Natural Product Neopeltolide as a Cytochrome bc1 Complex Inhibitor: Mechanism of Action and Structural Modification

Design, Synthesis, Antifungal Activity, and Action Mechanism of Pyrazole-4-carboxamide Derivatives Containing Oxime Ether Active Fragment As Succinate Dehydrogenase Inhibitors

The dearomatization at the hydrophobic tail of the boscalid was carried out to construct a series of novel pyrazole-4-carboxamide derivatives containing an oxime ether fragment. By using fungicide-likeness analyses and virtual screening, 24 target compounds with theoretical strong inhibitory effects against fungal succinate dehydrogenase (SDH) were designed and synthesized. Antifungal bioassays showed that the target compound E1 could selectively inhibit the in vitro growth of R. solani, with the EC50 value of 1.1 μg/mL that was superior to that of the agricultural fungicide boscalid (2.2 μg/mL). The observations by scanning electron microscopy (SEM) and transmission electron microscopy (TEM) demonstrated that E1 could reduce mycelial density and significantly increase the mitochondrial number in mycelia cytoplasm, which was similar to the phenomenon treated with boscalid. Enzyme activity assay showed that the E1 had the significant inhibitory effect against the SDH from R. solani, with the IC50 value of 3.3 μM that was superior to that of boscalid (7.9 μM). The mode of action of the target compound E1 with SDH was further analyzed by molecular docking and molecular dynamics simulation studies. Among them, the number of hydrogen bonds was significantly more in the SDH-E1 complex than that in the SDH-boscalid complex. This research on the dearomatization strategy of the benzene ring for constructing pyrazole-4-carboxamides containing an oxime ether fragment provides a unique thought to design new antifungal drugs targeting SDH.

Design, synthesis and antifungal activity of novel α-methylene-γ-butyrolactone derivatives containing benzothiophene moiety

BACKGROUND

The discovery of agricultural fungicide candidates from natural products is one of the key strategies for developing environment friendly agricultural fungicides with high efficiency, high selectivity and unique modes-of-action. Based on previous work, a series of novel α-methylene-γ-butyrolactone (MBL) derivatives containing benzothiophene moiety were designed and synthesized.

RESULTS

The majority of the proposed compounds displayed moderate to considerable antifungal efficacy against the tested pathogenic fungi and oomycetes, some exhibiting broad spectrum antifungal activity. Notably, compounds 2 (3-F-Ph) and 7 (4-Cl-Ph) showed excellent antifungal activity against Rhizoctonia with half maximal effective concentration (EC50) values of 0.94 and 0.99 mg L-1, respectively, comparable to the commercial fungicide tebuconazole (EC50 = 0.96 mg L-1), and also displayed significant inhibitory effects against V alsa mali with EC50 values of 2.26 and 1.67 mg L-1, respectively - better than famoxadone and carabrone. The in vivo protective and curative effects against R. solani of compound 2 were 57.2% and 53.7% at 100 mg L-1, respectively, which were equivalent to tebuconazole (51.6% and 52.4%). Further investigations found that compound 2 altered the ultrastructure of R. solani cell, significantly increased the relative conductivity of the cells, and reduced the activity of complex III in a dose-dependent manner. Molecular docking results showed that compound 2 matched well with the Qo pocket.

CONCLUSION

The results revealed that MBL derivatives containing benzothiophene moiety are promising antifungal candidates and provide a new backbone structure for further optimization of novel fungicides. © 2024 Society of Chemical Industry.

The Interaction Mechanism of Picolinamide Fungicide Targeting on the Cytochrome bc1 Complex and Its Structural Modification

Picolinamide fungicides, structurally related to UK-2A and antimycin-A, bind into the Qi-site in the bc1 complex. However, the detailed binding mode of picolinamide fungicides remains unknown. In the present study, antimycin-A and UK-2A were selected to study the binding mode of picolinamide inhibitors with four protonation states in the Qi-site by integrating molecular dynamics simulation, molecular docking, and molecular mechanics Generalized Born surface area (MM/GBSA) calculations. Subsequently, a series of new picolinamide derivatives were designed and synthesized to further understand the effects of substituents on the tail phenyl ring. The computational results indicated that the substituted aromatic rings in antimycin-A and UK-2A were the pharmacophore fragments and made the primary contribution when bound to a protein. Compound 9g-hydrolysis formed H-bonds with Hie201 and Ash228 and showed an IC50 value of 6.05 ± 0.24 μM against the porcine bc1 complex. Compound 9c, with a simpler chemical structure, showed higher control effects than florylpicoxamid against cucumber downy mildew and expanded the fungicidal spectrum of picolinamide fungicides. The structural and mechanistic insights obtained from the present study will provide a valuable clue for the future designing of new promising Qi-site inhibitors.

Structure-Based Discovery of New Succinate Dehydrogenase Inhibitors via Scaffold Hopping Strategy

Scaffold hopping strategy has become one of the most successful methods in the process of molecular design. Seeking to develop novel succinate dehydrogenase inhibitors (SDHIs), we employed a scaffold hopping strategy to design compounds featuring geminate dichloralkenes (gem-dichloralkenes) fragment. After stepwise modifications, a series of N-cyclopropyl-dichloralkenes-pyrazole-carboxamide derivatives was synthesized. Among them, compounds G28 (IC50 = 26.00 nM) and G40 (IC50 = 27.00 nM) were identified as the best inhibitory activity against porcine SDH, with IC50 values reaching the nanomolar range, outperforming the lead compound pydiflumetofen. Additionally, the greenhouse assay indicated that compounds G37 (EC90 = 0.031 mg/L) and G34 (EC90 = 1.67 mg/L) displayed extremely high activities against wheat powdery mildew (WPM) and cucumber powdery mildew (CPM), respectively. Computational results further revealed that the gem-dichloralkene fragment and fluorine substituted pyrazole form an extra hydrophobic interaction and dipolar-dipolar interaction with SDH. In summary, our study provides a novel gem-dichloralkene scaffold with outstanding fungicidal properties, obtained through scaffold hopping, that holds great potential for future research on PM control.

