Strong Electrophiles Research Articles

Evaluation of Quinazolin-2,4-Dione Derivatives as Promising Antibacterial Agents: Synthesis, In Vitro, In Silico ADMET and Molecular Docking Approaches

A series of new quinazolin-2,4-dione derivatives incorporating amide/eight-membered nitrogen-heterocycles 2a–c, in addition, acylthiourea/amide/dithiolan-4-one and/or phenylthiazolidin-4-one 3a–d and 4a–d. The starting compound 1 was prepared by reaction of 4-(2,4-dioxo-1,4-dihydro-2H-quinazolin-3-yl)-benzoyl chloride with ammonium thiocyanate and cyanoacetic acid hydrazide. The reaction of 1 with strong electrophiles, namely, o-aminophenol, o-amino thiophenol, and/or o-phenylene diamine, resulted in corresponding quinazolin-2,4-dione derivatives incorporating eight-membered nitrogen-heterocycles 2a–d. Compounds 3a–d and 4a–d were synthesized in good-to-excellent yield through a one-pot multi-component reaction (MCR) of 1 with carbon disulfide and/or phenyl isocyanate under mild alkaline conditions, followed by ethyl chloroacetate, ethyl iodide, methyl iodide, and/or concentrated HCl, respectively. The obtained products were physicochemically characterized by melting points, elemental analysis, and spectroscopic techniques, such as FT-IR, 1H-NMR, 13C-NMR, and MS. The antibacterial efficacy of the obtained eleven molecules was examined in vitro against two Gram-positive bacterial strains (Staphylococcus aureus and Staphylococcus haemolyticus). Furthermore, Computer-Aided Drug Design (CADD) was performed on the synthesized derivatives, standard drug (Methotrexate), and reported antibacterial drug with the target enzymes of bacterial strains (S. aureus and S. haemolyticus) to explain their binding mode of actions. Notably, our findings highlight compounds 2b and 2c as showing both the best antibacterial activity and docking scores against the targets. Finally, according to ADMET predictions, compounds 2b and 2c possessed acceptable pharmacokinetics properties and drug-likeness properties.

Utilizing MEDT analysis of [3 + 2] cycloaddition reaction: x-ray crystallography of spirooxindole linked with thiophene/furan heterocycles and triazole framework

Hybridization of spirooxindole with different pharmacophores such as triazole and heterocycle such as thiophene and furan moiety was achieved by the [3 + 2] cycloaddition (32CA) reaction approach. Structural investigations of the compounds 4a and 4b were performed using X-ray single crystal structure determinations and Hirshfeld analysis. Both compounds crystallized in monoclinic crystal system. The space group is P21/c for 4a and P21/n for 4b. The crystal parameters are a = 10.2619(3) Å, b = 13.6776(3) Å, c = 10.9318(3), β = 116.640(4)° for the former while a = 13.0012(1) Å, b = 14.9692(1) Å, c = 14.1178(1) Å, β = 97.101(1)° for the latter. In both compounds, the aryl group and the triazole moieties are twisted from one another. The twist angle is 84.75˚for 4a while 86.64˚ for 4b. Based on Hirshfeld calculations, the Cl…H, O…H, N…H and C…H non-covalent interactions in 4a while the O…H interactions in 4b are the most important. The molecular mechanism of the key 32CA reaction between the in situ generated azomethine ylides and the corresponding chalcones has been studied within the Molecular Electron Density Theory (MEDT). The MEDT study reveals that the low activation energies and high experimental selectivity are the result of the supernucleophilic character of the ylides and the strong electrophilicity of the chalcones, which favour the process through a high polar character. This high polar character accounts for the total endo selectivity experimentally found.

