Hospital-acquired pneumonia caused by Staphylococcus aureus is associated with patient morbidity and mortality, despite adequate antibiotic therapy. This illustrates the need for treatments beyond antibiotics. The pore-forming heptameric toxin α-hemolysin (Hla) is a major pathogenicity factor of S.aureus and a clinically validated target. We identify quinoxalinediones (QDS) as highly potent Hla inhibitors, conferring protection against the hallmarks of Hla-induced pathogenicity such as Ca2+ influx, cytotoxicity, hemolysis, and monolayer destruction. The effects were exerted across major Hla subtypes in all relevant cell types. QDS prevented the formation of functional pores by interacting with Hla near the phospholipid-binding site. The QDS analog, H052, was active in mouse models of S.aureus lung infections, when administered prophylactically or therapeutically, either as monotherapy or when given in combination with the antibiotic linezolid. The study provides evidence that complex bacterial toxins can be targeted invivo by drug-like small molecules.

In this study two new zinc(II) complexes involving oxygen and nitrogen donor sequences derived from 1,4-dihydroquinoxaline-2,3-dione (QXD), o-phenylenediamine (OPD) and hydroquinone (HQ) were synthesized through a template procedure. The structural elucidation of these complexes was carried out using measurement of molar conductance in 1x10-3 M solution of DMSO and various spectral techniques; 1H and 13C NMR, FT-IR, UV-VIS and AAS. The results showed that the zinc(II) ion coordinates with the Schiff base ligands in octahedral geometry, leading to the formation of stable macrocyclic and heterocyclic structures. The cyclic ligand (L) was found to coordinate as NNNN donor, through four imine nitrogen atoms which were formed up on condensation of the –NH2 groups on o-phenylenediamine with C=O group on quinoxaline dione in a 2:2 mole ratio, in the presence of one mole equivalent of ZnCl2 in ethanol medium. It also indicates the formation of a new mixed ligand zinc(II) complex with an OO OO O O coordination around zinc(II). The study contributes to the understanding of the coordination chemistry of zinc(II) with Schiff bases and provides insights into the development of novel zinc-based complex compounds. KEY WORDS: Macrocyclic and mixed ligand, 1,4-Dihydroquinoxaline-2,3-dione, o-Phenylenediamine, Hydroquinone Bull. Chem. Soc. Ethiop. 2025, 39(1), 49-64. DOI: https://dx.doi.org/10.4314/bcse.v39i1.4

Random copolymer design strategy towards excellent electrochromic display devices with fast responses

Analgesic and anti-inflammatory activity of quinoxaline derivatives: Design synthesis and characterization

The fundamentals of Pd-catalyzed Csp2−Csp2 Miyaura borylation, Suzuki cross-coupling, and Stille cross-coupling reactions for a variety of borylated precursors based on phenothiazine (PTZ), phenoxazine (POZ), carbazole (Cz), and quinoxaline (QX) units have been explored. Three palladium-based catalysts were chosen for this study: Pd(PPh3)4, Pd(PPh3)2Cl2, and Pd(dppf)Cl2, applying different reaction conditions. Around 16 desired chromophores were successfully designed and synthesized using C-C cross-coupling reactions in moderate to excellent yields, including PTZ, POZ, and Cz units coupled with QX, indolinium iodide, thienyl, phenyl, or triphenylamine moieties. Additionally, PTZ, POZ, and Cz have been employed in synthesizing various pinacol boronate ester derivatives in good to moderate yields. Interestingly, Pd(dppf)Cl2 was found to be the best catalyst for borylation, and C-C cross-coupling reactions occurred in as little as 30 min, with an excellent yield exceeding 98%. Pd(PPh3)4 and Pd(PPh3)2Cl2 catalyzed the reaction to obtain the desired products in moderate to good yields after a long time (20–24 h). On the other hand, the Suzuki-Miyaura cross-coupling between N-(2-methyl)hexyl carbazole pinacol boronate ester derivative 10c and three halogenated quinoxaline derivatives—4-(3-(5-bromothiophen-2-yl)quinoxalin-2-yl)benzaldehyde (27), 4-(5-(3-(5-bromothiophen-2-yl)quinoxalin-2-yl)thiophen-2-yl)benzaldehyde (30), and 4-(3-chloroquinoxalin-2-yl)benzaldehyde (25) catalyzed by Pd(PPh3)4—afforded three carbazole-quinoxaline chromophores (28, 30, and 31, respectively) in 2–3 h, with good to excellent yields reaching 86%. The electron-deficient QX couplers proved to be coupled efficiently using the Stille coupling reaction, which involves the coupling between electron-rich orgaostannane and electron-deficient halide. The synthesized precursors and desired chromophores were characterized by FTIR, 1H-NMR, 13C-NMR, and HRMS.

