Microwave-assisted synthesis and antifungal activity of novel fused Osthole derivatives

Discovery of novel 3-phenylhydrazone coumarin derivatives as potential antifungal agents against phytopathogenic fungi

Plant fungal diseases, such as rice sheath blight caused by Rhizoctonia solani, significantly impact crop yield and quality. To discover novel fungicides, 39 novel 3-phenylhydrazone coumarin compounds were synthesized using natural product modeling and active substructure merging strategies. Their bioactivity was tested against six plant pathogens, including Botrytis cinerea, Alternaria solani, Fusarium graminearum, Rhizoctonia solani, Colletotrichum orbiculare, and Alternaria alternata. The majority of compounds exhibited significant activity against B. cinerea and R. solani. Among them, B1 (4-chloro-3-phenylhydrazone-coumarin derivative) displayed outstanding antifungal efficacy, particularly against C. orbiculare (EC50 value = 0.98 μg/mL) and R. solani (EC50 value = 1.20 μg/mL), comparable to the control fungicide boscalid. Structural optimization revealed that introducing a fluorine group in the phenylhydrazone moiety improved activity. Preliminary mechanistic studies suggest that B1 disrupts cell membranes and mitochondrial function, indicating its potential as a novel fungicide candidate.

Coumarin derivatives containing the 1,3,4 oxadiazole/thiadiazole moiety discovered as potential anti-tobacco mosaic virus agents

In this paper, a series of oxadiazole/thidiazole containing coumarin derivative derivatives were designed, synthesized and characterized using NMR and HRMS. The evaluation of antiviral activity revealed that some of the synthesized compounds exhibited good in vivo antiviral efficacy against tobacco mosaic virus (TMV). Notably, compounds H6 and Y5 demonstrated exceptional therapeutic and protective effects against TMV, with EC50 values of 180.7, 190.3 and 215.8, 218.6 μg/mL, respectively, surpassing the efficacy of NingNanmycin, which exhibited EC50 values of 284.1 and 247.1 μg/mL. The preliminary mechanistic studies indicated that H6 and Y5 had ahigh binding affinity for the tobacco mosaic virus capsid protein (TMV-CP), potentially obstructing the self-assembly and replication processes of TMV particles. Furthermore, the chlorophyll content and superoxide dismutase (SOD) activity in tobacco leaves increased, while the malondialdehyde (MDA) content decreased. H6 has the potential to be developed as a novel antiviral.

Plant natural product-based pesticides in crop protection: semi-synthesis, mono-crystal structures and agrochemical activities of osthole ester derivatives, and study of their toxicology against Tetranychus cinnabarinus (Boisduval)

BACKGROUND

Owing to large amounts of synthetic pesticides being extensively and unreasonably used for crop protection, currently, resistance and negative impacts on human health and environment safety have appeared. Therefore, development of potential pesticide candidates is highly urgent. Herein, a series of ester derivatives of osthole were designed and synthesized as pesticidal agents.

RESULTS

Six spatial configurations of 4'-(p-toluenoyloxy)osthole (4b), 4'-(m-fluorobenzoyloxy)osthole (4f), 4'-(p-fluorophenylacetyloxy)osthole (4m), 4'-(3'',4''-methylenedioxybenzoyloxy)osthole (4q), 4'-formyloxyosthole (4u) and 4'-acetyloxyosthole (4v) were determined by X-ray mono-crystal diffraction. Compounds 4b, 4'-(p-chlorobenzoyloxy)osthole (4g), 4'-(m-chlorobenzoyloxy)osthole (4h), 4'-(p-bromobenzoyloxy)osthole (4i) and 4'-(2''-chloropyridin-3''-ylcarbonyloxy)osthole (4p) showed higher insecticidal activity than toosendanin against Mythimna separata Walker; notably, compound 4b displayed 1.8 times insecticidal activity of the precursor osthole. Against Tetranychus cinnabarinus Boisduval, compounds 4g and 4h showed 3.3 and 2.6 times acaricidal activity of osthole, and good control effects in the glasshouse. Scanning electron microscopy assay demonstrated that compound 4g can damage the cuticle layer of T. cinnabarinus resulting in death.

CONCLUSION

Compounds 4g and 4h can be further studied as lead pesticidal agents for the management of M. separata and T. cinnabarinus. These results will pave the way for application of osthole derivatives as agrochemicals. © 2024 Society of Chemical Industry.

Bioactivity evaluation and active compounds identification of Symphoricarpos orbiculatus as potential botanical herbicide

BACKGROUND

Evaluation of herbicidal activity and identification of active compounds are important bases for the development of new botanical herbicides.

RESULTS

This study confirmed that Symphoricarpos orbiculatus has high herbicidal activities against mono-dicotyledonous weeds, including Echinochloa crusgalli, Digitaria sanguinalis, Amaranthus retroflexus and Portulaca oleracea. By bioassay-guided isolation, 12 compounds were isolated and identified from S. orbiculatus for the first time, including iridoids: naucledal (K1), loganin (K2), loganigenin (K3), loganin acid (K4), glucologanin (K5) and vogeloside (K6), as well as flavonoids: quercetine (K7), luteolin (K8), nobiletin (K9), astragalin (K10), isorhamnetin 3-d-glucoside (K11) and rutin (K12). Biological assays showed that iridoids are the main active ingredients of S. orbiculatus. The compounds of K5 and K6 could inhibit both the root (IC50 = 37.54 and 38.91 μg mL-1, respectively) and shoot (IC50 = 42.78 and 45.72 μg mL-1, respectively) of Portulaca oleracea, which have a weeding toxicity similar to that of the commercialized plant-based herbicide pelargonic acid. In addition, the results of pot culture assay showed that S. orbiculatus ethanol extracts had high fresh weight control effect against Digitaria sanguinalis and P. oleracea at the concentration of 40 g L-1. After 7 days, both the soil treatment and the stem and leaf spray method resulted in severe leaf necrosis and significant leaf etiolation.

