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A few computational studies indicated that some inhibitors of viral RNA–polymerase such as favipiravir could also inhibit cysteine proteases. The potential dual action of favipiravir as an inhibitor for both RNA–polymerase and proteases promises enhanced therapeutic efficacy of the drug against coronaviruses. To shed more light on this phenomenon, in view of the chemical structure of favipiravir and the recent advances in this field, six novel derivatives of 3-methyl quinoxaline were synthesized. In silico methods confirmed the abilities of these compounds to occupy the active-site clefts of both 3CLpro and PLpro with favorable interactions, while the ADMET evaluations predicted low toxicity and high bioavailability for them. Then, due to the high similarities between PLpro and papain, the inhibitory impacts of favipiravir and the synthesized quinoxalines on the kinetics of papain were thoroughly investigated. The outcome revealed that the potential dual-action of favipiravir-like compounds is a possibility that should be taken into account in designing more effective and safe drugs against coronavirus. [ABSTRACT FROM AUTHOR]

Herein, we report the design and synthesis of a novel series of 6-((1H-1,2,3-triazol-4-yl)methyl)-6H-indolo[2,3-b]quinoxalines (22–29) via the copper(I)-catalyzed azide–alkyne cycloaddition (CuAAC) reaction. The target compounds formed through two pathways (A and B). The structures of the newly click synthesised 1,2,3-triazole-6H-indolo[2,3-b]quinoxalines (22–29) were confirmed on the basis of their elemental analysis and spectral data. Some of these compounds exhibited significant antiproliferative effects against tested cancer cells, including hepatocellular carcinoma (Hep-G2), breast cancer (MCF-7), and colon cancer (HCT116), relative to healthy noncancerous control skin fibroblast cells (BJ-1) to evaluate their cytotoxic effects. Among the tested compounds, compound 27 exhibited strong activity with IC50 = 9.3 ± 1.1, 1.5 ± 0.1, 2.4 ± 0.2, and 17.3 ± 1.2 against cancer cell lines HCT-116, HepG-2, MCF-7, and BJ-1, respectively. Therefore, compound 27 was selected for further investigation. Cell cycle analysis of liver cancer (HepG-2) cells treated with 27 showed cell cycle arrest in the S and G0/G1 phases and strong apoptotic activity, as indicated by Annexin V-FITC staining. Compound 27 was also found to fit in the ATP binding pocket during docking experiments combined with molecular dynamics simulation. Lastly, we conducted a Petra/Osiris/Molinspiration (POM) study on the synthesized compound. The most promising candidates were identified by evaluating primary in silico parameters, which showed considerable differences among individual synthesized compounds. These features can promote future drug candidate design to produce better derivatives in the search for anticancer agents, particularly those with favorable ADME parameters, low toxicity, anticipated bioactivity, and bright futures. [ABSTRACT FROM AUTHOR]

This study introduces novel Liquid Organic Hydrogen Carriers (LOHCs) derived from quinoxaline. It shows that strategically incorporating N atoms and methyl groups markedly improves the hydrogen release kinetics. This structural modulation optimizes the adsorption properties and enables low-temp C–H bond activation, providing valuable insights for developing efficient LOHCs. [ABSTRACT FROM AUTHOR]

Here, a cyclometalated Pt(II) clamshell dimer (complex 2) has been synthesized with the primary ligand of dibenzo(f,h)quinoxaline and an ancillary ligand of N,N′-diphenylformamidine. In addition, a mononuclear Pt(II) complex 1a and a binuclear Pt(II) complex 1b were also prepared. Complex 1a was coordinated by one cyclometalated ligand of dibenzo(f,h)quinoxaline, one chloride ion, and one N,N′-diphenylformamidine. Complex 1b was coordinated by one cyclometalated ligand of dibenzo(f,h)quinoxaline, two chloride ions, and two N,N′-diphenylformamidines. All of these three complexes were characterized by nuclear magnetic resonance (NMR) spectroscopy, high-resolution mass spectrometry (HRMS), elemental analyses, and single-crystal X-ray diffraction (XRD). The Pt–Pt distance in complex 2 was 2.8439(2) Å. It also exhibited a near-infrared (near-IR) emission at 887 nm in the pure solid state. On the other hand, complexes 1a and 1b exhibited triplet emission at 589 and 660 nm, respectively, in the pure solid state. Furthermore, in 2 wt% poly(Me methacrylate) (PMMA) films, complex 1a showed a triplet emission at 548 nm (with Φ = 84% and τ = 5.53 μs) and complex 1b showed an emission at 627 nm (with Φ = 79% and τ = 4.07 μs). Due to its great photophysical properties, complex 1b was deposited onto quartz plates for the detection of organic solvent vapors and it showed unique emission quenching for the vapor of tetrahydrofuran. [ABSTRACT FROM AUTHOR]