CoMFA Directed Molecular Design for Significantly Improving Fungicidal Activity of Novel [1,2,4]-Triazolo-[3,4-b][1,3,4]-thiadizoles

Target based molecular design via the aid of computation is one of the most efficient methods in the discovery of novel pesticides. Here, a combination of the comparative molecular field analysis (CoMFA) and molecular docking was applied for discovery of potent fungicidal [1,2,4]-triazolo-[3,4-b][1,3,4]-thiadiazoles. Bioassay results indicated that the synthesized target compounds 3a, 3b, and 3c exhibited good activity against Alternaria solani, Botrytis cinerea, Cercospora arachidicola, Fusarium graminearum, Physalospora piricola, Rhizoctonia solani, and Sclerotinia sclerotiorum with an EC50 value falling between 0.64 and 16.10 μg/mL. Specially, 3c displayed excellent fungicidal activity against C. arachidicola and R. solani, which was 5 times more potent than the lead YZK-C22. The enzymatic inhibition assay and fluorescence quenching analysis with R. solani pyruvate kinase (RsPK) showed a weaker binding affinity between RsPK and 3a, 3b, or 3c. Transcriptomic analyses showed that 3c exerted its fungicidal activity by disrupting steroid biosynthesis and ribosome biogenesis in eukaryotes. These findings support that 3c is a promising fungicide candidate, and a fine modification from a lead may lead to a totally different mode of action.

Neopeltolide and its synthetic derivatives: a promising new class of anticancer agents

Being the first or second cause of death worldwide, cancer represents the most significant clinical, social, and financial burden of any human illness. Despite recent progresses in cancer diagnosis and management, traditional cancer chemotherapies have shown several adverse side effects and loss of potency due to increased resistance. As a result, one of the current approaches is on with the search of bioactive anticancer compounds from natural sources. Neopeltolide is a marine-derived macrolide isolated from deep-water sponges collected off Jamaica's north coast. Its mechanism of action is still under research but represents a potentially promising novel drug for cancer therapy. In this review, we first illustrate the general structural characterization of neopeltolide, the semi-synthetic derivatives, and current medical applications. In addition, we reviewed its anticancer properties, primarily based on in vitro studies, and the possible clinical trials. Finally, we summarize the recent progress in the mechanism of antitumor action of neopeltolide. According to the information presented, we identified two principal challenges in the research, i) the effective dose which acts neopeltolide as an anticancer compound, and ii) to unequivocally establish the mechanism of action by which the compound exerts its antiproliferative effect.

Design, Synthesis, and Antifungal/Antioomycete Activity of Thiohydantoin Analogues Containing Spirocyclic Butenolide

Novel fungicidal agents were designed based on the combination of two privileged scaffolds, thiohydantoin and spirocyclic butenolide, which are widely found in natural products. The synthesized compounds were characterized by ¹H NMR, ¹³C NMR, and high-resolution electrospray ionisation mass spectrometry. The in vitro antioomycete activity evaluation showed that most of the compounds exhibited excellent inhibitory activities against different developmental stages in the life cycle of pathogenic oomycete Phytophthora capsici. Compound 5j could inhibit the mycelial growth, sporangium production, zoospore release, and cystospore germination significantly with EC₅₀ values of 0.38, 0.25, 0.11, and 0.026 μg/mL, respectively. The in vivo antifungal/antioomycete bioassay results revealed that the series of compounds generally showed outstanding control efficacies against the pathogenic oomycete Pseudoperonospora cubensis, and compounds 5j, 5l, 7j, 7k, and 7l possessed broad-spectrum antifungal activities against the test phytopathogens. The in vivo protective and curative efficacies against P. capsici of the representative compound 5j were excellent, which were better than those of azoxystrobin. More prominently, 5j significantly promoted the biomass accumulation of the root system and reinforced the cell wall by callose deposition. The pronounced upregulation of immune response-related genes indicated that the active oomycete inhibitor 5j also functioned as a plant elicitor. Transmission electron microscopy observation and the enzyme activity test demonstrated that the mechanism of action of 5j was to bind to the pivotal protein, complex III on the respiratory chain, which resulted in a shortage of energy supply. Molecular docking results exhibited that compound 5j appropriately matched with the Qo pocket and had no interaction with the most commonly mutated site Gly-142, which may be of significant benefit in Qo fungicide resistance management. Compound 5j showed great advantages and potential in oomycete control, resistance management, and induction of disease resistance. A further investigation of 5j with a unique structure might have direct implications for the creation of novel oomycete inhibitors against plant-pathogenic oomycetes.

Design, Synthesis, and Fungicidal Evaluation of Novel N-Methoxy Pyrazole-4-Carboxamides as Potent Succinate Dehydrogenase Inhibitors

Succinate dehydrogenase (SDH, EC 1.3.5.1, also known as complex II) has been recognized as one of the most promising targets of fungicides. Here, based on the binding mode of pydiflumetofen with SDH, the carbon-carbon double bond was introduced into the chemical of pydiflumetofen and then produced the target compounds 6a-6o. The enzymatic inhibitory activity and structure-activity relationship (SAR) study showed that the 2-position and 4-position in terminal benzene were positive to increasing activity. Furthermore, fungicidal activity results in greenhouses indicated that compound 6o showed good control effects against wheat powdery mildew (WPM), cucumber powdery mildew (CPM), and southern corn rust (SCR), showing its broad-spectrum property. Especially, compound 6o exhibited 95 and 75% control effects against CPM and SCR at 6.25 mg/L, respectively, which are better than pydiflumetofen (80% control effects against CPM and 15% against SCR), indicating its potency that is worthy of further development.