Fabrication of norepinephrine and ε-polylysine engineered magnetic nanocomposites tailored for phosphopeptides analysis

Protein phosphorylation is a highly prevalent post-translational modification that holds a vital position in numerous physiological processes. Prior to mass spectrometry detection, the enrichment of phosphopeptides is critically significant due to their susceptibility to interference from abundant non-phosphopeptides. In this study, the magnetic nanocomposite (Fe3O4@NE@PL) was successfully synthesized and characterized. Fe3O4@NE@PL exhibited strong hydrophilicity, electrophilicity and intermolecular interactions through hydrogen bonds, enabling it to effectively enrich phosphopeptides with excellent sensitivity (0.4 fmol β-casein) and selectivity (β-casein:BSA=1:1000). In addition, Fe3O4@NE@PL was successfully applied to enrich phosphopeptides from complex real biological samples such as human serum and saliva, achieving up to 4 recycles with favorable stability and reusability. This study demonstrates that Fe3O4@NE@PL is a promising adsorbent for phosphopeptides enrichment in proteomics research, providing new ideas for the construction of magnetic enrichment materials.

A Computational Analysis of the Proton Affinity and the Hydration of TEMPO and Its Piperidine Analogs.

The study investigated the impact of protonation and hydration on the geometry of nitroxide radicals using B3LYP and M06-2X methods. Results indicated that TEMPO exhibited the highest proton affinity in comparison to TEMPOL and TEMPONE. Two pathways contribute to hydrated protonated molecules. TEMPO shows lower first enthalpies of hydration (ΔH1-M), indicating stronger H-bonding interactions, while TEMPONE shows higher values, indicating weaker interactions with H2O. Solvent effects affect charge distribution by decreasing their atomic charge. Spin density (SD) is primarily concentrated in the NO segment, with minimal water molecule contamination. Protonation increases SD on N-atom, while hydration causes a more pronounced redistribution for water molecules. The stability of the dipolar structure (>N⋅+-O-) is evident in SD redistributions. The frontier molecular orbital (FMO) analysis of TEMPONE reveals a minimum EHOMO-LUMO gap (EH-L), enhancing the piperidine ring's reactivity. TEMPO is the most nucleophilic species, while TEMPONE exhibits strong electrophilicity. Transitioning from NO radicals to protonated forms increases the EH-L gap, indicating protonation stabilizes FMOs. Increased water molecules make the molecule less reactive, while increasing hydration decreases this energy gap, making the molecule more reactive. A smaller EH-L gap indicates the compound becomes softer and more prone to electron density and reactivity changes.

Frenkel defects facilitate oriented 1O2 formation in birnessite for enhanced catalytic oxidation of formaldehyde

Defect strategy is one of the most effective approaches for enhancing the efficiency of Mn-based catalysts in removing formaldehyde (HCHO) under ambient conditions. Herein, the interlayer Mn-O octahedra in birnessite synergistically form with Mn vacancies through proton exchange in acidic solutions, creating surface Frenkel defects. As evidenced by highly combined physicochemical characterization and density functional theory calculations, surface Frenkel defects are highly active sites on the surface of birnessite. The surface Frenkel defects can induce surface electronic reconstruction, generating strong electrophilicity, which promotes the evolution of superoxide radicals (O2•−) into singlet oxygen (1O2). In-situ quenching DRIFTS indicates that 1O2 is the most important ROS in the oxidation process of HCHO. Additionally, the surface Frenkel defects enhance the adsorption of HCHO, promoting the dehydrogenation of HCHO to form CO, which is then rapidly oxidized to CO2 and H2O under the action of 1O2. This provide a more effective kinetic and thermodynamic catalytic pathway. The defect-rich birnessite (R-Bir) achieved complete HCHO removal in the dynamic test at 10 ppm within 10 hours, significantly outperforming defect-free birnessite (F-Bir) and most previously reported catalysts. This study precisely reveals the catalytic mechanism of HCHO over R-Bir and provides valuable insights for the design of high-performance environmental catalysts.

Nanostructured electrochemical platform for sensitive detection of melatonin in human serum and tablets