The Y-type compound 67dTPA-FQ combining 2-phenylfuro[2,3-b]quinoxaline (FQ) with triphenylamine (TPA) demonstrated to be a green fluorescence emitter (519 nm) with a ΔES1T1 of 0.40 eV. Herein, TPA units in 67dTPA-FQ were replaced with 10-phenyl-10H-phenoxazine (Ph-PXZ) units to shift the S1 energy to a lower direction to reduce ΔES1T1 and realize thermally-activated delayed fluorescence (TADF). Thus, Y-shaped (67dPXZ-FQ) and T-shaped (58dPXZ-FQ) compounds were synthesized. As the donor changed from TPA to PXZ, the emission bands of the Y- and T-shaped compounds in toluene shifted to 585 nm and 631 nm, respectively. As we expected, ΔES1T1 for Y- and T-shaped compounds decreased to 0.12 eV and 0.15 eV, respectively, well lower than 0.3 eV. Unfortunately, the TADF feature was not observed. Theoretical calculations revealed that the HOMO and LUMO orbitals of both compounds were completely located at one of the PXZ fragment and 2-phenylfuro[2,3-b]quinoxaline moiety, respectively, yielding a complete electron separation by phenylene bridges between the acceptor FQ and PXZ. As a result, the oscillator strength (f) of the S1 → S0 transition was only 0.0001–0.0002, leading to weak radiative transition capability of the S1 state. As a result, a low fluorescent yield of 25–36% was obtained. Moreover, the calculated spin–orbital coupling value between the S1 and T1 was only 0.13 cm−1 for both 67dPXZ-FQ and 58dPXZ-FQ, suggesting weak driving capability for the reverse intersystem crossing process. As such, the TADF features of the two compounds were not observed. [ABSTRACT FROM AUTHOR]

2-Chloro-3-substituted quinoxalines (3) are significant precursors in the synthesis of 2,3-di-unsymmetrically substituted quinoxalines, including quinacillin, which has been shown to be effective against a number of transplantable diseases and cancer cells. Despite the fact that there are two ways to produce 2-chloro-3-substituted quinoxalines (3), both procedures are hampered by high temperatures, metal contamination, and toxic reagents. A visible-light-induced radical cascade cyclization of ortho-diisocyanoarenes (1) with alkyl(aryl)sulfinic acids (2) and trichloroisocyanuric acid has been developed. Also, a plausible reaction mechanism and synthetic uses of 2-chloro-3-substituted quinoxalines (3) towards a few 2,3-di-unsymmetrically-substituted quinoxalines have been described. This novel approach easily accesses 2-chloro-3-substituted quinoxalines (3) in good yields, without using elevated temperatures, or metal- or toxic reagents. [ABSTRACT FROM AUTHOR]

A simple method for the preparation of 2-aryl-3-(2-aminoaryl)quinoxalines from 2-alkynylnitrobenzenes and 1,2-diaminoarenes was described. The reactions could proceed under mild conditions. The 1-nitro-2-(phenylethynyl)benzenes, simple starting materials, could generate the key intermediate 3H-indole-3-ones in situ in the presence of PPh3. After a cyclization with 1,2-diaminobenzenes, the 3H-indole-3-ones were then transformed into biologically valuable quinoxalines. [ABSTRACT FROM AUTHOR]

The synthesis and characterisation of eleven different 2-(thienyl)quinoxaline species that incorporate different points of functionality, including at the thiophene or quinoxaline rings, are described. These species display variable fluorescence properties in the visible region (λem = 401–491 nm) depending upon the molecular structures and extent of conjugation. The series of 2-(thienyl)quinoxaline species were then investigated as cyclometalating agents for Ir(III) to yield [Ir(C^N)2(bipy)]PF6 (where C^N = the cyclometalated ligand; bipy = 2,2′-bipyridine). Eight complexes were successfully isolated and fully characterised by an array of spectroscopic and analytical techniques. Two Ir(III) examples were structurally characterised in the solid state using single crystal X-ray diffraction; both structures confirmed the proposed formulations and coordination spheres in each case showing that the thiophene coordinates via a Ir–C bond. The photophysical properties of the complexes revealed that each complex is luminescent under ambient conditions with a range of emission wavelengths observed (665–751 nm) indicating that electronic tuning can be achieved via both the thienyl and quinoxaline moieties. [ABSTRACT FROM AUTHOR]

Alkyl diacyl peroxides were demonstrated to be efficient alkylating reagents for the visible-light-induced 4CzIPN-catalyzed direct C–H alkylation of N-heteroaromatics. With this metal-/base-/additive-free photocatalytic system, 57 examples of alkylated N-heteroaromatics scaffolds including 1,2,4-triazine-3,5(2H,4H)-diones (i.e. azauracils), quinoxalin-2(1H)-ones, 2H-benzo[b][1,4]oxazin-2-ones and quinoxalines were successfully synthesized. [ABSTRACT FROM AUTHOR]

We herein report a direct and efficient protocol for phosphorylation of quinoxalines, which employs aerobic oxygen as the green oxidant under catalyst-free conditions. This methodology represents one of the most environmentally friendly and easily handled protocols, providing a series of phosphorylated quinoxalines in good to excellent yields. Control experiments clearly indicated that the reaction followed a dearomatization–rearomatization strategy. [ABSTRACT FROM AUTHOR]

Herein, we describe an efficient method involving the synthesis of diverse quinoxalines using the DMSO/tBuONa/O2 system as a single-electron oxidant to form α-imino radicals and nitrogen radicals for the direct construction of C–N bonds. This methodology provides a novel approach to form α-imino radicals with good reactivity. [ABSTRACT FROM AUTHOR]

A Cu(OTf)2-mediated regioselective dearomative aryl-hydroxylation across the C(sp2)＝N bond of 2-aryl quinoxalines and bis-N-arylation of (benz)imidazoles were developed using aryl boronic acids. For the dearomative aryl-hydroxylation, the C-center should be electrophilic (ca. 0.08), the N-center nucleophilic (ca. −0.50), and the C(sp2)＝N bond polarized (Δe = 0.609). [ABSTRACT FROM AUTHOR]

