Design, Synthesis, Insecticidal Activity, and SAR of Aryl Isoxazoline Derivatives Containing Pyrazole-5-carboxamide Motif

Studies on the synthesis, crystal structures, biological activities and molecular docking of novel natural methylxanthine derivatives containing piperazine moiety

A series of novel methylxanthine Mannich base derivatives containing substituted piperazine groups were synthesized through Mannich reaction. The structures of these new compounds were confirmed by NMR, HRMS or elemental analyses, and X-ray single crystal diffraction. Bioassay results showed that some of the compounds exhibit favorable fungicidal and insecticidal potentials. Particularly, compounds IIk, IIq, IIs and compounds If, IIk against Physalospora piricola and Rhizoctonia cerealis, respectively, were comparable with Azoxystrobin and Chlorothalonil; compound Ik exhibited higher potency than Triflumuron against Plutella xylostella L., suggesting its potential as a lead compound for further development in insecticidal applications. Despite possessing weak herbicidal activities, the target compounds, especially the methylxanthine S-Mannich base derivatives I displayed remarkable inhibitory activities toward ketol-acid reductoisomerase (KARI); compounds Ib, If, and Ik which had Ki values of 2.41-8.08 µmol/L can be novel potent KARI inhibitors for deeper exploration. The SARs were analyzed in detail. The molecular docking studies on the highly active inhibitors with KARI provided possible binding modes between inhibitor and the target enzyme. The physicochemical parameter predictions indicated that compounds Ik, IIk, IIq and IIs have "druglike structure" features. The research results in this article may bring a new inspiration to the extensive explorations on new methylxanthine derivatives in pesticide area.

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.

Design, synthesis, herbicidal activity, and the molecular docking study of novel phenylpyrazole derivatives with strobilurin moieties

Phenylpyrazole derivatives were innovatively designed and synthesized to fabricate novel herbicides containing strobilurin moieties. These resulting compounds were analyzed by nuclear magnetic resonance spectroscopy (NMR) and high-resolution mass spectrometry (HRMS), exhibiting high herbicidal properties against Amaranthus retroflexus. The target compounds were synthesized through cyclization, chlorination, Vilsmeier-Hack reaction, Suzuki coupling reaction, and esterification reactions. The experimental conditions were mild, and the starting materials were easy to obtain, with a separation yield of approximately 80%. Moreover, herbicidal activity of the title compounds was studied via a pot culture experiment. Compounds 7a, 7b, 7e-7g, 7i, and 7l demonstrated good inhibition on A. retroflexus, which was inferior to that of fomesafen at 150 g a.i./hm2. The docking results indicated that the binding energies of compound 7f with protoporphyrinogen oxidase (PPO) were both negative and spontaneous, with numerous interaction active sites. Thus, it is speculated that compound 7f is a PPO inhibitor.

Design, Synthesis, and Anti-Oomycete and Antifungal Activities of Novel Paeonol Derivatives Containing a Pyrazole Ring

Paeonol is the main active ingredient in the Chinese medicinal herb peony root bark. To discover biorational natural product-based fungicides, 25 paeonol derivatives (5a-y) containing a pyrazole ring were designed and synthesized by ingeniously introducing a pyrazole five-membered heterocyclic ring, and their structures were well characterized by 1H NMR, 13C NMR, high-resolution mass spectrometer (HRMS), and m.p. The stereochemical configurations of six target compounds, 5c, 5f, 5g, 5o, 5s, and 5v, were unambiguously subjected to single-crystal X-ray diffraction. Furthermore, we evaluated the bioactivities of these target compounds as anti-oomycete and antifungal agents against two serious agricultural diseases, Phytophthora capsici and Fusarium graminearum. Among all tested compounds, (1) nine compounds 5b-d, 5f, 5g, 5r, 5s, 5u, 5w displayed promising anti-oomycete against P. capsici, with EC50 values ranging from 22.1 to 34.5 mg/L, and the protective effect of the target compounds against P. capsici in vivo further confirmed the above results. (2) Six compounds 5g, 5k, 5m, 5t, 5w, 5x displayed promising antifungal against F. graminearum, with EC50 values ranging from 38.2 to 86.0 mg/L. Moreover, some interesting results of structure-activity relationships were also observed. The results of this study pave the way for further design, synthesis, and development of paeonol derivatives as potential botanical anti-oomycete and antifungal agents in crop protection.

