Recent Research Progress in and Perspectives of Mesoionic Insecticides: Nicotinic Acetylcholine Receptor Inhibitors

Computer-aided design of novel anthranilic diamides containing fluorinated alkoxy groups as potential ryanodine receptor insecticides

BACKGROUND

Increasing the diversity of lead compounds has been shown to enhance the efficacy of diamide insecticides. Fifty novel compounds were precisely designed and synthesized utilizing fragment-based assembly and virtual screening coupling.

RESULTS

The median lethal concentration (LC50) values of compounds X-30 and X-40 against Mythimna separata were 0.09 and 0.08 mg L-1, respectively, which are lower than that of chlorantraniliprole (CHL, 0.11 mg L-1). Notably, compounds X-10, X-18, X-25, X-32 and X-43 had corresponding LC50 values of 2.0 × 10-4, 5.0 × 10-4, 6.0 × 10-4, 9.0 × 10-4 and 7.0 × 10-4 mg L-1 against Plutella xylostella, respectively. The best compound X-10 exhibited five-fold greater efficacy than CHL (1.0 × 10-3 mg L-1). The LC50 values of compounds X-21, X-29, and X-40 against Spodoptera frugiperda were 0.27, 0.26 and 0.25 mg L-1, respectively, which are slightly lower than that of CHL (0.33 mg L-1). In the case of Ostrinia furnacalis, compound X-43 showed good efficacy with LC50 values comparable to those of CHL (1.38 versus 1.57 mg L-1). Calcium imaging experiments demonstrated that X-21 acted on S. frugiperda ryanodine receptors. Furthermore, this series of compounds showed safety toward nontarget mammals compared to CHL.

CONCLUSION

The introduction of fluorinated alkoxy groups at the 3-position of the pyrazole ring leads to good insecticidal activity and improved insect selectivity. © 2025 Society of Chemical Industry.

Novel Meta-Diamide Derivatives Bearing Triazole: Design, Synthesis, and Bioactivity

In searching for novel insecticide lead, 20 new meta-diamide compounds containing triazole were designed and synthesized regarding cyproflanilide as lead compound. All the compounds were characterized by 1H NMR, 13C NMR, and High-resolution mass spectra (HR MS). In preliminary bioassay, we found that one of the compounds: N-(cyclopropylmethyl)-N-(5-((2,6-dibromo-4-(1,2,2,2-tetrafluoro-1-(trifluoromethyl)ethyl)phenyl)carbamoyl)-2-(1H-1,2,4-triazol-1-yl)phenyl)-6-(trifluoromethyl) nicotinamide (16a) had high activity against the target organism Plutella xylostella at 1 mg/L and against the target organism Mythimna separata at 2 mg/L. It is obviously superior to the known compounds Ia and Ib, and it is equivalent to cyproflanilide, and the LC50 values of the compound against P. xylostella and M. separata were 0.90 mg/L and 0.64 mg/L, respectively. It is providing important clues for subsequent structure-activity relationship (SAR) studies. From this, we explored the SAR of these compounds. Through comprehensive analysis of their structural characteristics and insecticidal activity data, we found that different halogen substituents on benzene ring and different aromatic substituents on amino group in the compound had significant effects on insecticidal activity. This has certain guiding significance for further structural optimization and activity enhancement.

Application of Difluoromethyl Isosteres in the Design of Pesticide Active Molecules

Difluoromethyl (CF2H) groups have been found in many listed pesticides due to their unique physical and chemical properties and outstanding biological activity. In pesticide molecules, compared with the drastic changes brought by trifluoromethyl, difluoromethyl usually moderately regulates the metabolic stability, lipophilicity, bioavailability, and binding affinity of compounds. Therefore, difluoromethylation has become an effective means to modify the biological activity of pesticide molecules. This paper reviews the representative literatures and patents containing difluoromethyl groups in the past 10 years, and introduces the research progress. The aim is to provide an effective reference value for the study of difluoromethyl in pesticides.

