Synthesis, Nematicidal Evaluation, and 3D-QSAR Analysis of Novel 1,3,4-Oxadiazole-Cinnamic Acid Hybrids

Synthesis and agricultural antimicrobial evaluation of new quinazoline derivatives containing both a piperazine linker and the N-acetyl moiety

BACKGROUND

To discover more efficient agricultural antimicrobial agents, a series of new quinazoline derivatives containing both a piperazine linker and the N-acetyl moiety were prepared and assessed for their antibacterial and antifungal activities.

RESULTS

All the target compounds were characterized by 1H and 13C NMR as well as high-resolution mass spectrometry (HRMS), and the chemical structure of the most potent compound E19 incorporating a 4-trifluoromethoxy substituent was clearly confirmed via single crystal X-ray diffraction measurements. The bioassay results indicated that some compounds possessed notable inhibitory effects in vitro against the bacterium Xanthomonas oryzae pv. oryzicola (Xoc). For example, compound E19 had an EC50 (effective concentration for 50% activity) value of 7.1 μg/mL towards this pathogen, approximately 15- and 10-fold more effective than the commercial bactericides thiodiazole copper and bismerthiazol (EC50 = 110.2 and 72.4 μg/mL, respectively). Subsequently, the mechanistic studies showed that compound E19 likely exerted its antibacterial efficacies by altering the cell morphology, increasing the permeability of bacterial cytoplasmic membrane, suppressing the production of bacterial extracellular polysaccharides and the extracellular enzyme activities (amylase and cellulase), and blocking the swimming motility of Xoc. Moreover, the proteomic analysis revealed that compound E19 could reduce the bacterial flagellar biosynthesis and decrease the flagellar motility by down-regulating the expression of the related differential proteins.

CONCLUSION

Compound E19 exhibited good potential for further development as a bactericide candidate for control of Xoc. © 2024 Society of Chemical Industry.

Synthesis, biological evaluation, and molecular docking of novel ferulic acid derivatives containing a 1,3,4-oxadiazole thioether and trifluoromethyl pyrimidine skeleton

In this study, 24 novel ferulic acid derivatives containing 1,3,4-oxadiazole thioether and trifluoromethyl pyrimidine were designed and synthesized. Bioactivity assay showed that some of the target compounds exhibited moderate to good antifungal activity against Botryosphaeria dothidea BD), Phomopsis sp. (PS), Botrytis cinerea (BC), Fusarium spp. (FS), Fusarium graminearum (FG), and Colletotrichum sp. (CS). Especially, compound 6f demonstrated superior antifungal activity against Phomopsis sp., with an EC50 value of 12.64 μg mL-1, outperforming pyrimethanil (35.16 μg mL-1) and hymexazol (27.01 μg mL-1). Meanwhile, compound 6p showed strong antibacterial activity against X. axonopodis pv. citri (XAC) in vitro, with an inhibition ratio of 85.76%, which was higher than thiodiazole copper's 76.59% at 100 μg mL-1. Furthermore, molecular docking simulations elucidated that compound 6f engaged in hydrogen bonding with the succinate dehydrogenase (SDH) enzyme at SER-17, SER-39, ARG-14 and ARG-43 sites, clarifying its mode of action. This study highlights the potential of these novel ferulic acid derivatives as promising agents for controlling fungal and bacterial threats to plant health. To the best of our knowledge, this study represents the first report on the antifungal and antibacterial properties of ferulic acid derivatives containing 1,3,4-oxadiazole thioether and trifluoromethyl pyrimidine skeleton.

Discovery of Cadinane-Type Sesquiterpenoids from the Infected Stems of Hibiscus tiliaceus as Potential Agrochemical Fungicides

Ten new cadinane-type sesquiterpenoids, named hibisceusins I-R (1-10), along with 14 known sesquiterpenoids (11-24), were acquired from the tainted stems of Hibiscus tiliaceus. Their structures were identified via spectroscopic analysis, one-dimensional (1D) and two-dimensional (2D) NMR, and computer-assisted structure elucidation techniques, including infrared (IR) and mass spectrometry (MS) data. Additionally, subsequent DP4/DP4+ probability methods were used to resolve 3's relative configurations by comparing their experimental values to the predicted NMR data. The absolute configurations of compounds 1-4 were measured through electronic circular dichroism (ECD) spectra. The ability of all isolates to inhibit the growth of five phytopathogenic fungi (Rhizopus stolonifer, Verticillium dahliae Kleb., Thanatephorus cucumeris, Fusarium oxysporum Schltdl., and F. oxysporum HK-27) was evaluated. Aldehydated sesquiterpenoids (1, 6-9, 11, 12, and 22) and a known sesquiterpenoid quinine (18) exhibited significant inhibitory activities against V. dahliae, T. cucumeris, F. oxysporum, and F. oxysporum HK-27 with minimum inhibitory concentration (MIC) values of 2.5-50 μg/mL, but all isolates remained inactive against R. stolonifer. Moreover, the effects of the isolates on the mycelial morphology were watched through scanning electron microscopy. This study revealed that aldehydated cadinane-type sesquiterpenoids could be used as novel antifungal molecules to develop agrochemical fungicides in plant protection.

Synthesis, Bioactivities, and Antibacterial Mechanism of 5-(Thioether)-N-phenyl/benzyl-1,3,4-oxadiazole-2-carboxamide/amine Derivatives

1,3,4-Oxadiazole thioethers have shown exciting antibacterial activities; however, the current mechanism of action involving such substances against bacteria is limited to proteomics-mediated protein pathways and differentially expressed gene analysis. Herein, we report a series of novel 1,3,4-oxadiazole thioethers containing a carboxamide/amine moiety, most of which show good in vitro and in vivo bacteriostatic activities. Compounds A10 and A18 were screened through CoMFA models as optimums against Xanthomonas oryzae pv. oryzae (Xoo, EC50 values of 5.32 and 4.63 mg/L, respectively) and Xanthomonas oryzae pv. oryzicola (Xoc, EC50 values of 7.58 and 7.65 mg/L, respectively). Compound A10 was implemented in proteomic techniques and activity-based protein profiling (ABPP) analysis to elucidate the antibacterial mechanism and biochemical targets. The results indicate that A10 disrupts the growth and pathogenicity of Xoc by interfering with pathways associated with bacterial virulence, including the two-component regulation system, flagellar assembly, bacterial secretion system, quorum sensing, ABC transporters, and bacterial chemotaxis. Specifically, the translational regulator (CsrA) and the virulence regulator (Xoc3530) are two effective target proteins of A10. Knocking out the CsrA or Xoc3530 gene in Xoc results in a significant reduction in the motility and pathogenicity of the mutant strains. This study contributes available molecular entities, effective targets, and mechanism basis for the management of rice bacterial diseases.