Isoxazoline: An Emerging Scaffold in Pesticide Discovery

Isoxazolines are five-membered heterocycle compounds with a wide range of pharmacological and pesticidal activities. Numerous marketed pesticides contain an isoxazoline motif as a key skeleton. Isoxazoline compounds have relatively simple syntheses and wide biological activities against various weeds, bacteria, and other pests. In recent years, they have received increasing attention and are widely used in organic chemistry research, such as intermediate and catalyst ligands in organic synthesis. They also have excellent optoelectronic properties and are widely used in the field of materials. Hence, the exploration of isoxazoline derivatives remains an important research area in pesticide discovery. This review provides an up-to-date overview of isoxazoline heterocycle compounds utilized as pesticides and in pesticide discovery, highlighting their structure and biological properties. It summarizes relevant publications from the last 10 years, offering insights into the recent advancements in this field of research.

Novel 5-(Trifluoromethyl)-1,2,4-oxadiazole-Based Pyrimidin-4-ether Histone Deacetylase Inhibitors for Controlling Rust Disease: Design, Synthesis, Activity, and Structure-Activity Relationship

Rust disease, an important plant pathogen, can lead to reduced crop or fruit production. Trifluoromethyloxadiazole (TFMO) is a class of histone deacetylase inhibitors (HDACs). Herein, a series of 5-(trifluoromethyl)-1,2,4-oxadiazole (TFMO)-based pyrimidin-4-ether derivatives were designed and synthesized. Antirust bioassay results of TFMOs showed that some of them possessed excellent activities against plant rust pathogens, such as Puccinia sorghi, Phakopsora pachyrhizi, and Puccinia rubigo. The most active compound, 3-(5-(((6-(difluoromethyl)pyrimidin-4-yl)oxy)methyl)thiophen-2-yl)-5-(trifluoromethyl)-1,2,4-oxadiazole (XII6), exhibited 50% control against P. pachyrhizi at 0.780 mg/L, which was significantly better than the commercial fungicide azoxystrobin (0%) at the same concentration. The field trial results indicated that the compound exhibited an excellent control effect against P. rubigo at 116 g a.i./ha. The acute toxic results indicated that compound XII6 has low toxicity. Furthermore, the enzyme activity results showed that compound XII6 is a strong, nonselective HDAC inhibitor. Finally, the structure-activity relationship was established, and the compound XII6-HDAC binding mode was carried out based on the crystal structure of hHDAC1, hHDAC4, and hHDAC6. This work provided an excellent fungicide against rust for further optimization.

Discovery of the Chlorinated and Ammoniated Derivatives of Vanillin as Potential Insecticidal Candidates Targeting V-ATPase: Structure-Based Virtual Screening, Synthesis, and Bioassay

Vacuolar-type H+-ATPases (V-ATPases) play a crucial role in the life cycle of agricultural pests and represent a promising target for the development of novel insecticides. In this study, S18, a derivative of vanillin acquired from Specs database using a structure-based virtual screening methodology, was first identified as a V-ATPase inhibitor. It binds to subunit A of the enzyme with a Kd of 1 nM and exhibits insecticidal activity against M. separata. Subsequently, using S18 as the lead compound, a new series of vanillin derivatives were rationally designed and efficiently synthesized. and their biological activities were assessed. Among them, compound 3b-03 showed the strongest insecticidal activity against M. separata by effectively targeting the V-ATPase subunit A with Kd of 0.803 μM. Isothermal titration calorimetric measurements and docking results provided insights into its interaction with subunit A of V-ATPase, which could facilitate future research aimed at the development of novel chemical insecticides.

Design, Synthesis, and Acaricidal/Insecticidal Activities of New Phenylpyrazole Derivatives Comprising an Imide Moiety

Using nicofluprole as the lead compound, we designed and synthesized a series of new phenylpyrazole analogues through substituting the methyl group on the nitrogen atom of the amide with an acyl group. Bioassay results showed that compounds A12-A17 with a 1-cyanocyclopropimide group exhibited outstanding insecticidal activity. The LC50 values for compounds A12-A17 against Tetranychus cinnabarinus ranged from 0.58 to 0.91 mg/L. Compound A15 showed an LC50 value of 0.29 and 3.10 mg/L against Plutella xylostella and Myzus persicae, respectively. Molecular docking indicated the potential binding interactions of compound A15 with a gamma-aminobutyric acid receptor. Additionally, density functional theory calculations implied that the 1-cyanocyclopropimide structure might be essential for its biological activity. Phenylpyrazole derivatives, containing a 1-cyanocyclopropimide fragment, have the potential for further development as potential insecticides.