By incorporating a dithieno[3,2-f:2′,3′-h]quinoxaline unit into a PM6 polymer backbone, we developed a novel terpolymer family, demonstrating composition-dependent optical, electrochemical, and morphological characteristics. Organic solar cells based on the combination of a terpolymer and ternary strategy achieved a high power conversion efficiency of 17.60%, demonstrating the validity of our combination strategy. [ABSTRACT FROM AUTHOR]

Composite polymer materials doped with original push–pull chromophores with the quinoxaline core in the conjugated bridge have been developed. Chromophores with various substituents in the aniline donor moiety and tricyanofuran acceptor are characterized by high thermal stability and predicted values of first hyperpolarizability (up to 1000 × 10−30 esu). Nonlinear optical (NLO) coefficient d33 of corona-poled polymer films achieved 75 pm V−1 for materials doped with chromophore with N,N-dibutylamino-3-ethylbenzene donor at 25 wt% content, while doping with a similar chromophore with an additional bulky cyclohexylphenyl group in the acceptor leads to maximum d33 value 97 pm V−1 for 40 wt% chromophore content and 65 pm V−1 for neat chromophore material. The temporal and thermal stabilities of the NLO response at room temperature and heating to 50 °C during 100 hours is shown to be high: for some polymer materials the value of d33 remained almost constant for 24 months at room temperature and at least 94% of the response preserved after heating. [ABSTRACT FROM AUTHOR]

Supramolecular assemblies of quinoxaline derivative (QxPyA) have been developed for turn-on detection of cholesterol in human serum and in aqueous media with a detection limit of 4 nM. [ABSTRACT FROM AUTHOR]

The synthesis of pyrrolo[1,2-α]quinoxalines is of importance, because they possess a variety of biological activities, and interesting fluorescence/photophysical properties. Multifarious methods for the construction of pyrrolo[1,2-α]quinoxalines have been developed, but there remains no general means to exhibit broad substrate scope with high functional group tolerance under mild conditions. We report herein a practical and efficient oxidative cyclization for pyrrolo[1,2-α]quinoxalines using ethyl 2-(4-nitrophenyl)azocarboxylate. [ABSTRACT FROM AUTHOR]

Three compounds, bearing a quinoxaline–methanone unit as an acceptor moiety and dimethylacridan, carbazole, or phenothiazine donor moieties, were designed and synthesized by employing the single-step Buchwald–Hartwig cross-coupling reaction. The geometry and electronic characteristics of the compounds in the ground and the first singlet excited states were studied within density functional theory (DFT). It was shown that S0 → S1 excitation is characterised by intramolecular charge transfer (ICT) from the donor moieties to acceptor quinoxaline–methanone moiety for all the compounds. The extent of ICT depends on the dihedral angle between the donor moiety and the phenyl moiety. The red emission of the derivatives of quinoxaline–methanone and dimethylacridan or phenothiazine was found to be delayed fluorescence. The films of 2 wt% solid solutions of the derivatives of quinoxaline–methanone and dimethylacridan, or phenothiazine in poly(metylmethacrylate) showed moderate photoluminescence quantum yields of 16% and 11%, respectively, and the lifetimes of delayed fluorescence of 5.56 μs and 99.1 μs. The films demonstrated emission sensitivity to oxygen. [ABSTRACT FROM AUTHOR]

The functionalization of quinoxalinones is synthetically and biologically appealing, however, C2 functionalized quinoxalinones is not reported via environmentally friendly approach. Herein, we disclosed C2–O sulfonylation of quinoxalinones via our developed electrochemical oxidative O–S coupling strategy for synthesizing 2-sulfonyloxylated quinoxalines. Applying this protocol, quinoxalin-ones and sodium sulfinates as the starting materials, a wide range of 2-sulfonyloxyl quinoxaline derivatives were obtained in moderate to good yields with good functional-group tolerance under mild conditions without additional oxidants. The utility of this methodology and the sulfonyloxyl handles was demonstrated trough gram-scale preparation and the synthesis of 2-substituted quinoxaline-based bioactive molecules, respectively. [ABSTRACT FROM AUTHOR]

Recently, waste biomass-derived catalysts have emerged as sustainable and remarkable alternatives to petroleum (depleting resource)-based catalysts. We report here the application of a water extract of pomegranate peel ash (WEPA) as an effective catalyst in an aqueous medium for the construction of quinoxalines from aryl/heteroaryl 1,2-diamines and α-hydroxy ketones via a metal catalyst/added oxidant-free sequential condensation–cyclization–oxidation process with a sensible mechanism. The catalyst was systematically characterized using inductively coupled plasma mass spectrometry (ICP-MS), energy dispersive X-ray fluorescence (ED-XRF), Fourier transform infrared (FT-IR), powder X-ray diffraction (XRD), scanning electron microscopy(SEM), energy-dispersive X-ray spectroscopy (XEDS) and microwave plasma atomic emission spectroscopy (MP-AES) data. The quinoxalines were purified by recrystallization with excellent yields. The developed process shows very low E-factor (5.62 and 0.84 with and without the inclusion of water), along with multigram-scale (5.53 g) feasibility, and high regioselectivity in the case of unsymmetrical diamines and unsymmetrical α-hydroxy ketones. Furthermore, this method describes the use of a biorenewable catalyst and aqueous reaction medium for the construction of high-value heterocyclics and avoids volatile/problematic organic solvents, column-based product purifications, depleting material-based catalysts/axillaries/oxidants/purification agents/extraction agents and harsh reaction conditions. This biomimetic process can attract chemists' attention towards identifying the applicability of waste biomass-derived catalysts for the production of fine chemicals and biopotent chemical substances involving novel/interesting processes. [ABSTRACT FROM AUTHOR]