Design, Synthesis, Nematicidal Activity, and Mechanism of Novel Amide Derivatives Containing an 1,2,4-Oxadiazole Moiety

To discover new nematicides, a series of novel amide derivatives containing 1,2,4-oxadiazole were designed and synthesized. Several compounds showed excellent nematicidal activity. The LC50 values of compounds A7, A18, and A20-A22 against pine wood nematode (Bursaphelenchus xylophilus), rice stem nematode (Aphelenchoides besseyi), and sweet potato stem nematode (Ditylenchus destructor) were 1.39-3.09 mg/L, which were significantly better than the control nematicide tioxazafen (106, 49.0, and 75.0 mg/L, respectively). Compound A7 had an outstanding inhibitory effect on nematode feeding, reproductive ability, and egg hatching. Compound A7 effectively promoted the oxidative stress of nematodes and caused intestinal damage to nematodes. Compound A7 significantly inhibited the activity of succinate dehydrogenase (SDH) in nematodes, leading to blockage of electron transfer in the respiratory chain and thereby hindering the synthesis of adenosine triphosphate (ATP), which consequently affects the entire oxidative phosphorylation process to finally cause nematode death. Therefore, compound A7 can be used as a potential SDH inhibitor in nematicide applications.

Synthesis, X-ray Crystal Structure, and Antimicrobial Studies of New Quinazolin-4(3H)-one Derivatives Containing the 1,2,4-Triazolo[3,4-b][1,3,4]thiadiazole Moiety and 4-Piperidinyl Linker

A total of 35 new quinazolinone derivatives bearing the 1,2,4-triazolo[3,4-b][1,3,4]thiadiazole scaffold and the 4-piperidinyl linker were designed, prepared, and assessed for their antibacterial and antifungal activities. Among these derivatives, the chemical structure of compound F5 was clearly verified via single-crystal X-ray diffraction analysis. The experimental results revealed that some of the compounds displayed good even excellent inhibitory effects toward the tested phytopathogenic bacteria. For instance, compound F33 was capable of strongly inhibiting Xanthomonas oryzae pv. oryzae (Xoo) in vitro with an EC50 (half-maximal effective concentration) value of 4.1 μg/mL, about 16-fold more effective than the commercialized bactericide bismerthiazol. Significantly, this compound also effectively suppressed the proliferation of Xoo in the potted rice plants, showing a good in vivo protection efficacy of 47.6% at 200 μg/mL. Subsequently, the antibacterial mechanisms of compound F33 were explored by means of different biophysical and biochemical methods. Last, some of the compounds were found to possess relatively good antifungal activities in vitro, like compound F19 against Phytophthora nicotianae (with an inhibition rate of 67.2% at 50 μg/mL). In a word, the current experimental results imply that the 4-piperidinyl-bridged quinazolinone-1,2,4-triazolo[3,4-b][1,3,4]thiadiazole derivatives possess potential as lead compounds for developing more efficient anti-Xoo bactericides.

Design, synthesis, and antimicrobial evaluation of 2-aminothiazole derivatives bearing the 4-aminoquinazoline moiety against plant pathogenic bacteria and fungi

BACKGROUND

To find more effective agricultural antibiotics, a class of new 2-aminothiazole derivatives containing the 4-aminoquinazoline moiety were synthesized and evaluated for their antimicrobial properties against phytopathogenic bacteria and fungi of agricultural importance.

RESULTS

All the target compounds were fully characterized by 1 H NMR, 13 C NMR, and high-resolution mass spectrometry. The bioassay results showed that compound F29 with a 2-pyridinyl substituent exhibited an outstanding antibacterial effect against Xanthomonas oryzae pv. oryzicola (Xoc) in vitro, having an half-maximal effective concentration (EC50 ) value as low as 2.0 μg/mL (over 30-fold more effective than the commercialized agrobactericide bismerthiazol, with an EC50 value of 64.3 μg/mL). In addition, compound F8 with a 2-fluorophenyl group demonstrated a good inhibitory activity toward the bacterium Xanthomonas axonopodis pv. citri (Xac), around twofold more active than bismerthiazol in terms of their EC50 values (22.8 versus 71.5 μg/mL). Interestingly, this compound also demonstrated a notable fungicidal effect against Phytophthora parasitica var. nicotianae, with an EC50 value largely comparable with that of the commercialized fungicide carbendazim. Finally, mechanistic studies revealed that compound F29 exerted its antibacterial effects by increasing the permeability of bacterial membranes, reducing the release of extracellular polysaccharides, and triggering morphological changes of bacterial cells.

CONCLUSION

Compound F29 has promising potential as a lead compound for developing more efficient bactericides to fight against Xoc. © 2023 Society of Chemical Industry.