Recent innovations in crop protection research

As the world's population continues to grow and demand for food increases, the agricultural industry faces the challenge of producing higher yields while ensuring the safety and quality of harvests, operators, and consumers. The emergence of resistance, pest shifts, and stricter regulatory requirements also urgently calls for further advances in crop protection and the discovery of new innovative products for sustainable crop protection. This study reviews recent highlights in innovation as presented at the 15th IUPAC International Congress of Crop Protection Chemistry held in New Delhi, in 2023. The following new products are discussed: the insecticides Indazapyroxamet, Dimpropyridaz and Fenmezoditiaz, the fungicides Mefentrifluconazole and Pyridachlomethyl, the nematicide Cyclobutrifluram, the herbicides Rimisoxafen, Dimesulfazet, and Epyrifenacil as well as the abiotic stress management product Anisiflupurin. In addition, the latest innovative research areas and discovery highlights in all areas of crop protection will be presented, including insecticidal alkyl sulfones and 1,3,4-trisubstituted pyrazoles, fungicidal picolinamides, herbicidal ketoenols, and trifluoromethylpyrazoles, as well as the latest advances in crop enhancement and green pest control research. © 2024 The Author(s). Pest Management Science published by John Wiley & Sons Ltd on behalf of Society of Chemical Industry.

Novel Evodiamine-Based Sulfonamide Derivatives as Potent Insecticide Candidates Targeting Insect Ryanodine Receptors

Pests represent an important impediment to efficient agricultural production and pose a threat to global food security. On the basis of our prior research focused on identifying insecticidal leads targeting insect ryanodine receptors (RyRs), we aimed to identify evodiamine scaffold-based novel insecticides. Thus, a variety of evodiamine-based derivatives were designed, synthesized, and assessed for their insecticidal activity against the larvae of Mythimna separata (M. separata) and Plutella xylostella (P. xylostella). The preliminary bioassay results revealed that more than half of the target compounds exhibited superior activity compared to evodiamine, matrine, and rotenone against M. separata. Among these, compound 21m displayed the most potent larvicidal efficiency, with a remarkable mortality rate of 93.3% at 2.5 mg/L, a substantial improvement over evodiamine (10.0% at 10 mg/L), matrine (10.0% at 200 mg/L), and rotenone (30.0% at 200 mg/L). In the case of P. xylostella, compounds 21m and 21o displayed heightened larvicidal activity, boasting LC50 values of 9.37 × 10-2 and 0.13 mg/L, respectively, surpassing that of evodiamine (13.41 mg/L), matrine (291.78 mg/L), and rotenone (18.39 mg/L). A structure-activity relationship analysis unveiled that evodiamine-based derivatives featuring a cyclopropyl sulfonyl group at the nitrogen atom of the B ring and a fluorine atom in the E ring exhibited more potent larvicidal effects. This finding was substantiated by calcium imaging experiments and molecular docking, which suggested that 21m could target insect RyRs, including resistant mutant RyRs of P. xylostella (G4946E and I4790M), with higher affinity than chlorantraniliprole (CHL). Additionally, cytotoxicity assays highlighted that the potent compounds 21i, 21m, and 21o displayed favorable selectivity and low toxicity toward nontarget organisms. Consequently, compound 21m emerges as a promising candidate for further development as an insecticide targeting insect RyRs.

Discovery of novel thiazolyl anthranilic diamide derivatives as insecticidal candidates

BACKGROUND

Agricultural pests have caused huge losses in agricultural production and threaten global food security. Synthetic insecticides remain the major control method. However, with the rapid development of pest resistance and the increasingly stringent regulations on pesticide usage, the development of efficient insecticides with novel structures is particularly urgent.

