Synthesis of novel antibacterial and antifungal quinoxaline derivatives

Flavonol derivatives containing piperazine and quinoxaline fragments: synthesis and antifungal activity

A series of flavonol derivatives containing piperazine and quinoxaline had been designed and synthesized. The biological activity test results showed that some of the target compounds had good antifungal activity against various fungi. N5 had the best antifungal activity against Phomopsis sp (P.s.) and Phytophthora capsica (P.c.). The half maximal effective concentration (EC50) was 12.9 and 25.8 μg/mL against P.s. and P.c., respectively, which were better than azoxystrobin (Az, 25.4 and 71.1 μg/mL). In addition, the protective and curative activities of N5 against kiwifruit were 85.9 and 67.0% at 200 μg/mL in vivo, which were better than that of Az (65.9 and 57.0%). The protective and curative activities against chili leaves were 80.6 and 66.5% at 200 μg/mL, which were better than that of Az (77.6 and 60.0%). The scanning electron microscopy (SEM) experiment showed that the action of N5 caused the mycelium to bend and fold, changed its morphology and caused damaged to the mycelium. Through the measurement of relative conductivity, leakage of cytoplasmic contents and determination of malondialdehyde (MDA) content indicated that N5 could damage the integrity of pathogenic fungal cell membranes, change the permeability of cell membranes, and affect the normal growth of mycelium.

Discovery of Potential Antifungal Agents: Chalcone Derivatives Containing Thiourea and Piperidine Moieties

Twenty-two chalcone derivatives containing thiourea and piperidine moieties were synthesized. The in vitro antifungal activities of these compounds against nine fungi were evaluated. The results demonstrated that a majority of these compounds exhibited exceptional antifungal activities. Especially, K2 displayed the most potent fungicidal activity against Phytophthora capsici (P. capsici), with a half-effective concentration (EC50) of 5.96 μg/mL, surpassing that of the control drug azoxystrobin (Az, 25.2 μg/mL). The in vivo antifungal experiments of K2 were conducted on pepper leaves and fruits. It exhibited significant protective efficacy against P. capsici in pepper leaves (95.3%) at 200 μg/mL, which surpassed that of Az (79.0%). Morphological investigations utilizing scanning electron microscopy (SEM) and fluorescence microscopy (FM) unveiled the disruptive impact of K2 on P. capsici mycelium. Moreover, mechanistic studies have demonstrated that K2 exhibited the capacity to disrupt the integrity of the cellular membrane in pathogenic fungi, influence lipid peroxidation processes within the membrane, and induce cellular content release. These experimental findings provided a new idea for effectively preventing plant fungal diseases and developing novel green chemical pesticide products.

Design and Synthesis of Unsymmetric Benzils, Quinoxalines, and Evaluations of their Anticancer Activities against Human Non-Small Lung Cancer Cells

Quinoxaline and its derivatives exhibit a broad spectrum of biological activity, making them valuable for various therapeutic applications. However, most quinoxalines are synthetically produced due to their scarcity in nature. In this article, a series of unsymmetric benzils were synthesized and subsequently condensed with 1,2-diaminobenzene to produce unsymmetric quinoxalines. The novel synthetic benzils and quinoxalines were evaluated for their anticancer activities against human non-small-cell lung cancer (NSCLC) cells harboring different gene mutations, to explore their potential as anticancer agents. Among these synthesized molecules, compound 5 g demonstrated inhibitory effects comparable to those of cisplatin.

Synthetic Methods of Quinoxaline Derivatives and their Potential Anti-inflammatory Properties

Quinoxaline molecule has gathered great attention in medicinal chemistry due to its vide spectrum of biological activities and has emerged as a versatile pharmacophore in drug discovery and development. Its structure comprises a bicyclic ring of benzopyrazine and displays a range of pharmacological properties, including antibacterial, antifungal, antiviral, anticancer, and antiinflammatory. This study aims to summarize the different strategies for the synthesis of quinoxalines and their anti-inflammatory properties acting through different mechanisms. Structure-activity relationships have also been discussed in order to determine the effect of structural modifications on anti-inflammatory potential. These analyses illuminate critical structural features required for optimal activity, driving the design and synthesis of new quinoxaline analogues with better antiinflammatory activities. The anti-inflammatory properties of quinoxalines are attributed to their inhibitory action on the expression of several inflammatory modulators such as cyclooxygenase, cytokines, nuclear factor kappa-light-chain-enhancer of activated B cells (NFκB) and p38α Mitogen Activated Protein Kinase (p38α MAPK). Activators of nuclear factor erythroid 2-related factor 2 (NRF2) and agonistic effect on opioid receptors have also been discussed. Hence, this study may provide a future template for the design and development of novel quinoxaline derivatives acting through different molecular targets as potential anti-inflammatory agents with better efficacy and safety profiles.