Structural optimization based on 4,5-dihydropyrazolo[1,5-a]quinazoline scaffold for improved insecticidal activities

The long-term and irrational application of insecticides has increased the rate of development of pest resistance and caused numerous environmental issues. To address these problems, our previous work reported that 4,5-dihydropyrazolo[1,5-a]quinazoline (DPQ) is a class of gelled heterocyclic compounds that act on insect γ-aminobutyric acid receptors (GABAR). DPQ scaffold has no cross-resistance to existing insecticides, so the development of this scaffold is an interesting task for integrated pest management. In the present study, a novel series of 4,5-dihydropyrazolo[1,5-a]quinazolines (DPQs) were designed and synthesized based on pyraquinil, a highly insecticidal compound discovered in our previous work. Insecticidal activities of the target compounds against diamondback moth (Plutella xylostella), beet armyworm (Spodoptera exigua), fall armyworm (Spodoptera frugiperda), and red imported fire ant (Solenopsis invicta Buren) were evaluated. Compounds 6 and 12 showed the best insecticidal activity against Plutella xylostella (P. xylostella) (LC50 = 1.49 and 0.97 mg/L), better than pyraquinil (LC50 = 1.76 mg/L), indoxacarb and fipronil (LC50 = 1.80 mg/L). Meanwhile, compound 12 showed slow toxicity to Solenopsis invicta Buren (S. invicta), with a 5 d mortality rate of 98.89% at 0.5 mg/L that is similar to fipronil. Moreover, Electrophysiological studies against the PxRDL1 GABAR heterologously expressed in Xenopus oocytes indicated that compound 12 could act as a potent GABA receptor antagonist (2 μΜ, inhibition rate, 68.25%). Molecular docking results showed that Ser285 (chain A) and Thr289 (chain D) of P. xylostella GABAR participated in hydrogen bonding interactions with compound 12, and density functional theory (DFT) calculations suggested the importance of pyrazolo[1,5-a]quinazoline core in potency. This systematic study provides valuable clues for the development of DPQ scaffold in the field of agrochemicals, and compound 12 can be further developed as an insecticide and bait candidate.

Research Progress of Benzothiazole and Benzoxazole Derivatives in the Discovery of Agricultural Chemicals

Benzoxazole and benzothiazole have a broad spectrum of agricultural biological activities, such as antibacterial, antiviral, and herbicidal activities, which are important fused heterocyclic scaffold structures in agrochemical discovery. In recent years, great progress has been made in the research of benzoxazoles and benzothiazoles, especially in the development of herbicides and insecticides. With the widespread use of benzoxazoles and benzothiazoles, there may be more new products containing benzoxazoles and benzothiazoles in the future. We systematically reviewed the application of benzoxazoles and benzothiazoles in discovering new agrochemicals in the past two decades and summarized the antibacterial, fungicidal, antiviral, herbicidal, and insecticidal activities of the active compounds. We also discussed the structural-activity relationship and mechanism of the active compounds. This work aims to provide inspiration and ideas for the discovery of new agrochemicals based on benzoxazole and benzothiazole.

Synthesis, Antifungal Evaluation, 3D-QSAR, and Preliminarily Mechanism Study of Novel Chiral Mandelic Acid Derivatives

To investigate the effect of spatial configuration on the biological activity of the compounds, a series of chiral mandelic acid derivatives with a moiety of 1,3,4-oxadiazole thioether have been designed and synthesized. Bioassay results demonstrated that most title compounds with the S-configuration exhibited better in vitro antifungal activity against three plant fungi, such as H3' (EC₅₀ = 19.3 μg/mL) against Gibberella saubinetii, which was approximately 16 times higher than that of H3 (EC₅₀ = 317.0 μg/mL). CoMFA and CoMSIA models were established for 3D-QSAR analysis and provided an important support for further optimization of this series of compounds. Comparing the preliminary mechanism studies between enantiomers (H3 and H3') found that the S-configuration compound (H3') exhibited a stronger ability to destroy the surface structure of G. saubinetii mycelia, causing the leakage of intracellular substances to accelerate and the growth of the hyphae to be inhibited. The results provided a novel view for the further optimization of this series of active compounds and deep mechanism study of chiral pesticides.

Systematic Study on Turpentine-Derived Amides from Natural Plant Monoterpenes as Potential Antifungal Candidates

To overcome the high volatility, low aqueous solubility, and few definite action sites of monoterpenoid pesticides and improve their properties and effectiveness in the control of crop pathogenic fungi, herein, a series of natural turpentine-based amide derivatives exhibiting satisfactory antifungal activity were designed and synthesized. A systematic study was conducted on antifungal activity and the physiological and biochemical response of compounds 5o (EC₅₀ = 1.139 μg/mL) and 5j (EC₅₀ = 1.762 μg/mL) against Rhizoctonia solani. The effect of the target compound on the potential target-site succinate dehydrogenase was evaluated. The soluble concentrates of compounds 5o and 5j possessing good performance and control effects were prepared for practical application. To conduct a comprehensive analysis of the relationship between structural descriptors and activity, four representative title compounds were selected for theoretical calculation: 5o, 5j, 5k, and 5j. The binding mode of compound 5o and boscalid with succinate dehydrogenase was analyzed via molecular docking. This study provides a reference for the development of monoterpene pesticides with high efficiency, elucidated target sites, and the appropriate formula.

New Inspiration of 1,3,4-Oxadiazole Agrochemical Candidates: Manipulation of a Type III Secretion System-Induced Bacterial Starvation Mechanism to Prevent Plant Bacterial Diseases

Discovering new anti-virulent agents to control plant bacterial diseases by preventing bacterial pathogenesis/pathogenicity rather than affecting bacterial growth is a sensible strategy. However, the effects of compound-manipulated bacterial virulence factors on host response are still not clear. In this work, 35 new 1,3,4-oxadiazole derivatives were synthesized and systematically evaluated for their anti-phytopathogenic activities. Bioassay results revealed that compound C₇ possessed outstanding antibacterial activity in vitro (half-maximal effective concentration: 0.80 μg/mL) against Xanthomonas oryzae pv. oryzae (Xoo) and acceptable bioactivity in vivo toward rice bacterial leaf blight. Furthermore, virulence factor-related biochemical assays showed that C₇ was a promising anti-virulent agent. Interestingly, C₇ could indirectly reduce the inducible expression of host SWEET genes and thereby alleviate nutrient supply in the infection process of phytopathogenic bacteria. Our results highlight the potential of 1,3,4-oxadiazole-based agrochemicals for manipulating type III secretion system-induced phytopathogenic bacteria starvation mechanisms to prevent plant bacterial diseases.