CONCLUSION

Symphoricarpos orbiculatus and its herbicidal active compounds have the potential to develop into botanical herbicides, and are first reported in the present study. © 2024 Society of Chemical Industry.

PIDA-promoted metal-free [3 + 2] heteroannulation of β-ketothioamides with 4-hydroxy coumarins: chemo-/regioselective access to furo[3,2-c]chromen-4-ones at room temperature

Herein, we report a viable protocol to access furo[3,2-c]chromen-4-ones by engaging easily accessible 4-hydroxy coumarins as a three-atom CCO unit and thioamides as a C2 coupling partner, mediated by phenyliodine(III) diacetate (PIDA) at room temperature in a highly efficient and pot-/step-economical manner. This strategy not only avoids potential toxicity and tiresome workup conditions, but also features operational simplicity, a broad substrate scope, good functional group tolerance, high yields, easy scalability and exclusive selectivity. A mechanistic study has shown that this metal-free reaction is triggered by PIDA via activation of the β-carbon of 4-hydroxy coumarin, followed by a nucleophilic addition/intramolecular cyclization/dethiohydration cascade. High-resolution mass spectra (HRMS) study confirms the key intermediates involved during the course of the reaction, elucidating the reaction pathways, and demonstrates the excellent regio- and chemoselectivity of this approach.

Bio-organic fertilizer facilitated phytoremediation of heavy metal(loid)s-contaminated saline soil by mediating the plant-soil-rhizomicrobiota interactions

Bio-organic fertilizer (BOF) was effective to promote the phytoremediation efficiency of heavy metal(loid)s-contaminated saline soil (HCSS) by improving rhizosphere soil properties, especially microbiome. However, there existed unclear impacts of BOF on plant metabolome and plant-driven manipulation on rhizosphere soil microbiota in HCSS, which were pivotal contributors to stress defense of plants trapped in adverse conditions. Here, a pot experiment was conducted to explore the mechanisms of BOF in improving alfalfa (Medicago sativa)-performing phytoremediation of HCSS. BOF application significantly increased the biomass (150.87-401.58 %) to support the augments of accumulation regarding heavy metal(loid)s (87.50 %-410.54 %) and salts (38.27 %-271.04 %) in alfalfa. BOF promoted nutrients and aggregates stability but declined pH of rhizosphere soil, accompanied by the boosts of rhizomicrobiota including increased activity, reshaped community structure, enriched plant growth promoting rhizobacteria (Blastococcus, Modestobacter, Actinophytocola, Bacillus, and Streptomyces), strengthened mycorrhizal symbiosis (Leohumicola, Funneliformis, and unclassified_f_Ceratobasidiaceae), optimized co-occurrence networks, and beneficial shift of keystones. The conjoint analysis of plant metabolome and physiological indices confirmed that BOF reprogrammed the metabolic processes (synthesis, catabolism, and long-distance transport of amino acid, lipid, carbohydrate, phytohormone, stress-resistant secondary metabolites, etc) and physiological functions (energy supply, photosynthesis, plant immunity, nutrients assimilation, etc) that are associated intimately. The consortium of root metabolome, soil metabolome, and soil microbiome revealed that BOF facilitated the exudation of metabolites correlated with rhizomicrobiota (structure, biomarker, and keystone) and rhizosphere oxidative status, e.g., fatty acyls, phenols, coumarins, phenylpropanoids, highlighting the plant-driven regulation on rhizosphere soil microbes and environment. By compiling various results and omics data, it was concluded that BOF favored the adaptation and phytoremediation efficiency of alfalfa by mediating the plant-soil-rhizomicrobiota interactions. The results would deepen understanding of the mechanisms by which BOF improved phytoremediation of HCSS, and provide theoretical guidance to soil amelioration and BOF application.

Iodine-Catalyzed Cascade Annulation of 4-Hydroxycoumarins with Aurones: Access to Spirocyclic Benzofuran-Furocoumarins

An attractive approach for the preparation of spirocyclic benzofuran-furocoumarins has been developed through iodine-catalyzed cascade annulation of 4-hydroxycoumarins with aurones. The reaction involves Michael addition, iodination, and intramolecular nucleophilic substitution in a one-step process, and offers an efficient method for easy access to a series of valuable spirocyclic benzofuran-furocoumarins in good yields (up to 99%) with excellent stereoselectivity. Moreover, this unprecedented protocol provides several advantages, including readily available materials, an environmentally benign catalyst, a broad substrate scope, and a simple procedure.

Design, Synthesis, Antifungal Activity, and 3D-QASR of Novel Oxime Ether-Containing Coumarin Derivatives as Potential Fungicides

Structural modification of natural products is an effective approach for improving antifungal activity and has, therefore, been used extensively in the development of new agrochemical products. In this work, a series of novel coumarin derivatives containing oxime ether structures were designed, synthesized, and evaluated for antifungal activity. Some of the designed compounds exhibited promising antifungal activities against tested fungi, and compounds 4a, 4c, 5a, and 6b had EC50 values equivalent to those of commercial fungicides. Compound 6b was the most promising candidate fungicide against Rhizoctonia solani (EC50 = 0.46 μg/mL). In vivo antifungal bioassays suggested that compounds 5a and 6b could serve as novel agricultural antifungals. Furthermore, microscopy demonstrated that compound 6b induced the sprawling growth of hyphae, distorted the outline of cell walls, and reduced mitochondrial numbers. Additionally, the effects of the substituent steric, electrostatic, hydrophobic, and hydrogen-bond fields were elucidated using an accurate and reliable three-dimensional quantitative structure-activity relationship (3D-QSAR) model. The results presented here will guide the discovery of potential novel fungicides for plant disease control in agriculture.