RESULTS

Twenty-six novel anthranilic diamide derivatives containing the thiazole moiety were designed based on the scaffold hopping strategy. Bioassay results indicated that compound 6e exhibited excellent insecticidal activity against a susceptible strain of diamondback moth (Plutella xylostella) with a median lethal concentration (LC50 ) of 0.65 mg L-1 , which was similar to chlorantraniliprole (LC50  = 0.53 mg L-1 ). Compound 6e showed marginally lower (LC50  = 50.45 mg L-1 ) insecticidal activity than chlorantraniliprole (LC50  = 31.98 mg L-1 ) on chlorantraniliprole-resistant P. xylostella larvae, suggesting a cross-resistance of compound 6e with chlorantraniliprole (resistance ratios, 77.6-fold and 60.3-fold, respectively). Compound 6e also showed good insecticidal activity against fall armyworm and beet armyworm with pest mortalities of 74% and 64%, respectively, at 5 mg L-1 concentration. In addition, compounds 6e and 12a showed delayed toxicity against red imported fire ant with mortality rates of 84% and 85% (respectively) after 5 days of treatment at 1.0 mg L-1 , which were superior to that of chlorantraniliprole.

CONCLUSION

The introduction of thiazole into anthranilic diamide scaffolds resulted in insecticidal leads 6e and 12a with excellent insecticidal activities and potential application in controlling red imported fire ants. The work also guides the discovery of insecticidal molecules with thiazole-containing anthranilic diamide scaffold. © 2023 Society of Chemical Industry.

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.

Synthesis of stable class 5 mesoionic benzo[c]tetrazolo[2,3-a]cinnolinium thiolate, dicyanomethylide, and amides

Although class 5 mesoionic compounds show interesting electrical behaviour, they are generally unstable, readily undergoing ring-opening reactions. We designed and synthesized a bridged mesoionic derivative, benzo[c]tetrazolo[2,3-a]cinolinium (BTC), as a stable class 5 mesoionic compound, which was further transformed to the corresponding thiolate, cicyanomethylide, and amide. The intramolecular bridging imparted stability to the BTC thiolates and amides: the BTC thiolates were unsusceptible to ring-opening at high temperatures, and the BTC amides were stable in the absence of electron-withdrawing groups on the amide nitrogen. The properties of the BTC thiolate were compared with those of 2,3-diphenyltetrazolium derivatives based on UV-Vis absorption spectroscopy, single-crystal X-ray diffraction and quantum calculations.

3D-QSAR Directed Discovery of Novel Halogenated Phenyl 3-Trifluoroethoxypyrazole Containing Ultrahigh Active Insecticidal Anthranilic Diamides

Pests are one of the major factors causing crop damage and food security problems worldwide. Based on our previous studies on the discovery of insecticidal leads targeting the ryanodine receptors (RyRs), a three-dimensional quantitative structure-activity relationship (3D-QSAR) model was established to design and synthesize a series of anthranilic diamides containing a halogenated phenyl 3-trifluoroethoxypyrazole moiety. The preliminary bioassays disclosed that IIb, IIIb, and IIIf against Mythimna separata showed comparable activity to chloranthraniliprole (LC₅₀: 0.16, 0.16, 0.14, and 0.13 mg·L^-1, respectively). More than half of the target compounds displayed good activity against Plutella xylostella, where IIIf was the most active compound, 25 times more active than chloranthraniliprole (LC₅₀: 6.0 × 10^-6 versus 1.5 × 10^-4 mg·L^-1). For Spodoptera frugiperda, IIIf displayed slightly inferior potency to chlorantraniliprole (LC₅₀: 0.47 versus 0.31 mg·L^-1). For RyR mutants of S. frugiperda (G4891E, I4734M), compound IIIf could show higher affinity than chlorantraniliprole according to the binding mode and energy in molecular docking experiments. Calcium imaging technique, molecular docking, density functional theory calculations, and electrostatic potential studies validated that the RyR was the target of the most active candidate IIIf, which deserves further development.