The selectivity and efficiency of benzene and toluene uptake at the gas–solid interface by quinoxaline cavitands is strongly enhanced by partial rigidification of the receptor cavity and immobilization of the cavitand onto silica gel particles. [ABSTRACT FROM AUTHOR]

According to Global Cancer Statistics 2021, female breast cancer has exceeded lung cancer as the most frequently diagnosed cancer. As a result of this widespread breast cancer, it is necessary to discover new drug candidates that avoid the side effects of current ones. So, researchers have studied and researched many heterocyclic chemical structures that were found to have strong anti-breast cancer activity. Among these structures are N-heterocycles, benzodiazines, a sequence of bicyclic heterocycles in which benzene rings are fused with 6-membered heterocycles containing two nitrogens. The quinoxaline moiety is a well-known and promising scaffold with previously known anticancer properties. This study covers the published work on anti-breast cancer compounds based on previous reference documents from recent years. It also shows the properties of new compounds with attractive anti-breast cancer properties that could be seen to be safer and free of adverse reactions. The compounds discussed here are attractive and promising scaffolds for treating breast cancer. [ABSTRACT FROM AUTHOR]

Functionalized quinoxalines, embedding acid sensitive protecting groups, can be prepared with a fast (5 min) and high yielding (>90%) protocol using a choline chloride/water NADES at room temperature without any additional activation. The products obtained after solvent extraction do not require any further purification. The NADES used can be recycled up to six times maintaining the same efficiency level. [ABSTRACT FROM AUTHOR]

Herein, we demonstrate that a thiophene-modified quinoxaline core small molecule can be applied in Sb2(S,Se)3 solar cells. We reveal that the interaction between thiophene and Sb2(S,Se)3 through the Sb-S bond essentially improves the interfacial holeextraction ability. This study provides a cost-effective dopant-free hole-transporting material for inorganic thin film solar cell applications with excellent stability. [ABSTRACT FROM AUTHOR]

A novel molecular scaffold, dibenzo[f,h]furo[2,3-b]quinoxaline (diBFQ), and its derivatives, 3,6-bis(4-isopropylphenyl)-11-phenyldibenzo[f,h]furo[2,3-b]quinoxaline (dP-diBFQ) and furo[2′,3′:5,6]pyrazino[2,3-f][1,10]phenanthroline (FPPhen), were designed and synthesized, showing highly efficient pure and deep blue emission. The unsubstituted molecular scaffolds diBFQ and FPPhen exhibit emission from 424–445 nm with PLQYs of ∼70%, and the disubstituted derivative of diBFQ, dP-diBFQ, shows a PLQY of 79.1%. Our experimental and theoretical investigations revealed that the additional N atoms in FPPhen facilitate the electron distribution of the HOMO orbital localizing on a smaller π-conjugate fragment compared with diBFQ, which resulted in the emission peak blue-shifting from 445 nm for diBFQ to 424 nm for FPPhen. Furthermore, introducing the steric substituent isopropylphenyl into the diBFQ scaffold would help to suppress aggregates of dP-diBFQ molecules and improve the fluorescence efficiency. OLEDs using dP-diBFQ as dopants show pure blue emission with CIE coordinates of (0.154, 0.102) and an EQE of 2.28%. Upon increasing the dopant concentration, the EQE and current efficiency could be improved to 2.63% and 4.7 cd A−1, but aggregate emission with a peak from 472–476 nm was clearly observed due to molecular aggregation. Our studies clearly suggested that diBFQ and FPPhen scaffolds are promising fluorescence cores for deep and pure-blue emission. [ABSTRACT FROM AUTHOR]

This study reports a straightforward heterogeneous catalytic (Al-MCM-41) approach to synthesize nitrogen heterocycle moieties from primary amines under solvent-free conditions. The Al-MCM-41 catalyst was prepared using a hydrothermal method and characterized by various analytical techniques. The probability and limitations of the catalytic methodology were presented with various substrates. The catalytic method grants an attractive route to a wide variety of benzimidazole and quinoxaline moieties with good to excellent yields. The gram scale reaction and reusability (up to five cycles) of the Al-MCM-41 catalyst would greatly benefit industrial applications. [ABSTRACT FROM AUTHOR]

Current research based on the development of promising anticancer chemotherapeutics is a great challenge to scientists to combat the pervasiveness of pernicious cancer. In line with this, the aim of this work is to develop a set of 9-arylacenaphtho[1,2-b]quinoxaline analogues with the capability of imaging, as well as terminating, cancer cells in the human body, exploiting the powerful anticancer activity of the quinoxaline and acenaphthene moieties. The rigid, planar disc like framework of acenapthoquinoxalines gives them the ability to intercalate to helical DNA via π–π stacking, and the fluorescence properties of these compounds has been increased with the extension of π-conjugation by introducing various aryl groups to the core moiety via a Suzuki coupling reaction. Precise cytotoxicity screening has revealed that compound 5a is the most potent and selective (with respect to HEK 293 cells) compound among all members of this series, showing IC50 values of 1.97 ± 1.29 μM, 3.06 ± 1.07 μM and 22.01 ± 0.77 μM against the human cervical cancer (HeLa), human breast cancer (MCF-7) and human brain cancer (U87MG) cell lines, respectively. Compound 5c has been recognised as the fluorescent imaging agent with the highest quantum yield (ϕ = 0.1458). Furthermore, the considerable cellular uptake, nucleus targeting aptitude and DNA damaging qualities of these compounds, and above all the annihilation of cancer cells, have been certified by flow cytometry, colocalisation studies, binding studies and DNA gel ladder assays, along with morphological analysis and scratch wound healing assays. [ABSTRACT FROM AUTHOR]