Design, Synthesis, and Biological Activities of Novel Coumarin Derivatives as Pesticide Candidates

Food security is an important issue in the 21st century; preventing and controlling crop diseases and pests are the key to solve this problem. The creation of new pesticides based on natural products is an important and effective method. Herein, coumarins were selected as parent structures, and a series of their derivatives were designed, synthesized, and evaluated for their antiviral activities, fungicidal activities, and insecticidal activities. We found that coumarin derivatives exhibited good to excellent antiviral activities against tobacco mosaic virus (TMV). The antiviral activities of I-1, I-2a, I-4b, II-2c, II-2g, II-3, and II-3b are better than that of ribavirin at 500 μg/mL. Molecular docking research showed that these compounds had a strong interaction with TMV CP. These compounds also showed broad-spectrum fungicidal activities against 14 plant pathogenic fungi. The EC50 values of I-1, I-2a, I-3c, and II-2d are in the range of 1.56-8.65 μg/mL against Rhizoctonia cerealis, Physalospora piricola, Sclerotinia sclerotiorum, and Pyricularia grisea. Most of the compounds also displayed good insecticidal activities against Mythimna separata. Pesticide-likeness analysis showed that these compounds are following pesticide-likeness and have the potential to be developed as pesticide candidates. The present work lays a foundation for the discovery of novel pesticide lead compounds based on coumarin derivatives.

Decarboxylative [3 + 2] cycloaddition of propargyl cyclic carbonates with C,O-bis(nucleophile)s to access dihydrofuro[3,2-c]coumarins and dihydronaphtho[1,2-b]furans with quaternary center

The development of efficient and straightforward strategies for obtaining chiral complex molecules from readily available starting materials is of great value in drug discovery. The stereodivergent synthesis of heterocycles bearing quaternary centers remains a challenge due to inherent steric issues. Herein, we report an enantioselective copper-catalyzed decarboxylative [3 + 2] cycloaddition of propargyl cyclic carbonates/carbamates with 4-hydroxycoumarins to afford a wide range of dihydrofuro[3,2-c]coumarins in excellent yields and enantioselectivity. The strategy has been successfully applied to other C,O-bisnucleophiles, such as α-naphthols, to obtain dihydronaphtho[1,2-b]furans with good yields.

Design, Synthesis and Fungicidal Activity of Ester Derivatives of 4-(3,4-Dichloroisothiazole) 7-Hydroxy Coumarin

The development of new fungicides is vital for safeguarding crops and ensuring sustainable agriculture. Building on our previous finding that 4-(3,4-dichloroisothiazole)-7-hydroxy coumarins can be used as fungicidal leads, 44 novel coumarin ester derivatives were designed and synthesized to evaluate whether esterification could enhance their fungicidal activity. In vitro fungicidal bioassays indicated that compound 2ai displayed good activity against Alternaria solani, Botrytis cinereal, Cercospora arachidicola, Physalospora piricola and Sclerotinia sclerotiorum, with an EC₅₀ value ranging from 2.90 to 5.56 μg/mL, comparable to the lead compound 1a, with its EC₅₀ value ranging from 1.92 to 9.37 μg/mL. In vivo bioassays demonstrated that compounds 1a, 2ar and 2bg showed comparable, excellent efficacy against Pseudoperonospora cubensis at a dose of 25 µg/mL. Our research shows that the esterification of 4-(3,4-dichloroisothiazole) 7-hydroxycoumarins results in a fungicidal activity equivalent to that of its lead compounds. Furthermore, our density functional theory (DFT) calculations and 3D-QSAR modeling provide a rational explanation of the structure-activity relationship and offer valuable insights to guide further molecular design.

Lignin-based carbon fibers: Insight into structural evolution from lignin pretreatment, fiber forming, to pre-oxidation and carbonization

Lignin remains the second abundant source of renewable carbon with an aromatic structure. However, most of the lignin is burnt directly for power generation, with an effective utilization rate of <2 %, making value addition on lignin an urgent requirement. From this perspective, preparation of lignin-based carbon fibers has been widely studied as an effective way to increase value addition on lignin. However, lignin species are diverse and complex in structure, and the pathway that enables changes in lignin structure during pretreatment, fiber formation, stabilization, and carbonization is still uncertain. In this review, we condense the common structural evolution route from the previous studies, which can serve as a guide towards engineered lignin carbon fibers with high performance properties.