Synthesis, insecticidal activity, and mode of action of novel imidazopyridine mesoionic derivatives containing an amido group

BACKGROUND

In our previous work, we applied a new synthetic strategy to design and synthesize a series of imidazopyridine mesoionic derivatives with an ester group. The newly synthesized compounds had excellent insecticidal activity against aphids; however, insecticidal activity against planthoppers was less than satisfactory. In the present study, we designed and synthesized a series of novel imidazopyridine mesoionic compounds, containing an amido group, and these compounds were found to have improved insecticidal activity against planthoppers.

RESULTS

The bioassay results demonstrated that most of the target compounds had moderate-to-good insecticidal activity against Sogatella furcifera, and some exhibited good-to-excellent insecticidal activity against Aphis craccivora. Among them, compound C6 had the highest insecticidal activity against S. furcifera and A. craccivora, with LC₅₀ values of 10.5 and 2.09 μg mL^-1 , respectively. Proteomic results suggested that the differentially expressed proteins mainly were enriched in the nervous system-related pathways after compound C6 treatment. Enzymatic assay results showed that compound C6 and triflumezopyrim had a certain inhibitory effect on acetylcholinesterase. Molecular docking and real-time quantitative PCR results indicated that compound C6 not only may act on the nicotinic acetylcholine receptor, but also may interact with the α4 and β1 subunits of this receptor.

CONCLUSION

The results reported here contribute to the development of new mesoionic insecticides and further our understanding of the mode-of-action of imidazopyridine mesoionic derivatives. © 2022 Society of Chemical Industry.

Pyrido [1,2-a] Pyrimidinone Mesoionic Compounds Containing Vanillin Moiety: Design, Synthesis, Antibacterial Activity, and Mechanism

Xanthomonas oryzae pv. oryzicola (Xoo) is a plant pathogen responsible for rice bacterial blight disease that remains challenging for prevention and cure. To discover innovative and extremely potent antibacterial agents, vanillin moiety was introduced to develop a series of novel mesoionic derivatives. Compound 15 demonstrated excellent in vitro antibacterial activity against Xoo, with a 50% effective concentration value (EC₅₀) of 27.5 μg/mL, which was superior to that of the positive control agent thiodiazole copper (97.1 μg/mL) and comparable to that of compound "A11" (17.4 μg/mL). The greenhouse pot experiment also revealed that compound 15 had 38.5% curative and 36.8% protective efficacy against rice bacterial leaf blight in vivo at 100 μg/mL, which was higher than those of thiodiazole copper (31.2 and 32.6%, respectively) and compound "A11" (29.6 and 33.2%, respectively). Compound 15 enhanced the activities of related defense enzymes, increased chlorophyll content, and promoted the resistance of rice to bacterial infection by modulating the photosynthetic pathway. This study provides a basis for the subsequent structural modification and mechanism research of mesoionic derivatives.

Green Design, Synthesis, and Molecular Docking Study of Novel Quinoxaline Derivatives with Insecticidal Potential against Aphis craccivora

An efficient and environmentally friendly method was established for designing novel 3-amino-1,4-dihydroquinoxaline-2-carbonitrile (1) via the reaction of bromomalononitrile and benzene-1,2-diamine under microwave irradiation in an excellent yield (93%). This targeted amino derivative was utilized for the construction of a series of Schiff bases (8-13). A new series of thiazolidinone derivatives (15-20) were synthesized in high yields (89-96%) via treatment of thioglycolic acid with Schiff bases (8-13) under microwave irradiation in high yields (89-96%). Moreover, new pyrimidine derivatives (26-30 and 35-38) were prepared by treatment of compound 1 with arylidenes (21-25) and/or alkylidenemalononitriles (31-34) using piperidine as a basic catalyst under microwave conditions. Based on elemental analyses and spectral data, the structures of the new assembled compounds were determined. The newly synthesized quinoxaline derivatives were screened and studied as an insecticidal agent against Aphis craccivora. The obtained results indicate that compound 16 is the most toxicological agent against nymphs of cowpea aphids (Aphis craccivora) compared to the other synthesized pyrimidine and thiazolidinone derivatives. The molecular docking study of the new quinoxaline derivatives registered that compound 16 had the highest binding score (-10.54 kcal/mol) and the thiazolidinone moiety formed hydrogen bonds with Trp143.