Discovery of Novel Quinazoline-2-Aminothiazole Hybrids Containing a 4-Piperidinylamide Linker as Potential Fungicides against the Phytopathogenic Fungus Rhizoctonia solani

A total of 29 novel quinazoline-2-aminothiazole hybrids containing a 4-piperidinylamide linker were designed, synthesized, and evaluated for their anti-microbial properties against phytopathogenic fungi and bacteria of agricultural importance. The anti-fungal assays indicated that some of the target compounds exhibited excellent inhibitory effects in vitro against Rhizoctonia solani. For example, 11 compounds within this series (including 4a, 4g, 4h, 4j, 4o, 4s, 4t, 4u, 4v, 4y, and 4b') were found to possess EC₅₀ values (effective concentration for 50% activity) ranging from 0.42 to 2.05 μg/mL against this pathogen. In particular, compound 4y with a 2-chloro-6-fluorophenyl substituent displayed a potent anti-R. solani efficacy with EC₅₀ = 0.42 μg/mL, nearly threefold more effective than the commercialized fungicide Chlorothalonil (EC₅₀ = 1.20 μg/mL) and also slightly superior to the other fungicide Carbendazim (EC₅₀ = 0.53 μg/mL). Moreover, compound 4y could efficiently inhibit the growth of R. solani in vivo on the potted rice plants, displaying an impressive protection efficacy of 82.3% at 200 μg/mL, better than those of the fungicides Carbendazim (69.8%) and Chlorothalonil (48.9%). Finally, the mechanistic studies showed that compound 4y exerted its anti-fungal effects by altering the mycelial morphology, increasing the cell membrane permeability, and destroying the cell membrane integrity. On the other hand, some compounds demonstrated good anti-bacterial effects in vitro against Xanthomonas oryzae pv. oryzae (Xoo). Overall, the presented results implied that 4-piperidinylamide-bridged quinazoline-2-aminothiazole hybrids held the promise of acting as lead compounds for developing more efficient fungicides to control R. solani.

MIA-QSAR analysis of an increased data set of 1,3,4-oxa/thiadiazole nematicides to enhance the molecular diversity and agrochemical candidacy

Tylenchulus semipenetrans nematodes affect citrus crops and may develop resistance to commercially available nematicides. In this sense, two series of 1,3,4-oxa- and thiadiazole compounds have been recently synthesised and tested as nematicides against T. semipenetrans, demonstrating promising results. We report herein a molecular modelling study that combines these two series of congeneric compounds to form a single and enhanced data set. The chemical structures of these compounds were correlated with the respective nematicidal activities (pLC50) using multivariate image analysis (MIA) descriptors in quantitative structure-activity relationship (QSAR) analysis. The partial least squares (PLS) regression yielded reliable and predictive models (, , and ). Therefore, novel 1,3,4-oxa- and thiadiazole derivatives were proposed and a few of them exhibited predicted nematicidal performance better than those of the parent compounds.

Design, Synthesis and in Vitro Antifungal Mechanism of Novel Phenylalanine Derivatives

To explore novel molecules with unique mechanisms against plant pathogenic fungi, a series of phenylalanine derivatives containing a 1,3,4-oxadiazothioether moiety were designed and synthesized. Bioassays revealed that some target compounds at 100 μg/mL exhibited excellent antifungal activities against Thanatephorus cucumeris, such as G₆ (92.1 %), G₁₀ (94.3 %), G₁₈ (99.1 %), and G₁₉ (98.7 %), better than that of the commercial fungicide azoxystrobin (90.6 %), and the EC₅₀ value of G₁₀ against T. cucumeris was 31.9 μg/mL. Further mechanism studies of T. cucumeris treated with G₁₀ demonstrated that this compound can affect the growth of mycelia by disrupting the integrity of the membrane, and the higher the concentration of the compound is, the greater the degree of membrane integrity damage, similar to the commercial fungicide azoxystrobin. These conclusions provide important information for further mechanism studies of this series of phenylalanine derivatives.

Nematicidal activity of furanoeremophilenes against Meloidogyne incognita and Nacobbus aberrans

BACKGROUND

While searching for novel small molecules for new organic pesticide agents against plant-parasitic nematodes, we found that the hexane extract from the roots of Senecio sinuatos and its main secondary metabolite, 3β-angeloyloxy-6β-hydroxyfuranoeremophil-1(10)-ene (1), possess nematicidal activity against the second stage juvenile (J2) of Meloidogyne incognita and Nacobbus aberrans. Both species reduce yield of various vegetable crops. These results encouraged us to synthesize esters 3-9 formed by diol 2, obtained by alkaline hydrolysis of 1 and acetic anhydride, benzoic acid, 2-nitrobenzoic acid, 2-bromobenzoic acid, 4-nitrobenzoic acid, 4-bromobenzoic acid, and 4-methoxybenzoic acid, respectively. The nematicidal activity of these esters was evaluated and compared with that of the free benzoic acids.

RESULTS

Natural product 1 and derivatives 2-9 were obtained and characterized by their physical and spectroscopic properties, including one-dimensional (1D) and two-dimensional (2D) nuclear magnetic resonance (NMR) experiments; X-ray diffraction analysis established their absolute configuration. The nematicidal activity of compounds 1-9 was assessed in vitro against M. incognita and N. aberrans J2 and was compared to activity shown by benzoic acid, 2-nitrobenzoic acid, 2-bromobenzoic acid, 4-nitrobenzoic acid, 4-bromobenzoic acid, and 4-methoxybenzoic acid. The esters suppressed nematodes more than free benzoic acid. Nacobbus aberrans J2 were suppressed, with compounds 5, 6, and 8 being the most active.

CONCLUSION

Esters formed by 3β,6β-dihydroxyfuranoeremophil-1(10)-ene and ortho- or para-substituted benzoic acids containing electron acceptor groups had nematicidal activity against N. aberrans. These compound can potentially serve as a model for the development of new organic nematicidal agents. © 2022 Society of Chemical Industry.