Preparation and Biological Evaluation of Novel Osthole-Derived N-Benzoylthioureas as Insecticide Candidates

To discover novel natural-product-based insecticide candidates, herein, a variety of osthole-derived N-benzoylthioureas were synthesized and assessed for their insecticidal activities against three insect pests. An insecticidal assay showed that most of the target osthole-derived N-benzoylthioureas displayed a more potent and broad-spectrum insecticidal effect than the parent osthole after the introduction of N-benzoylthioureas on the C-3' position of osthole. Compound B24 displayed the most potent growth inhibitory (GI) effect on Mythimna separata Walker, with a final corrected mortality rate of 82.1% when treated with a concentration of 1 mg/mL, which was 1.64- and 1.53-fold higher in comparison to osthole and the botanical insecticide toosendanin, respectively. Compounds B22, B23, and B25 displayed a more promising aphicidal effect on Myzus persicae Sulzer, and their LD₅₀ values were 0.015, 0.017, and 0.019 μg/larvae, respectively, superior to the commercially available insecticide rotenone (0.024 μg/larvae). Derivatives B19, B20, B23, and B25 displayed more potent larvicidal activity against Plutella xylostella Linnaeus, with LC₅₀ values of 0.22, 0.26, 0.15, and 0.30 mg/mL, respectively, exceeding that of rotenone (0.37 mg/mL). Furthermore, both compounds B19 and B23 against P. xylostella were found to be more effective than rotenone in a control efficacy assay under greenhouse conditions. The structure-activity relationship (SAR) suggested that osthole-derived N-benzoylthioureas are more active in most cases when the R group is an electron-withdrawing group than when it is an electron-donating group, especially for halogenated groups. Additionally, the potent compounds B19 and B23 possessed good selectivity and were less toxic to non-target organisms. This study suggests that these osthole-derived N-benzoylthioureas could be further studied in depth as eco-friendly natural product pesticides in crop protection.

Novel Coumarin 7-Carboxamide/Sulfonamide Derivatives as Potential Fungicidal Agents: Design, Synthesis, and Biological Evaluation

Coumarin compounds have a variety of biological activities such as anti-tumor, anti-coagulation, anti-HIV, anti-fungal, and insecticidal. Amide and sulfonamide compounds have been used as fungicides for half a century, and dozens of varieties have been developed so far. This study focused on the introduction of carboxamide and sulfonamide moieties in a coumarin core to discover novel derivatives. Based on this strategy, we synthesized two series of novel carboxamide and sulfonamide substituted coumarin derivatives, and their fungicidal activity was also investigated. Some designed compounds possessed potential activities against six phytopathogenic fungi in the primary assays, highlighted by compound 6r. Compound 6r exhibited stronger fungicidal activity against Botrytis cinerea (EC₅₀ = 20.52 µg/mL) and will be the lead structure for further study.

Osthole: Synthesis, Structural Modifications and Biological Properties

Abstract:

Osthole, a naturally occurring coumarin-type compound, is isolated from a Chinese herbal medicine Cnidium monnieri (L.), and exhibits a broad range of biological properties. In this review, the total synthesis and structural modifications of osthole and its analogs are described. Additionally, the progress on bioactivities of osthole and its analogs is outlined since 2016. Moreover, the structure-activity relationships and mechanisms of action of osthole and its derivatives are discussed. These can provide references for future design, development and application of osthole and its analogs as drugs or pesticides in the fields of medicine and agriculture.

Copper(II)-Catalyzed Tandem Reaction: Synthesis of Furo[3,2-c]coumarin Derivatives and Evaluation for Photophysical Properties

An efficient protocol for synthesizing furo[3,2-c]coumarin derivatives is described. The novel reaction could afford the desired furocoumarins with good to excellent yields in a mild and rapid manner. Large substrate scope screening and scale-up preparation have also been accomplished, and selected compounds were evaluated for their photophysical properties.

Simple Osthole/Nanocarrier Pesticide Efficiently Controls Both Pests and Diseases Fulfilling the Need of Green Production of Strawberry

The application of botanical pesticides is a good choice in organic agriculture. However, most botanical pesticides have limitations of slow action and short persistence for pest and disease management, which constrain their further application. With the objective of exploring a green pesticide for controlling strawberry pests and diseases simultaneously, a star polymer (SPc) with a low production cost was synthesized as a pesticide nanocarrier through simple reactions. The SPc complexed with osthole quickly through electrostatic interaction and hydrophobic association, which decreased the particle size of osthole down to the nanoscale (17.66 nm). With the help of SPc, more nano-sized osthole was delivered into cytoplasm through endocytosis, leading to the enhanced cytotoxicity against insect cells. As a green botanical pesticide, the control efficacy of the osthole/SPc complex was improved against main strawberry pests (green peach aphid and two-spotted spider mite) and disease (powdery mildew), which fulfilled the need of both pest and disease management in sustainable production of strawberry. Meanwhile, the introduction of SPc not only improved plant-uptake but also decreased the residue of osthole due to the higher degradation rate. Furthermore, the application of the osthole/SPc complex exhibited no influence on the strawberry fruit quality and nontarget predators. To our knowledge, it is the first success to control plant pests and diseases simultaneously for sustainable agriculture by only one pesticidal formulation based on nanoparticle-delivered botanical pesticides.

Synthesis of osthol-based botanical fungicides and their antifungal application in crop protection

Plant pathogenic fungi decrease the quality and productivity of plant production. The botanical fungicides have better biocompatibility and rapid biodegradation, little or no cross resistance, and the structural diversity, and thus are beneficial to deal with plant fungal diseases. Osthole has been widely used as the commercial botanical fungicide against powdery mildew in China. In this article, a series of osthole derivatives were synthesized, which respectively contain different substituents on the benzene ring, at the C8-position and pyrone ring. All the target compounds were evaluated in vitro for their antifungal activity against resistant phytopathogenic fungi. Colletotrichum fragariae, Strawberry Botrytis Cinerea, Kiwifruit Botrytis Cinerea, Kiwifruit brown Rots, which are common in fruit fungal diseases. The compound C₄ was identified as the most promising candidate with the EC₅₀ values at 38.7 µg/mL against Colletotrichum Fragariae, 14.5 µg/mL against Strawberry Botrytis Cinerea and 24.3 µg/mL against Kiwifruit Botrytis Cinerea, respectively, whereas the antifungal activity against resistant phytopathogenic fungi. of osthole is too low to be used (EC₅₀ > 400 ppm). The results of mycelial relative conductivity determination, PI uptake and fluorescence spectroscopy indicated that the cell membrane of fungi is the key action site of C₄. Besides, C₄ has the potent inhibitory activity against both of plant and human pathogenic bacteria. Our studies showed that C₄ was worthy for further attention as a promising botanical fungicide candidate in crop protection.