Tailoring the physical properties of molecular crystals though the construction of solid solutions requires the existence of isostructural crystals. Simple substitutions of a given molecular framework can give a range of different crystal structures. A set of quinoxaline derivatives, C8H4N2(C6H4X)2, Q3,3′X2, has been investigated (X = F, Cl, Br, I and Me) where kinetic factors generated a set of isostructural crystals for the lighter halogens (F, Cl, Br) alone. Computational analysis shows that the stabilising interactions are maximal for Cl, while DSC studies demonstrate the existence of more stable polymorphs for both F and Br containing systems. Steric factors appear to have a lower contribution than the balance of weaker hydrogen and halogen bonding shown by the Me and I containing systems displaying different packing driven by CH⋯N/CH⋯π bonds and I⋯I bonds respectively. [ABSTRACT FROM AUTHOR]

Three novel donor–accepter–donor (D–A–D) type monomers (TPAQ-Ph, TPAQ-PhOMe and TPAQ-Phen) consisting of triphenylamine (TPA) and substituted quinoxaline moieties were synthesized, and further electropolymerized for electrochromic devices. Polymers PTPAQ-Ph and PTPAQ-PhOMe with two twisted substituents on the π-conjugated backbone exhibited efficient electrochromic properties, involving high optical contrast up to 70%, short response time less than 3 s, high color coloration efficiency over 200 cm2 C−1, and good cycle stability. However, polymer PTPAQ-Phen employing a fused electron acceptor unit with high coplanarity showed poor electrochromic performance and low stability. Moreover, electrochromic devices based on these three polymers were fabricated and characterized. The result demonstrates that the molecular configuration of the designed monomer is crucial for electrochromic performance. [ABSTRACT FROM AUTHOR]

The synthesis, photophysics and reverse saturable absorption of two cationic dinuclear Ir(III) complexes bearing fluorenyl-tethered 2-(quinolin-2-yl)quinoxaline (quqo) ligands are reported in this paper. The two complexes possess intense and featureless diimine ligand localized 1ILCT (intraligand charge transfer)/1π,π* absorption bands at ca. 330 and 430 nm, and a weak 1,3MLCT (metal-to-ligand charge transfer)/1,3LLCT (ligand-to-ligand charge transfer) absorption band at >500 nm. Both complexes exhibit weak dual phosphorescence at ca. 590 nm and 710 nm, which are attributed to the 3ILCT/3π,π* and 3MLCT/3LLCT states, respectively. The low-energy 3MLCT/3LLCT state also gives rise to a moderately strong triplet excited-state absorption at 490–800 nm. Because of the stronger triplet excited-state absorption than the ground-state absorption of these complexes at 532 nm, both complexes manifest a moderate reverse saturable absorption (RSA) at 532 nm for ns laser pulses. Expansion of the π-conjugation of the fluorenyl-tethered diimine ligand in Ir-1 causes a slight red-shift of the 1ILCT/1π,π* absorption bands in its UV-vis absorption spectrum and the 3MLCT/3LLCT absorption band in the transient absorption spectrum and slightly enhances the RSA at 532 nm compared to that in Ir-2. This work represents the first report on dinuclear Ir(III) complexes that exhibit RSA at 532 nm. [ABSTRACT FROM AUTHOR]

Hazardous volatile organic compounds (VOCs) can significantly impact human health and the environment. Hence, the detection of VOCs is of foremost importance. A quinoxaline-based fluorimetric probe (1) unveils a notable "turn-on" fluorescence response towards mesitylene in the presence of other VOCs and common interfering ions in aqueous media. The sensing phenomenon involves specific 1 : 1 stoichiometric binding of the probe with mesitylene with a ∼2.66 ppm detection limit. Furthermore, the probe experiences morphological transformations from a fibril-network to a stone-shaped hetero-structure upon treatment with mesitylene, indicating mesitylene induced self-assembly. The detection induced self-assembly of the probe was further corroborated by dynamic-light-scattering (DLS) and fluorescence microscopy study. Importantly, this proposed approach is applicable to detect mesitylene in natural water sources and in the vapor phase using portable, low-cost filter paper strips. [ABSTRACT FROM AUTHOR]

Quinoxalines are a class of N-heterocycles which are present in a variety of natural and synthetic compounds. They act as a versatile building block in synthesizing novel heterocyclic scaffolds and are important intermediates in many bioactive compounds. They have achieved immense significance in organic as well as medicinal chemistry. Several synthetic approaches have been developed to afford a variety of quinoxaline derivatives. In this review, we have summarized the recent progress in the transition metal-catalyzed synthesis of quinoxalines. [ABSTRACT FROM AUTHOR]

A straightforward catalyst-free synthetic approach has been developed for the synthesis of a quinoxaline derivative, 4-phenyl-4-(pyridin-2-yl)-4,5-dihydropyrrolo[1,2-a]quinoxaline (L), by the reaction of 2-benzoyl pyridine and pyrrole-1-anillin in ethanol. L in the presence of a stoichiometric amount of copper(II) perchlorate becomes decomposed unprecedentedly to produce a copper(II) complex, [CuL′2(H2O)2](ClO4)2 (1) (L′ = 2-benzoylpyridine), in aqueous methanolic medium. X-ray structures show that both L and 1 crystallize in the monoclinic crystal system with the P21/n space group. The structure of 1 is a copper centred centrosymmetric axially elongated octahedron with two (N,O) chelating ligands L′ occupying the equatorial positions (Cu–O of 2.013(2) Å and Cu–N of 1.963(2) Å) and two aqua ligands occupying the axial positions (Cu–O(aqua) bonds of 2.377(3) Å). Detailed computational analysis encompassed a combination of density functional theory (DFT) calculations and molecular dynamics (MD) simulations. The structural features of the compounds, local reactivity properties, stability, and spin density surfaces including frontier orbital energies were studied with DFT calculations in detail. [ABSTRACT FROM AUTHOR]