Discovery of N-Methoxy-(biphenyl-ethyl)-pyrazole-carboxamides as Novel Succinate Dehydrogenase Inhibitors

Succinate dehydrogenase (SDH) inhibitor is one of the research hotspots for the development of fungicides. Herein, we describe the design and synthesis of N-methoxy-(biphenyl-ethyl)-pyrazole-carboxamide derivatives with enhanced fungicidal activity by employing fragment combination strategy. The SDH enzymatic activity was evaluated for 24 title compounds, and compound 7s was identified as the highest activity against porcine SDH with an IC₅₀ value of 0.014 μM, 205-fold greater than that of fluxapyroxad. Furthermore, the greenhouse experiments showed that compound 7u exhibited potent fungicidal activity against wheat powdery mildew with an EC₅₀ value of 0.633 mg/L, higher activity than fluxapyroxad and benzovindiflupyr. The computational results showed that the fluorine atom substituted on the pyrazole ring formed an extra dipolar-dipolar interaction with C_S42 and then increased the van der Waals interaction between the compound and SDH. The structural and mechanistic insights obtained from the present work will provide a valuable clue to developing novel SDH inhibitors.

Indole-Containing Natural Products 2019-2022: Isolations, Reappraisals, Syntheses, and Biological Activities

Indole alkaloids represent a large subset of natural products, with more than 4100 known compounds. The majority of these alkaloids are biologically active, with some exhibiting excellent antitumor, antibacterial, antiviral, antifungal, and antiplasmodial activities. Consequently, the natural products of this class have attracted considerable attention as potential leads for novel therapeutics and are routinely isolated, characterized, and profiled to gauge their biological potential. However, data on indole alkaloids, their various structures, and bioactivities are complex due to their diverse sources, such as plants, fungi, bacteria, sponges, tunicates, and bryozoans; thus, isolation methods produce an incredible trove of information. The situation is exacerbated when synthetic derivatives, as well as their structures, bioactivities, and synthetic schemes, are considered. Thus, to make such data comprehensive and inform researchers about the current field's state, this review summarizes recent reports on novel indole alkaloids. It deals with the isolation and characterization of 250 novel indole alkaloids, a reappraisal of previously reported compounds, and total syntheses of indole alkaloids. In addition, several syntheses and semi-syntheses of indole-containing derivatives and their bioactivities are reported between January 2019 and July 2022.

Mitochondrion-Targeted Triphenylphosphonium-Based Kresoxim-Methyl Analogues: Synthesis, Fungicidal Activity, and Action Mechanism Approach

β-Methoxyacrylate fungicides as complex III Q_o site inhibitors play a crucial role in the control of crop diseases. In this study, the triphenylphosphonium (TPP)-driven mitochondrion-targeting strategy was used to modify the kresoxim-methyl scaffold at the toxicophore or side chain to develop novel mitochondrion-targeted Q_oI fungicides. These kresoxim-methyl analogues exhibited different fungicidal activities, depending on the position of TPP conjugation and the linker length. Among them, 2A-5 and 2C-4 showed excellent characteristics superior to kresoxim-methyl as candidate fungicides, in which the activity enhancement against Phytophthora capsici was the most remarkable, with an EC₅₀ value of about 5 μM. Notably, both hyphal and zoospore structures of the pathogens were severely damaged after treatment with them. The action mechanism approach revealed that they might cause a significant decrease in ATP synthesis and ROS outbreak in different ways. The results also provided a new insight into the contribution of targeting group TPP to the fungicidal activity in TPP-driven fungicides.

High Value-Added Application of Natural Plant Products in Crop Protection: Honokiol Monoester/Diester Derivatives Containing the Novel Core Scaffold of Benzodihydrofuran and Their Agricultural Bioactivities and Control Effects

To discover new potential botanical insecticides from plant secondary metabolites, a series of new honokiol-type monoester/diester derivatives containing the core scaffold of benzodihydrofuran were synthesized by structural modification of honokiol. Against Mythimna separata Walker, 2-hydroxymethy-5-(2'-(para-chlorobenzoyloxy)-5'-(1″,2″-epoxypropanyl))phenyl-2,3-dihydrobenzofuran (5) and 2-(2″-chloropyridin-5″-ylcarbonyloxy)methylene-5-(2'-(2″-chloropyridin-5″-ylcarbonyloxy)-5'-(1″,2″-epoxypropanyl))phenyl-2,3-dihydrobenzofuran (37) displayed >2.1-fold promising insecticidal activity of the precursor honokiol. Against Aphis citricola Van der Goot, 2-hydroxymethy-5-(2'-(tridecylcarbonyloxy)-5'-(1″,2″-epoxypropanyl))phenyl-2,3-dihydrobenzofuran (21) (LD₅₀: 0.049 μg/nymph) and 2-(para-fluorobenzylcarbonyloxy)methylene-5-(2'-(para-fluorobenzylcarbonyloxy)-5'-(1″,2″-epoxypropanyl))phenyl-2,3-dihydrobenzofuran (31) (LD₅₀: 0.040 μg/nymph) showed 3.5- and 4.3-folds potent aphicidal activity of honokiol (LD₅₀: 0.171 μg/nymph), respectively. Interestingly, 2-(tridecylcarbonyloxy)methylene-5-(2'-(tridecylcarbonyloxy)-5'-(1″,2″-epoxypropanyl))phenyl-2,3-dihydrobenzofuran (46) (LC₅₀: 0.186 mg/mL) and 2-(dodecylcarbonyloxy)methylene-5-(2'-(dodecylcarbonyloxy)-5'-(1″,2″-epoxypropanyl))phenyl-2,3-dihydrobenzofuran (53) (LC₅₀: 0.159 mg/mL: >6.4-fold of honokiol (LC₅₀: 1.024 mg/mL)) exhibited promising acaricidal activity and control efficiency against Tetranychus cinnabarinus Boisduval. Structure-activity relationships indicated that a specific length of the aliphatic chain is necessary for the agricultural activities of honokiol monoester/diester derivatives, especially for the acaricidal activity of diester derivatives.

Enigmazole C: A Cytotoxic Macrocyclic Lactone and Its Ring-Opened Derivatives from a New Species of Homophymia Sponge

A new macrolide, enigmazole C (1), and two additional analogues, enigmazoles E (2) and D (3), were obtained from a new species of the Homophymia genus as part of an ongoing discovery program at PharmaMar to study cytotoxic substances from marine sources. The structures were fully characterized by cumulative analyses of NMR, IR, and MS spectra, along with density functional theory computational calculations. All three of the new compounds feature an unusual 2,3-dihydro-4H-pyran-4-one moiety, but only enigmazoles C (1) and D (3) showed cytotoxic activity in the micromolar range against A-549 (lung), HT-29 (colon), MDA-MB-231 (breast), and PSN-1 (pancreas) tumor cells.