Recent Research Progress in Oxime Insecticides and Perspectives for the Future

In recent decades, the unique structural attributes and purported insecticidal properties of oximes have garnered increasing attention. A variety of insecticides, encompassing fluxametamide, fluhexafon, and lepimectin, have been synthesized, all of which incorporate oximes. This review endeavors to encapsulate the insecticidal efficacy, structure-activity correlations, and operative mechanisms of oxime-containing compounds. Furthermore, it delves into the conceptual frameworks underpinning the design of innovative oxime-based insecticides, thereby shedding light on prospective advancements in this field.

Novel Insecticidal Butenolide-Containing Methylxanthine Derivatives: Synthesis, Crystal Structure, Biological Activity Evaluation, DFT Calculation and Molecular Docking

The design of novel agrochemicals starting from bioactive natural products is one of the most effective ways in the discovery and development of new pesticidal agents. In this paper, a series of novel butenolide-containing methylxanthine derivatives (Ia-Ir) were designed based on natural methylxanthine caffeine and stemofoline, and the derivatized insecticide flupyradifurone of the latter. The structures of the synthesized compounds were confirmed via 1H-NMR, 13C NMR, HRMS and X-ray single crystal diffraction analyses. The biological activities of the compounds were evaluated against a variety of agricultural pests including oriental armyworm, bean aphid, diamondback moth, fall armyworm, cotton bollworm, and corn borer; the results indicated that some of them have favorable insecticidal potentials, particularly toward diamondback moth. Among others, Ic and Iq against diamondback moth possessed LC50 values of 6.187 mg ⋅ L-1 and 3.269 mg ⋅ L-1, respectively, - 2.5- and 4.8-fold of relative insecticidal activity respectively to that of flupyradifurone (LC50=15.743 mg ⋅ L-1). Additionally, both the DFT theoretical calculation and molecular docking with acetylcholine binding protein were conducted for the highly bioactive compound (Ic). Ic and Iq derived from the integration of caffeine (natural methylxanthine) and butenolide motifs can serve as novel leading insecticidal compounds for further optimization.

Comparative Biological Half-Life of Penthiopyrad and Tebufenpyrad in Angelica Leaves and Establishment of Pre-Harvest Residue Limits (PHRLs)

To prevent pesticides from exceeding maximum residue limits (MRLs) in crops during export and shipment, it is necessary to manage residue levels during the pre-harvest stages. Therefore, the Republic of Korea establishes pre-harvest residue limits (PHRLs) per crop and pesticide. This study was conducted to set PHRLs for penthiopyrad and tebufenpyrad in angelica leaves, where the exceedance rates of MRLs are expected to be high. The LOQ of the analytical method used was 0.01 mg/kg and it demonstrated good linearity, with a correlation coefficient of 0.999 or higher within the quantitation range of 0.005 to 0.5 mg/kg. The recovery and storage stability accuracy values were in the range of 94.5-111.1%, within the acceptable range (70-120%, RSD ≤ 20%). The matrix effect for both pesticides was in the medium-to-strong range, and it did not significantly impact the quantitative results as a matrix-matched calibration method was employed. Using the validated method, residue concentrations of penthiopyrad 20 (%) EC and tebufenpyrad 10 (%) EC were analyzed. Both pesticides exhibited a decreasing residue trend over time. In Fields 1-3 and their integrated results, the biological half-life was within 2.6-4.0 days for penthiopyrad and 3.0-4.2 days for tebufenpyrad. The minimum value of the regression coefficient in the dissipation curve regression equation was selected as the dissipation constant. The selected dissipation constants for penthiopyrad in Fields 1-3 and their integration were 0.1221, 0.2081, 0.2162, and 0.1960. For tebufenpyrad, the dissipation constants were 0.1451, 0.0960, 0.1725, and 0.1600, respectively. The dissipation constant was used to calculate PHRL per field. Following the principles of the PHRL proposal process, residue levels (%) on PHI dates relative to MRLs were calculated, and fields for proposing PHRLs were selected. For penthiopyrad, since the residue level (%) was less than 20%, the PHRL for Field 3 with the largest dissipation constant was proposed. For tebufenpyrad, as the residue level (%) exceeded 80%, the PHRL proposal could not established. It is deemed necessary to reassess the MRL and 'guidelines for safe use' for tebufenpyrad in angelica leaves.