Design, synthesis, and insecticidal activity evaluation of piperine derivatives

Structural optimization of natural products has become one of the most effective ways to develop novel pesticides. In this study, 30 novel pesticide derivatives containing a linear bisamide were synthesized. Then, their insecticidal activities against P. xylostella were evaluated. Results indicate that different bisamide substitutes show different larvicidal structure–activity relationships. At the same time, 2-trifluoroethyl is the most efficient substituent. The bioactivity results showed that most of the desired compounds exhibited better insecticidal activity against P. xylostella than piperine. Among them, compound D28 resulted in 90% mortality at 1 mg/ml concentration. This study provides a novel protocol for the discovery of new insecticides. The molecular docking results indicated that compound D28 could act on γ-aminobutyric acid receptors.

Bioactivity-Guided Synthesis Accelerates the Discovery of Evodiamine Derivatives as Potent Insecticide Candidates

Pests threaten worldwide food security by decreasing crop yields and damaging their quality. Natural product-based molecular design and structural optimization have been one of the most effective ways to innovate pesticides for integrated insect management. To continue our previous studies on the discovery of insecticidal lead, a series of evodiamine derivatives were designed, synthesized, and evaluated for their insecticidal activities. The bioassay results demonstrated that compounds Ian and Iao exhibited 90 and 80% insecticidal activities against Mythimna separata at 2.5 mg/L, respectively, which were superior to evodiamine (10% at 10 mg/L), matrine (45% at 600 mg/L), and rotenone (30% at 200 mg/L). Compounds Ian-Iap showed 90% insecticidal activities against Plutella xylostella at 1.0 mg/L, far more potent than those of evodiamine, matrine, and rotenone. Compound Ian displayed 60% insecticidal activity against Helicoverpa armigera at 5.0 mg/L, while evodiamine, matrine, and rotenone showed very poor activities. The study on the insecticidal mechanism of action by a calcium imaging experiment indicated that the insect ryanodine receptors (RyRs) could be the potential target of Ian. Furthermore, the molecular docking indicated that Ian anchored in the binding site of the RyR of P. xylostella. The above results manifested the potential of evodiamine derivatives as potent insecticide candidates.

New Synthetic Method and Insecticidal Activities of Novel Imidazopyridine Mesoionic Derivatives Containing an Ester Group

To develop novel insecticides with high efficiency, a new mode of action, and safety to nontarget organisms and the environment, a series of imidazopyridine mesoionic compounds containing an ester group have been designed and synthesized via a new synthetic method discovered by our group. The bioactivity results showed that most of the target compounds exhibited significant insecticidal activities against Aphis craccivora, and some of them showed moderate insecticidal activities against Sogatella furcifera. Among them, compounds C2, C4-C11, and D3 showed excellent insecticidal activities against A. craccivora (LC₅₀ values were lower than 4.5 μg/mL), which were superior to those of pymetrozine (LC₅₀ = 6.19 μg/mL) and triflumezopyrim (LC₅₀ = 4.68 μg/mL). Remarkably, the insecticidal activity of compound C9 was 5.9-fold greater than that of triflumezopyrim with an LC₅₀ value of 0.8 μg/mL. Proteomics and molecular docking results indicated that compound C9 may affect the nervous system of A. craccivora and act on nicotinic acetylcholine receptors like triflumezopyrim.