Recent synthetic strategies for the functionalization of fused bicyclic heteroaromatics using organo-Li, -Mg and -Zn reagents

This review highlights the use of functionalized organo-Li, -Mg and -Zn reagents for the construction and selective functionalization of 5- and 6-membered fused bicyclic heteroaromatics. Special attention is given to the discussion of advanced syntheses for the preparation of highly functionalized heteroaromatic scaffolds, including quinolines, naphthyridines, indoles, benzofurans, benzothiophenes, benzoxazoles, benzothiazoles, benzopyrimidines, anthranils, thienothiophenes, purine coumarins, chromones, quinolones and phthalazines and their fused heterocyclic derivatives. The organometallic reagents used for the desired functionalizations of these scaffolds are generally prepared in situ using the following methods: (i) through directed selective metalation reactions (DoM), (ii) by means of halogen/metal exchange reactions, (iii) through oxidative metal insertions (Li, Mg, Zn), and (iv) by transmetalation reactions (organo-Li and Mg transmetalations with ZnCl2 or ZnO(Piv)2). The resulting reactive organometallic reagents allow a wide range of C-C, C-N and C-X cross-coupling reactions with different electrophiles, employing in particular Kumada or Negishi protocols among other transition metal (Pd, Ni, Co, Cu, Cr, Fe, etc.)-catalyzed processes. In addition, key developments concerning selective metalation techniques will be presented, which rely on the use of RLi, LDA and TMP metal bases. These methods are now widely employed in organic synthetic chemistry and have proven to be particularly valuable for drug development programs in the pharmaceutical industry. New and improved protocols have resulted in many Li, Mg and Zn organyls now being compatible with functionalized aryl, heteroaryl, alkenyl, alkynyl and alkyl compounds even in the presence of labile functional groups, making these reagents well-suited for C(sp2)-C(sp2), C(sp2)-C(sp) and C(sp2)-C(sp3) cross-coupling reactions with fused heteroaryl halides. In addition, the use of some transition metal-catalyzed processes occasionally allows a reversed role of the reactants in cross-coupling reactions, providing alternative synthetic routes for the preparation of fused heteroaromatic-based bioactive drugs and natural products. In line with this, this article points to novel methods for the functionalization of bicyclic heteroaromatic scaffolds by organometallic reagents that have been published in the period 2010-2023.

Novel Flavonol Derivatives Containing Quinoxaline: Insights into the Antifungal Mechanism against Sclerotinia sclerotiorum

In this study, 12 pairs of tautomeric flavonol derivatives containing quinoxaline were synthesized. The results of antifungal activity showed that in the enol-keto tautomerism, the target compounds containing keto (YB series) had better inhibitory activity against Sclerotinia sclerotiorum (S.s.) than compounds containing enol (YA series). YB9 showed the strongest antifungal activity against S.s., and the median effective concentration (EC50) value was 1.0 μg/mL, which was better than azoxystrobin (Az, 35.3 μg/mL). In vivo fungal inhibition experiments showed that the protective activity of YB9 against rape leaves was 83.4% at 200 μg/mL, which was superior to that of Az (70.2%). The activity of succinate dehydrogenase and molecular docking results showed that YB9 had a stronger antifungal effect than YA9. The results of oxalic acid content determination showed that YB9 could reduce the pathogenic ability of S.s. Then, the inhibitory effect of YB9 against S.s. was further verified by scanning electron microscopy, fluorescence microscopy, cell membrane permeability, cell content leakage, and malondialdehyde content.

Exploring quinoxaline derivatives: An overview of a new approach to combat antimicrobial resistance

Antimicrobial resistance (AMR) has emerged as a long-standing global issue ever since the introduction of penicillin, the first antibiotic. Scientists are constantly working to develop innovative antibiotics that are more effective and superior. Unfortunately, the misuse of antibiotics has resulted in their declining effectiveness over the years. By 2050, it is projected that approximately 10 million lives could be lost annually due to antibiotic resistance. Gaining insight into the mechanisms behind the development and transmission of AMR in well-known bacteria including Escherichia coli, Bacillus pumilus, Enterobacter aerogenes, Salmonella typhimurium, and the gut microbiota is crucial for researchers. Environmental contamination in third world and developing countries also plays a significant role in the increase of AMR. Despite the availability of numerous recognized antibiotics to combat bacterial infections, their effectiveness is diminishing due to the growing problem of AMR. The overuse of antibiotics has led to an increase in resistance rates and negative impacts on global health. This highlights the importance of implementing strong antimicrobial stewardship and improving global monitoring, as emphasized by the World Health Organization (WHO) and other organizations. In the face of these obstacles, quinoxaline derivatives have emerged as promising candidates. They are characterized by their remarkable efficacy against a broad spectrum of harmful bacteria, including strains that are resistant to multiple drugs. These compounds are known for their strong structural stability and adaptability, making them a promising and creative solution to the AMR crisis. This review aims to assess the effectiveness of quinoxaline derivatives in treating drug-resistant infections, with the goal of making a meaningful contribution to the global fight against AMR.

