters obtained as hybrid compounds represent promising new anti-tubercular agents to overcome TB multidrug resistance.

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New menadione-derived selenoesters were synthesized.

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The compounds demonstrated excellent activity against M. tuberculosis H37Rv.

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8a, 8c and 8f showed potent activity against multidrug resistant clinical isolates.

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Compounds 8a and 8c were found to be non-toxic.

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These organoselenium compounds represent promising new anti-tubercular agents.

Sweet Selenium: Synthesis and Properties of Selenium-Containing Sugars and Derivatives

In the last decades, organoselenium compounds gained interest due to their important biological features. However, the lack of solubility, which characterizes most of them, makes their actual clinical exploitability a hard to reach goal. Selenosugars, with their intrinsic polarity, do not suffer from this issue and as a result, they can be conceived as a useful alternative. The aim of this review is to provide basic knowledge of the synthetic aspects of selenosugars, selenonium salts, selenoglycosides, and selenonucleotides. Their biological properties will be briefly detailed. Of course, it will not be a comprehensive dissertation but an analysis of what the authors think is the cream of the crop of this interesting research topic.

Insights into the Design of Inhibitors of the Urease Enzyme - A Major Target for the Treatment of Helicobacter pylori Infections

Expressed by a variety of plants, fungi and bacteria, the urease enzyme is directly associated with the virulence factor of many bacteria, including Helicobacter pylori, a gram-negative bacterium related to several gastrointestinal diseases and responsible for one of the most frequent bacterial infections throughout the world. The Helicobacter pylori Urease (HPU) is a nickel-dependent metalloenzyme expressed in response to the environmental stress caused by the acidic pH of the stomach. The enzyme promotes the increase of gastric pH through acid neutralization by the products of urea hydrolysis, then critically contributing to the colonization and pathogenesis of the microorganism. At the same time, standard treatments for Helicobacter pylori infections have limitations such as the increasing bacterial resistance to the antibiotics used in the clinical practice. As a strategy for the development of novel treatments, urease inhibitors have proved to be promising, with a wide range of chemical compounds, including natural, synthetic and semisynthetic products to be researched and potentially developed as new drugs. In this context, this review highlights the advances in the field of HPU inhibition, presenting and discussing the basis for the research of new molecules aiming at the identification of more efficient therapeutic entities.

Fast and easy conversion of ortho amidoaryldiselenides into the corresponding ebselen-like derivatives driven by theoretical investigations

The in silico predicted Se⋯N interaction on amidoarylselenenyl iodides has been experimentally exploited for the efficient synthesis of N-substituted benzoisoselenazol-3(2H)-ones, benzoisothiazol-3(2H)-ones and ebselen, recently reported as potent antiviral agent against Sars-Cov2.

Development and Therapeutic Potential of Selenazo Compounds

Incorporation of selenium (Se) atom into small molecules can substantially enhance their antioxidant, anti-inflammatory, antimutagenic, antitumoral or chemopreventive, antiviral, antibacterial, antifungal, antiparasitic, and neuroprotective effects. Specifically, selenazo compounds have received great attention owing to their chemical properties, pharmaceutical applications, and low toxicity. In this Perspective, we compile extensive literature evidence with the description and discussion of the most recent advances in different selenazo and selenadiazo motifs as potential pharmacological candidates. We also provide some perspectives on the challenges and future directions in the advancement of these selenazo compounds, each of which could generate drug candidates for various diseases.

Ebselen bearing polar functionality: Identification of potent antibacterial agents against multidrug-resistant Gram-negative bacteria

Antibiotic-resistant bacteria has become one of the greatest challenges to global human health today. Innovative strategies are needed to identify new therapeutic leads to tackle infections of drug-resistant Gram-negative bacteria. We herein synthesize a series of EB analogues to investigate their antibacterial activities. Select polar functionality at N-terminus of EB exhibited higher activities against multi-drug-resistant Gram-negative pathogens, including E. coli, P. aeruginosa and K. pneumoniae. EB analogue 4g and 4i exhibited potent antibacterial activities against E. coli-ESBL (MIC = 1-4 µg/mL) and E. coli producing NDM-1 (MIC = 4-32 µg/mL), which is superior to the traditional antibiotics (cefazolin, imipenem). Furthermore, the time-kill kinetics studies and the inhibition zone tests indicated that analogue 4i effectively and rapidly cause death of E. coli-ESBL and E. coli-NDM-1. Additionally, accumulation assays and SEM images showed that 4i could permeate bacterial membranes, leading to an irregular cell morphology. Importantly, bacterial resistance for analogue 4i was difficult to induce against E. coli-ESBL. EB analogues here reported low cytotoxicity against L-929 cells and mice model in vivo. We believe that EB analogues with polar functionality could play a pivotal role in the development of novel antibacterial agents in eradicating multi-drug-resistant Gram-negative pathogens infections.