Discovery of Novel Cytochrome bc1 Complex Inhibitor Based on Natural Product Neopeltolide

Background:

Natural products (NPs) are important sources for the design of new drugs and agrochemicals. Neopeltolide, a marine NP, has been identified as a potent Qo-site inhibitor of cytochrome bc1 complex.

Methods:

In this study, a series of neopeltolide derivatives was designed and synthesized by the simplification of its 14-membered macrolactone ring with a diphenyl ether fragment. The enzymatic inhibition bioassays and mycelium growth inhibition experiments against a range of fungi were performed to determine their fungicidal activities.

Results:

The derivatives have potent activity against the porcine bc1 complex. Compound 8q showed the best activity with an IC50 value of 24.41 nM, which was 8-fold more effective than that of positive control azoxystrobin. Compound 8a exhibited a 100% inhibitory rate against Zymoseptoria tritici and Alternaria solani at a 20 mg/L dose.

Conclusion:

Computational results indicated that compounds with suitable physicochemical properties, as well as those forming a hydrogen bond with His161, would have good fungicidal activity. These data could be useful for the design of bc1 complex inhibitors in the future.

Ursolic acid as a potential inhibitor of Mycobacterium tuberculosis cytochrome bc1 oxidase-a molecular modelling perspective

The escalating burden of tuberculosis disease and drastic effects of current medicine has stimulated a search for alternative drugs. A medicinal plant Warburgia salutaris has been reported to possess inhibitory properties against M. tuberculosis. In this study, we apply computational methods to investigate the probability of W. salutaris compounds as potential inhibitors of M. tuberculosis QcrB protein. We performed molecular docking, molecular dynamics simulations, radius of gyration, principal component analysis (PCA), and molecular mechanics-generalized born surface area (MM-GBSA) binding-free energy calculations in explicit solvent to achieve our objective. The results suggested that ursolic acid (UA) and ursolic acid acetate (UAA) could serve as preferred potential inhibitors of mycobacterial QcrB compared to lansoprazole sulphide (LSPZ) and telacebec (Q203)-UA and UAA have a higher binding affinity to QcrB compared to LSPZ and Q203 drugs. UA binding affinity is attributed to hydrogen bond formation with Val120, Arg364 and Arg366, and largely resonated from van der Waals forces resulting from UA interactions with hydrophobic amino acids in its vicinity. UAA binds to the porphyrin ring binding site with higher binding affinity compared to LSPZ. The binding affinity results primarily from van der Waals forces between UAA and hydrophobic residues of QcrB in the porphyrin ring binding site where UAA binds competitively. UA and UAA formed stable complexes with the protein with reduced overall residue mobility, consequently supporting the magnitude of binding affinity of the respective ligands. UAA could potentially compete with the porphyrin ring for the binding site and deprive the mycobacterial cell from oxygen, consequently disturbing mycobacterial oxygen-dependent metabolic processes. Therefore, discovery of a compound that competes with porphyrin ring for the binding site may be useful in QcrB pharmocological studies. UA proved to be a superior compound, although its estimated toxicity profile revealed UA to be hepatotoxic within acceptable parameters. Although preliminary findings of this report still warrant experimental validation, they could serve as a baseline for the development of new anti-tubercular drugs from natural resources that target QcrB.

Development of Novel (+)-Nootkatone Thioethers Containing 1,3,4-Oxadiazole/Thiadiazole Moieties as Insecticide Candidates against Three Species of Insect Pests

To improve the insecticidal activity of (+)-nootkatone, a series of 42 (+)-nootkatone thioethers containing 1,3,4-oxadiazole/thiadiazole moieties were prepared to evaluate their insecticidal activities against Mythimna separata Walker, Myzus persicae Sulzer, and Plutella xylostella Linnaeus. Insecticidal evaluation revealed that most of the title derivatives exhibited more potent insecticidal activities than the precursor (+)-nootkatone after the introduction of 1,3,4-oxadiazole/thiadiazole on (+)-nootkatone. Among all of the (+)-nootkatone derivatives, compound 8c (1 mg/mL) exhibited the best growth inhibitory (GI) activity against M. separata with a final corrected mortality rate (CMR) of 71.4%, which was 1.54- and 1.43-fold that of (+)-nootkatone and toosendanin, respectively; 8c also displayed the most potent aphicidal activity against M. persicae with an LD₅₀ value of 0.030 μg/larvae, which was closer to that of the commercial insecticidal etoxazole (0.026 μg/larvae); and 8s showed the best larvicidal activity against P. xylostella with an LC₅₀ value of 0.27 mg/mL, which was 3.37-fold that of toosendanin and slightly higher than that of etoxazole (0.28 mg/mL). Furthermore, the control efficacy of 8s against P. xylostella in the pot experiments under greenhouse conditions was better than that of etoxazole. Structure-activity relationships (SARs) revealed that in most cases, the introduction of 1,3,4-oxadiazole/thiadiazole containing halophenyl groups at the C-13 position of (+)-nootkatone could obtain more active derivatives against M. separata, M. persicae, and P. xylostella than those containing other groups. In addition, toxicity assays indicated that these (+)-nootkatone derivatives had good selectivity to insects over nontarget organisms (normal mammalian NRK-52E cells and C. idella and N. denticulata fries) with relatively low toxicity. Therefore, the above results indicate that these (+)-nootkatone derivatives could be further explored as new lead compounds for the development of potential eco-friendly pesticides.

