Quinolone alkaloids with nitric oxide production inhibitory activity from Orixa japonica

Design, Synthesis, Nematicidal Evaluation, and Molecular Docking Study of Pyrano[3,2-c]pyridones against Meloidogyne incognita

Root-knot nematodes pose a serious threat to crops by affecting production and quality. Over a period of time, substantial work has been done toward the development of effective and environmentally benign nematicidal compounds. However, due to the inefficiencies of previously reported synthetics in achieving the target of safe, selective, and effective treatment, it is necessary to develop new efficacious and safer nematicidal agents considering human health and environment on top priority. This work aims to highlight the efficient and convenient l-proline catalyzed synthesis of pyrano[3,2-c]pyridone and their use as potential nematicidal agents. In vitro results of larval mortality and egg hatching inhibition revealed maximum nematicidal activity against Meloidogyne incognita from compounds 15b, 15m, and 15w with LC50 values of 28.8, 46.8, and 49.18 μg/mL at 48 h, respectively. Under similar conditions, pyrano[3,2-c]pyridones derivatives 15b (LC50 = 28.8 μg/mL) was found at par with LC50 (26.92 μg/mL) of commercial nematicide carbofuran. The in vitro results were further validated with in silico studies with the most active compound 15b nematicidal within the binding to the pocket of acetylcholine esterase (AChE). In docking, binding free energy values for compound 15b were found to be -6.90 kcal/mol. Results indicated that pyrano[3,2-c]pyridone derivatives have the potential to control M. incognita.

Biological activity of natural 2-quinolinones

While natural products have undeniably played a crucial role in drug discovery, challenges such as limited availability and complex synthesis methods have hindered the identification of lead compounds. At the core of numerous natural and synthetic compounds, each displaying distinct biological behaviours, lies the foundational structure of 2-quinolinone. Compounds with this structural motif exhibit a broad range of effects in different tissues. Furthermore, specific members showcase therapeutic potential for various disorders. Despite the significance of these compounds, the current review literature has not provided a comprehensive overview, underscoring the essential contribution of this article in exploring their biological functions. This study examines the biological activity of selected 2-quinolinone alkaloids across diverse organisms, unveiling their potential as a source of innovative bioactive natural products.

Insights from the Endophytic Fungi in Amphisphaeria (Sordariomycetes): A. orixae sp. nov. from Orixa japonica and Its Secondary Metabolites

Endophytic fungi are a remarkably diverse group of microorganisms that have imperceptible associations with their hosts for at least a part of their life cycle. The enormous biological diversity and the capability of producing bioactive secondary metabolites such as alkaloids, terpenoids, and polyketides have attracted the attention of different scientific communities, resulting in numerous investigations on these fungal endophytes. During our surveys of plant-root-based fungi in the mountain areas of Qingzhen, Guizhou Province, several isolates of endophytic fungi were identified. In this study, a novel endophytic fungus was discovered in the roots of a medicinal plant (Orixa japonica) in Southern China and introduced as a new species (Amphisphaeria orixae) based on morphological evidence and molecular phylogenetic analysis (combined ITS and LSU sequence data). To the best of our knowledge, A. orixae is the first reported endophyte as well as the first hyphomycetous asexual morph in Amphisphaeria. A new isocoumarin, (R)-4,6,8-trihydroxy-5-methylisochroman-1-one (1), and 12 known compounds (2-13) were isolated from the rice fermentation products of this fungus. Using 1D- and 2D-NMR, mass spectrometry, and ECD studies, their structures were identified. The antitumor activity of these compounds was tested. Unfortunately, none of the compounds tested showed significant antitumor activity.

