Design, Synthesis, and Biological Activity of Novel Heptacyclic Pyrazolamide Derivatives: A New Candidate of Dual-Target Insect Growth Regulators

Sodium Iodide-Promoted Construction of Fully Substituted 4-Sulfenyl-5-aminopyrazole Derivatives

Transition-metal-free synthesis of diversely substituted 4-sulfenyl-5-aminopyrazoles was developed under mild conditions through NaI-mediated three-component reaction of β-ketonitriles, disulfides, and hydrazines. The pyrazole products were constructed via consecutive cleavage of C-O and S-S bonds and recombination of C-N and C-S bonds. The methodology features broad substrate scope, mild transition-metal-free conditions, and easy manipulation.

Discovery of novel seven-membered ring derivatives of ONC212 as caseinolytic protease P protein activators using the ring expansion strategy: Rational design, synthesis, and antibacterial evaluation

Caseinolytic protease P (ClpP) protein is essential for prokaryotic and eukaryotic protein homeostasis, and has emerged as a promising bactericidal target for controlling bacterial infection and evading the emergent of drug-resistance risk. As the unique bactericidal mechanism, ClpP loses its substrate specificity and undergoes uncontrolled protein hydrolysis in the presence of an activator, leading to causing bacterial death. To further expand the chemotype of ClpP activator, a series of ONC212 derivatives were synthesized using a ring expansion strategy. Surprisingly, compound A14 showed optimal antibacterial activity against Xanthomonas oryzae pv. oryzae (Xoo) in vitro (EC50 value = 3.86 μg/mL), which was >6 × more potent than the EC50 value of ONC212 (26.42 μg/mL). Molecular docking, fluorescence titration and degradation experiments of the XooFtsZ protein indicated that compound A14 was a strong degrader of XooClpP towards XooFtsZ. In vivo assays showed that the control activity of compound A14 (200 μg/mL) reached 47.47 %, compared to 41.57 %, 36.72 %, and 30.43 % for ONC212, thiodiazole copper, and bismerthiazol, respectively. Overall, this study led to the identification compound A14, which not only showed improved antibacterial potency, and maintained the binding XooClpP, but also highlighted the ring expansion strategy as a promising approach for bactericide discovery.

A Potential Multitarget Insect Growth Regulator Candidate: Design, Synthesis, and Biological Activity of Novel Acetamido Derivatives Containing Hexacyclic Pyrazole Carboxamides

Insect growth regulators (IGRs) are important green insecticides that disrupt normal growth and development in insects to reduce the harm caused by pests to crops. The ecdysone receptor (EcR) and three chitinases OfChtI, OfChtII, and OfChi-h are closely associated with the molting stage of insects. Thus, they are considered promising targets for the development of novel insecticides such as IGRs. Our previous work identified a dual-target compound 6j, which could act simultaneously on both EcR and OfChtI. In the present study, 6j was first found to have inhibitory activities against OfChtII and OfChi-h, too. Subsequently, taking 6j as a lead compound, 19 novel acetamido derivatives were rationally designed and synthesized by introducing an acetamido moiety into the amide bridge based on the flexibility of the binding cavities of 6j with EcR and three chitinases. Then, their insecticidal activities against Plutella xylostella (P. xylostella), Ostrinia furnacalis (O. furnacalis), and Spodoptera frugiperda (S. frugiperda) were carried out. The bioassay results revealed that most of these acetamido derivatives possessed moderate to good larvicidal activities against three lepidopteran pests. Especially, compound I-17 displayed excellent insecticidal activities against P. xylostella (LC50, 93.32 mg/L), O. furnacalis (LC50, 114.79 mg/L), and S. frugiperda (86.1% mortality at 500 mg/L), significantly better than that of 6j. In addition, further protein validation and molecular docking demonstrated that I-17 could act simultaneously on EcR (17.7% binding activity at 8 mg/L), OfChtI (69.2% inhibitory rate at 50 μM), OfChtII (71.5% inhibitory rate at 50 μM), and OfChi-h (73.9% inhibitory rate at 50 μM), indicating that I-17 is a potential lead candidate for novel multitarget IGRs. This work provides a promising starting point for the development of novel types of IGRs as pest management agents.