Discovery of a Fungicide Candidate Targeting Succinate Dehydrogenase via Computational Substitution Optimization

Succinate dehydrogenase (SDH, EC 1.3.5.1) has proven to be an important fungicidal target, and the inhibition of SDH is useful in the treatment of plant pathogens. The discovery of a novel active SDH inhibitor is of high value. Herein, we disclose the discovery of a potent, highly active inhibitor as a fungicide candidate by using a computational substitution optimization method, a fast drug design method developed in our laboratory. The greenhouse experiments showed that compound 17c exhibited high protective activity against south corn rust, soybean rust (SBR), and rice sheath blight at a very low dosage of 0.781 mg/L. Moreover, the field trials indicated that compound 17c is comparable to and even better than commercial fungicides against SBR and cucumber powdery mildew at 50 mg/L concentration. Most surprisingly, compound 17c resulted to be strictly better in curative activity than the commercial fungicide benzovindiflupyr. The computation results indicated that 17c could form another hydrogen bond with C_S42 and then lead to strong van der Waals and electronic interactions with SDH. Our results suggested that 17c is a potential fungicide candidate for SDH.

Construction of spiro-1,2,4-oxadiazoline-fused matrine-type alkaloids as pesticidal agents

In order to increase the agricultural properties of matrine, a series of novel matrine-type alkaloidscontaining spiro-1,2,4-oxadiazoline fragment at the C-15 position were prepared. Eight target molecules were elucidated by X-ray single-crystal diffraction. The antifeedant activities of Ig and IIIh against Mythimna separata Walker were>1.7 folds of the precursor matrine. The acaricidal activities of Ij, IIe, IIg, IIi and IIIa against Tetranychus cinnabarinus Boisduval were 2.6-3.7 folds of matrine. Especially IIg (R¹ = R² = 4-Cl) and IIi (R¹ = 4-Cl; R² = 4-Br) exhibited the pronounced antifeedant and acaricidal activities. SARs showed that their pesticidal activities were related to the substitutents and their positions on the phenyl rings at the C-3 and N-4 positions of 1,2,4-oxadiazoline skeleton.

Synthesis, 3D-QSAR and Molecular Docking Study of Nopol-Based 1,2,4-Triazole-Thioether Compounds as Potential Antifungal Agents

Cytochrome bc 1 complex is an important component of cellular respiratory chain, and it is also an important target enzyme to inhibit the growth of plant pathogens. Using cytochrome bc 1 complex as the target enzyme, twenty-three novel nopol-based 1,2,4-triazole-thioether compounds were designed and synthesized from natural preponderant resource β-pinene, and their structures were confirmed by FT-IR, NMR, ESI-MS and elemental analysis. The in vitro antifungal activity of the target compounds 5a-5w was preliminarily evaluated against eight plant pathogens at the concentration of 50 µg/ml. The bioassay results showed that the target compounds exhibited the best antifungal activity against Physalospora piricola, in which compounds 5b (R= o-CH3 Ph), 5e (R= o-OCH3 Ph), 5h (R= o-F Ph), 5m (R= o-Br Ph), 5o (R= m,m-OCH3 Ph), and 5r (R= p-OH Ph) had inhibition rates of 91.4, 83.3, 86.7, 83.8, 91.4 and 87.3%, respectively, much better than that of the positive control chlorothalonil. Also, compound 5a (R= Ph) had inhibition rate of 87.9% against Rhizoeotnia solani, and compound 5b (R= o-CH3 Ph) had inhibition rates of 87.6 and 89% against Bipolaris maydis and Colleterichum orbicala, respectively. In order to develop novel and promising antifungal compounds against P. piricola, the analysis of three-dimensional quantitative structure-activity relationship (3D-QSAR) was carried out using the CoMFA method on the basis of their antifungal activity data, and a reasonable and effective 3D-QSAR model (r 2 = 0.944, q 2 = 0.685) has been established. In addition, the theoretical study of molecular docking revealed that the target compounds could bind to and interact with the site of cytochrome bc 1 complex.

Activity of the Novel Fungicide SYP-34773 against Plant Pathogens and Its Mode of Action on Phytophthora infestans

SYP-34773 is a pyrimidinamine derivative and a novel fungicide modified from diflumetorim. This study determined the antimicrobial spectrum of SYP-34773, which showed it could strongly inhibit the growth of some important plant pathogens including fungi and oomycetes. In particular, Phytophthora infestans is an oomycete sensitive to SYP-34773, and the mycelium growth stage was found to be the most sensitive stage, with an EC₅₀ value of 0.2030 μg/mL. At a concentration of 200 μg/mL, SYP-34773 displayed an excellent control efficacy of 69.55% and 81.48% against potato and tomato blight disease caused by P. infestans under field conditions, respectively. Mode of action investigations showed that this fungicide could cause severe ultrastructure damage to the mycelia of P. infestans, inhibit its respiration, and increase the cell membrane permeability of this pathogen. The results of this study could provide useful information for the fungicide registration and application of SYP-34773 as a novel fungicide.

Discovery of a Novel Fusarium Graminearum Mitogen-Activated Protein Kinase (FgGpmk1) Inhibitor for the Treatment of Fusarium Head Blight

Mitogen-activated protein kinase FgGpmk1 plays vital roles in the development and virulence of Fusarium graminearum (F. graminearum), the causative agent of Fusarium head blight (FHB). However, to date, the druggability of FgGpmk1 still needs verification, and small molecules targeting FgGpmk1 have never been reported. Here, we reported the discovery of a novel inhibitor 94 targeting FgGpmk1. First, a novel hit (compound 21) with an EC₅₀ value of 13.01 μg·mL^-1 against conidial germination of F. graminearum was identified through virtual screening. Then, guided by molecular modeling, compound 94 with an EC₅₀ value of 3.46 μg·mL^-1 was discovered, and it can inhibit the phosphorylation level of FgGpmk1 and influence the nuclear localization of its downstream FgSte12. Moreover, 94 can inhibit deoxynivalenol biosynthesis without any damage to the host. This study reported a group of FgGpmk1 inhibitors with a novel scaffold, which paves the way for the development of potent fungicides to FHB management.

Agrochemical properties evaluation of some imines alkaloids of matrine/oxymatrine

To discover non-food renewable forest bioactive products as new potential pesticidal alternatives for crop protection, a series of C15-imines alkaloids were obtained by structural modification of matrine and oxymatrine. Compounds Id, Ih, Ii and IIg (>2-3 folds of their precursors) showed the most potent antifeedant activity against armyworm. Against red spider mite, compounds Ie, Il, IIb, IIc and IIg displayed 1.8-3.1 folds acaricidal activity of their precursors. Notably, compound IIg exhibiting the most pronounced pesticidal activities, can be used as a promising bio-sourced agrochemical agent. The study of stress responses showed that the nAChR subunit α5 and VGSC might be the targets of action of matrine, oxymatrine and IIg against red spider mite.