Quinoline Alkaloids from the Roots of Orixa japonica with the Anti-Pathogenic Fungi Activities

A new quinoline alkaloid, 5-hydroxy-6-methoxy-N-methyl-2-phenylquinoline-4-one (1), and seventeen known quinoline alkaloids (2-18) were isolated from the roots of Orixa japonica. The structure of 1 was determined by analysis of spectroscopic data. Among them, compounds 2, 3, and 13 were isolated from this plant for the first time. All isolates were screened for the anti-pathogenic fungi activities, including Rhizoctonia solani, Magnaporthe oryzae, and Phomopsis sp. The results showed that five compounds (4, 8, 10, 11, and 12) exhibited significant anti-pathogenic fungi effects at 50.0 μg/mL. In special, compound 10 exhibited the best antifungal activities toward R. solani and M. oryzae with the IC₅₀ values of 37.86 and 44.72 μM, respectively, better than that of the positive control, hymexazol (IC₅₀ 121.21 and 1518.18 μM, respectively). Moreover, eleven new quinoline alkaloids derivatives (12a-12k) were designed and synthesized to investigate the structure-activity relationships (SARs). The SARs analysis indicated that the furo[2,3-b]quinoline skeleton and the methoxy at C-7 (compounds 8, 11, and 12) played a key role for improving the antifungal activities.

Alkaloids and Coumarins with Adiponectin-Secretion-Promoting Activities from the Leaves of Orixa japonica

Fractionation of a methanol extract of Orixa japonica leaves led to the identification of five new quinoline alkaloids (1, 2, 4, 8, and 9), three new coumarins (15, 17, and 19), and 20 known compounds. The structures were determined by analysis of 1D and 2D NMR spectroscopic data. The absolute configuration of 19 was proposed by electronic circular dichroism calculation. Among the compounds tested in the phenotypic screening to measure adiponectin secretion in human bone marrow mesenchymal stem cells, metabolites 4 and 12 stimulated adiponectin secretions with EC₅₀ values of 13.8 and 25.8 μM, respectively. Further PPARγ binding assay and molecular modeling suggested that compounds 4 and 12 are selective PPARγ agonists.

Construction of 4-Acyl-2-quinolones through Sc(OTf)3-Catalyzed Ring-Closing Alkyne-Carbonyl Metathesis

An atom-economical protocol to construct densely substituted 4-acyl-2-quinolones from N-(2-alkynylphenyl)-α-ketoamides has been developed through Sc(OTf)₃-catalyzed ring-closing alkyne-carbonyl metathesis. Mechanistic experimental studies support that coordinative interaction between Sc(OTf))₃ and the substrate, the formation of an oxetene intermediate, and an electrocyclic ring-opening of the oxetene might be involved.

[Studies on the Isolation and Molecular Mechanisms of Bioactive Phytochemicals]

Studies on the isolation and molecular mechanisms of phytochemicals with anti-tumor or anti-inflammatory properties are important to developing new drugs for cancer and neurodegenerative disorders such as Alzheimer's disease and Parkinson's disease. In the course of a study to screen bioactive isoflavones from Erythrina poeppigiana (Leguminosae), we isolated an isoflavone with potent apoptosis-inducing activity against human leukemia HL-60 cells. It was designated erypoegin K. The studies demonstrated an enantiomer, (S)-erypoegin K, displayed selective cytotoxic activity, was a novel inhibitor of topoisomerase II, and possessed anti-tumor activity both in vitro and in vivo. We identified other apoptosis-inducing isoflavones with the ability to inhibit glyoxalase I. Dimeric acridone alkaloids, carbazole alkaloids, and coumarin and quinoline derivatives-all obtained mainly from plants in the family Rutaceae-induced apoptosis of HL-60 cells via the production of reactive oxygen species and mitochondrial dysfunction. We also identified terpenoid coumarins, carbazole quinones, rotenoid derivatives, and quinolone alkaloids with anti-inflammatory activities. These compounds reduced nitric oxide (NO) production from RAW264.7 macrophage cells stimulated with lipopolysaccharides and interferon-γ. Some of the compounds displayed neuroprotective activity by reducing NO production. This review primarily describes our recent studies on erypoegin K, and other compounds with apoptosis-inducing and anti-inflammatory activities.