Synthesis, Antifungal Activity and 3D-QSAR Study of Novel Anisaldehyde-Derived Amide-Thiourea Compounds

Succinate dehydrogenase (SDH) is an important target enzyme for designing agricultural chemical fungicides. In order to explore novel natural product-based antifungal agents, twenty-one unreported anisaldehyde-derived amide-thiourea compounds were designed and synthesized using the principle of active splicing, and structurally confirmed by ¹ H-NMR, ¹³ C-NMR, ESI-MS, FT-IR, and element analysis. In vitro antifungal activity of the target compounds was evaluated by the agar dilution method. The results showed that some target compounds exhibited better or comparable antifungal activity than that of the commercial fungicide chlorothalonil, in which compounds 5c, 5o, and 5r displayed excellent antifungal activity of 92.6 %, 92.6 % and 99.1 % against P. piricola, respectively, better than that of the positive control. In addition, 3D-QSAR analysis was carried out by the CoMFA method to reveal the relationship between the structures of the target compounds and their inhibitory activities. The simulative binding mode of the target compounds and SDH was also studied by molecular docking.

Thiophenes-Naturally Occurring Plant Metabolites: Biological Activities and In Silico Evaluation of Their Potential as Cathepsin D Inhibitors

Naturally, thiophenes represent a small family of natural metabolites featured by one to five thiophene rings. Numerous plant species belonging to the family Asteraceae commonly produce thiophenes. These metabolites possessed remarkable bioactivities, including antimicrobial, antiviral, anti-inflammatory, larvicidal, antioxidant, insecticidal, cytotoxic, and nematicidal properties. The current review provides an update over the past seven years for the reported natural thiophene derivatives, including their sources, biosynthesis, spectral data, and bioactivities since the last review published in 2015. Additionally, with the help of the SuperPred webserver, an AI (artificial intelligence) tool, the potential drug target for the compounds was predicted. In silico studies were conducted for Cathepsin D with thiophene derivatives, including ADMET (drug absorption/distribution/metabolism/excretion/and toxicity) properties prediction, molecular docking for the binding interaction, and molecular dynamics to evaluate the ligand-target interaction stability under simulated physiological conditions.

Synthesis, Structural Characterization, and Antibacterial and Antifungal Activities of Novel 1,2,4-Triazole Thioether and Thiazolo[3,2-b]-1,2,4-triazole Derivatives Bearing the 6-Fluoroquinazolinyl Moiety

A total of 52 novel 1,2,4-triazole thioether and thiazolo[3,2-b]-1,2,4-triazole derivatives bearing the 6-fluoroquinazolinyl moiety were designed, synthesized, and evaluated as antimicrobial agents in agriculture based on the molecular hybridization strategy. Among them, molecular structures of compounds 5g and 6m were further confirmed via the single-crystal X-ray diffraction method. The bioassay results indicated that some of the target compounds possessed excellent antibacterial activities in vitro against the pathogen Xanthomonas oryzae pv. oryzae (Xoo). For example, compound 6u demonstrated a strong anti-Xoo efficacy with an EC₅₀ value of 18.8 μg/mL, nearly 5-fold more active than that of the commercialized bismerthiazol (EC₅₀ = 93.6 μg/mL). Moreover, the anti-Xoo mechanistic studies revealed that compound 6u exerted its antibacterial effects by increasing the permeability of bacterial membrane, reducing the content of extracellular polysaccharide, and inducing morphological changes of bacterial cells. Importantly, in vivo assays revealed its pronounced protection and curative effects against rice bacterial blight, proving its potential as a promising bactericide candidate for controlling Xoo. Moreover, compound 6u had a good pesticide-likeness based on Tice's criteria. More interestingly, compound 6u with high anti-Xoo activity also demonstrated a potent inhibitory effect of 80.8% against the fungus Rhizoctonia solani at 50 μg/mL, comparable to that of the commercialized chlorothalonil (85.9%). Overall, the current study will provide useful guidance for the rational design of more efficient agricultural antimicrobial agents using the thiazolo[3,2-b]-1,2,4-triazole derivatives bearing the 6-fluoroquinazolinyl moiety as lead compounds.

Synthesis, Anti-Tomato Spotted Wilt Virus Activities, and Interaction Mechanisms of Novel Dithioacetal Derivatives Containing a 4(3H)-Quinazolinone Pyrimidine Ring

A series of unreported novel dithioacetal derivatives containing a 4(3H)-quinazolinone pyrimidine ring were synthesized, and their antiviral activities were evaluated against tomato spotted wilt virus (TSWV). A three-dimensional quantitative structure-activity relationship (3D-QSAR) analysis was established, and compound D32 was designed and synthesized according to the analysis results of the CoMFA and CoMSIA models. The bioassay results showed that compound D32 exhibited excellent inactivation activity against TSWV, with EC₅₀ values of 144 μg/mL, which was better than those of ningnanmycin (149 μg/mL) and the lead compound xiangcaoliusuobingmi (525 μg/mL). The binding ability of compound D32 to TSWV CP was tested by microscale thermophoresis (MST), and the binding constant value was 4.4 μM, which was better than those of ningnanmycin (6.2 μM) and xiangcaoliusuobingmi (59.1 μM). Therefore, this study indicates that novel dithioacetal derivatives containing a 4(3H)-quinazolinone pyrimidine ring may be applied as new antiviral agents.

Novel Cinnamic Acid Derivatives Containing the 1,3,4-Oxadiazole Moiety: Design, Synthesis, Antibacterial Activities, and Mechanisms

There is a lack of effective antibacterial agents against rice bacterial leaf streak and leaf blight. Cinnamic acid derivatives containing the 1,3,4-oxadiazole moiety were synthesized, and their antibacterial activities against Xanthomonas oryzae pv. oryzicola (Xoc) and X. oryzae pv. oryzae (Xoo) were evaluated. Based on the three-dimensional quantitative structure-activity relationship (3D-QSAR) model, compound 31 with better antibacterial activity against Xoc was designed and synthesized, and the 50% effective concentration (EC₅₀) value was 0.2 mg/L. The curative and protective activities of compound 31 against rice bacterial leaf streak at 100 mg/L were 39.5 and 35.4%, respectively, which were higher than those of thiodiazole copper (28.4 and 20.7%, respectively). The antibacterial activity of compound 31 against rice bacterial leaf streak is closely associated with the activity of related defensive enzymes and the increase in glutathione metabolism.