1,2,4-Triazole benzamide derivative TPB against Gaeumannomyces graminis var. tritici as a novel dual-target fungicide inhibiting ergosterol synthesis and adenine nucleotide transferase function

BACKGROUND

Isopropyl 4-(2-chloro-6-(1H-1,2,4-triazol-1-yl)benzamido)benzoate (TPB) was a 1,2,4-triazole benzoyl arylamine derivative with excellent antifungal activity, especially against Gaeumannomyces graminis var. tritici (Ggt). Its mechanism of action was investigated by transmission electron microscopy (TEM) observation, assays of sterol composition, cell membrane permeability, intracellular ATP and mitochondrial membrane potential, and mPTP permeability, ROS measurement, RNA sequencing (RNA-seq) analysis.

RESULTS

TPB interfered with ergosterol synthesis, reducing ergosterol content, increasing toxic intermediates, and finally causing biomembrane disruption such as increasing cell membrane permeability and content leakage, and destruction of organelle membranes such as coarse endoplasmic reticulum and vacuole. Moreover, TPB destroyed the function of adenine nucleotide transferase (ANT), leading to ATP transport obstruction in mitochondria, inhibiting mPTP opening, inducing intracellular ROS accumulation and mitochondrial membrane potential loss, finally resulting in mitochondrial damage including mitochondria swelled, mitochondrial membrane dissolved, and cristae destroyed and reduced. RNA-seq analyses showed that TPB increased the expression of ERG11, ERG24, ERG6, ERG5, ERG3 and ERG2 genes in ergosterol synthesis pathway, interfered with the expression of genes (NDUFS5, ATPeV0E, NCA2 and Pam17) related to mitochondrial structure, and inhibited the expression of genes (WrbA and GST) related to anti-oxidative stress.

CONCLUSIONS

TPB exhibited excellent antifungal activity against Ggt by inhibiting ergosterol synthesis and destroying ANT function. So, TPB was a novel compound with dual-target mechanism of action and can be considered a promising novel fungicide for the control of wheat Take-all. The results provided new guides for the structural design of active compounds and powerful tools for pathogen resistance management. © 2023 Society of Chemical Industry.

Discovery of New Botanical Insecticides: Identification and Insecticidal Activity of Saponins from Clematis obscura Maxim and Insights into the Stress Response of Acyrthosiphon pisum Harris

To discover new botanical products-based insecticide candidates, 14 triterpenoid saponins (1-14) including four new ones, obscurosides A-D (1-4), were isolated from Clematis obscura Maxim as potential agrochemicals against Acyrthosiphon pisum Harris and Plutella xylostella (L.). Compounds 1-3 were characterized by a rare ribose substitution at C-3, and 4 was a bidesmoside glycosylated at the rare C-23 and C-28 positions of the oleanane aglycone. Compounds 10 (median antifeeding concentration, AFC50 = 1.10 mg/mL; half-lethal concentration, LC50 = 1.21 mg/mL) and 13 (AFC50 = 1.09 mg/mL, LC50 = 1.37 mg/mL) showed significant insecticidal activities against third larvae of P. xylostella at 72 h. All saponins displayed antifeedant activities against A. pisum with the deterrence index of 0.20-1.00 at 400 μg/mL. Compound 8 showed optimal oral toxicity (LC50 = 50.09 μg/mL) against A. pisum, followed by compounds 1, 5-7, 9, and 14 (LC50 = 90.21-179.25 μg/mL) at 72 h. The shrinkage of the cuticle and the destruction of intestinal structures of microvilli, nucleus, endoplasmic reticulum, and mitochondria were toxic symptoms of 8-treated A. pisum. The significantly declined Chitinase activity in 8-treated A. pisum with an inhibition rate of 79.1% at LC70 (70% lethal concentration) could be the main reason for its significant oral toxicities. Molecular docking revealed favorable affinities of compounds 1 and 8 with group I Chitinase OfChtI (Group I Chitinase from Ostrinia furnacalis) through conventional hydrogen bonds and alkey/π-alkey interactions by different patterns. These results will provide valuable information for the development of novel botanical pesticides for the management of insect pests, especially against A. pisum.