A series of light-emitting analogues, [4-(2,3-diphenyl-quinoxalin-6-yl)-phenyl]-diphenyl-amine (TPA–DPQ) and [4-(2,3-diphenyl-pyrido[2,3-b]pyrazin-7-yl)-phenyl]-diphenyl-amine (TPA–DPP) are synthesized and characterized. TPA–DPQ and TPA–DPP possess similar donor–acceptor structures, in which triphenylamine is used as an electron donor while 2,3-diphenyl-quinoxaline (DPQ) and its analogue 2,3-diphenyl-pyridine[2,3-b]pyrazine (DPP) serve as electron acceptors. Due to the stronger electron-withdrawing ability of DPP compared with DPQ, TPA–DPP exhibits longer but weaker emission than TPA–DPQ as expected. However, TPA–DPQ and TPA–DPP show different mechanochromic luminescence (MCL) properties with emission color changes of 42 and 10 nm, respectively. Crystallographic analysis demonstrates that changes of CH⋯π and CH⋯N intermolecular interactions are responsible for the significantly different MCL behaviors of the two compounds. This work will provide some guidance for the rational design of MCL-active fluorophores. [ABSTRACT FROM AUTHOR]

A method for the synthesis of coupling compounds of benzimidazoles and pyrrolo[1,2-a]quinoxalines via Mamedov Heterocycle Rearrangement is reported here. This method was conducted at room temperature and only solvent (HOAc) was required. A series of 4-(1H-benzo[d]imidazol-2-yl)pyrrolo[1,2-a]quinoxaline derivatives were obtained in moderate to good yields. [ABSTRACT FROM AUTHOR]

C-Alkylations of nine different classes of methyl-substituted N-heteroarenes, including quinolines, quinoxalines, benzimidazoles, benzoxazoles, pyrazines, pyrimidines, pyridazines, pyridines, and triazines are disclosed. A bench stable earth-abundant Mn(I)-complex catalyzed the chemoselective hydrogen-transfer reaction utilizing a diverse range of primary alcohols as the non-fossil fuel-derived carbon source. The diversified N-heteroarenes (41 examples) were isolated in high yields and selectivities. Water is produced as the sole byproduct, making the protocol environmentally benign. [ABSTRACT FROM AUTHOR]

Visible light promoted domino synthesis of 2-aryl benzimidazoles is reported through the reaction of ortho-phenylenediamines and arylmethyl amines under aerobic conditions. The methodology has wide substrate scope and tolerates a wide range of functional groups affording the products in high yields. The use of arylethyl amines instead of arylmethyl amines gives 2-aryl quinoxalines. [ABSTRACT FROM AUTHOR]

In view of their DNA intercalation activities as anticancer agents, 17 novel [1,2,4]triazolo[4,3-a]quinoxaline derivatives have been designed, synthesized and evaluated against HepG2, HCT-116 and MCF-7 cells. Molecular docking studies were performed to investigate the binding modes of the proposed compounds with the DNA active site. The data obtained from biological testing highly correlated with those obtained from the molecular modeling studies. MCF-7 was found to be the most sensitive cell line to the influence of the new derivatives. In particular, compound 12d was found to be the most potent derivative of all the tested compounds against the three HepG2, HCT116 and MCF-7 cancer cell lines, with IC50 = 22.08 ± 2.1, 27.13 ± 2.2 and 17.12 ± 1.5 μM, respectively. Although this compound displayed nearly one third of the activity of doxorubicin (IC50 = 7.94 ± 0.6, 8.07 ± 0.8 and 6.75 ± 0.4 μM, respectively), it may be useful as a template for future design, optimization, and investigation to produce more potent anticancer analogs. Compounds 12a, 10c and 10d displayed very good anticancer activities against the three HepG2, HCT116 and MCF-7 cancer cell lines, with IC50 = 31.40 ± 2.8, 28.81 ± 2.4 and 19.72 ± 1.5 μM for 12a, 33.41 ± 2.9, 29.96 ± 2.5 and 24.78 ± 1.9 μM for 10c, and 37.55 ± 3.3, 30.22 ± 2.6 and 25.53 ± 2.0 μM for 10d. The most active derivatives, 10c, 10d, 10h, 12a, 12b and 12d, were evaluated for their DNA binding activities. Compound 12d displayed the highest binding affinity. This compound potently intercalates DNA at a decreased IC50 value (35.33 ± 1.8 μM), which is nearly equipotent to that of doxorubicin (31.27 ± 1.8 μM). Compounds 12a and 10c exhibited good DNA-binding affinities, with IC50 values of 39.35 ± 3.9 and 42.35 ± 3.9 μM, respectively. Finally, compounds 10d, 10h and 12b showed moderate DNA-binding affinities, with IC50 values of 50.35 ± 3.9, 57.08 ± 3.3 and 59.35 ± 3.2 μM, respectively. [ABSTRACT FROM AUTHOR]