Discovery of Novel 3,4-Dichloroisothiazole-Containing Coumarins as Fungicidal Leads

Natural products are one of the resources for discovering novel fungicidal leads. As a natural fungicide, osthole was used as a coumarin-based lead compound for the development of novel fungicides. Here, a series of 3,4-dichloroisothiazole-containing 7-hydroxycoumarins were rationally designed, synthesized, and characterized by introducing a bioactive substructure, 3,4-dichloroisothiazole, into the coumarin skeleton. In vitro bioassay indicated that compound 7g displayed good activity against Rhizoctonia solani, Physalospora piricola, Sclerotinia sclerotiorum, and Botrytis cinerea. Its median effective concentration (EC₅₀) value against each of these fungi fell between 0.88 and 2.50 μg/mL, which was much lower than that of osthole against the corresponding pathogen (between 7.38 and 74.59 μg/mL). In vivo screening validated that 7k exhibited 100%, 60%, and 20% efficacy against R. solani Kühn at 200, 100, and 50 μg/mL, respectively. RNA sequence analysis implied that growth inhibition of R. solani by 7k might result from potential disruptions of fungal membrane formation and intracellular metabolism. Furthermore, a field experiment with cucumber plants indicated that 7b showed 62.73% and 74.03% efficacy against Pseudoperonospora cubensis (Berk. & Curt.) Rostov. at rates of 12.5 g a.i./ha and 25 g a.i./ha, respectively, which showed no significant difference between 7b and osthole at 30 g a.i./ha. Our studies suggested that 7b, 7g, and 7k might be used as fungicidal leads for further optimization.

Design, synthesis and fungicidal activity of 3,4-dichloroisothiazolocoumarin-containing strobilurins

Twenty-one novel 3,4-dichloroisothiazolocoumarin-containing strobilurins were rationally designed and synthesized. Preliminary bioassay showed that compounds 7c, 7h and 7l exhibited over 80% inhibitory rate against Sclerotinia sclerotiorum at 50 μg/mL, 7c exhibited good activity against S. sclerotiorum with median effective concentration (EC₅₀) of 4.08 μg/mL, while the positive control coumoxystrobin showed EC₅₀ of 1.00 μg/mL. In addition, 7d showed better fungicidal activity with a lower EC₅₀ value of 7.65 μg/mL against Botrytis cinerea than that of positive control trifloxystrobin with its EC₅₀ value of 21.96 μg/mL. This study indicated that 3,4-dichloroisothiazolocoumarin-containing strobilurin was a promising fungicide lead deserved for further study.

De Novo and Divergent Synthesis of Highly Functionalized Furans by Cascade Reactions of 2-Hydroxy-1,4-diones with Nucleophiles

Herein, a divergent synthesis of a variety of 2α- and 5α-substituted furan derivatives from 2-hydroxy-1,4-diones is reported. By using appropriate substrates and an acid catalyst, the reactions occurred selectively through cyclization/1,6-conjugate addition or cyclization/Friedel-Crafts-type cascade reactions. A broad range of nucleophilic reagents (>10 types for the 1,6-conjugate addition for 5α substitution and >20 types for the Friedel-Crafts-type cascade reaction for 2α substitution), including alcohols, amides, furan, thiophene, pyrrole, indole, phenols, and many others, can successfully participate in the reactions, providing a universal strategy for a diversity-oriented synthesis of α-substituted furan derivatives. Deuteriation experiments and DFT calculations were carried out to support the proposed reaction mechanisms. Antifungal activity experiments revealed that products with an indole or 4-hydroxycoumarin core substituted at the 2α position showed moderate activities against Rhizoctorzia solani and Botrytis cinerea, respectively.

Novel Fluorinated 7-Hydroxycoumarin Derivatives Containing an Oxime Ether Moiety: Design, Synthesis, Crystal Structure and Biological Evaluation

A series of fluorinated 7-hydroxycoumarin derivatives containing an oxime ether moiety have been designed, synthesized and evaluated for their antifungal activity. All the target compounds were determined by ¹H-NMR, ¹³C-NMR, FTIR and HR-MS spectra. The single-crystal structures of compounds 4e, 4h, 5h and 6c were further confirmed using X-ray diffraction. The antifungal activities against Botrytis cinerea (B. cinerea), Alternariasolani (A. solani), Gibberella zeae (G. zeae), Rhizoctorzia solani (R. solani), Colletotrichum orbiculare (C. orbiculare) and Alternaria alternata (A. alternata) were evaluated in vitro. The preliminary bioassays showed that some of the designed compounds displayed the promising antifungal activities against the above tested fungi. Strikingly, the target compounds 5f and 6h exhibited outstanding antifungal activity against B. cinerea at 100 μg/mL, with the corresponding inhibition rates reached 90.1 and 85.0%, which were better than the positive control Osthole (83.6%) and Azoxystrobin (46.5%). The compound 5f was identified as the promising fungicide candidate against B. cinerea with the EC₅₀ values of 5.75 μg/mL, which was obviously better than Osthole (33.20 μg/mL) and Azoxystrobin (64.95 μg/mL). Meanwhile, the compound 5f showed remarkable antifungal activities against R. solani with the EC₅₀ values of 28.96 μg/mL, which was better than Osthole (67.18 μg/mL) and equivalent to Azoxystrobin (21.34 μg/mL). The results provide a significant foundation for the search of novel fluorinated 7-hydroxycoumarin derivatives with good antifungal activity.