Biology of quinoline and quinazoline alkaloids

Quinoline and quinazoline alkaloids, two important classes of N-based heterocyclic compounds, have attracted scientific and popular interest worldwide since the 19th century. More than 600 compounds have been isolated from nature to date. To build on our two prior reviews, we reexamined the promising molecules described in previous reports and provided updated literature on novel quinoline and quinazoline alkaloids isolated over the past 5 years. This chapter reviews and discusses 205 molecules with a broad range of bioactivities, including antiparasitic and insecticidal, antibacterial and antifungal, cardioprotective, antiviral, anti-inflammatory, and other effects. This survey should provide new clues or possibilities for the discovery of new and better drugs from the original naturally occurring quinoline and quinazoline alkaloids.

Synthesis of pyrano[3,2-c]quinolones and furo[3,2-c]quinolones via acid-catalyzed tandem reaction of 4-hydroxy-1-methylquinolin-2(1H)-one and propargylic alcohols

Two acid-catalyzed tandem reactions between 4-hydroxy-1-methylquinolin-2(1H)-one and propargylic alcohols are described. Depending mainly on the propargylic alcohol used, these tandem reactions proceed via either a Friedel–Crafts-type allenylation followed by 6-endo-dig cyclization sequence to form pyrano[3,2-c]quinolones or a Friedel–Crafts-type alkylation and 5-exo-dig ring closure sequence to afford furo[3,2-c]quinolones in moderate-to-high yields. The pyrano[3,2-c]quinolones products could be further transformed to tetracyclic 4,9-dihydro-5H-cyclopenta[lmn]phenanthridin-5-one derivatives.

Two acid-catalyzed tandem reactions between 4-hydroxy-1-methylquinolin-2(1H)-one and propargylic alcohols are described.

Progress of Plant Medicine Derived Extracts and Alkaloids on Modulating Viral Infections and Inflammation

Viral infectious diseases are serious threats to human health in both developing and developed countries. Although there is the continued development of new drugs from synthetic sources as antiviral agents, medicinal plants continue to provide the basic raw materials for some of the most important antiviral drugs. Alkaloids are a class of pharmacologically active plant compounds that are usually alkaline in nature. In this review, we tried to summarize recent progress in herb-based antiviral research, the advantages of using active plant compounds as antiviral agents, and the inflammatory responses initiated by alkaloids, based on the literature from 2009 to 2019, for the treatment of conditions, including influenza, human immunodeficiency virus, herpes simplex virus, hepatitis, and coxsackievirus infections. Articles are retrieved from PubMed, Google Scholar, and Web of Science using relevant keywords. In particular, the alkaloids from medicinal plants responsible for the molecular mechanisms of anti-inflammatory actions are identified and discussed. This review can provide a theoretical basis and approaches for using various alkaloids as antiviral treatments. More research is needed to develop alkaloidal compounds as antiviral therapeutic agents and potential regulators of the anti-inflammatory response.

Iodination/Amidation of the N-Alkyl (Iso)quinolinium Salts

The NaIO₄-mediated sequential iodination/amidation reaction of N-alkyl quinolinium iodide salts has been first developed. This cascade process provides an efficient way to rapidly synthesize 3-iodo-N-alkyl quinolinones with high regioselectivity and good functional group tolerance. This protocol was also amenable to the isoquinolinium salts, thus providing a complementary method for preparing the 4-iodo-N-alkyl isoquinolinones.

One-pot copper-catalyzed three-component reaction: a modular approach to functionalized 2-quinolones

A copper-catalyzed three-component annulation for the synthesis of functionalized 2-quinolones was developed. Three reactions including an S_N2, a Knoevenagel, and finally C–N bond formation are involved in the designed cascade reaction using 2-bromoacylarenes, 2-iodoacetamide, and nucleophiles as the three components. A new catalytic system was discovered during the study and this modular approach is highly efficient to access functionalized 2-quinolone derivatives, compatible with a broad range of functional groups, scalable, and step-economic. Further derivatization of the obtained product demonstrates the synthetic utility of this method.