Melatonin (MT) is a crucial hormone for biological rhythms that influences sleep-wake cycles. The therapeutic value of MT in neurological disorders highlights the need for precise detection. However, challenges like low concentrations in biological samples and complex matrix interferences persist, necessitating rapid and precise analytical techniques. This study presents the novelty of designing a novel sensor that combines a molecularly imprinted polymer with polytoluidine blue O (PTBO) and multi-walled carbon nanotubes on a glassy carbon electrode for MT detection and the study of the interaction between MT and the proposed sensor using density functional theory (DFT). DFT showed that MT has a high nucleophilic character and low electrophilicity compared to TBO, which is a strong electrophile. This supports electron transfer from MT to TBO/PTBO, as indicated by the electronic chemical potentials and molecular electrostatic potentials. Scanning electron microscopy was used to see the morphology. Electrochemical measurements using differential pulse voltammetry demonstrated enhanced sensitivity and selectivity. Under optimized conditions, the sensor exhibited a linear response ranging from 1 to 1000 µM with a limit of detection and limit of quantification of 0.027 µM and 0.092 µM respectively. The performance of the sensor was evaluated in pharmaceutical tablets and human serum. Validation experiments confirmed the reliability of the sensor, with recovery rates of 97.5 % for serum and 98.0 % for pharmaceutical tablets, alongside low relative standard deviations indicating good precision. Interference studies showed minimal effects from coexisting substances, highlighting the selectivity of the proposed sensor. Comparative analysis with existing sensors showed superior performance.

Fabrication of self-N-doped porous biochar by synergistic pyrolysis activation for efficient tetracycline and CO2 adsorption

The development of green and economical adsorption materials with high pollutant adsorption performance is of great significance to meet environmental challenges. Herein, self N-doped porous carbon materials with excellent tetracycline and CO2 adsorption properties are successfully prepared by synergistic pyrolysis activation of corn stalk and Chlorella mixture. The addition of N-riched Chlorella significantly affects the nanopore and surface chemical structure of biochar, forming rich micro-mesopores, changing the intrinsic N doping form and surface oxygen-containing functional groups. An ultra-high tetracycline adsorption capacity of 1159.7 mg/g can be achieved by using the prepared KBC-3:1 as an adsorbent. A series of kinetic isothermal adsorption models, thermodynamic calculations, as well as comparative characterization analysis show that multiple adsorption mechanisms coexist. The pore filling of micro-mesopores (1.5–3 nm), π-π interactions of CC bonds, H bonding interactions of CO and the strong electrophilicity of pyrrolic N contribute to the excellent tetracycline adsorption performance of KBC-3:1. Furthermore, the material shows great resistance to cationic (K+, Mg2+, Cu2+) interference and excellent cycling performance. In addition, KBC-3:1 also exhibits excellent adsorption capacity for CO2, and the adsorption capacity of 5.21 mmol/g can be achieved at 273 K and 1 bar, which could be attributed to the synergistic activation effect leading to KBC-3:1 having the most abundant pyrrolic and pyridinic N species as well as the rich microporous structure. This work can provide guidance for the development of green and economical high performance carbon materials based on the intrinsic characteristics of biomass.

Enhanced electrical insulation properties of 2-isopropenyl-2-oxazoline grafted polypropylene for high voltage direct current power cables

Polymers have been extensively used for high voltage direct current transmission systems as insulation power cables. Space charge accumulation consistently remains the primary factor contributing to the degradation of the electrical insulation properties of polymers. Grafting modification is a valid approach for suppressing the injection of space charges and free electrons by inducing deep traps. In this paper, the modified polypropylene grafted the group with low ionization energy is reported. The deep traps are revealed by the thermally stimulated depolarization current experiment and the band structure as well as the electrostatic potential by density functional theory simulation. The method with the innovative hybrid functional and basis set is adopted to establish the average local ionization distribution of the grafting group, thus confirming its strong electrophilicity. Furthermore, the modified polypropylene has been proved to obtain higher breakdown strength and operational stability by experiments. This work can provide insights for the design and selection of power cables with excellent electrical insulation properties.

Design of dual-functional protic porous ionic liquids for boosting selective extractive desulfurization

Porous ionic liquids have demonstrated excellent performance in the field of separation, attributed to their high specific surface area and efficient mass transfer. Herein, task-specific protic porous ionic liquids (PPILs) were prepared by employing a novel one-step coupling neutralization reaction strategy for extractive desulfurization. The single-extraction efficiency of PPILs reached 75.0% for dibenzothiophene. Moreover, adding aromatic hydrocarbon interferents resulted in a slight decrease in the extraction efficiency of PPILs (from 45.2% to 37.3%, 37.9%, and 33.5%), indicating the excellent extraction selectivity of PPILs. The experimental measurements and density functional theory calculations reveal that the surface channels of porous structures can selectively capture dibenzothiophene by the stronger electrophilicity (Eint(HS surface channel/DBT) = −39.8 kcal mol−1), and the multiple extraction sites of ion pairs can effectively enrich and transport dibenzothiophene from the oil phase into PPILs through π···π, C–H···π and hydrogen bonds interactions. Furthermore, this straightforward synthetic strategy can be employed in preparing porous liquids, offering new possibilities for synthesizing PPILs with tailored functionalities.