Synthesis of quinoxalines and assessment of their inhibitory effects against human non-small-cell lung cancer cells

Twenty-six quinoxalin derivatives were synthesized to assess their biological activities against human non-small-cell lung cancer cells (A549 cells). Compound 4b (IC50 = 11.98 ± 2.59 μM) and compound 4m (IC50 = 9.32 ± 1.56 μM) possess anticancer activity comparable to 5-fluorouracil (clinical anticancer drug) (IC50 = 4.89 ± 0.20 μM). Western blot tests further confirmed that compound 4m effectively induced apoptosis of A549 cells through mitochondrial- and caspase-3-dependent pathways. The introduction of bromo groups instead of nitro groups into the quinoxaline skeleton has been shown to provide better inhibition against lung cancer cells in this article. This modification in the molecular structure could enhance the biological activity and effectiveness of quinoxaline derivatives in the design and synthesis of anticancer drugs, making bromo-substituted quinoxalines a promising avenue for further research and development in anticancer therapeutics.

Synthesis and Antifungal Activity of Chalcone Derivatives Containing 1,3,4-Thiadiazole

24 chalcone derivatives containing 1,3,4-thiadiazole were synthesized. The results of bioactivity tests indicated that some of the target compounds exhibited superior antifungal activities in vitro. Notably, the EC50 value of D4 was 14.4 μg/mL against Phomopsis sp, which was significantly better than that of azoxystrobin (32.2 μg/mL) and fluopyram (54.2 μg/mL). The in vivo protective activity of D4 against Phomopsis sp on kiwifruit (71.2 %) was significantly superior to azoxystrobin (62.8 %) at 200 μg/mL. The in vivo protective activities of D4 were 74.4 and 57.6 % against Rhizoctonia solani on rice leaf sheaths and rice leaves, respectively, which were slightly better than those of azoxystrobin (72.1 and 49.2 %) at 200 μg/mL. Scanning electron microscopy (SEM) results showed that the mycelial surface collapsed, contracted and grew abnormally after D4 treatment. Finally, the results were further verified by in vivo antifungal assay, fluorescence microscopy (FM) observation, determination of relative conductivity, membrane lipid peroxidation degree assay, and determination of cytoplasmic content leakage. Molecular docking results suggested that D4 could be a potential SDHI.

Mono-quinoxaline-induced DNA structural alteration leads to ZBP1/RIP3/MLKL-driven necroptosis in cancer cells

Evading the cellular apoptosis mechanism by modulating multiple pathways poses a sturdy barrier to effective chemotherapy. Cancer cell adeptly resists the apoptosis signaling pathway by regulating anti and pro-apoptotic proteins to escape cell death. Nevertheless, bypassing the apoptotic pathway through necroptosis, an alternative programmed cell death process, maybe a potential therapeutic modality for apoptosis-resistant cells. However, synthetic mono-quinoxaline-based intercalator-induced cellular necroptosis as an anti-cancer perspective remains under-explored. To address this concern, we undertook the design and synthesis of quinoxaline-based small molecules (3a-3l). Our approach involved enhancing the π-surface of the mandatory benzyl moiety to augment its ability to induce DNA structural alteration via intercalation, thereby promoting cytotoxicity across various cancer cell lines (HCT116, HT-29, and HeLa). Notably, the potent compound 3a demonstrated the capacity to induce DNA damage in cancer cells, leading to the induction of ZBP1-mediated necroptosis in the RIP3-expressed cell line (HT-29), where Z-VAD effectively blocked apoptosis-mediated cell death. Interestingly, we observed that 3a induced RIP3-driven necroptosis in combination with DNA hypomethylating agents, even in the RIP3-silenced cell lines (HeLa and HCT116). Overall, our synthesized compound 3a emerged as a promising candidate against various cancers, particularly in apoptosis-compromised cells, through the induction of necroptosis.