A copper-catalyzed three-component annulation for the synthesis of functionalized 2-quinolones was developed.

Step-economical synthesis of 3-amido-2-quinolones by dendritic copper powder-mediated one-pot reaction

The one-pot protocol by the dendritic copper powder-mediated Knoevenagel condensation/annelation is delineated here for the synthesis of 3-amido-2-quinolones. It is practical with moisture tolerance and easy setup, and is compatible with many functional groups under mild conditions. This method was applied for the preparation of the key intermediates of biologically relevant 3-amido-2-quinolones.

Computational and experimental studies on copper-mediated selective cascade C-H/N-H annulation of electron-deficient acrylamide with arynes

An efficient and convenient copper-mediated method has been developed to achieve direct cascade C-H/N-H annulation to synthesize 2-quinolinones from electron-deficient acrylamides and arynes. This method highlights an emerging but simple strategy to transform inert C-H bonds into versatile functional groups in organic synthesis to provide a new method of synthesizing 2-quinolinones efficiently. Mechanistic investigations by experimental and density functional theory (DFT) studies suggest that an organometallic C-H activation via a Cu(iii) intermediate is likely to be involved in the reaction.

Synthesis of 3-substituted quinolin-2(1H)-ones via the cyclization of o-alkynylisocyanobenzenes

A facile synthesis of various functionalized 3-substituted quinolin-2(1H)-ones through Ag(i) nitrate-catalyzed cyclization of o-alkynylisocyanobenzenes is described. The reaction allows rapid and convenient access to 3-substituted quinolin-2(1H)-one scaffolds in moderate to good yields.

Biologically active quinoline and quinazoline alkaloids part I

Quinoline and quinazoline alkaloids, two important classes of N-based heterocyclic compounds, have attracted tremendous attention from researchers worldwide since the 19th century. Over the past 200 years, many compounds from these two classes were isolated from natural sources, and most of them and their modified analogs possess significant bioactivities. Quinine and camptothecin are two of the most famous and important quinoline alkaloids, and their discoveries opened new areas in antimalarial and anticancer drug development, respectively. In this review, we survey the literature on bioactive alkaloids from these two classes and highlight research achievements prior to the year 2008 (Part I). Over 200 molecules with a broad range of bioactivities, including antitumor, antimalarial, antibacterial and antifungal, antiparasitic and insecticidal, antiviral, antiplatelet, anti-inflammatory, herbicidal, antioxidant and other activities, were reviewed. This survey should provide new clues or possibilities for the discovery of new and better drugs from the original naturally occurring quinoline and quinazoline alkaloids.

Use of Nanocrystalline ZnO as an Efficient and Reusable Catalyst for a One-Pot, Three-Component Synthesis of 6-Chloro- and 5,7-Dichloro-4-Hydroxy-3-[Aryl (Piperidin-1-yl)Methyl]Quinolin-2(1H)-Ones in Water

A one-pot, green, efficient and facile procedure was applied for the preparation of a series of 4-hydroxy-3-[aryl(piperidin-1-yl)methyl] quinolin-2(1 H)-ones via the reaction of 6-chloro-4- hydroxyquinoline-2(1 H)-one 1 and/or 5,7-dichloro-4-hydroxyquinoline-2(1 H)-one 2, piperidine and aromatic aldehydes in water in the presence of nanocrystalline ZnO under reflux conditions. The desired products were obtained in satisfactory yields. The nanocrystalline ZnO can be separated and reused at least up to three times with almost the same catalytic activity.

Stereoselective synthesis of natural product inspired carbohydrate fused pyrano[3,2-c]quinolones as antiproliferative agents

Design and efficient synthesis of new carbohydrate fused pyrano[3,2-c]quinolone derivatives and their submicromolar anticancer activity.

