Methyl Esters of (E)-Cinnamic Acid: Activity against the Plant-Parasitic Nematode Meloidogyne incognita and In Silico Interaction with Histone Deacetylase

Design, Synthesis, and Nematicidal Activity of Novel Amide Derivatives Containing an 1,2,4/1,3,4-Oxadiazole Moiety against Bursaphelenchus xylophilus

To discover novel structural nematicides, 79 amide compounds containing 1,2,4/1,3,4-oxadiazole moiety were designed, synthesized, and evaluated for nematicidal efficacy against second-stage juveniles of Bursaphelenchus xylophilus (B. xylophilus). Notably, some compounds exhibited superior nematicidal efficacy, for example, the LC50 values of compounds 11, 39, 40, 48, 49, 51, 52, and 54 were 7.4, 31.0, 35.3, 10.3, 12.7, 6.9, 21.5, and 52.2 mg/L, respectively, with nematicidal activities significantly surpassing that of tioxazafen (79.3 mg/L). Compound 51 exhibited multifaceted nematicidal activity through suppression of motility, feeding, and reproduction, combined with induction of oxidative stress. Compound 51 significantly reduced nematode protein content and impaired antioxidant capacity. Meanwhile, compound 51 demonstrates superior binding energy and interaction mode with succinate dehydrogenase (SDH), showing potent SDH inhibition (IC50 = 15.0 μmol/L). Therefore, compound 51, which may become a potential SDH inhibitor, interferes with nematode energy metabolism by inhibiting SDH activity, resulting in nematode death.

Naturally-occurring nematicides of plant origin: two decades of novel chemistries

Plant-parasitic nematodes are among the most destructive plant pathogens, resulting in a global annual economic loss of about 358 billion dollars. Using synthetic nematicides to control plant-parasitic nematodes has resulted in broad-spectrum toxicity to the environment. Plant-derived secondary metabolites have recently emerged as viable options that provide effective, greener, and renewable routes for managing plant-parasitic nematodes in various cropping systems. However, limited comprehensive information on plant-derived secondary metabolites sources, chemical structures, and nematicidal activities is available. This study aims to compile and analyze data on plant-based secondary metabolites with nematicidal properties collected over the last two decades. In this review, we identified 262 plant-based metabolites with nematicidal activities that were isolated from 35 plant families and 65 plant species. Alkaloids, terpenoids, saponins, flavonoids, coumarins, thiophenes, and annonaceous acetogenins were among the most studied compounds. In addition to the structure-activity relation for specific metabolites with nematicidal potency, various techniques for their extraction and isolation from plant material are discussed. Our findings demonstrate the potential of plants as a feedstock for sourcing nematicidal compounds and discovering new chemistries that could potentially be used for developing the next generation of nematicides. © 2024 The Author(s). Pest Management Science published by John Wiley & Sons Ltd on behalf of Society of Chemical Industry.

Discovery of 2-Naphthol from the Leaves of Actephila merrilliana as a Natural Nematicide Candidate

To identify natural nematicides that can replace chemical nematicides, 2-naphthol with high activity against Meloidogyne incognita was isolated from Actephila merrilliana. The nematicidal activity of 2-naphthol against M. incognita was 100% at 100 μg/mL with an EC50 value of 38.00 μg/mL. Moreover, 2-naphthol had a significant negative effect on egg incubation. 2-Naphthol effectively inhibited the invasion of M. incognita into crops in both a pot experiment and field trial. In addition, the structure-activity relationship indicated that the naphthalene ring and its β-site hydroxyl group were the key pharmacophores for the nematicidal activity of 2-naphthol. Nematodes were stimulated by 2-naphthol to produce excessive reactive oxygen species, which may be the underlying mechanism of 2-naphthol nematicidal activity. A systemic evaluation of 2-naphthol in tomato plants demonstrated that 2-naphthol remained mainly fixed in the roots after being absorbed by the crop and was not transported to the stems or leaves. Thus, 2-naphthol can be developed as a natural nematicide candidate.

Discovery of 1,2,4-Oxadiazole Derivatives Containing Haloalkyl as Potential Acetylcholine Receptor Nematicides

Plant-parasitic nematodes pose a serious threat to crops and cause substantial financial losses due to control difficulties. Tioxazafen (3-phenyl-5-thiophen-2-yl-1,2,4-oxadiazole) is a novel broad-spectrum nematicide developed by the Monsanto Company, which shows good prevention effects on many kinds of nematodes. To discover compounds with high nematocidal activities, 48 derivatives of 1,2,4-oxadiazole were obtained by introducing haloalkyl at the 5-position of tioxazafen, and their nematocidal activities were systematically evaluated. The bioassays revealed that most of 1,2,4-oxadiazole derivatives showed remarkable nematocidal activities against Bursaphelenchus xylophilus, Aphelenchoides besseyi, and Ditylenchus dipsaci. Notably, compound A1 showed excellent nematocidal activity against B. xylophilus with LC50 values of 2.4 μg/mL, which was superior to that of avermectin (335.5 μg/mL), tioxazafen (>300 μg/mL), and fosthiazate (436.9 μg/mL). The transcriptome and enzyme activity results indicate that the nematocidal activity of compound A1 was mainly related to the compound which affected the acetylcholine receptor of B. xylophilus.

Discovery of novel inhibitors targeting nematode chitinase CeCht1: Virtual screening, biological evaluation, and molecular dynamics simulation

Plant-parasitic nematodes are a main limiting factor for worldwide agriculture. To reduce the global burden of nematode infections, chemical nematicides are still the most effective methods to manage nematodes. With the increasing resistance of nematodes, the development of new anti-nematicides drug is urgent. Nematode chitinases are found to play important roles in various physiological functions, such as larva moulting, hatching from eggshell, and host infection. Inhibition of nematode chitinase is considered a promising strategy for the development of eco-friendly nematicides. In this study, to develop novel nematode chitinase CeCht1 inhibitors, virtual screening of the ZINC database was performed using the pesticide-likeness rules, pharmacophore-based and docking-based approach in turn. Compounds HAU-4 and HAU-7 were identified as potent CeCht1 inhibitors with the IC50 values of 4.2 μM and 10.0 μM, respectively. Moreover, molecular dynamics simulations combined with binding free energy and free energy decomposition calculations were conducted to investigate the basis for the potency of the two inhibitors toward CeCht1. This work gives an insight into the future rational development of novel and potent nematode chitinase inhibitors.

Design, Synthesis, and Herbicidal Activity of Naphthalimide-Aroyl Hybrids as Potent Transketolase Inhibitors

Transketolase (TK) was identified as a new target for the development of novel herbicides. In this study, a series of naphthalimide-aroyl hybrids were designed and prepared based on TK as a new target and tested for their herbicidal activities. In vitro bioassay showed that compounds 4c and 4w exhibited stronger inhibitory effects against Digitaria sanguinalis (DS) and Amaranthus retroflexus (AR) with the inhibition over 90% at 200 mg/L and around 80% at 100 mg/L. Also, compounds 4c and 4w exhibited excellent postemergence herbicidal activity against DS and AR with the inhibition around 90% at 90 g [active ingredient (ai)]/ha and 80% at 50 g (ai)/ha in the greenhouse, which was comparable with the activity of mesotrione. The fluorescent quenching experiments of At TK revealed the occurrence of electron transfer from compound 4w to At TK and the formation of a strong exciplex between them. Molecular docking analyses further showed that compounds 4w exhibited profound affinity with At TK through the interaction with the amino acids in the active site, which results in its strong inhibitory activities against TK. These findings demonstrated that compound 4w is potentially a lead candidate for novel herbicides targeting TK.