Superior aggregation, morphology and photovoltaic performance enabled by fine tuning of fused electron-deficient units in polymer donors

Some new structural motifs containing the quinoxaline nucleus have been synthesized and examined for their pharmacological properties. In this study, 6-chloroquinoxaline-2,3(1H, 4H)-dione and 6 nitroquinoxaline-2,3(1H, 4H)-dione were synthesized as basic nuclei for the preparation of the new quinoxaline-2,3-diones by alkylation reactions under the conditions of phase transfer catalysis. The products were characterized by spectroscopic methods 1 H and 13 C NMR. Then, the synthesized products were tested for their antibacterial effects against two bacterial strains. The values of minimum inhibitory concentrations (MIC) vary according to the nature of the alkyl bonded to the quinoxaline nucleus.

Catalyst-transfer polymerization has revolutionized the field of polymer synthesis due to its living character, but for a given catalyst system, the polymer scope is rather narrow. Herein we report a highly efficient Suzuki-Miyaura catalyst-transfer polymerization (SCTP) that covers a wide range of monomers from electron-rich (donor, D) to electron-deficient (acceptor, A) (hetero)arenes by rationally designing boronate monomers and using commercially available Buchwald RuPhos and SPhos Pd G3 precatalysts. Initially, we optimized the controlled polymerization of 3,4-propylenedioxythiophene (ProDOT), benzotriazole (BTz), quinoxaline (QX), and 2,3-diphenylquinoxaline (QXPh) by introducing new boronates, such as 4,4,8,8-tetramethyl-1,3,6,2-dioxazaborocane and its N-benzylated derivative, to modulate the reactivity and stability of the monomers. As a result, PProDOT, PBTz, PQX, and PQXPh were prepared with controlled molecular weight and narrow dispersity (Đ < 1.29) in excellent yield (>85%). A detailed investigation of the polymer structures using 1H NMR and MALDI-TOF spectrometry supported the chain-growth mechanism and the high initiation efficiency of the SCTP method. In addition, the use of RuPhos-Pd showing excellent catalyst-transfer ability on both D/A monomers led to unprecedented controlled D-A statistical copolymerization, thereby modulating the HOMO energy level (from -5.11 to -4.80 eV) and band gap energy (from 1.68 to 1.91 eV) of the resulting copolymers. Moreover, to demonstrate the living nature of SCTP, various combinations of D-A and A-A block copolymers (PBTz-b-PProDOT, PQX-b-PProDOT, and PQX-b-PBTz) were successfully prepared by the sequential addition method. Finally, simple but powerful one-shot D-A block copolymerization was achieved by maximizing the rate difference between a fast-propagating pinacol boronate donor and a slow-propagating acceptor to afford well-defined poly(3-hexylthiophene)-b-poly(benzotriazole).

Understanding the aqueous chemistry of quinoline and the diazanaphthalenes: insight from DFT study