Self-assembled monolayer mediated fast charge transport of Sb2(S,Se)3 photocathode enabling high-performance unbiased water splitting

The photoelectrochemical (PEC) water splitting system, capable of generating green hydrogen fuel, is crucial for achieving carbon net zero. However, the performance of the photocathode, responsible for the hydrogen evolution reaction, remains suboptimal. We propose bottom interface engineering using a self-assembled monolayer (SAM) to enhance the quality of the Sb2(S,Se)3 absorber layer. The SAM, composed of (3-aminopropyl)triethoxysilane (APTES), is introduced on the Au substrate to enhance adhesion between the substrate and the Sb2(S,Se)3 absorber. Notably, the APTES treatment facilitates the formation of strong electrophile functional groups on the substrate, which predominantly attract tartrate-Sb-Se ionic clusters in the precursor ink. This interaction between the precursor and the substrate induces preferential nucleation of Sb2Se3 near the substrate, followed by Sb2S3 formation at a later stage near the top surface. The APTES-treated Sb2(S,Se)3 photocathodes exhibit a steep band energy gradient, resulting in a photocurrent density of 16 mA cm–2, an onset potential of 0.24 V versus the standard hydrogen electrode, and stability of 24 h in neutral electrolyte (0.5 M K-Pi, pH 6.13). By combining the APTES-treated Sb2(S,Se)3 photocathode with a perovskite photoanode, the co-planar PEC–PEC water splitting device achieves a remarkable solar-to-hydrogen efficiency of 6.5 % under unbiased conditions, along with operating stability for over 120 min. This study suggests that SAM treatment-based interface engineering could be a potential breakthrough in improving the performance of chalcogenide photocathodes in solar-driven water splitting systems.

A novel ionic-liquid-mediated covalent organic framework as a strong electrophile for high-performance iodine removal

The research on the adsorption and conversion of non-polar gases (carbon dioxide, hydrogen, iodine, etc.) has attracted global attention. Extensive work has revealed the intuitive impact of the heteroatom effect on the adsorption performance of covalent organic framework (COF) adsorbents for non-polar gases. However, more influencing factors must be studied to more precisely design and construct target-specific COF adsorbents. In this work, an underlying influencing factor, local polarity, is discovered, which is defined as the polarity of the functional moiety. Due to the substitution of strong electrophile, the electron cloud distribution of the COF framework is regulated, and the local polarity that better matches the adsorption of target electrophilic gas (iodine) has been observed. The local polarity of COF has been controlled through several strong electrophilic ionic liquids, dramatically improving adsorption performance. The saturated adsorption capacity increases from 1.5 to 5.2 g·g−1, and the adsorption kinetics index k80% value increases from 0.51 to 2.69 g·g−1·h−1. The insight would support precise chemical regulation of target-specific COF in energy and environment science.

Sulfonium-Based Activity-Based Probes for Lysine-Selective Protein Profiling under Alkaline Conditions

AbstractDue to their strong nucleophilicities, nucleophilic lysine and cysteine residues can be easily recognized and modified by electrophilic groups, thus, acting as the targets for covalent ligands or drugs. Therefore, the development of site-specific protein-modification chemistry for various nucleophilic residues has been explored to label proteins selectively for many biological and therapeutic applications. In this study, we constructed a series of sulfonium-based small molecules to react with the amine group of lysine residues by utilizing the strong electrophilicity of sulfonium, resulting in lysine-selective labeling via the formation of classical amide bonds under alkaline conditions (pH 9.0–11.0). After systematic optimization of the labeling conditions, this strategy was utilized for protein labeling across various bacteria’s lysates. Finally, combined with the activity-based protein profiling (ABPP) strategy, we successfully identified and analyzed hundreds of labeled lysine residues in the bacterial proteome.