(NH4)2S2O8 promoted tandem radical cyclization of quinazolin-4(3H)-ones with oxamic acids for the construction of fused quinazolinones under metal-free conditions

A novel cascade radical addition/cyclization reaction of non-activated olefins and oxamic acids has been proposed. Under transition metal-free conditions, 36 quinazolinone derivatives containing an amide moiety were successfully synthesized, with the highest yield being 81%. This method involves the preparation of aminoacyl fused quinazolinone derivatives under mild conditions, offering advantages such as a high yield, a broad substrate compatibility, and a high atom economy.

Synthesis and Biological Activities of Novel Pyrazole Carboxamides Containing an Aryloxypyridyl Ethylamine Module

Pyrazole carboxamide is widely utilized in agricultural crop protection. In this research, we synthesized two classes of compounds, namely, pyrazole-5-carboxamide (4a) and pyrazole-4-carboxamide (4b), which are distinguished by the inclusion of the N-1-(6-aryloxypyridin-3-yl) ethylamine skeleton. This design was inspired by the frequent occurrence of diaryl ether modules in pesticide molecules. The bioassay results revealed that some compounds 4a exhibit higher insecticidal activity (IA) than 4b, while some compounds 4b display stronger fungicidal activity compared to 4a. This suggests that pyrazolyl plays a crucial role in determining the selectivity of these compounds toward different biological species. Notably, compound 4a-14 not only retains the potent activity of tolfenpyrad, the exact lead compound of 4a, against Lepidoptera pest Plutella xylostella and Thysanoptera pest Frankliniella occidentalis but also shows excellent IA against pests with piercing-sucking mouthparts, such as Aphis craccivora Koch and Nilaparvata lugens. This research has important implications for the control of pests with piercing-sucking mouthparts and the development of new insecticides and fungicides. The findings highlight the potential of inhibitory complex I as an effective control target for these pests, particularly those that have developed resistance to traditional insecticides. Additionally, it sheds light on the binding mode of 4b-11 and complex II, which serves as a negative reference for the design of SDHI fungicides. The study emphasizes the significance of pyrazolyl in determining selectivity in biological species and identifies avenues for future research in enhancing the biological activity of amino modules. The discovery of (S)-4a-14 not only presents a promising candidate compound for pesticide development but also provides valuable insights into the inhibitory effect of a respiratory chain complex on piercing-sucking insect pests. These findings have important implications in both theory and practice, offering new directions for pest control strategies and pesticide and fungicide development.

Novel Pyrazole Acyl(thio)urea Derivatives Containing a Biphenyl Scaffold as Potential Succinate Dehydrogenase Inhibitors: Design, Synthesis, Fungicidal Activity, and SAR

As part of a program to discover novel succinate dehydrogenase inhibitor fungicides, a series of new pyrazole acyl(thio)urea compounds containing a diphenyl motif were designed and synthesized. Their structures were confirmed by 1H NMR, HRMS, and single X-ray crystal diffraction analysis. Most of these compounds possessed excellent activity against 10 fungal plant pathogens at 50 μg mL-1, especially against Rhizoctonia solani, Alternaria solani, Sclerotinia sclerotiorum, Botrytis cinerea, and Cercospora arachidicola. Interestingly, compounds 3-(difluoromethyl)-1-methyl-N-((3',4',5'-trifluoro-[1,1'-biphenyl]-2-yl)carbamoyl)-1H-pyrazole-4-carboxamide (9b, EC50 = 0.97 ± 0.18 μg mL-1), 1,3-dimethyl-N-((3',4',5'-trifluoro-[1,1'-biphenyl]-2-yl)carbamoyl)-1H-pyrazole-4-carboxamide (9a, EC50 = 2.63 ± 0.41 μg mL-1), and N-((4'-chloro-[1,1'-biphenyl]-2-yl)carbamoyl)-1,3-dimethyl-1H-pyrazole-4-carboxamide (9g, EC50 = 1.31 ± 0.15 μg mL-1) exhibited activities against S. sclerotiorum that were better than the commercial fungicide bixafen (EC50 = 9.15 ± 0.05 μg mL-1) and similar to the positive control fluxapyroxad (EC50 = 0.71 ± 0.11 μg mL-1). These compounds were not significantly phytotoxic to monocotyledonous and dicotyledonous plants. Structure-activity relationships (SAR) are discussed by substituent effects/molecular docking, and density functional theory analysis indicated that these compounds are succinate dehydrogenase inhibitors.