The assemblage of covalent and metal binding dual functional scaffold for cross-class metallo-β-lactamases inhibition

Aim: The discovery and development of novel broad-spectrum MβLs inhibitors are urgent to overcome antibiotic resistance mediated by MβLs. Methods & results: Herein, the synthesized 21 compounds exhibited potent inhibition to the clinically important MβLs (NDM-1, IMP-1 and ImiS) and effectively restored the antibacterial efficacy of cefazolin and imipenem against Escherichia coli harboring MβLs. 5b was first identified to be dual functional broad-spectrum MβLs inhibitor through assemblage of covalent and metal binding scaffold, which irreversibly inhibited B1, B2 MβLs via forming a Se–S covalent bond, and competitively inhibited B3 MβLs by coordinating the metals at active site. Conclusion: The designed compounds can serve as potent broad-spectrum MβLs inhibitors and combat MβLs-producing ‘superbug’ in combination with β-lactams.

Diselenides and Benzisoselenazolones as Antiproliferative Agents and Glutathione-S-Transferase Inhibitors

A series of variously functionalized selenium-containing compounds were purposely synthesized and evaluated against a panel of cancer cell lines. Most of the compounds showed an interesting cytotoxicity profile with compound 5 showing a potent activity on MCF7 cells. The ethyl amino derivative 5 acts synergistically with cis-platin and inhibits the GST enzyme with a potency that well correlates with the cytotoxicity observed in MCF7 cells. A computational analysis suggests a possible binding mode on the GST enzyme. As the main outcome of the present study, the ethyl amino derivative 5 emerged as a valid lead compound for further, future developments.

Cryptococcal Meningitis and Anti-virulence Therapeutic Strategies

Fungal infections of the central nervous system are responsible for significant morbidity and mortality. Cryptococcus neoformans (Cn) is the primary cause of fungal meningitis. Infection begins in the lung after inhalation of fungal spores but often spreads to other organs, particularly the brain in immunosuppressed individuals. Cn’s ability to survive phagocytosis and endure the onslaught of oxidative attack imposed by the innate immune response facilitates dissemination to the central nervous system (CNS). Despite the success of Cn at bypassing innate immunity, entry into the heavily protected brain requires that Cn overwhelm the highly restricted blood-brain barrier (BBB). This is a formidable task but mounting evidence suggests that Cn expresses surface-bound and secreted virulence factors including urease, metalloprotease, and hyaluronic acid that can undermine the BBB. In addition, Cn can exploit multiple routes of entry to gain access to the CNS. In this review, we discuss the cellular and molecular interface of Cn and the BBB, and we propose that the virulence factors mediating BBB crossing could be targeted for the development of anti-virulence drugs aimed at preventing fungal colonization of the CNS.

Further insights of selenium-containing analogues of WC-9 against Trypanosoma cruzi

As a continuation of our project aimed at searching for new chemotherapeutic agents against American trypanosomiasis (Chagas disease), new selenocyanate derivatives were designed, synthesized and biologically evaluated against the clinically more relevant dividing form of Trypanosoma cruzi, the etiologic agent of this illness. In addition, in order to establish the role of each part of the selenocyanate moiety, different derivatives, in which the selenium atom or the cyano group were absent, were conceived, synthesized and biologically evaluated. In addition, in order to study the optimal position of the terminal phenoxy group, new regioisomers of WC-9 were synthesized and evaluated against T. cruzi. Finally, the resolution of a racemic mixture of a very potent conformationally rigid analogue of WC-9 was accomplished and further tested as growth inhibitors of T. cruzi proliferation. The results provide further insight into the role of the selenocyanate group in its antiparasitic activity.