Synthesis, antifungal activity and mechanism of action of novel chalcone derivatives containing 1,2,4-triazolo-[3,4-b]-1,3,4-thiadiazole

A series of chalcone derivatives containing 1,2,4-triazolo-[3,4-b]-1,3,4-thiadiazole was designed and synthesized. Structures of all compounds were characterized by 1H NMR, 13C NMR, 19F NMR, and HRMS. The biological activities of the compounds were determined with the mycelial growth rate method, and further studies showed that some compounds had good antifungal activities at the concentration of 100 μg/mL. The EC50 value of compound L31 was 15.9 μg/mL against Phomopsis sp., which were better than that of azoxystrobin (EC50 value was 69.4 μg/mL). In addition, the mechanism of action of compound L31 shown that compound can affect mycelial growth by disrupting membrane integrity against Phomopsis sp., and that the higher the concentration of the compound is, the greater the disruption of membrane integrity is.

Synthesis, antibacterial and antifungal activity of myricetin derivatives containing piperidine and amide fragments

BACKGROUND

Continuous use of synthetic bactericides and fungicides is causing pathogens to develop resistance, resulting in increased use of pesticides and affecting food security. The green pesticides derived from natural products could reduce or avoid 'pesticide hazards' caused by synthetic pesticides as a result of their unique mechanism of action. Therefore, it is of great significance to create green pesticides with novel structures.

RESULTS

Herein, 30 novel myricetin derivatives containing piperidine and amide fragments were designed and synthesized using active group splicing. Among them, compound Z30 had excellent inhibitory effect against Xanthomonas oryzae pv. Oryzae (Xoo) with the half effective concentration (EC50 ) of 2.7 μg mL-1 . Compound Z26 not only exhibited better antibacterial activity against Xaxonopodis pv. Citri (Xac) with EC50 of 3.9 μg mL-1 , but also displayed higher antifungal activity against Rhizoctonia solani (Rs) with EC50 of 8.3 μg mL-1 . In vivo experiments proved that Z30 against bacterial blight of rice and Z26 against rice blast exhibits significant protective and curative effect. Scanning electron microscopy (SEM) and transmission electron microscopy (TEM) showed that Z26 and Z30 could change the integrity of cell wall and membrane of pathogen Xoo, Xac and Rs, resulting in cytoplasmic leakage and eventually death. Enzymatic assay, molecular docking and molecular dynamics simulations (MDs) indicated that Z26 could be used as a potential succinate dehydrogenase inhibitor (SDHI).

CONCLUSION

Z26 and Z30 significantly reduced the pathogenicity of the pathogens, which provided a new idea and direction for the development of green pesticides. © 2023 Society of Chemical Industry.

Synthesis and Biological Activity of Myricetin Derivatives Containing Pyrazole Piperazine Amide

In this paper, a series of derivatives were synthesized by introducing the pharmacophore pyrazole ring and piperazine ring into the structure of the natural product myricetin through an amide bond. The structures were determined using carbon spectrum and hydrogen spectrum high-resolution mass spectrometry. Biological activities of those compounds against bacteria, including Xac (Xanthomonas axonopodis pv. Citri), Psa (Pseudomonas syringae pv. Actinidiae) and Xoo (Xanthomonas oryzae pv. Oryzae) were tested. Notably, D6 exhibited significant bioactivity against Xoo with an EC₅₀ value of 18.8 μg/mL, which was higher than the control drugs thiadiazole-copper (EC₅₀ = 52.9 μg/mL) and bismerthiazol (EC₅₀ = 69.1 μg/mL). Furthermore, the target compounds were assessed for their antifungal activity against ten plant pathogenic fungi. Among them, D1 displayed excellent inhibitory activity against Phomopsis sp. with an EC₅₀ value of 16.9 μg/mL, outperforming the control agents azoxystrobin (EC₅₀ = 50.7 μg/mL) and fluopyram (EC₅₀ = 71.8 μg/mL). In vitro tests demonstrated that D1 possessed curative (60.6%) and protective (74.9%) effects on postharvest kiwifruit. To investigate the active mechanism of D1, its impact on SDH activity was evaluated based on its structural features and further confirmed through molecular docking. Subsequently, the malondialdehyde content of D1-treated fungi was measured, revealing that D1 could increase malondialdehyde levels, thereby causing damage to the cell membrane. Additionally, the EC₅₀ value of D16 on P. capsici was 11.3 μg/mL, which was superior to the control drug azoxystrobin (EC₅₀ = 35.1 μg/mL), and the scanning electron microscopy results indicated that the surface of drug-treated mycelium was ruffled, and growth was significantly affected.