Construction of Cholesterol Oxime Ether Derivatives Containing Isoxazoline/Isoxazole Fragments and Their Agricultural Bioactive Properties/Control Efficiency

To explore natural-product-based pesticidal candidates and high value-added application of cholesterol in agriculture, oximinoether derivatives of cholesterol-containing isoxazoline/isoxazole fragments (I-1∼I-16 and II-1∼II-18) were semiprepared by structural optimization of cholesterol. Their structures were characterized by optical rotation, high-resolution mass spectrometry (HRMS), IR, and ¹H NMR spectroscopy. Particularly, the Z configurations of oxime fragments at the C-7 position of target compounds were undoubtedly determined by X-ray crystallography. Against Mythimna separata Walker, compounds 3e, I-8, I-14, and II-3 showed 2.4-2.7-fold growth inhibitory activity of the precursor cholesterol. Against Plutella xylostella Linnaeus, compounds I-6, I-7, and I-9 showed 2.4-2.7-fold oral toxicity of cholesterol. Against Aphis citricola Van der Goot, compounds 2e and II-15 exhibited 4.9 and 5.8-fold aphicidal activity of cholesterol, respectively. Notably, they showed good control effects (3.0-5.0-fold promising control efficiency of 1) against A. citricola in the greenhouse. Structure-activity relationships (SARs) suggested that the C-3 hydroxyl group and the C-7 position of cholesterol are two important modification sites. It will pave the way for future structural optimization and application of cholesterol derivatives as potential pesticidal agents in agriculture.

Insecticidal activity of twin compounds from podophyllotoxin and cytisine

To explore natural-product-based insecticide candidates, and high value-added application of natural plants in agriculture, a series of twin compounds were prepared from two natural products podophyllotoxin and cytisine, which are isolated from the plants Podophyllum hexandrum and Thermopsis lanceolata, respectively. Compounds IIa (X = Cl, Y = R¹ = R² = H), IIIc (X = Y = R¹ = R² = Cl) and IVd (X = R¹ = R² = Br, Y = H) exhibited >2-fold potent insecticidal activity of podophyllotoxin against armyworm with FMRs greater than 60%. SARs were also observed. It is noteworthy that the idea of twin insecticides was addressed for the first time. We hope this idea will be conducive to design new twin insecticidal agents, and lay the foundation for future high value-added application of the plants P. hexandrum and T. lanceolata as potentially botanical pesticides in agriculture.

Catalytic Reactions and Energy Conservation in the Cytochrome bc1 and b6f Complexes of Energy-Transducing Membranes

This review focuses on key components of respiratory and photosynthetic energy-transduction systems: the cytochrome bc1 and b6f (Cytbc1/b6f) membranous multisubunit homodimeric complexes. These remarkable molecular machines catalyze electron transfer from membranous quinones to water-soluble electron carriers (such as cytochromes c or plastocyanin), coupling electron flow to proton translocation across the energy-transducing membrane and contributing to the generation of a transmembrane electrochemical potential gradient, which powers cellular metabolism in the majority of living organisms. Cytsbc1/b6f share many similarities but also have significant differences. While decades of research have provided extensive knowledge on these enzymes, several important aspects of their molecular mechanisms remain to be elucidated. We summarize a broad range of structural, mechanistic, and physiological aspects required for function of Cytbc1/b6f, combining textbook fundamentals with new intriguing concepts that have emerged from more recent studies. The discussion covers but is not limited to (i) mechanisms of energy-conserving bifurcation of electron pathway and energy-wasting superoxide generation at the quinol oxidation site, (ii) the mechanism by which semiquinone is stabilized at the quinone reduction site, (iii) interactions with substrates and specific inhibitors, (iv) intermonomer electron transfer and the role of a dimeric complex, and (v) higher levels of organization and regulation that involve Cytsbc1/b6f. In addressing these topics, we point out existing uncertainties and controversies, which, as suggested, will drive further research in this field.

Synthesis and evaluation of a large library of nitroxoline derivatives as pancreatic cancer antiproliferative agents

Pancreatic cancer (PC) is one of the deadliest carcinomas and in most cases, which are diagnosed with locally advanced or metastatic disease, current therapeutic options are highly unsatisfactory. Based on the anti-proliferative effects shown by nitroxoline, an old urinary antibacterial agent, we explored a large library of newly synthesised derivatives to unravel the importance of the OH moiety and pyridine ring of the parent compound. The new derivatives showed a valuable anti-proliferative effect and some displayed a greater effect as compared to nitroxoline against three pancreatic cancer cell lines with different genetic profiles. In particular, in silico pharmacokinetic data, clonogenicity assays and selectivity indexes of the most promising compounds showed several advantages for such derivatives, as compared to nitroxoline. Moreover, some of these novel compounds had stronger effects on cell viability and/or clonogenic capacity in PC cells as compared to erlotinib, a targeted agent approved for PC treatment.

Synthesis and fungicidal activity of methyl (E)-1-(2-((E)-2-methoxy-1-(methoxyimino)-2-oxoethyl)benzyl)-2-(1-arylidene)hydrazine-1-carboxylates †‡

To discover novel strobilurin fungicides, a series of methyl (E)-1-(2-((E)-2-methoxy-1-(methoxy-imino)-2-oxoethyl)benzyl)-2-(1-arylidene)hydrazine-1-carboxylates were designed based on the principle of biologically active splicing and the receptor target structure. The fungicidal activity results show that this class of compounds has excellent fungicidal activity, especially against S. sclerotiorum (Lib.) deBary, wheat white powder and puccinia polysora. The result of structure-activity relationship implied that the introduction of t-butyl in the side chain facilitates the hydrophobic interaction between the compound and the active site. The electrostatic effect of the substituents on the benzene ring is also a key factor affecting such activities. Among them, the compound I-1 not only showed a fungicidal effect comparable to that of kresoxim-methyl in vivo, but also had an excellent inhibitory effect on spore germination of P. oryzae Cav in vitro, which indicated that it could be used as a potential commercial fungicide for plant disease control.