Phosphonation of quinoxalines and quinoxalin-2(1H)-ones utilizing aerobic oxygen as green oxidant under visible light conditions at room temperature has been described. Both quinoxalines and quinoxalin-2(1H)-ones are compatible with alkyl or aryl phosphonates and provided good yields of products through regioselective C–P bond formation under base/ligand-free conditions. Competitive experiments showed quinoxalin-2(1H)-ones are more reactive than quinoxalines under the present conditions, and the control experiments revealed the present transformation proceeds through a radical mechanism. [ABSTRACT FROM AUTHOR]

A new family of radical-bridged compounds, (Cp*2Co)[M2Cl4(dpq)] (M = Fe (1), Co (2), Zn (3)), (dpq = 2,3-di(2-pyridyl)-quinoxaline) is reported. Magnetic studies, DFT and ab initio calculations reveal strong antiferromagnetic metal–radical interactions with coupling constants of J = −213.1 and −218.8 cm−1 for 1 and 2, respectively. [ABSTRACT FROM AUTHOR]

Two new non-fullerene acceptors, namely QIP-4F and QIP-4Cl, containing a novel imide-functionalized quinoxaline (QI) moiety fused with a thienylthiophene unit as the central building block, and fluorinated or chlorinated 2-(3-oxo-2,3-dihydro-1H-inden-1-ylidene)malononitrile as end-capping groups, were designed and synthesized, respectively. An optimized device based on P2F-EHp:QIP-4Cl presented a power conversion efficiency of 13.3%, with an impressively high open-circuit voltage of 0.94 V. These results demonstrate the great potential of QI-containing fused units as central building blocks for high-performance acceptors. [ABSTRACT FROM AUTHOR]

In this study, new fluorescent quinoxalines were developed as G4 topology-selective probes. Among them, the most promising one could light up parallel G4s at two separate excitation wavelengths, exhibiting dual-channel emission, and light up nonparallel G4s at one excitation wavelength, showing mono-channel emission. [ABSTRACT FROM AUTHOR]

Quinoxaline derivatives play versatile roles in various fields of science. Thus different types of scaffolds have been designed with these quinoxaline moieties to make them more efficient for preparation of various biologically active materials in the pharmaceutical industry. The ability of quinoxaline moieties has been reinforced by introducing triazole rings into them with the aid of a "click reaction" following environmentally friendly green techniques in the presence of a Cu(II) catalyst as well as in the presence of a CuO nanomaterial under microwave irradiation. The novelty of our work is being highly focussed on the introduction of unsymmetrical triazole rings with the isolation of mono triazolyl quinoxaline derivatives using an Ir(I) catalyst in aqueous medium and on the capability of the CuO nanomaterial in catalyzing a "click reaction" in various biological media. The role of our synthsized bis(trizolylmethyl)quinoxaline compounds as cytotoxic agents has been confirmed with clear evidence from a DNA and BSA binding study, stability study, viscosity study and MTT assay. Due to the detecting ability of live cancer cells, high cellular uptake, biocompatibility and high cytoselectivity of these scaffolds, ultimately compound 6g has been established as a cancer theranostic drug. [ABSTRACT FROM AUTHOR]

A series of donor–acceptor-based 6H-indolo[2,3-b]quinoxaline amine derivatives were synthesized with different donor amines. The impact of the different donor moieties on 6H-indolo[2,3-b]quinoxaline was systematically examined by absorption-emission spectroscopy, cyclic voltammetry and theoretical studies. The photophysical properties of these molecules, such as intramolecular charge transfer transitions (400 to 462 nm) and emission (491 to 600 nm), were influenced by the nature of the peripheral amines. Further, the solid-state emission demonstrated by some of the dyes aroused our interest in performing photophysical studies on the aggregation-induced emission phenomenon; these dyes showed nanoparticle formation in THF/H2O solvent mixtures. Varying the strength of the peripheral amines in the derivatives also tuned the electrochemical data, with lower band gaps (1.56 to 2.21 eV) and comparable HOMO–LUMO energy levels with reported ambipolar materials. The donor–acceptor architectures and HOMO–LUMO energies were further rationalized using DFT/TDDFT calculations. Thus, the opto-electrochemical studies and high thermal stability of these molecules indicate their potential application as solid-state emissive, ambipolar materials in optoelectronic devices. [ABSTRACT FROM AUTHOR]

RNA-biased small molecules with a monoquinoxaline core target the L-shaped structure of subdomain IIa of Hepatitis C virus internal ribosome entry site (IRES) RNA in proximity to the Mg2+ binding site. The binding event leads to the destacking of RNA bases, resulting in the inhibition of IRES-mediated translation and HCV RNA replication. [ABSTRACT FROM AUTHOR]

The accurate and sensitive quantification of DNA methylation is significant for the early diagnosis of cancer. In this work, an alkaline phosphatase (ALP) triggered in situ fluorogenic reaction between ascorbic acid (AA) and 2,3-DAN was employed as a ratiometric fluorescent probe for the accurate and sensitive detection of DNA methylation with the assistance of ALP encapsulated liposomes. The quinoxaline derivative with a yellow fluorescence emission ( I 525 ) was generated from the reaction between AA and 2,3-DAN. Meanwhile, the consumption of 2,3-DAN declined its fluorescence intensity ( I 386 ). A ratiometric fluorescent probe ( I 525 / I 386 ) constructed by the above in situ fluorogenic reaction was applied for the accurate detection of DNA methylation. The methylated DNA was first captured by its complementary DNA in 96-well plates. Then, 5mC antibody (Ab) linked liposomes that were encapsulated with ALP recognized and combined with the methylation sites of the target DNA. After the liposomes were lysed by Triton X-100, the released ALP triggered the hydrolysis of ascorbic acid diphosphate (AAP) to form AA, participating in the fluorogenic reaction with 2,3-DAN to produce a quinoxaline derivative. Thus, the ratiometric fluorescence detection of DNA methylation was achieved using I 525 / I 386 values. Using the ALP-enzyme catalyzed reaction and liposomes as signal amplifiers, a low detection limit of 82 fM was obtained for DNA methylation detection. Moreover, the accuracy of the assay could be improved using ratiometric fluorescent probes. We hope that the proposed assay will pave a new way for the accurate determination of low-abundance biomarkers.