Novel amide derivatives containing an imidazo[1,2-a]pyridine moiety: Design, synthesis as potential nematicidal and antibacterial agents

To discover new nematicides, a series of novel amide derivatives containing an imidazo[1,2-a]pyridine moeity were designed and synthesized. Among the title compounds, compounds 3 and 27 exhibited good nematicidal activities against Aphelenchoides besseyi (rice white-tip nematode), with LC₅₀ values against of 27.3 and 35.9 mg/L, respectively, which were superior to that of fosthiazate (45.4 mg/L). Meanwhile, the LC₅₀ value of compound 27 against Caenorhabditis elegans was 5.7 mg/L, which was superior to that of fosthiazate (77.2 mg/L). Compound 27 not only binds well to acetylcholinesterase (AChE) of nematodes, but also has a good inhibitory activity against AChE. Thus, AChE may be a potential target of compound 27 against nematodes. Unexpectedly, compound 28 exhibited excellent antibacterial activities with EC₅₀ values of 1.2 and 3.1 mg/L against Xanthomonas oryzae pv. oryzae (Xoo) and Xanthomonas oryzae pv. oryzicola (Xoc), respectively, which were superior to those of bismerthiazol (68.6 and 77.1 mg/L) and thiodiazole copper (80.8 and 96.6 mg/L). The curative and protective activities of compound 28 against bacterial leaf blight were 37.0% and 36.8% at 50 mg/L, respectively, which were higher than those of thiodiazole copper (16.1% and 15.5%). In addition, compound 28 may inhibit the growth of Xoo by affecting the production of cell membranes and extracellular polysaccharides. Amide derivatives containing an imidazo[1,2-a]pyridine moeity can be used as good lead-structures to discover new nematicidal and antibacterial agents in the future.

Design, synthesis and antifungal evaluation of novel mandelic acid derivatives containing a 1,3,4-oxadiazothioether moiety

A series of novel mandelic acid derivatives containing a 1,3,4-oxadiazothioether moiety were designed and synthesized. Bioassay results showed that some target compounds exhibited certain antifungal activity against six kinds of pathogenic fungi in vitro. Among the compounds, the EC₅₀ values of T₄₁ against Gibberella saubinetii, Verticillium dahlia and Sclerotinia sclerotiorum were 31.0, 27.0 and 32.1 μg/ml, respectively, and the EC₅₀ value of T₁₄ against S. sclerotiorum was 14.7 μg/ml. The antifungal activity against the resistant fungus S. sclerotiorum indicated that this series of target compounds may have the similar action modes or sites as the commercialized succinate dehydrogenase inhibitor carboxin. A morphological study with fluorescence microscope demonstrated that T₄₁ can significantly destroy the membrane integrity of G. saubinetii.

Design, synthesis, and biological activity of novel 1,2,4-oxadiazole derivatives

Background

Plant diseases seriously threaten food security, it is urgent to discover efficient and low-risk chemical pesticides. 1,2,4-Oxadiazole derivatives exhibit broad spectrum of agricultural biological activities. For discovering novel molecules with excellent agricultural activities, novel 1,2,4-oxadiazole derivatives were synthesized and evaluated for their agricultural activities.

Result

Bioassays results showed that the title compounds exhibited moderate nematocidal activity against Meloidogyne incognita and anti-fungal activity to Rhizoctonia solani. It’s worth noting that compounds 5m, 5r, 5u, 5v, 5x and 5y showed strong antibacterial effects on Xanthomonas oryzae pv. oryzae (Xoo), with EC₅₀ values of 36.25, 24.14, 28.82, 19.44, 25.37 and 28.52 μg/mL, respectively, superior to bismerthiazol (BMT, EC₅₀ = 77.46 μg/mL) and thiodiazole copper (TDC, EC₅₀ = 99.31 μg/mL). Compounds 5p, 5u and 5v exhibited excellent antibacterial ability against Xanthomonas oryzae pv. oryzicola (Xoc), with EC₅₀ values of 31.40, 19.04 and 21.78 μg/mL, respectively, better than that of BMT (EC₅₀ = 68.50 μg/mL) and TDC (EC₅₀ = 91.05 μg/mL). In addition, compound 5v exerted moderate antibacterial effects on rice bacterial leaf blight.

Conclusions

Twenty-six novel 1,2,4-oxadiazole derivatives were obtained and their biological activities were evaluated. Compound 5u and 5v exhibited excellent antibacterial activity Xoo and Xoc. These results indicated that 1,2,4-oxadiazole derivatives containing a trifluoromethyl pyridine moiety could be as potential alternative templates for discovering novel antibacterial agents.

Chemical Nematicides: Recent Research Progress and Outlook

Plant-parasitic nematodes have caused huge economic losses to agriculture worldwide and seriously threaten the sustainable development of modern agriculture. Chemical nematicides are still the most effective means to manage nematodes. However, the long-term use of organophosphorus and carbamate nematicides has led to a lack of field control efficacy and increased nematode resistance. To meet the huge market demand and slow the growth of resistance, new nematicides are needed to enter the market. The rational design and synthesis of new chemical scaffolds to screen for new nematicides is still a difficult task. We reviewed the latest research progress of nematicidal compounds in the past decade, discussed the structure-activity relationship and mechanism of action, and recommended some nematicidal active fragments. It is hoped that this review can update the recent progress on nematicide discoveries and provide new ideas for the design and mechanism of action studies of nematicides.

Novel Bithiophene Dimers from Echinops latifolius as Potential Antifungal and Nematicidal Agents

Three novel dimeric bithiophenes, echinbithiophenedimers A-C (1-3), along with two known thiophenes, 4 and 5, were obtained from Echinops latifolius, and their structures were identified through extensive spectroscopic analysis and electronic circular dichroism calculations. Compounds 1-3 possessed new carbon skeletons; they are dimeric bithiophenes with 1 and 2 featuring an unprecedented 1,3-dioxolane ring system and 3 featuring an unusual 1,4-dioxane ring. These compounds are the first examples of bithiophene dimers furnished by different cyclic diethers. Dimeric bithiophenes 1-3 had good antifungal activities against five phytopathogenic fungi, and compound 3 showed excellent activity against Alternaria alternate and Pyricularia oryzae, with a minimal inhibitory concentration value of 8 μg/mL, which was close to or higher than that of carbendazim. Moreover, its effect on the mycelial morphology was observed by scanning electron microscopy. Compounds 1-3, which were demonstrated to be nonphototoxic thiophenes, exhibited better nematicidal activity than the commercial nematicide ethoprophos against Meloidogyne incognita. This study revealed that dimeric bithiophenes containing 1,3-dioxolane or 1,4-dioxane rings could be used as novel antifungal and nematicidal agents for controlling plant fungal and nematode pathogens.