Design, synthesis and bioactivity of myricetin derivatives for control of fungal disease and tobacco mosaic virus disease

A series of myricetin derivatives containing isoxazole were designed and synthesized. All the synthesized compounds were characterized by NMR and HRMS. In terms of antifungal activity, Y3 had a good inhibitory effect on Sclerotinia sclerotiorum (Ss), and the median effective concentration (EC₅₀) value was 13.24 μg mL^-1, which was better than azoxystrobin (23.04 μg mL^-1) and kresoxim-methyl (46.35 μg mL^-1). Release of cellular contents and cell membrane permeability experiments further revealed that Y3 causes the destruction of the cell membrane of the hyphae, which in turn plays an inhibitory role. The anti-tobacco mosaic virus (TMV) activity in vivo showed that Y18 had the best curative and protective activities, with EC₅₀ values of 286.6 and 210.1 μg mL^-1 respectively, the effect was better than ningnanmycin. Microscale thermophoresis (MST) data showed that Y18 had a strong binding affinity with tobacco mosaic virus coat protein (TMV-CP), with a dissociation constant (K _d) value of 0.855 μM, which was better than ningnanmycin (2.244 μM). Further molecular docking revealed that Y18 interacts with multiple key amino acid residues of TMV-CP, which may hinder the self-assembly of TMV particles. Overall, after the introduction of isoxazole on the structure of myricetin, its anti-Ss and anti-TMV activities have been significantly improved, which can be further studied.

Synthesis and biological activities of novel chalcone derivatives containing pyrazole oxime ethers

A series of novel chalcone derivatives containing pyrazole oxime ethers were designed and synthesized. The structures of all the target compounds were determined by NMR and HRMS. The structure of H5 was further confirmed via single-crystal X-ray diffraction analysis. The results of biological activity test showed that some of the target compounds exhibited significant antiviral and antibacterial activities. The test results of EC₅₀ value against tobacco mosaic virus showed that H9 had the best curative and protective effect, and the EC₅₀ value of curative activity of H9 was 166.9 μg/mL, which was superior to ningnanmycin (NNM) 280.4 μg/mL, the EC₅₀ value of protective activity of H9 was 126.5 μg/mL, which was superior to ningnanmycin 227.7 μg/mL. Microscale thermophoresis (MST) experiments demonstrated that H9 (K_d = 0.0096 ± 0.0045 μmol/L) exhibited a strong binding ability with tobacco mosaic virus capsid protein (TMV-CP), which was far superior to ningnanmycin (K_d = 1.2987 ± 0.4577 μmol/L). In addition, molecular docking results showed that the affinity of H9 to TMV protein was significantly higher than ningnanmycin. The results of against bacterial activity showed that H17 has a good inhibiting effect against Xanthomonas oryzae pv. oryzae (Xoo), the EC₅₀ value of H17 was 33.0 μg/mL, which was superior to the commercial drugs thiodiazole copper (68.1 μg/mL) and bismerthiazol (81.6 μg/mL), and the antibacterial activity of H17 was verified by scanning electron microscopy (SEM).

Green Design, Synthesis, and Molecular Docking Study of Novel Quinoxaline Derivatives with Insecticidal Potential against Aphis craccivora

An efficient and environmentally friendly method was established for designing novel 3-amino-1,4-dihydroquinoxaline-2-carbonitrile (1) via the reaction of bromomalononitrile and benzene-1,2-diamine under microwave irradiation in an excellent yield (93%). This targeted amino derivative was utilized for the construction of a series of Schiff bases (8-13). A new series of thiazolidinone derivatives (15-20) were synthesized in high yields (89-96%) via treatment of thioglycolic acid with Schiff bases (8-13) under microwave irradiation in high yields (89-96%). Moreover, new pyrimidine derivatives (26-30 and 35-38) were prepared by treatment of compound 1 with arylidenes (21-25) and/or alkylidenemalononitriles (31-34) using piperidine as a basic catalyst under microwave conditions. Based on elemental analyses and spectral data, the structures of the new assembled compounds were determined. The newly synthesized quinoxaline derivatives were screened and studied as an insecticidal agent against Aphis craccivora. The obtained results indicate that compound 16 is the most toxicological agent against nymphs of cowpea aphids (Aphis craccivora) compared to the other synthesized pyrimidine and thiazolidinone derivatives. The molecular docking study of the new quinoxaline derivatives registered that compound 16 had the highest binding score (-10.54 kcal/mol) and the thiazolidinone moiety formed hydrogen bonds with Trp143.