ClpP Peptidase as a Plausible Target for the Discovery of Novel Antibiotics.

Antimicrobial resistance (AMR) to currently available antibiotics/drugs is a global threat. It is desirable to develop new drugs that work through a novel target(s) to avoid drug resistance. This review discusses the potential of the caseinolytic protease P (ClpP) peptidase complex as a novel target for finding novel antibiotics, emphasising the ClpP's structure and function. ClpP contributes to the survival of bacteria via its ability to destroy misfolded or aggregated proteins. In consequence, its inhibition may lead to microbial death. Drugs inhibiting ClpP activity are currently being tested, but no drug against this target has been approved yet. It was demonstrated that Nblocked dipeptides are essential for activating ClpP's proteolytic activity. Hence, compounds mimicking these dipeptides could act as inhibitors of the formation of an active ClpP complex. Drugs, including Bortezomib, Cisplatin, Cefmetazole, and Ixazomib, inhibit ClpP activation. However, they were not approved as drugs against the target because of their high toxicity, likely due to the presence of strong electrophiles in their warheads. The modifications of these warheads could be a good strategy to reduce the toxicity of these molecules. For instance, a boronate warhead was replaced by a chloromethyl ketone, and this new molecule was shown to exhibit selectivity for prokaryotic ClpP. A better understanding of the structure and function of the ClpP complex would benefit the search for compounds mimicking N-blocked dipeptides that would inhibit ClpP complex activity and cause bacterial death.

In silico evaluations of phytochemicals from Withania somnifera exhibiting anticancer activity against NAD[P]H-quinone oxidoreductase.

Cancer is a leading cause of death globally and in the US, prompting research into medicinal plants with anticancer properties. Withania somnifera, or Ashwagandha, is one such plants, known for its diverse pharmacological effects. Withaferin A and Viscosalactone B are two compounds found in Ashwagandha with known anticancer activity. The protein NQO1, overexpressed in various cancers, was the focus of this study. We hypothesize that specific phytochemicals in Withania somnifera can effectively interact with and inhibit the NQO1 protein, thereby exhibiting anticancer properties. This study aims to identify these interactions using in silico approaches. CFDT was performed using the Gaussian 16 program package, followed by QSAR analysis of the compounds in the PASS online web server. The Schrodinger suite was used to carry out ligand and protein preparation, molecular docking, and molecular dynamic simulation to analyse the interaction of these compounds with NQO1 and ADME studies. Protox-II and SWISSADME tools were used to predict the toxicity and blood-brain barrier permeability of the phytochemicals. CDFT and frontier molecular orbital analyses predicted the stability and reactivity of all the selected molecules. QSAR analysis predicted the biological activity and toxicity of the compounds. Withaferin A exhibited the highest glide gscore (-4.953kcal/mol) and demonstrated 6 hydrogen bond interactions with NQO1, suggesting its potential as an anticancer agent. Conceptual density functional theory-based analysis suggested the strong electrophilicity of the ligands, further supporting their potential anticancer activities. Viscosalactone B, another phytochemical from Ashwagandha, also showed interactions involving 6 hydrogen bonds with NQO1, with a glide gscore of (-4.593kcal/mol). Molecular dynamic simulations validated the stability of the Withaferin A-NQO1 complex. ADME-T properties predicted high oral absorption for the selected ligands, indicating that Withaferin A could be a viable orally administered drug.

(Invited) Electrochemical Synthesis of Chelation-Stabilized Organo-Λ 3-Bromanes

The chemistry of hypervalent halogen species has made enormous progress over the last few decades, and hypervalent iodine(III) compounds have become common reagents in nowadays organic synthesis. The related isoelectronic hypervalent bromine(III) species feature superior reactivity to the I(III) counterparts due to the higher oxidizing ability, stronger electrophilicity and better leaving group ability (nucleofugality) of the bromanyl moiety. However, the hypervalent bromine chemistry appears to be significantly less developed than that of the iodine(III) compounds. This notable imbalance appears to be due to the relatively low stability and high oxidizing power of bromine(III) reagents, resulting in reactivity that is difficult to control. Furthermore, there is a clear shortage of simple method for the synthesis of bromine (III) species, but known methods often require handling of the highly toxic and corrosive BrF3 precursor. In this context, we have proposed the electrochemical generation of chelation-stabilized hypervalent bromine(III) compounds as a possible solution to the above problems. This presentation will give an overview of our current progress in this field.