Synthesis and Insecticidal Activity Evaluation of Virtually Screened Phenylsulfonamides

The fastest and most effective way to control pests is to use pesticides. However, with the accumulation of pesticide resistance and the difficulties of rapidly producing new pesticides, it is of great significance to create new pesticides through new synthetic methods. In this study, we report a computer-aided drug design (CADD)-assisted method to obtain two lead sulfonamides by homology modeling and virtual screening. On this basis, the lead compounds were synthesized from p-chlorocresol by four steps of esterification, sulfonation, sulfonamidation, and amidation. Further, 71 derivatives were synthesized by optimizing the lead compounds, and their insecticidal activities against Mythimna separata were evaluated by the leaf-dipping method. Notably, seven sulfonamides (5a, 5g, 5h, 5m, 6b, 6g, and 6m) with excellent insecticidal activity were obtained, and the possible binding modes between receptors and active groups in sulfonamides were verified by structure-activity relationship and docking simulation, which provided theoretical support for the subsequent development of these novel candidate insecticides.

Synthesis, extracorporeal nephrotoxicity, and 3D-QSAR of andrographolide derivatives

Andrographolide is a traditional Chinese medicine monomer with many pharmacological activities, but has potential nephrotoxicity. Here, we aim to investigate the relationship between modification of andrographolide structure and its nephrotoxicity. Twenty-three andrographolide derivatives were synthesized, and their structures were confirmed by ¹ H-NMR and HRMS. Nephrotoxicity of these compounds against human renal tubular epithelial (HK-2) cells was evaluated using the MTT assay. The results indicated that most of them had significantly reduced nephrotoxicity, especially compounds III, V, and IX_c , with IC₅₀ values of 1,985, 1,300, and 806.9 μmol/L, respectively, which were obviously superior to andrographolide (IC₅₀ 30.60 μmol/L). However, compounds I_a -I_f (IC₅₀ values < 30 μmol/L), the 14-OH derivatives of andrographolide, showed higher nephrotoxicity than that of andrographolide. Three-dimensional quantitative structure-activity relationship (3D-QSAR) models of COMFA and COMSIA were established (COMFA: q²  = 0.639, r²  = 0.951; COMSIA: q²  = 0.569, r²  = 0.857). This model allowed proposing five new compounds with lower theoretical nephrotoxicity, which would be worthwhile to synthesize and evaluate. We believe that predicted models will help us to understand the structural modification requirements of andrographolide to reduce the nephrotoxicity, and further investigations will be needed to determine the mechanism involved in the effect of less nephrotoxic compounds.

Design, Synthesis, Crystal Structure, and Antimicrobial Evaluation of 6-Fluoroquinazolinylpiperidinyl-Containing 1,2,4-Triazole Mannich Base Derivatives against Phytopathogenic Bacteria and Fungi

A total of 20 1,2,4-triazole Mannich base derivatives bearing the 6-fluoroquinazolinylpiperidinyl moiety were designed, synthesized, and evaluated as antimicrobial agents against phytopathogenic bacteria and fungi according to the molecular hybridization strategy. Of note, the structure of target compound 4h was clearly confirmed through single-crystal X-ray diffraction analysis. The turbidimetric assays indicated that some compounds exhibited excellent antibacterial efficacies in vitro against Xanthomonas oryzae pv. oryzae (Xoo). For example, compounds 4c, 4f, 4j, and 7j had EC₅₀ values of 23.6, 18.8, 23.4, and 24.3 μg/mL, respectively, which were far superior to that of agrobactericide bismerthiazol (EC₅₀ = 92.4 μg/mL). In particular, compound 4f demonstrated a potent anti-Xoo activity approximately five times more active than that of bismerthiazol. Moreover, in vivo assays showed the excellent protective and curative activities of compound 4f against rice bacterial blight, having the potential as an alternative bactericide for controlling Xoo. The structure-activity relationship analysis showed a good pesticide-likeness concerning compound 4f, following Tice's criteria. The anti-Xoo mechanism of compound 4f was preliminarily explored by scanning electron microscopy measurements in living bacteria. Finally, several compounds also exhibited good antifungal activities in vitro against Gibberella zeae at 50 μg/mL. In short, the presented work showed the potential of 6-fluoroquinazolinylpiperidinyl-containing 1,2,4-triazole Mannich base derivatives as effective bactericides for controlling Xoo.

Putting deep learning in perspective for pest management scientists

'Deep learning' is causing rapid technological changes in many fields of science, and conjectures about its potential for transforming everyone's work and lives is a matter of great debate. Unfortunately, it is all too easy to apply it as a 'black box' tool with little consideration of its potential limitations, especially when the data it is being applied to is less than perfect. In this Perspective, I try to put deep learning into a broader mechanistic and historical context by showing how it relates to older forms of artificial intelligence; by providing a general explanation of how it operates; and by exploring some of the challenges involved in its implementation. Examples wherein it has been applied to pest management problems are provided to illustrate how the technology works and the challenges deep learning faces. At least in the near term, its biggest impact on agrochemical development seems likely to come in automating the tedious work involved in assessing agrochemical efficacy, but getting there will require major investments in building large, well-curated data sets to work from and in providing the expertise required to assess the resulting model predictions in real-world scenarios. Deep learning may also come to complement the machine learning methodologies already available for use in pesticide discovery and development, but it seems unlikely to supplant them. © 2020 The Authors. Pest Management Science published by John Wiley & Sons Ltd on behalf of Society of Chemical Industry.