An efficient synthesis of 4H-pyrano quinolinone derivatives catalysed by a versatile organocatalyst tetra-n-butylammonium fluoride and their pharmacological screening

A new series of indole-based pyranoquinoline derivatives P_1-24 has been synthesized by a one-pot cyclocondensation reaction of 2-(4-substituted)phenyl-N-allyl-indole-3-carbaldehydes 1a-d; active methylenes 2a-c; and 4-hydroxy-1-substituted quinolin-2(1H)-one 3a-b catalysed by an organocatalyst tetra-n-butylammonium fluoride (TBAF) in aqueous ethanol. The easy experimental procedure of the reaction leads to excellent yields of pyranoquinoline derivatives. All the compounds were screened against a representative panel of bacteria and fungi. Some of the compounds are found to be equipotent or more potent than standard drugs as evident from the structural activity relationship study.

Effect of iNOS inhibitor LNMMA along with antibiotics Chloramphenicol or Ofloxacin in murine peritoneal macrophages regulates S.aureus infection as well as inflammation: An in vitro study

Death due to sepsis by S. aureus is rapidly increasing because of their potent weaponries against macrophage mediated killing. Macrophages serve as intracellular reservoirs of S. aureus. Although significant resources have been invested during the last decade in new treatments for sepsis, only antibiotic therapy has failed to improve outcomes. Moreover the host pathogen interaction resulted in host cell death triggering inflammation. So, successful therapy requires amalgamation of therapies to delineate pathogen along with providing protection to host cell. With this idea, LNMMA, the iNOS inhibitor is used along with antibiotics Ofloxacin or Chloramphenicol on S. aureus infected mouse peritoneal macrophage. ROS like H₂O₂, O₂^- production has been measured. NO inhibition by iNOS inhibitor and antioxidant levels has been analysed. COX2, TLR2 and iNOS expression along with proinflammatory cytokine level was studied. It was found that the use of iNOS inhibitor LNMMA along with antibiotics not only enhances bacterial clearance but also decreases proinflammatory responses in Staphylococcus aureus infected macrophages. Inhibition of TLR2 as well as COX2 has also been found in combined treatment groups. The use of iNOS inhibitor LNMMA plus Ofloxacin or Chloramphenicol pretreatment enhanced bacterial clearance by increasing ROS. Decreases in NO protect the cell from harmful peroxynitril as well as inflammatory damage by changes in iNOS, COX2 activity along with reduced proinflammatory cytokines like TNFα, IFNγ, IL1-β etc. Changes in antioxidant level has been found. This in-vitro realm of augmented bacterial clearance and regulated inflammation may be considered as a novel and important therapeutic intervention.

Bioactivities of a New Pyrrolidine Alkaloid from the Root Barks of Orixa japonica

A new pyrrolidine alkaloid named (Z)-3-(4-hydroxybenzylidene)-4-(4-hydroxyphenyl)-1-methylpyrrolidin-2-one was isolated from the ethanol extract of the root barks of Orixa japonica. The structure of the new alkaloid was elucidated on the basis of NMR and MS analysis. The compound exhibited larvicidal activity against the fourth instar larvae of Aedes aegypti (LC₅₀ = 232.09 μg/mL), Anopheles sinensis (LC₅₀ = 49.91 μg/mL), and Culex pipiens pallens (LC₅₀ = 161.10 μg/mL). The new alkaloid also possessed nematicidal activity against Bursaphelenchus xylophilus (LC₅₀ = 391.50 μg/mL) and Meloidogynein congnita (LC₅₀ = 134.51 μg/mL). The results indicate that the crude ethanol extract of O. japonica root barks and its isolated pyrrolidine alkaloid have potential for development into natural larvicides and nematicides.

Phytochemistry of the genus Skimmia (Rutaceae)

The genus Skimmia is a rich source of interesting secondary metabolites, including 20 alkaloids derived from anthranilic acid, 45 coumarins, 21 limonoids, four cholestane derivatives, six pentacyclic triterpenes, six flavonoids, and two unusual fatty acid derivatives. Skimmia is employed in folk medicine e.g. against fever, inflammations, and rheumatism. Skimmia extracts, Skimmia essential oils and pure compounds isolated from Skimmia extracts have been experimentally shown to have various bioactivities such as antioxidant, anti-inflammatory, antimicrobial, and insecticidal. In this review we discuss the exact structures of compounds isolated from members of the genus Skimmia, bioactivities of Skimmia extracts and pure compounds derived from them, and systematic implications of the patterns of occurrence of these compounds. Moreover, research gaps and interesting avenues for future research are discussed briefly.