Modulating excited state properties of thermally activated delayed fluorescence molecules by hybrid long-range and short-range charge transfer strategy

Balancing the rapid radiative decay process and the fast reverse intersystem crossing (RISC) process of thermally activated delayed fluorescence (TADF) molecule remains a great challenge and efficient molecular design strategies are highly desired. Herein, from a theoretical perspective, excited state properties of three reported TADF molecules (1TICz, 1BOICz and 2BOICz) are investigated based on density functional theory (DFT) and time-dependent density functional theory (TD-DFT) calculations coupled with the thermal vibration correlation function (TVCF) method. Results indicate that, by introducing the multi-resonance (MR) acceptor, 1BOICz possesses hybrid long-range and short-range charge transfer features, balanced small energy gap (ΔEST) and large oscillator strength (f) is obtained. Furthermore, by incorporating double equivalent MR acceptors in 2BOICz, largely enhanced f with slightly changed ΔEST is achieved, inner mechanism for remarkable photophysical property is illustrated. Keep this strategy, seven new TADF molecules (2pDBA-bICz-1, 2pDBA-bICz-2, 2OSBA-bICz, 2DQAO-bICz, 2QAO-bICz, 2SQAO-bICz and 2OQAO-bICz) are theoretically designed, detailed physical parameters are analyzed and excited state energy consumption process is studied. Strong electrophilicity on acceptor is determined and the strength of nucleophilic sites on the bridge-phenyl of 2DQAO-bICz, 2QAO-bICz, 2SQAO-bICz and 2OQAO-bICz is increased, this promotes the short-range charge transfer property. In addition, the excitation processes for all studied molecules are dominated by long-range charge transfer from donor to acceptors, and supplemented by the short-range charge transfer on the bridge-phenyl with MR effect. Compromise energy gap and oscillator strength as well as large spin orbit coupling (SOC) constant are obtained for designed molecules. Thus, by regulating the long-range and short-range charge transfer ratios, excited state properties are successfully modulated and new efficient TADF molecules are proposed. Our research aims to provide deeper insight into long-range and short-range charge transfer features in balancing small ΔEST and large f, which could facilitate the development of novel efficient TADF molecules.

Aza-Michael Addition in Explicit Solvent: A Relative Energy Gradient - Interacting Quantum Atoms Study.

Aza-Michael additions are key reactions in organic synthesis. We investigate, from a theoretical and computational point of view, several examples ranging from weak to strong electrophiles in dimethylsulfoxide treated as explicit solvent. We use the REG-IQA method, which is a quantum topological energy decomposition (Interacting Quantum Atoms, IQA) coupled to a chemical-interpretation calculator (Relative Energy Gradient, REG). We focus on the rate-limiting addition step in order to unravel the different events taking place in this step, and understand the influence of solvent on the reaction, with an eye on predicting the Mayr electrophilicity. For the first time a link is established between an REG-IQA analysis and experimental values.

Plasmepsin II inhibitory potential of phytochemicals isolated from African antimalarial plants: a computational approach

Plamepsin II has been identified as a therapeutic target in the Plasmodium falciparum’s life cycle and may lead to a drastic reduction in deaths caused by malaria worldwide. Africa flora is rich in medicinal qualities and possesses both simple and complex bioactive phytochemicals. This study utilized computational approaches like molecular docking, molecular dynamics simulation, quantum chemical calculations and ADMET to evaluate the plasmepsin II inhibitory properties of phytochemicals isolated from African antimalarial plants. Molecular docking was carried out to estimate the binding affinity of 229 phytochemicals whereby ekeberin A, dichamanetin, 10-hydroxyusambaresine, chamuvaritin and diuvaretin were selected. Further, RMSD and RMSF plots from the 100 ns simulation results showed that the screened phytochemicals were stable in the enzyme’s binding pocket. The quantum chemical calculation revealed that all the phytochemicals are strong electrophiles, while ekeberin A was identified as the most stable and dichamanetin as the most reactive. Also, ADMET studies established the drug candidacy of the phytochemicals. Thus, these phytochemicals could act as good antimalarial agents after extensive in vitro and in vivo studies. Communicated by Ramaswamy H. Sarma

The neutrophil oxidant hypothiocyanous acid causes a thiol-specific stress response and an oxidative shift of the bacillithiol redox potential in Staphylococcus aureus.