Here, we have designed a series of dyes following the donor–π–acceptor (D–π–A) architecture by incorporating tetrathiafulvalene (TTF) as the donor unit and phthalazine (PTZ), diketopyrrolopyrrole (DPP) and quinoxaline (QNX) as the acceptor units, along with the thiophene unit as a π-bridge. The designed dyes have been designated as TTF-PTZ, TTF-DPP and TTF-QNX respectively. We have used cyanoacrylic acid as the anchoring group for the dyes TTF-PTZ and TTF-DPP, while for the third dye, TTF-QNX, we used a carboxylic group. The structural, electronic and photochemical properties of the designed dyes are investigated under the regime of density functional theory (DFT) and time-dependent density functional theory (TD-DFT) methods. In this regard, the dihedral angle, energies of the highest occupied molecular orbital (HOMO) and lowest unoccupied molecular orbital (LUMO), energy difference between the HOMO and LUMO (ΔH–L values), partial density of states (PDOS), ground state oxidation potential (GSOP), excited state oxidation potential (ESOP), ionization potential (IP), electron affinity (EA), molecular electrostatic potential surface (MEPS) analysis, reorganization energy (λ), electronic coupling matrix element (V), charge transfer rate (kCT), hopping mobility (μhop), absorption spectra, exciton binding energy (EBE) and electron density difference (EDD) of the designed dyes are calculated. This study reveals that the dyes TTF-DPP-4 and TTF-DPP-6′ exhibit the lowest ΔH–L values. The study also reveals that the attachment of the –NH2 group at the donor unit and the –NO2 and –CF3 groups at the acceptor units lower the ΔH–L values of all of the designed dyes. We have also observed that the GSOP of all the designed dyes lie below the redox potential of the I−/I3− electrolyte couple. However, the ESOP of the TTF-PTZ and TTF-QNX groups of dyes, along with the most of the dyes belonging to the TTF-DPP group, lie above the conduction band of the TiO2 semiconducting surface. Moreover, the total reorganization energy (λtot) values are low for the TTF-DPP and TTF-QNX groups of dyes, which confirm the better electron–hole separation efficiency in these groups of dyes. Furthermore, the absorption properties of the designed dyes indicate that the TTF-DPP groups of dyes possess the maximum absorption wavelength (λmax) values and attachment of the –CH3 group at the donor part increases the electron density of the dyes, which in turn results into the maximum red-shift. Therefore, the study reveals that the designed dyes are likely to exhibit facile charge transport. Moreover, the electronic properties of the dye–TiO2 clusters strengthen the performance of the dyes compared to those of the isolated dyes. Hence, our study provides good recommendations for the further design of dyes to enhance the performance of dye-sensitized solar cells (DSSCs).

Anionic pentameric thiophene acetates can be used for fluorescence detection and diagnosis of protein amyloid aggregates. Replacing the central thiophene unit by benzothiadiazole (BTD) or quinoxaline (QX) leads to large emission shifts and basic spectral features have been reported [Chem. Eur. J. 2015, 21, 15133‐13137]. Here we present new detailed experimental results of solvent effects, time‐resolved fluorescence and examples employing multi‐photon microscopy and lifetime imaging. Quantum chemical response calculations elucidate how the introduction of the BTD/QX groups changes the electronic states and emissions. The dramatic red‐shift follows an increased conjugation and quinoid character of the π‐electrons of the thiophene backbone. An efficient charge transfer in the excited states S1 and S2 compared to the all‐thiophene analogue makes these more sensitive to the polarity and quenching by the solvent. Taken together, the results guide in the interpretation of images of stained Alzheimer disease brain sections employing advanced fluorescence microscopy and lifetime imaging, and can aid in optimizing future fluorescent ligand development.

Synthesis and characterization of donor–acceptor type quinoxaline-based polymers and the corresponding electrochromic devices with satisfactory open circuit memory

A series of D–π–A architectures dyes with Coumarin-based derivatives as difluorenylaminocoumarin (DF) and diphenylaminocoumarin (DP) have been designed by modifying the π-bridge for potential application in dye-sensitized solar cells (DSSCs). Three different π-bridges viz. benzothiadiazole (BTD), diketopyrrolopyrrole (DPP) and quinoxaline (QX) with are used to design six different dye systems DFi (i = 1–3) on difluorenylaminocoumarin-thiophene-cyanoacrylic acid (R1) and DPi (i = 1–3) on diphenylaminocoumarin-thiophene-cyanoacrylic acid (R2). The electronic, optical and photovoltaic properties have been evaluated, using the density functional theory (DFT), and time dependant DFT methods to study the effect of these spacers on the cell performance. In addition, we have used four functionals to establish our calculation method, in order to compare the theoretical with the experimental results of R1 and R2 dyes. Thus, the CAM-B3LYP functional was sufficient to predict the UV–visible spectra. Moreover, the gap energy (Egap), Voc, the electronic injection free energy (ΔGinject), light harvesting efficiency (LHE), total reorganization energy (λtotal), and absorption spectra of all dyes were discussed. In addition the DF2, DP2 dyes are displayed smaller Egap, negative ΔGinject and absorption spectra shifted to red compared to R1 and R2, respectively. The results of these dyes reveal that the DF2 and DP2 dyes molecules are favourable candidates for DSSCs application.