A visible-light-induced radical cascade cyclization of aryl isonitriles and cyclobutanone oxime esters for the synthesis of cyclopenta[b]quinoxalines has been accomplished for the first time. The key to the success of this process was the integration of the in situ-formed nitrile radical followed by the cascade radical isonitrile/nitrile insertion-cyclization. The easy introduction of substituents for both substrates and the high functional group tolerance of the reaction make it an efficient strategy to give various quinoxaline derivatives in moderate to good yields. [ABSTRACT FROM AUTHOR]

Herein, an efficient methodology for the synthesis of a diverse class of N-heterocyclic moieties, such as quinoxalines, benzimidazoles and quinazolines, was developed in water using bio-renewable alcohols. The quinoxalines were successfully synthesized from a wide range of diamines and nitroamines with diols in air. Interestingly, benzimidazoles and quinazolines were synthesized with excellent isolated yields without using any external base. Finally, the preparative scale synthesis of various N-heterocycles and pharmaceutically active quinoxalines established the practicability of this protocol. For this iridium system, a metal–ligand cooperative mechanism was proposed based on kinetic and DFT studies. [ABSTRACT FROM AUTHOR]

An ion detection methodology employing synergistic interaction between copper(ii) ions and fluoride with 2,3-dipyrrol-2′-yl-quinoxaline (SR1) is investigated with a particular target to detect fluoride in an aqueous environment. The theme of this work simultaneously exploits the H-bonding and metal–ligand interactions of SR1 in the presence of fluoride and Cu(ii) ions in a DMSO/water mixture. The cooperative ion detection event in the presence of SR1 and fluoride reveals in situ reduction of Cu(ii) to Cu(i) species, which causes a sharp colorimetric change from green to red differentiable to the naked eye. The mechanism of the reaction is comprehensively investigated using UV-Vis, 1H NMR, 19F NMR, EPR spectroscopy and Differential Pulse Voltammetry (DPV) techniques, and is further justified by DFT study and subsequent NBO analysis. The limit of detection (LOD) is found to be 0.15 ppm, which is below the limit set by WHO for the fluoride content in drinking water. The real time application of the protocol is also tested in groundwater samples collected from a fluoride affected area and toothpaste samples. [ABSTRACT FROM AUTHOR]

Quinoxaline derivatives have attracted considerable attention due to their vast range of applications that includes electroluminescence and biomedicine. Concerning the latter, the literature has shown that compounds with a quinoxaline motif bind quite efficiently to phosphatidylinositol-4,5-bisphosphate 3-kinases (PI3Ks), which are enzymes found to be overexpressed in some types of neoplasms. In the present study, gold nanoparticles (AuNPs) were easily functionalized with 2,3-diethanolminoquinoxaline (DEQX) and 2-(2,3-dihydro-[1,4]oxazino[2,3-b]quinoxalin-4-yl)ethanol (OAQX). We made use of glycerol in alkaline media as reducing agent and the quinoxalines served as capping ligands to stabilize the AuNPs. This is the first report on the modification of a nanostructure with quinoxalines. Functionalization confers nanoparticles the required specificity to target only cancer cells, which opens possibilities for phototherapy since the modified AuNPs would concentrate in the tumor tissue as a consequence of PI3Kα overexpression. Molecular dynamics simulations have shown that DEQX and OAQX are potential inhibitors of PI3Kα since they bind to the active site of the enzyme in a way similar to other known inhibitors. [ABSTRACT FROM AUTHOR]

A facile and reliable method to monitor strongly acidic pH was developed. The sensing mechanism was found to involve the protonation–deprotonation equilibrium of the synthesized probe HQphy (1) (N-phenyl-N′-quinoxalin-2-ylmethylene-hydrazine) within a working range of pH 0.7–2.7. The eventual sensing of Fe3+ was the outcome of acidity imparted by [Fe(H2O)6]3+ ions in solution during the formation of [Fe(H2O)5(OH)]2+. The protonation–deprotonation phenomenon of HQphy was investigated using 1H NMR and single crystal X-ray diffraction experiments. The protonated probe, H2Qphy+, was crystallized with FeCl4−/ClO4− counter anions as [H2Qphy][FeCl4]·H2O (2)/[H2Qphy][ClO4]·H2O (3). A further complex containing the [H2Qphy] cation (4) was also formed. The complexes were characterized by SC-XRD experiments. Moreover, single crystal to single crystal transformation is observed between 1 and 3. In order to understand the sensing mechanism, various analytical studies, such as UV-Vis titration, ESI-MS spectrometry analysis and 1H NMR, were carried out in detail. A theoretical study correlates well with the experimental data, where the π(L) →π*(L) transition of the ligand is red shifted by 100 nm due to protonation of the quinoxaline moiety. The probe enables discrimination of trihalo acetic acid from its mono- and di-analogues. [ABSTRACT FROM AUTHOR]