Discovery of Highly Efficient Novel Antifungal Lead Compounds Targeting Succinate Dehydrogenase: Pyrazole-4-carboxamide Derivatives with an N-Phenyl Substituted Amide Fragment

Developing environmentally friendly fungicides is crucial to tackle the issue of rising pesticide resistance. In this study, a series of novel pyrazole-4-carboxamide derivatives containing N-phenyl substituted amide fragments were designed and synthesized. The structures of target compounds were confirmed by 1H NMR, 13C NMR, and HRMS, and the crystal structure of the most active compound N-(1-(4-(4-(tert-butyl)benzamido)phenyl)propan-2-yl)-3-(difluoromethyl)-N-methoxy-1-methyl-1H-pyrazole-4-carboxamide (U22) was further determined by X-ray single-crystal diffraction. The bioassay results indicated that the 26 target compounds possessed good in vitro antifungal activity against Sclerotinia sclerotiorum with EC50 values for compounds U12, U13, U15, U16, U18, U22, and U23 being 4.17 ± 0.46, 8.04 ± 0.71, 7.01 ± 0.71, 12.77 ± 1.00, 8.11 ± 0.70, 0.94 ± 0.11, and 9.48 ± 0.83 μg·mL-1, respectively, which were the similar to controls bixafen (6.70 ± 0.47 μg·mL-1), fluxapyroxad (0.71 ± 0.14 μg·mL-1), and pydiflumetofen (0.06 ± 0.01 μg·mL-1). Furthermore, in vivo antifungal activity results against S. sclerotiorum indicated that compounds U12 (80.6%) and U22 (89.9%) possessed excellent preventative efficacy at 200 μg·mL-1, which was the same as the control pydiflumetofen (82.4%). Scanning electron microscopy and transmission electron microscopy studies found that the compound U22 could destroy the hyphal morphology and damage mitochondria, cell membranes, and vacuoles. The results of molecular docking of compound U22 and pydiflumetofen with succinate dehydrogenase (SDH) indicated they interact well with the active site of SDH. This study validated our approach and design strategy to produce compounds with an enhanced biological activity as compared to the parent structure.

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.

Synthesis, Herbicidal Activity, Mode of Action, and In Silico Analysis of Novel Pyrido[2,3-d]pyrimidine Compounds

Natural products are a main source of new chemical entities for use in drug and pesticide discovery. In order to discover lead compounds with high herbicidal activity, a series of new pyrido[2,3-d] pyrimidine derivatives were designed and synthesized using 2-chloronicotinic acid as the starting material. Their structures were characterized with 1H NMR, 13C NMR and HRMS, and the herbicidal activities against dicotyledonous lettuce (Lactuca sativa), field mustard (Brassica campestris), monocotyledonous bentgrass (Agrostis stolonifera) and wheat (Triticum aestivum) were determined. The results indicated that most of the pyrido[2,3-d] pyrimidine derivatives had no marked inhibitory effect on lettuce at 1 mM. However, most of the pyrido[2,3-d] pyrimidine derivatives possessed good activity against bentgrass at 1 mM. Among them, the most active compound, 3-methyl-1-(2,3,4-trifluorophenyl)pyrido[2,3-d]pyrimidine-2,4(1H,3H)-dione (2o), was as active as the positive controls, the commercial herbicides clomazone and flumioxazin. Molecular simulation was performed with molecular docking and DFT calculations. The docking studies provided strong evidence that 2o acts as an herbicide by inhibition of protoporphyrinogen oxidase. However, the physiological results indicate that it does not act on this target in vivo, implying that it could be metabolically converted to a compound with a different molecular target.