Discovery of Pyrazine-Carboxamide-Diphenyl-Ethers as Novel Succinate Dehydrogenase Inhibitors via Fragment Recombination

The discovery of novel succinate dehydrogenase inhibitors (SDHIs) has attracted great attention worldwide. Herein, a fragment recombination strategy was proposed to design new SDHIs by understanding the ligand-receptor interaction mechanism of SDHIs. Three fragments, pyrazine from pyraziflumid, diphenyl-ether from flubeneteram, and a prolonged amide linker from pydiflumetofen and fluopyram, were identified and recombined to produce a pyrazine-carboxamide-diphenyl-ether scaffold as a new SDHI. After substituent optimization, compound 6y was successfully identified with good inhibitory activity against porcine SDH, which was about 2-fold more potent than pyraziflumid. Furthermore, compound 6y exhibited 95% and 80% inhibitory rates against soybean gray mold and wheat powdery mildew at a dosage of 100 mg/L in vivo assay, respectively. The results of the present work showed that the pyrazine-carboxamide-diphenyl-ether scaffold could be used as a new starting point for the discovery of new SDHIs.

Natural Compound-derived Cytochrome bc1 Complex Inhibitors as Antifungal Agents

The high incidence of fungal pathogens has become a global issue for crop protection. A promising strategy to control fungal plant infections is based on the use of nature-inspired compounds. The cytochrome bc1 complex is an essential component of the cellular respiratory chain and is one of the most important fungicidal targets. Natural products have played a crucial role in the discovery of cytochrome bc1 inhibitors, as proven by the development of strobilurins, one of the most important classes of crop-protection agents, over the past two decades. In this review, we summarize advances in the exploration of natural product scaffolds for the design and development of new bc1 complex inhibitors. Particular emphasis is given to molecular modeling-based approaches and structure-activity relationship (SAR) studies performed to improve the stability and increase the potency of natural precursors. The collected results highlight the versatility of natural compounds and provide an insight into the potential development of nature-inspired derivatives as antifungal agents.

Design, synthesis, and fungicidal evaluation of novel oxysterol binding protein inhibitors for combatting resistance associated with oxathiapiprolin

Oxathiapiprolin, the first successful oxysterol binding protein (OSBP) inhibitor for oomycete control, is regarded as an important milestone in the history of fungicide discovery. However, its interaction with OSBP remain unclear. Moreover, some plant pathogenic oomycetes have developed medium to high resistance to oxathiapiprolin. In this paper, the three-dimensional (3D) structure of OSBP from Phytophthora capsici (pcOSBP) was built, and its interaction with oxathiapiprolin was systematically investigated by integrating molecular docking, molecular dynamics simulations, and molecular mechanics Poisson-Boltzmann surface area (MM/PBSA) calculations. The computational results showed that oxathiapiprolin bound to pcOSBP forms H-bonds with Leu73, Lys74, Ser69, and water molecules. Then, based on its interaction with pcOSBP, oxathiapiprolin was structurally modified to discover new analogs with high fungicidal activity and a low risk of resistance. Fortunately, compound 1e was successfully designed and synthesized as the most potent candidate, and it showed a much lower resistance risk (RF < 1) against LP3-M and LP3-H in P. capsici. The present work indicated that the piperidinyl-thiazole-isoxazoline moiety is useful for further optimization. Furthermore, compound 1e could be used as a lead compound for the discovery of new OSBP inhibitors.

Diaryl Ether: A Privileged Scaffold for Drug and Agrochemical Discovery

Diaryl ether (DE) is a functional scaffold existing widely both in natural products (NPs) and synthetic organic compounds. Statistically, DE is the second most popular and enduring scaffold within the numerous medicinal chemistry and agrochemical reports. Given its unique physicochemical properties and potential biological activities, DE nucleus is recognized as a fundamental element of medicinal and agrochemical agents aimed at different biological targets. Its drug-like derivatives have been extensively synthesized with interesting biological features including anticancer, anti-inflammatory, antiviral, antibacterial, antimalarial, herbicidal, fungicidal, insecticidal, and so on. In this review, we highlight the medicinal and agrochemical versatility of the DE motif according to the published information in the past decade and comprehensively give a summary of the target recognition, structure-activity relationship (SAR), and mechanism of action of its analogues. It is expected that this profile may provide valuable guidance for the discovery of new active ingredients both in drug and pesticide research.

Virtual screening, synthesis, and bioactivity evaluation for the discovery of β-N-acetyl-D-hexosaminidase inhibitors

BACKGROUND

Molting is an essential insect developmental process, in which a variety of enzymes are involved. The inhibition of these enzymes effect normal insect growth and development and may even cause death. OfHex1, one of the β-N-acetyl-D-hexosaminidases, is a key enzyme involved in the molting process of the Asian corn borer (Ostrinia furnacalis), and is deemed a potential insecticidal target.

RESULTS

Based on the crystal structure of OfHex1, virtual screening was carried out to obtain a novel class of OfHex1 inhibitors, of which, 28 compounds were subjected to bioactivity evaluation. The compound 3, N-(3-cyano-4,5,6,7-tetrahydrobenzo[b]thiophen-2-yl)benzamide, showed good inhibition against OfHex1 with a K_i value of 11.2 μM. Structure optimization and molecular docking were applied for the structure-activity relationship analysis. The results also showed that the cyano group of this compound was essential for the maintenance of its inhibitory activity against OfHex1. Additionally, the interaction between this compound and Trp490, Glu328, Tyr475 and Trp524 were important for inhibitory activity.

CONCLUSION

The advantages of the derivatives of 2-amino-4,5,6,7-tetrahydrobenzo[b]thiophene-3-carbonitrile, which have simple chemical structures and are easily synthesized, suggests them to be developed further as potential OfHex1 inhibitors for pest control. © 2020 Society of Chemical Industry.