Synthesis and SAR studies of novel 6,7,8-substituted 4-substituted benzyloxyquinolin-2(1H)-one derivatives for anticancer activity

BACKGROUND AND PURPOSE

4-Phenylquinolin-2(1H)-one (4-PQ) derivatives can induce cancer cell apoptosis. Additional new 4-PQ analogs were investigated as more effective, less toxic antitumour agents.

EXPERIMENTAL APPROACH

Forty-five 6,7,8-substituted 4-substituted benzyloxyquinolin-2(1H)-one derivatives were synthesized. Antiproliferative activities were evaluated using a 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazoliun bromide assay and structure-activity relationship correlations were established. Compounds 9b, 9c, 9e and 11e were also evaluated against the National Cancer Institute-60 human cancer cell line panel. Hoechst 33258 and Annexin V-FITC/PI staining assays were used to detect apoptosis, while inhibition of microtubule polymerization was assayed by fluorescence microscopy. Effects on the cell cycle were assessed by flow cytometry and on apoptosis-related proteins (active caspase-3, -8 and -9, procaspase-3, -8, -9, PARP, Bid, Bcl-xL and Bcl-2) by Western blotting.

KEY RESULTS

Nine 6,7,8-substituted 4-substituted benzyloxyquinolin-2(1H)-one derivatives (7e, 8e, 9b, 9c, 9e, 10c, 10e, 11c and 11e) displayed high potency against HL-60, Hep3B, H460, and COLO 205 cancer cells (IC₅₀ < 1 μM) without affecting Detroit 551 normal human cells (IC₅₀ > 50 μM). Particularly, compound 11e exhibited nanomolar potency against COLO 205 cancer cells. Mechanistic studies indicated that compound 11e disrupted microtubule assembly and induced G2/M arrest, polyploidy and apoptosis via the intrinsic and extrinsic signalling pathways. Activation of JNK could play a role in TRAIL-induced COLO 205 apoptosis.

CONCLUSION AND IMPLICATIONS

New quinolone derivatives were identified as potential pro-apoptotic agents. Compound 11e could be a promising lead compound for future antitumour agent development.

Brønsted acidic ionic liquid catalyzed tandem reaction of 4-hydroxy-1-methyl-2-quinolone with chalcone: regioselective synthesis of pyrano[3,2-c]quinolin-2-ones

Task specific ionic liquid [1-methyl-3-(4-sulfobutyl)imidazolium-4-methylbenzenesulfonate] is an excellent catalyst for the synthesis of pyrano[3,2-c]quinolin-2-one derivatives.

Synthesis, characterization, and antimicrobial evaluation of carbostyril derivatives of 1H-pyrazole

A new series of 12 derivatives of 4-pyrazolyl-N-arylquinoline-2,5-dione (4a-l) were synthesized by one pot base catalyzed cyclocondensation reaction of 1-aryl-5-chloro-3-methyl-1H-pyrazole-4-carbaldehyde (1a-c), Meldrum's acid (2) and 3-arylamino-5,5-disubstitutedcyclohex-2-enone (3a-d). All the compounds were characterized by elemental analysis, FT-IR, (1)H NMR and (13)C NMR spectral data and were screened, against six bacterial pathogens, namely Bacillus subtilis, Clostridium tetani, Streptococcus pneumoniae, Salmonella typhi, Vibrio cholerae, Escherichia coli and antifungal activity, against two fungal pathogens Aspergillus fumigatus and Candida albicans, using broth microdilution MIC (minimum inhibitory concentration) method. Some of the compounds were found to be equipotent or more potent than commercial drugs, against most of the employed strains, as evident from the screening data.