Anthranilic Diamides Containing Monofluoroalkene Amide Linkers as Potential Insect RyR Activators: Design, Synthesis, Bio-evaluation, and Computational Study

Design, Synthesis, and Bioactivity of Trifluoroethylthio-Substituted Phenylpyrazole Derivatives

As the first marketed phenylpyrazole insecticide, fipronil exhibited remarkable broad-spectrum insecticidal activity. However, it poses a significant threat to aquatic organisms and bees due to its high toxicity. Herein, 35 phenylpyrazole derivatives containing a trifluoroethylthio group on the 4 position of the pyrazole ring were designed and synthesized. The predicted physicochemical properties of all of the compounds were within a reasonable range. The biological assay results revealed that compound 7 showed 69.7% lethality against Aedes albopictus (A. albopictus) at the concentration of 0.125 mg/L. Compounds 7, 7g, 8d, and 10j showed superior insecticidal activity for the control of Plutella xylostella (P. xylostella). Notably, compound 7 showed similar insecticidal activity against Aphis craccivora (A. craccivora) compared with fipronil. Potential surface calculation and molecular docking suggested that different lipophilicity and binding models to the Musca domestica (M. domestica) gamma-aminobutyric acid receptors may be responsible for the decreased activity of the tested derivatives. Toxicity tests indicated that compound 8d (LC50 = 14.28 mg/L) induced obviously 14-fold lower toxicity than fipronil (LC50 = 1.05 mg/L) on embryonic-juvenile zebrafish development.

Discovery of Trisubstituted N-Phenylpyrazole Containing Diamides with Improved Insecticidal Activity

To increase the structural diversity of insecticides and meet the needs of effective integrated insect management, the structure of chlorantraniliprole was modified based on a previously established three-dimensional quantitative structure-activity relationship (3D-QSAR) model. The pyridinyl moiety in the structure of chlorantraniliprole was replaced with a 4-fluorophenyl group. Further modifications of this 4-fluorophenyl group by introducing a halogen atom at position 2 and an electron-withdrawing group (e.g., iodine, cyano, and trifluoromethyl) at position 5 led to 34 compounds with good insecticidal efficacy against Mythimna separata, Plutella xylostella, and Spodoptera frugiperda. Among them, compound IV f against M. separata showed potency comparable to that of chlorantraniliprole. IV p against P. xylostella displayed a 4.5 times higher potency than chlorantraniliprole. In addition, IV d and chlorantraniliprole exhibited comparable potencies against S. frugiperda. Transcriptome analysis showed that the molecular target of compound IV f is the ryanodine receptor. Molecular docking was further performed to verify the mode of action and insecticidal activity against resistant P. xylostella.

Discovery of Trifluorobutene Amide Derivatives as Potential Nematicides: Design, Synthesis, Nematicidal Activity Evaluation, SAR, and Mode of Action Study

Plant-parasitic nematodes are one of the major threats to crop protection. However, only limited nematicides are currently available and are confronted with a growing resistance problem, which necessitates the development of novel nematicides. In this study, a series of trifluorobutene amide derivatives was synthesized through the strategy of amide bond reversal, and their nematicidal activity against Meloidogyne incognita was evaluated. The bioassay showed that compounds C2, C10, and C18 and some analogues thereof exhibited good nematicidal activity. Among them, the derivatives of compound C2 containing a benzene ring [C26 (R = 2-CH3) and C33 (R = 2-Cl)] exhibited excellent bioactivity against M. incognita in vitro. The LC50/72h values reached 14.13 and 14.71 mg·L-1, respectively. Moreover, analogues of compounds C10 and C18 containing a thiophene ring [C43 (R = 5-CH3), C44 (R = 4-CH3), and C50 (R = 5-Cl)] exhibited significant bioactivity against M. incognita in vivo with inhibition rates of 68.8, 65.5, and 69.8% at 2.5 mg·L-1 in a matrix, respectively. Meanwhile, C44 and C50 also showed excellent control effects against M. incognita in both cups and microplots. The structure-activity relationship (SAR) of synthesized compounds was discussed in detail. Comparative molecular field analysis (CoMFA) was also conducted to develop the SAR profile. The preliminary mode of action investigation showed that compound C33 exhibited strong inhibition on egg hatching, motility, feeding behavior, and growth of Caenorhabditis elegans. At the same time, the impact of active compounds on biochemical indicators related to oxidative stress showed that compound C33 influenced the production of ROS (reactive oxygen species), and the accumulation of lipofuscin and lipids on C. elegans.