During infections, Staphylococcus aureus is exposed to hypochlorous acid (HOCl) and hypothiocyanous acid (HOSCN), which are produced by the neutrophil myeloperoxidase as potent antimicrobial killing agents. In this work, we applied RNAseq transcriptomics, Brx-roGFP2 biosensor measurements, and phenotype analyses to investigate the stress responses and defense mechanisms of S. aureus COL toward HOSCN stress. Based on the RNAseq transcriptome profile, HOSCN exerts strong thiol-specific oxidative, electrophile, and metal stress responses as well as protein damage in S. aureus, which is indicated by the strong induction of the HypR, TetR1, PerR, QsrR, MhqR, CstR, CsoR, CzrA, AgrA, HrcA, and CtsR regulons. Phenotype analyses of various mutants in HOSCN-responsive genes revealed that the HOSCN reductase MerA conferred the highest resistance toward HOSCN stress in S. aureus COL, whereas the QsrR and MhqR electrophile stress regulons do not contribute to protection. Brx-roGFP2 biosensor measurements and bacillithiol (BSH)-specific Western blot analyses revealed a strong oxidative shift of the bacillithiol redox potential (EBSH) and increased S-bacillithiolations in S. aureus, indicating that BSH is oxidized to bacillithiol disulfide (BSSB) under HOSCN stress. While the ΔmerA mutant was delayed in recovery of the reduced EBSH, overproduction of MerA in the ΔhypR mutant enabled faster recovery of EBSH due to efficient HOSCN detoxification. Moreover, both MerA and BSH were shown to contribute to HOSCN resistance in growth assays. In summary, HOSCN provokes a thiol-specific oxidative, electrophile, and metal stress response, an oxidative shift in EBSH and increased S-bacillithiolation in S. aureus.IMPORTANCEStaphylococcus aureus colonizes the skin and the airways but can also lead to life-threatening systemic and chronic infections. During colonization and phagocytosis by immune cells, S. aureus encounters the thiol-reactive oxidant HOSCN. The understanding of the adaptation mechanisms of S. aureus toward HOSCN stress is important to identify novel drug targets to combat multi-resistant S. aureus isolates. As a defense mechanism, S. aureus uses the flavin disulfide reductase MerA, which functions as HOSCN reductase and protects against HOSCN stress. Moreover, MerA homologs have conserved functions in HOSCN detoxification in other bacteria, including intestinal and respiratory pathogens. In this work, we studied the comprehensive thiol-reactive mode of action of HOSCN and its effect on the reversible shift of the EBSH to discover new defense mechanisms against the neutrophil oxidant. These findings provide new leads for future drug design to fight the pathogen at the sites of colonization and infections.

Synthesis and Characterization of New Spirooxindoles Including Triazole and Benzimidazole Pharmacophores via [3+2] Cycloaddition Reaction: An MEDT Study of the Mechanism and Selectivity.

A new series of spirooxindoles based on benzimidazole, triazole, and isatin moieties were synthesized via a [3+2] cycloaddition reaction protocol in one step. The single X-ray crystal structure of the intermediate triazole-benzimidazole 4 was solved. The new chemical structures of these spirooxindole molecules have been achieved for the first time. The final synthesized chemical architecture has differently characterized electronic effects. An MEDT study of the key 32CA reaction between in situ generated azomethine ylide (AY) and chalcones explained the low reaction rates and the total selectivities observed. The supernucleophilic character of AY and the strong electrophilicity of chalcones favor these reactions through a highly polar two-stage one-step mechanism in which bond formation at the β-conjugated carbon of the chalcones is more advanced. The present combined experimental and theoretical study reports the synthesis of new spirooxindoles with potential biological activities and fully characterizes the molecular mechanisms for their formation through the key 32CA reaction step.