The Effects of Structural Alterations in the Polyamine and Amino Acid Moieties of Philanthotoxins on Nicotinic Acetylcholine Receptor Inhibition in the Locust, Schistocerca gregaria

Alterations in the polyamine and amino acid (tyrosine) moieties of philanthotoxin-343 (PhTX-343) were investigated for their effects on the antagonism of nicotinic acetylcholine receptors (nAChRs) isolated from the locust (Schistocerca gregaria) mushroom body. Through whole-cell patch-clamp recordings, the philanthotoxin analogues in this study were shown to cause inhibition of the inward current when co-applied with acetylcholine (ACh). PhTX-343 (IC₅₀ = 0.80 μM at -75 mV) antagonised locust nAChRs in a use-dependent manner, suggesting that it acts as an open-channel blocker. The analogue in which both the secondary amine functionalities were replaced with methylene groups (i.e., PhTX-12) was ~6-fold more potent (IC₅₀ (half-maximal inhibitory concentration) = 0.13 μM at -75 mV) than PhTX-343. The analogue containing cyclohexylalanine as a substitute for the tyrosine moiety of PhTX-343 (i.e., Cha-PhTX-343) was also more potent (IC₅₀ = 0.44 μM at -75 mV). A combination of both alterations to PhTX-343 generated the most potent analogue, i.e., Cha-PhTX-12 (IC₅₀ = 1.71 nM at -75 mV). Modulation by PhTX-343 and Cha-PhTX-343 fell into two distinct groups, indicating the presence of two pharmacologically distinct nAChR groups in the locust mushroom body. In the first group, all concentrations of PhTX-343 and Cha-PhTX-343 inhibited responses to ACh. In the second group, application of PhTX-343 or Cha-PhTX-343 at concentrations ≤100 nM caused potentiation, while concentrations ≥ 1 μM inhibited responses to ACh. Cha-PhTX-12 may have potential to be developed into insecticidal compounds with a novel mode of action.

(E)-3-((2-Fluorophenyl)(hydroxy)methylene)imidazo[1,2-a]pyridin-2(3H)-one

Treatment of a N-2-pyridyl-β-ketoamide precursor with bromine afforded the first example of the 3-aryl(α-hydroxy)methylenelimidazo[1,2-a]pyridin-2(3H)-one framework. This transformation proceeded through a domino process comprising an initial bromination, cyclization via an intramolecular SN reaction, and a final keto-enol tautomerism, and allows generation of the fused heterocyclic system and installation of the acyl substituent in a single operation.

Discovery of a polysubstituted phenyl containing novel N-phenylpyrazole scaffold as potent ryanodine receptor activator

To develop the novel ryanodine receptors (RyRs) insecticides, encouraged by our previous research work, a series of novel N-phenylpyrazole derivatives containing a polysubstituted phenyl ring scaffold were designed and synthesized. The bioassays results indicated that some title compounds exhibited excellent insecticidal activity. For oriental armyworm (Mythimna separata), compounds 7f, 7g, 7i and 7o at 0.5 mg L^-1 displayed 100% larvicidal activity, and even at 0.1 mg L^-1, 7o was 30% larvicidal activity, comparable to chlorantraniliprole (30%) and better than cyantraniliprole (10%). Compounds 7f and 7o had the median lethal concentrations (LC₅₀) of 8.83 × 10^-2 and 7.12 × 10^-2 mg L^-1, respectively, close to chlorantraniliprole (6.79 × 10^-2 mg L^-1). Additionally, for diamondback moth (Plutella xylostella), the larvicidal activity of compounds 7f and 7i were 90% and 70% at 0.01 mg L^-1, respectively, better than chlorantraniliprole (50%) and cyantraniliprole (40%). More impressively, the LC₅₀ value of 7f was 4.2 × 10^-3 mg L^-1, slightly lower than that of chlorantraniliprole (5.0 × 10^-3 mg L^-1). The molecular docking between compound 7f and RyRs of diamondback moth validated our molecular designation. Furthermore, the calcium imaging experiment explored the influence of compound 7o on the calcium homeostasis in the central neurons of the third larvae of oriental armyworm. The results of this study indicated that 7o is a potent novel lead targeting at RyRs.