4-Chloro-3-formylcoumarin as a multifaceted building block for the development of various bio-active substituted and fused coumarin heterocycles: a brief review

This review presents the diverse synthesis of 3,4-substituted coumarins and 5-, 6- and 7-membered ring fused coumarins using 4-chloro-3-formylcoumarin as the precursor via classical reactions including metal-catalyzed and green reaction protocols.

A review: Biologically active 3,4-heterocycle-fused coumarins

The combination of heterocycles offers a new opportunity to create novel multicyclic compounds having improved biological activity. Coumarins are ubiquitous natural heterocycle widely adopted in the design of various biologically active compounds. Fusing different heterocycles with coumarin ring is one of the interesting approaches to generating novel hybrid molecules having highlighted biological activities. In the efforts to develop heterocyclic-fused coumarins, a wide range of 3,4-heterocycle-fused coumarins have been introduced bearing outstanding biological activity. The effect of heterocycles annulation at 3,4-positions of coumarin ring on the biological activity of the target structures were discussed. This review focuses on the important progress of 3,4-heterocycle-fused coumarins providing better insight for medicinal chemists on the design and preparation of biologically active heterocycle-fused coumarins with a significant therapeutic effect in the future.

Synthesis and anticancer activities of some new coumarin derivatives including the triazole ring and their in silico molecular docking studies

The synthesis, docking study, and investigation of the anticancer activities of some coumarin derivatives containing the triazole ring are reported in this study. The newly synthesized compounds were screened for their in vitro anticancer activity against the cell lines CRL5807 (human bronchioalveolar carcinoma), CRL5826 (human squamous cell carcinoma), MDA-MB231 (human breast cancer cells), HTB177 (human lung cancer), PC-3 (human prostate adenocarcinoma), PANC-1 (human pancreatic cancer cells), used as cancer cells, and CCD34Lu (normal human lung fibroblasts), used as a healthy cell line. Cytotoxicity effects of the samples were determined by the MTT (3-(4,5-dimethyl-2-thiazolyl)-2,5-diphenyl-2H-tetrazolium bromide) assay. In silico studies were also performed to explore the binding interactions of the molecules.

Construction of oxime ester derivatives of osthole from Cnidium monnieri, and evaluation of their agricultural activities and control efficiency

BACKGROUND

In order to discover natural-product-based pesticidal candidates, a series of coumarin-like derivatives containing oxime ester fragments at the C-8 position were prepared by structural modification of osthole, a natural plant product isolated from Cnidium monnieri. Their pesticidal activities were evaluated against two typically fruit trees/crop-threatening agricultural pests, Mythimna separata Walker and Tetranychus cinnabarinus Boisduval.

RESULTS

Osthole was regioselectively oxidized by selenium dioxide to give the E-isomer, (2'E)-3'-formaldehydylosthole (2). Four key steric structures of 2, (2'E, 4'E)-(o-chloropyrid-3-ylcarbonyl)oximinylosthole (4o), (2'E, 4'E)-(styrylcarbonyl)oximinylosthole (4t), and (2'E, 4'E)-(acetyl)oximinylosthole (4w) were undoubtedly confirmed by X-ray crystallography. Against T. cinnabarinus, it is noteworthy that (2'E, 4'E)-(p-chlorophenylcarbonyl)oximinylosthole (4c) exhibited over three-fold more potent acaricidal activity of the precursor osthole, with especially good control efficiency observed in the glasshouse. Against M. separata, compounds 4c and (2'E, 4'E)-(p-nitrophenylcarbonyl)oximinylosthole (4f) showed the most pronounced growth inhibitory activity. The relationships between their structures and agricultural activities also were studied.

CONCLUSION

These results demonstrate that compound 4c could be further structurally modified as pesticidal agents. It will lay the foundation for future application of osthole derivatives as pesticides. © 2020 Society of Chemical Industry.

Furo[3,2-c]coumarins carrying carbon substituents at C-2 and/or C-3. Isolation, biological activity, synthesis and reaction mechanisms

The isolation, biological activity and synthesis of natural furo[3,2-c]coumarins are presented, covering mainly the developments in the last 35 years. The most relevant approaches toward the synthesis of 2-substituted, 3-substituted and 2,3-disubstituted heterocycles are also discussed, with emphasis on the efficiency of the processes and their mechanisms.

Application of natural products as insecticide candidates: Semisynthesis and biological evaluation of some novel osthole-based esters

Natural products are very important sources for the development of new pesticides. Osthole, derived from many medical plants such as Cnidium, Angelica and Citrus plants, is a naturally occurring coumarin compound. To discover the new natural products-based insecticides, thirty-one osthole-based esters containing O-acyl-hydroxylamine groups were prepared, and their structures were identified by different spectral analysis methods. Derivatives A7, A17, A20 and A25 displayed more potent growth inhibitory (GI) activity than the botanical insecticide, toosendanin. Over half of target osthole derivatives had more effective larvicidal effect on P. xylostella than toosendanin. Among all title derivatives, compound A18 displayed more pronounced larvicidal activity (LC₅₀ = 0.64 μmol mL^-1) when compared with toosendanin (LC₅₀ = 0.94 μmol mL^-1). Some interesting results of structure-activity relationships (SARs) of these osthole derivatives were also discussed. In addition, the hemolysis and cytotoxicity assays indicated that these osthole derivatives showed very low toxicity toward normal mammalian cells.