Control of nonradiative deactivation of triplet states and tuning the singlet-triplet energy gap (ΔEST) are the major challenges to develop materials exhibiting thermally activated delayed fluorescence (TADF) and room temperature phosphorescence (RTP). Herein, we propose a new class of multichromophoric tridonor-acceptor (D3-A) compounds with rigid and flexible π-spacer having N-rich pyridoquinoxaline (PQ) and pyridopyrazine (PZ) acceptor core, respectively. The molecule with carbazole (Cz) donors at meta to quinoxaline (QX) nitrogen of rigid PQ core exhibits TADF. Whereas, the variation of the linkage position of Cz to PQ as well as twisted and flexible PZ core show predominantly RTP due to relatively higher singlet-triplet energy gap (ΔEST). Increasing the donor strength with phenoxazine (PO) in PZ system leads to simultaneous TADF and RTP. Further, we demonstrate the promising scope of all-organic triplet harvesting materials in solid-state security encryption.

o-Phenylenediamine/gold nanocluster-based nanoplatform for ratiometric fluorescence detection of alkaline phosphatase activity

A simple, highly efficient and green procedure for the condensation of aryl and alkyl 1,2-diamines with α-diketones in the presence of catalytic amount of boron sulfonic acid (BSA) and silica trimethyl borat (STMB) and silica triisopropyl borate (STIPB), as two novel heterogeneous Lewis acid catalysts at room temperature, is described. In this method, we proved that the BrOnsted acidic power of boron sulfonic acid (BSA) is more important than its Lewis acidity. Using this method, quinoxaline derivatives as biologically interesting compounds are produced in high to excellent yields.

Uncommon condensations of 1,2,3-triketone 2-oximes with o-phenylenediamine

Side chain engineering for the regulation of quinoxaline based D-A copolymers

Introducing alkylthio side chains into acceptor units to improve the photovoltaic performance of a quinoxaline based D-A polymer

Introduction : Quinoxalines belong to the N-containing heterocyclic compounds that stand out as having promising biological activity due to their privileged scaffold. Quinoxaline derivatives constitute the basis of many insecticides, fungicides, herbicides, as well as being important in human health and as receptor antagonists. On the other, the compounds containing thiazolidine-2,4-dione have demonstrated wide range of pharmacological activities, which include antimicrobial, antiviral, antidiabetic and anticancer activity. In this research, we have synthesised a new quinoxaline derivatives containing N-substituted thiazolidine-2,4-dione derivatives and evaluated for antitumor activity against a 3-cell line panel, consisting of MCF7 (breast), NCI-H460 (lung), and SF-268 (CNS). Methods and Results: In a 250 ml three necked flask equipped with teflon coated mechanical stir bar, chloroacetic acid and thiourea have been dissolved in distilled water and the contents of the flask were heated in the presence of hydrochloric acid. The precipitate was filtered and washed with water and dried before recrystalization. Consequently, the new synthesized thiazolidinedione derivatives were condensed in situ by quinoxaline aldehydes and substituted benzyl halides in N,N-Dimethylformamide. The resulted products were washed with water and then recrystallized in appropriate solvent. Structures of all the synthesized compounds were confirmed by IR, 1 H NMR, 13 CNMR, and Mass spectral data. The MTT assay of synthesized hybrids showed promising and effective anti-cancer activity against 3-cell cell lines. The current results indicate that these quinoxaline derivatives are novel and promising agents for further development towards a treatment for cancer. conclusion: In the present study, series of new N-thiazolidine-2,4-dione incorporated quinoxaline ring were synthesized. All compounds were screened against two different cancer cell lines using MTT assay method. Keywords : Thiazolidine-2, 4- Dione, Anticancer activity, MTT assay method