Synthesis and Antibacterial Evaluation of N-phenylacetamide Derivatives Containing 4-arylthiazole Moieties

A series of new N-phenylacetamide derivatives containing 4-arylthiazole moieties was designed and synthesized by introducing the thiazole moiety into the amide scaffold. The structures of the target compounds were confirmed by ¹H-NMR, ¹³C-NMR and HRMS. Their in vitro antibacterial activities were evaluated against three kinds of bacteria-Xanthomonas oryzae pv. Oryzae (Xoo), Xanthomonas axonopodis pv. Citri (Xac) and X.oryzae pv. oryzicola (Xoc)-showing promising results. The minimum 50% effective concentration (EC₅₀) value of N-(4-((4-(4-fluoro-phenyl)thiazol-2-yl)amino)phenyl)acetamide (A₁) is 156.7 µM, which is superior to bismerthiazol (230.5 µM) and thiodiazole copper (545.2 µM). A scanning electron microscopy (SEM) investigation has confirmed that compound A₁ could cause cell membrane rupture of Xoo. In addition, the nematicidal activity of the compounds against Meloidogyne incognita (M. incognita) was also tested, and compound A₂₃ displayed excellent nematicidal activity, with mortality of 100% and 53.2% at 500 μg/mL and 100 μg/mL after 24 h of treatment, respectively. The preliminary structure-activity relationship (SAR) studies of these compounds are also briefly described. These results demonstrated that phenylacetamide derivatives may be considered as potential leads in the design of antibacterial agents.

Tomato Chlorosis Virus Minor Coat Protein as a Novel Target To Screen Antiviral Drugs

Minor coat protein (mCP), an important component of tomato chlorosis virus (ToCV), plays a significant role in the process of virus assembly and movement and is directly related to the virus-insect transmission. Therefore, ToCV mCP could be considered as a potent target for anti-ToCV drugs. In this study, ToCV mCP was first cloned, expressed, purified, and a novel target to screen the antiviral agents. The results showed that some antiviral compounds bound to ToCV mCP with strongly affinities in vitro, including quinazoline derivatives 4a and 4b, Ningnanmycin, and Ribavirin. Subsequently, three-dimensional-quantitative structure-activity relationship (3D-QSAR) analysis was performed based on the binding affinities, and the model indicated that 4a and 4b had indeed stronger binding effects on ToCV mCP than other quinazoline derivatives. Finally, the anti-ToCV activities of compounds 4a and 4b were evaluated by quantitative real-time polymerase chain reaction in vivo. Compounds 4a and 4b inhibited infection of ToCV in the host and as well as reduced the level of ToCV mCP gene expression. Thus, ToCV mCP can be used as a novel drug target for screening anti-ToCV agents, and the ligand-based 3D-QSAR analysis of quinazoline derivatives provided new insights into the design and optimization of novel anti-ToCV drug molecules based on ToCV mCP.

Novel pyrrolidine-2,4-dione derivatives containing pharmacophores of both hydrazine and diphenyl ether as potential antifungal agents: design, synthesis, biological evaluation, and 3D-QSAR study

Novel pyrrolidine-2,4-dione derivatives were designed based on natural products. Some synthesized compounds showed excellent antifungal activity. Scanning electron microscopy was used to observe mycelium morphology. 3D-QSAR was also studied.

Structure-based design of human pancreatic amylase inhibitors from the natural anthocyanin database for type 2 diabetes

Malvidin 3-O-arabinoside is identified as a novel human pancreatic amylase inhibitor from the natural anthocyanin database with a structure-based design approach.

Synthesis and antiviral activity of novel myricetin derivatives containing ferulic acid amide scaffolds

A variety of myricetin derivatives bearing ferulic acid amide scaffolds were designed and synthesized.

Design, Synthesis, and Bioactivity Evaluation of Novel Isoxazole-Amide Derivatives Containing an Acylhydrazone Moiety as New Active Antiviral Agents

As a continuation of our efforts to discover and develop "me-better" active molecules, in this study, a series of novel isoxazole-amide derivatives containing an acylhydrazone moiety were synthesized and evaluated for their antiviral activities against tobacco mosaic virus (TMV) and cucumber mosaic virus (CMV). Antiviral bioassays indicated that some of the target compounds exhibited better in vivo antiviral activities against TMV and CMV than those of Ningnanmycin (NNM). Especially, the compound 7t exhibited the best curative, protection, and inactivation activities against TMV and CMV which were superior to those of NNM. Meanwhile, our present work also revealed that compound 7t could enhance the defense-related enzyme activity and increase the chlorophyll content in tobacco leaves to induce resistance and enhance plant tolerance to TMV infection.

Novel 1,3,4-Oxadiazole Derivatives Containing a Cinnamic Acid Moiety as Potential Bactericide for Rice Bacterial Diseases

Rice bacterial leaf blight and leaf streak are two important bacterial diseases of rice, which can result in yield loss. Currently, effective antimicrobials for rice bacterial diseases are still lacking. Thus, to develop highly effective and low-risk bactericides, 31 novel 1,3,4-oxadiazole derivatives containing a cinnamic acid moiety were designed and synthesized. Bioassay results demonstrated that all compounds exhibited good antibacterial activities in vitro. Significantly, compounds 5r and 5t showed excellent antibacterial activities against Xanthomonas oryzae pv. oryzae (Xoo) and X. oryzae pv. oryzicola (Xoc), with the 50% effective concentration (EC₅₀) values of 0.58 and 0.34, and 0.44 and 0.20 μg/mL, respectively. These compounds were much better than thiodiazole copper (123.10 and 161.52 μg/mL) and bismerthiazol (85.66 and 110.96 μg/mL). Moreover, compound 5t had better protective and curative activities against rice bacterial leaf blight and leaf streak than thiodiazole copper and bismerthiazol in vivo. Simultaneously, the in vivo efficacy of the compounds was demonstrated by real-time quantitative PCR to quantify bacterial titers. In addition, a three-dimensional quantitative structure⁻activity relationship model was created and presented good predictive ability. This work provides support for 1,3,4-oxadiazole derivatives containing a cinnamic acid moiety as a potential new bactericide for rice bacterial diseases.