Synthesis of benzofurans from the cyclodehydration of α-phenoxy ketones mediated by Eaton’s reagent

Cyclodehydration of α-phenoxy ketones promoted by Eaton’s reagent (phosphorus pentoxide–methanesulfonic acid) is used to prepare 3-substituted or 2,3-disubstituted benzofurans with moderate to excellent yields under mild conditions. The method provides a facile access to benzofurans from readily available starting materials such as phenols and α-bromo ketones. The reaction is highly efficient, which is attributed to the good reactivity and fluidity of Eaton’s reagent. The reaction can be applied to prepare naphthofurans, furanocoumarins, benzothiophenes, and benzopyrans.

Promising antifungal agents: A minireview

In the recent past, prevalence of life threatening fungal diseases have increased rapidly in immune-compromised cases such as acquired immunodeficiency syndrome (AIDS), cancer, organ transplant etc. Side by side, the appearance of drug resistance to the presently available antifungal therapeutics is on a rapid rise. It has become a top priority for the academia and pharmaceutical industries to develop new antifungal agents able to combat this resistance, and at the same time, possess potential broad spectrum of activity and minimum toxicity. An understanding of the pharmacological interactions between antifungal agents and their targets offers opportunities for design of new therapeutics. This review discusses the various methodology of drug design, structure activity relationships (SARs), and mode of action of variety of new antifungal agents.

Coumarins: antifungal effectiveness and future therapeutic scope

The antifungals that are in current clinical practice have a high occurrence of a side effect and multidrug resistance (MDR). Researchers across the globe are trying to develop a suitable antifungal that has minimum side effect as well as no MDR issues. Due to serious undesired effects connected with individual antifungals, it is now necessary to introduce novel and effective drugs having numerous potentials to regulate complex therapeutic targets of several fungal infections simultaneously. Thus, by taking a lead from this subject, synthesis of potent antifungals from coumarin moiety could contribute to the development of promising antifungal. Its resemblance and structural diversity make it possible to produce an auspicious antifungal candidate. Due to the natural origin of coumarin, its presence in diversity, and their broad spectrum of pharmacological activities, it secures an important place for the researcher to investigate and develop it as a promising antifungal in future. This manuscript discusses the bioavailability of coumarin (natural secondary metabolic molecule) that has privileged scaffold for many mycologists to develop it as a broad-spectrum antifungal against several opportunistic mycoses. As a result, several different kinds of coumarin derivatives were synthesized and their antifungal properties were evaluated. This review compiles various coumarin derivatives broadly investigated for antifungal activities to understand its current status and future therapeutic scope in antifungal therapy.

Synthesis of Novel 2-(Het)arylpyrrolidine Derivatives and Evaluation of Their Anticancer and Anti-Biofilm Activity

A library of novel 2-(het)arylpyrrolidine-1-carboxamides were obtained via a modular approach based on the intramolecular cyclization/Mannich-type reaction of N-(4,4-diethoxybutyl)ureas. Their anti-cancer activities both in vitro and in vivo were tested. The in vitro activity of some compounds towards M-Hela tumor cell lines was twice that of the reference drug tamoxifen, whereas cytotoxicity towards normal Chang liver cell did not exceed the tamoxifen toxicity. In vivo studies showed that the number of surviving animals on day 60 of observation was up to 83% and increased life span (ILS) was up to 447%. Additionally, some pyrrolidine-1-carboxamides possessing a benzofuroxan moiety obtained were found to effectively suppress bacterial biofilm growth. Thus, these compounds are promising candidates for further development both as anti-cancer and anti-bacterial agents.

Visible-Light-Driven, Photoredox-Catalyzed Cascade of ortho-Hydroxycinnamic Esters To Access 3-Fluoroalkylated Coumarins

A general and straightforward protocol for di-/perfluoroalkylation of ortho-hydroxycinnamic esters via a photoredox-catalyzed cascade was developed to access a variety of 3-fluoroalkylated coumarins. This method was characterized by all-in-one synthetic design, simplified operation, mild reaction conditions, and broad substrate scope. Moreover, a sequential one-pot procedure starting from commercially available salicylaldehyde was also successfully realized to synthesize 3-fluoroalkylated coumarins.

One-Pot Synthesis of Novel Dibenzoxanthenes, Diarylbutanes, and Calix[4]resorcinarenes via Consecutive Pyrrolidine Ring-Closure/Ring-Opening Reactions

Herein, we report the approach to the otherwise hardly accessible dibenzoxanthenes, diarylbutanes, and calix[4]resorcinarenes possessing urea moieties based on the reaction of N-(4,4-diethoxybutyl)ureas with electron-rich aromatics in strongly acidic media. Unlike the previously developed methods, the proposed approach benefits from one-pot procedure and allows to obtain the target compounds with much higher yields.

Design, synthesis and antifungal activities of novel pyrrole- and pyrazole-substituted coumarin derivatives

We synthesized a series of novel pyrrole- and pyrazole-substituted coumarin derivatives and evaluated their antifungal activity against six phytopathogenic fungi in vitro. The primary assay results demonstrated that some designed compounds displayed potent activities. Among them, compounds 5g, 6a, 6b, 6c, 6d and 6h exhibited more effective control than Osthole against Cucumber anthrax and Alternaria leaf spot. Furthermore, compound 5g displayed stronger antifungal activity against Rhizoctorzia solani (EC₅₀ = 15.4 µg/mL) than positive control Osthole (EC₅₀ = 67.2 µg/mL).