Novel Nitrophenyl Substituted Anthranilic Diamide Derivatives: Design, Synthesis, Selectivity, and Antiresistance

Diamide insecticides have gained popularity due to their high efficacy and low toxicity to nontarget organisms. However, diamide-associated resistance has emerged recently, causing a significant reduction in their potency, thereby hindering sustainable agricultural development. Here, we explored novel diamide insecticide analogs and, using a structure-based approach, rationally designed and synthesized 28 nitrophenyl substituted anthranilic diamides. Most of the compounds showed moderate to good activity against Mythimna separata, Plutella xylostella, and Spodoptera frugiperda. Among them, compounds Ia and Im showed extraordinarily high activity and their mode of action was verified on isolated neurons. Additionally, Im exhibited over 10-fold greater potency than chlorantraniliprole in a HEK293 cell line stably expressing S. frugiperda ryanodine receptors (SfRyRs) containing the resistance mutations, G4891E and I4734M. The binding modes of Im in the SfRyRs were predicted using in silico molecular docking analysis. Our novel nitrophenyl substituted anthranilic diamide derivatives provide valuable insights for the design of insecticidal RyR-targeting compounds to effectively control both wild type and diamide insecticide-resistant lepidopteran pests.

3D-QSAR Combination with Molecular Dynamics Simulations to Effectively Design the Active Ryanodine Receptor Agonists against Spodoptera frugiperda

Computer-aided molecular modeling was applied to design a series of Spodoptera frugiperda RyR agonists. Comparative molecular field analysis (CoMFA) and comparative molecular similarity indices analysis (CoMSIA) were used to generate 3D-QSAR models. MD simulations in the complex with S. frugiperda native, mutant RyR, and mammalian RyR1 under physiological conditions were used to validate the detailed binding mechanism. Binding free energy calculation by molecular mechanics generalized surface area (MM-GBSA) explained the role of key amino acid residues in ligand-receptor binding. Therefore, 14 new compounds were effectively designed and synthesized, and a bioassay indicated that compounds A-2 and A-3 showed comparable activity to that of chloranthraniliprole with LC50 values of 0.27, 0.18, and 0.20 mg L-1, respectively, against S. frugiperda. Most target compounds also displayed good activity against Mythinma separata at 0.1 mg L-1. Molecular docking and MM-GBSA calculations demonstrated that A-3 had a better binding capacity with native and mutant S. frugiperda RyRs.

Discovery of Novel Diamides Scaffold Containing Monofluoro-acrylamides Activating the Insect Ryanodine Receptor

The research and development of organofluorine chemistry has flourished; in particular, monofluoroalkene has aroused considerable interest from medicinal and organic chemists. It is a significant attempt to introduce monofluoroalkene into agrochemicals. In this study, monofluoroalkene was introduced into diamide molecules and inserted between the aliphatic amide and benzene ring, and 44 compounds have been successfully synthesized. The bioassay results showed that compounds with monofluoro-acrylamide moiety (Z-isomers) had excellent larvicidal activity against lepidopteran pests at 5 mg·L-1. The LC50 values of compounds B16, B18, and B21 against Mythimna separata were 1.02, 1.32, and 0.78 mg·L-1, respectively. 3D-QSAR analysis including the CoMFA model and the CoMSIA model was conducted to illustrate the contributions of steric, electrostatic, hydrophobic, and hydrogen bond fields on the bioactivity. Moreover, typical symptoms caused by chlorantraniliprole including dehydration, shrinkage, and blackening were also observed on the test larvae treated with monofluoro-acrylamide diamide compounds. M. separata central neurons calcium imaging experiment of compound B18 indicated that the monofluoro-acrylamide diamide compounds were potential insect ryanodine receptor activators. The molecular docking was performed in the CHL binding domain of Plutella xylostella RyR and revealed that the predicted binding mode of compound B21 was slightly different from that of CHL. The MM|GBSA dG Bind values of B21 and CHL with P. xylostella RyR were respectively -85.797 and -95.641 kcal·mol-1. The present work explored the insecticidal properties of a new diamide scaffold containing a monofluoro-acrylamide fragment and extended the application of monofluoroalkene in the agrochemical field.

Design, Synthesis, and Insecticidal Evaluation of N-Pyridylpyrazole Amide Derivatives Containing 4,5-Dihydroisoxazole Amide as Potential Ryanodine Receptor Activators

Using the 4,5-dihydroisoxazol amide structure to expand the aliphatic amide moiety of chlorantraniliprole, a series of 28 novel N-pyridylpyrazolecarboxamide derivatives containing 4,5-dihydroisoxazol amide fragment were designed and synthesized. All target compounds had been properly characterized and confirmed by 1H NMR, 13C NMR, and HRMS, and the effects were evaluated against Mythimna separata (M. separata) and Plutella xylostella (P. xylostella). The bioassay results indicated that most of the target compounds exhibited good insecticidal activities against M. separata and P. xylostella at 50 mg/L; especially, compound A4 showed an LC50 value of 3.27 mg/L against M. separata. Calcium imaging experiments indicated that the target compound A4 had a similar mechanism of action to chlorantraniliprole, causing an increase in the cytoplasmic Ca2+ concentration. The molecular docking revealed the possible binding mode of compound A4 with a ryanodine receptor.