Design, Synthesis, and Structure-Activity Relationship of Economical Triazole Sulfonamide Aryl Derivatives with High Fungicidal Activity

Plant fungal diseases have caused great decreases in crop quality and yield. As one of the considerable agricultural diseases, cucumber downy mildew (CDM) caused by pseudoperonospora cubensis seriously influences the production of cucumber. Amisulbrom is a commercial agricultural fungicide developed by Nissan Chemical, Ltd., for the control of oomycetes diseases that is highly effective against CDM. However, the synthesis of amisulbrom has a high cost because of the introduction of the bromoindole ring. In addition, the continuous use of amisulbrom might increase the risk of resistance development. Hence, there is an imperative to develop active fungicides with new scaffolds but low cost against CDM. In this study, a series of 1,2,4-triazole-1,3-disulfonamide derivatives were designed, synthesized, and screened. Compound 1j showed a comparable fungicidal activity with amisulbrom, but it was low cost and ecofriendly. It has the potential to be developed as a new fungicide candidate against CDM. Further investigations of structure-activity relationship exhibited the structural requirements of 1,2,4-triazole-1,3-disulfonamide and appropriate modification in N-alkyl benzylamine groups with high fungicidal activity. This research will provide powerful guidance for the design of highly active lead compounds with a novel skeleton and low cost.

Design and synthesis of potent inhibitors of bc1 complex based on natural product neopeltolide

Neopeltolide, a natural product isolated from deep-water sponge specimen of the family neopeltidae, has been proven to be a novel inhibitor of cytochrome bc₁. In this study, a series of neopeltolide derivatives was designed by replacing the 14-membered macrolactone with indole ring and confirmed by ¹H NMR, ¹³C NMR, and HRMS. Based on the binding mode of 12h with bc₁ complex, the IC₅₀ values of compounds 16a-f (ranging from 0.70 to 1.46 μM) were improved significantly than the ester derivatives 12a-u by replacing the ester with amide linker. Subsequently, the molecular docking results indicated that compound 16e could form a π-π interaction with Phe274 and two H-bonds with Glu271 and His161 and the latter H-bond was found to account for its high activity. The present work accelerates the discovery of novel bc₁ complex inhibitors to deal with the resistance that the existing bc₁ complex inhibitors are facing and provides a valuable idea for the design of new fungicides.

Marine Natural Products with High Anticancer Activities

This review covers recent literature from 2012-2019 concerning 170 marine natural products and their semisynthetic analogues with strong anticancer biological activities. Reports that shed light on cellular and molecular mechanisms and biological functions of these compounds, thus advancing the understanding in cancer biology are also included. Biosynthetic studies and total syntheses, which have provided access to derivatives and have contributed to the proper structure or stereochemistry elucidation or revision are mentioned. The natural compounds isolated from marine organisms are divided into nine groups, namely: alkaloids, sterols and steroids, glycosides, terpenes and terpenoids, macrolides, polypeptides, quinones, phenols and polyphenols, and miscellaneous products. An emphasis is placed on several drugs originating from marine natural products that have already been marketed or are currently in clinical trials.

Preparation of Matrinic/Oxymatrinic Amide Derivatives as Insecticidal/Acaricidal Agents and Study on the Mechanisms of Action against Tetranychus cinnabarinus

In continuation of our program to develop natural-product-based pesticidal candidates, matrinic/oxymatrinic amides were obtained through structural optimization of matrine. N'-(4-Fluoro)phenyl-N-(4-bromo)phenylsulfonyloxymatrinic amide (IIm) showed potent insecticidal activity against Mythimna separata. N-(Un)substituted phenylsulfonylmatrinic acids (3a-c) exhibited promising acaricidal activity against Tetranychus cinnabarinus. By qRT-PCR analysis of nAChR subunits and AChE genes and determination of AChE activity of (un)treated T. cinnabarinus, it suggested that the open lactam ring of matrine and carboxyl group and (4-methyl)phenylsulfonyl of N-(4-methyl)phenylsulfonylmatrinic acid (3b) were necessary for action with α2, α4, α5, and β3 nAChR subunits; compound 3b was an inhibitor of AChE in T. cinnabarinus, and AChE was one possible target of action in T. cinnabarinus against 3b; and compound 3b may be an antagonist of nAChR and AChE in T. cinnabarinus.

Fragment-based drug design of nature-inspired compounds

Natural product (NP)-derived drugs can be extracts, biological macromolecules, or purified small molecule substances. Small molecule drugs can be originally purified from NPs, can represent semisynthetic molecules, natural fragments containing small molecules, or are fully synthetic molecules that mimic natural compounds. New semisynthetic NP-like drugs are entering the pharmaceutical market almost every year and reveal growing interests in the application of fragment-based approaches for NPs. Thus, several NP databases were constructed to be implemented in the fragment-based drug design (FBDD) workflows. FBDD has been established previously as an approach for hit identification and lead generation. Several biophysical and computational methods are used for fragment screening to identify potential hits. Once the fragments within the binding pocket of the protein are identified, they can be grown, linked, or merged to design more active compounds. This work discusses applications of NPs and NP scaffolds to FBDD. Moreover, it briefly reviews NP databases containing fragments and reports on case studies where the approach has been successfully applied for the design of antimalarial and anticancer drug candidates.

Design and Synthesis of Anti-Cancer Chimera Molecules Based on Marine Natural Products

In this paper, the chemical conjugation of marine natural products with other bioactive molecules for developing an advanced anti-cancer agent is described. Structural complexity and the extraordinary biological features of marine natural products have led to tremendous research in isolation, structural elucidation, synthesis, and pharmacological evaluation. In addition, this basic scientific achievement has made it possible to hybridize two or more biologically important skeletons into a single compound. The hybridization strategy has been used to identify further opportunities to overcome certain limitations, such as structural complexity, scarcity problems, poor solubility, severe toxicity, and weak potency of marine natural products for advanced development in drug discovery. Further, well-designed marine chimera molecules can function as a platform for target discovery or degradation. In this review, the design, synthesis, and biological evaluation of recent marine chimera molecules are presented.