Activity of the pterophyllins 2 and 4 against postharvest fruit pathogenic fungi. Comparison with a synthetic analog and related intermediates

The antifungal activity of pterophyllin 2, pterophyllin 4, a 5-desmethyl analog of the latter and some of their synthetic intermediates, against three postharvest phytopathogenic fungi, was evaluated. The target fungi were Rhizopus stolonifer, Botrytis cinerea and Monilinia fructicola, which affect fruits worldwide, causing important economic losses. The tests were carried out with imazalil and carbendazim as positive controls. Minimum inhibitory concentrations and minimum fungicidal concentrations were determined, and the morphology of the colonies was examined microscopically. In liquid medium, it was found that pterophyllin 4 exhibited selective fungicidal activity toward M. fructicola, whereas its congener pterophyllin 2 proved to be less potent and not selective and the 5-desmethyl analog of pterophyllin 4 displayed a different activity profile. Morphological changes were observed in the colonies exposed to pterophyllin 4. The results highlighted the importance of small structural features for the antifungal behavior and also suggested that, in Nature, the pterophyllins may act as plant defenses against pathogens.

An efficient synthesis and antifungal evaluation of natural product streptochlorin and its analogues

Streptochlorin, a small indole alkaloid isolated from marine Streptomyces sp., exhibits a wide range of potent biological activities. An efficient and economic synthetic protocol for streptochlorin has been developed and validated, 4 steps from indole in a total yield of 45%, and further applied for the synthesis of its analogues. Biological testing showed that most of the target compounds exhibited potential antifungal activity in the primary assays, especially compounds 6, 7 and 9c were the most active ones, representing effective activity against the phytopathogenic fungi screened in preliminary test and might be explored for the study of mode of action in the future.

Design, Synthesis and Antifungal Activity of Psoralen Derivatives

A series of linear furanocoumarins with different substituents have been designed and synthesized. Their structures were confirmed by ¹H-NMR spectroscopy, high resolution mass spectra (EI-MS), IR, and X-ray single-crystal diffraction. All of the target compounds were evaluated in vitro for their antifungal activity against Rhizoctorzia solani, Botrytis cinerea, Alternaria solani, Gibberella zeae, Cucumber anthrax, and Alternaria leaf spot at 100 μg/mL, and some of the designed compounds exhibited potential antifungal activities. Compound 3a (67.9%) exhibited higher activity than the control Osthole (66.1%) against Botrytis cinerea. Furthermore, compound 4b (62.4%) represented equivalent antifungal activity as Osthole (69.5%) against Rhizoctonia solani. The structure-activity relationship (SAR) study demonstrates that linear furanocoumarin moiety has an important effect on the antifungal activity, promoting the idea of the coumarin ring as a framework that might be exploited in the future.

Synthesis and Fabrication of Collagen-Coated Ostholamide Electrospun Nanofiber Scaffold for Wound Healing

A novel scaffold for effective wound healing treatment was developed utilizing natural product bearing collagen-based biocompatible electrospun nanofibers. Initially, ostholamide (OSA) was synthesized from osthole (a natural coumarin), characterized by ¹H, ¹³C, DEPT-135 NMR, ESI-MS, and FT-IR spectroscopy analysis. OSA was incorporated into polyhydroxybutyrate (PHB) and gelatin (GEL), which serve as templates for electrospun nanofibers. The coating of OSA-PHB-GEL nanofibers with collagen resulted in PHB-GEL-OSA-COL nanofibrous scaffold which mimics extracellular matrix and serves as an effective biomaterial for tissue engineering applications, especially for wound healing. PHB-GEL-OSA-COL, along with PHB-GEL-OSA and collagen film (COLF), was characterized in vitro and in vivo to determine its efficacy. The developed PHB-GEL-OSA-COL nanofibers posed an impressive mechanical stability, an essential requirement for wound healing. The presence of OSA had contributed to antimicrobial efficacy. These scaffolds exhibited efficient antibacterial activity against common wound pathogens, Pseudomonas aeruginosa (P. aeruginosa) and Staphylococcus aureus (S. aureus). The zones of inhibition were observed to be 14 ± 22 and 10 ± 2 mm, respectively. It was observed that nanofibrous scaffold had the ability to release OSA in a controlled manner, and hence, OSA would be present at the site of application and exhibit bioactivity in a sustained manner. PHB-GEL-OSA-COL nanofiber was determined to be stable against enzymatic degradation, which is the most important parameter for promoting proliferation of cells contributing to repair and remodeling of tissues during wound healing applications. As hypothesized, PHB-GEL-OSA-COL was observed to imbibe excellent cytocompatibility, which was determined using NIH 3T3 fibroblast cell proliferation studies. PHB-GEL-OSA-COL exhibited excellent wound healing efficacy which was confirmed using full thickness excision wound model in Wistar rats. The rats treated with PHB-GEL-OSA-COL nanofibrous scaffold displayed enhanced healing when compared to untreated control. Both in vitro and in vivo analysis of PHB-GEL-OSA-COL presents a strong case of therapeutic biomaterial suiting wound repair and regeneration.

Total syntheses of gerberinol I and the pterophyllins 2 and 4 using the Casnati–Skattebøl reaction under different conditions

The total syntheses of the title compounds were achieved from a single coumarin precursor, taking advantage of the temperature-dependent divergent outcomes of the Casnati–Skattebøl reaction.