Design, Synthesis, and Herbicidal Activity of Pyrazole Amide Derivatives as Potential Transketolase Inhibitors

The design and synthesis of new herbicidal active compounds based on a new target are of great significance for the development of new herbicides. Transketolase (TK) plays a key role in the Calvin cycle of plant photosynthesis and has been confirmed as a potential candidate target to develop and discover new herbicides. To obtain compounds with ultraefficient targeting of TK, a series of pyrazole amide derivatives were designed and synthesized through structural optimization for lead compound 4u based on TK as the new target. The bioassay results showed that compounds 6ba and 6bj displayed a highly inhibitory effect with the root inhibition of about 90% against Digitaria sanguinalis (DS) and 80% against Amaranthus retroflexus (AR) and Setaria viridis (SV) by the small cup method, which was better than the positive control mesotrione and nicosulfuron. Furthermore, compounds 6ba and 6bj exhibited an excellent inhibitory effect with the inhibition of about 80% (against DS) and over 80% (against SV) at the dosage of 150 g of active ingredient/ha by the foliar spray method. The TK enzyme activity inhibition test showed that the inhibition effect of target compounds against TK was consistent with the results of herbicidal activities. Also, molecular docking analysis showed that compounds 6ba and 6bj went deep into the active cavity of TK, bound to TK by a strong interaction, and might act on the enzyme TK. Above of all, compounds 6ba and 6bj are promising herbicide lead compounds targeting TK. Hence, they could be developed into more efficient herbicides by further structural optimization.

Synthesis and Insecticidal Activity Study of Azidopyridryl Containing Dichlorolpropene Ether Derivatives

Pyridalyl, as a novel insecticide with an unknown mode of action, has shown excellent control efficacy against lepidopterous larvae and thrips. Previous modifications of this compound have mostly focused on the pyridine moiety, with limited information available about modifications to other parts of pyridalyl. In this paper, we report the synthesis and insecticidal activity of a series of azidopyridryl-containing dichlorolpropene ether derivatives, based on modifications to the middle alkyl chain of pyridalyl. Screening results for insecticidal activity indicate that our synthesized compounds show moderate to high activities at the tested concentrations against P. xylostella. Particularly, compound III-10 exhibits a LC50 value of 0.831 mg L-1, compared to the LC50 value of pyridalyl at 2.021 mg L-1. Furthermore, compound III-10 also displays a relatively broad insecticidal spectrum against Lepidoptera pests M. separata, C. suppressalis, O. nubilalis, and C. medinalis. Finally, in field trials, III-10 demonstrates better control efficiency against Chilo suppressalis compared to pyridalyl. Overall, our findings suggest that the modification of the middle alkyl chain of pyridalyl may be a promising approach for developing insecticides with improved efficacy.

Discovery of Novel Isoxazoline Derivatives Containing Diaryl Ether against Fall Armyworms

With the continuous evolution of insect resistance, it is a tremendous challenge to control the fall armyworm (Spodoptera frugiperda) with traditional insecticides. To solve this pending issue, a series of novel isoxazoline derivatives containing diaryl ether structures were designed and synthesized, and most of the target compounds exhibited excellent insecticidal activity. Based on the three-dimensional quantitative structure-activity relationship (3D-QSAR) model analysis, we further optimized the molecular structure with compound L35 obtained and tested for its activity. Compound L35 (LC₅₀ = 1.69 mg/L) exhibited excellent insecticidal activity against S. frugiperda, which was better than those of commercial fipronil (LC₅₀ = 70.78 mg/L) and indoxacarb (LC₅₀ = 5.37 mg/L). The enzyme-linked immunosorbent assay showed that L35 could upregulate the levels of GABA in insects. In addition, molecular docking and transcriptomic results also indicated that compound L35 may affect the nervous system of S. frugiperda by acting on GABA receptors. Notably, through high-performance liquid chromatography (HPLC), we were able to obtain the two enantiomers of compound L35, and the insecticidal activity test revealed that S-(+)-L35 was 44 times more active than R-(-)-L35 against S. frugiperda. This study established the chemistry basis and mechanistic foundations for the future development of pesticide candidates against fall armyworms.

A Potential Lead for Insect Growth Regulator: Design, Synthesis, and Biological Activity Evaluation of Novel Hexacyclic Pyrazolamide Derivatives

Ecdysone receptor (EcR) and chitinase play a critical role in the molting stage of insect pests. Each of them is considered a promising target for the development of novel insect growth regulators (IGRs). In the present paper, a total of 24 (23 novel) hexacyclic pyrazolamide derivatives were designed and synthesized by reducing the heptacycle and inserting small flexible linkers on the basis of the previously discovered dual-target compound D-27 acting simultaneously on EcR and Ostrinia furnacalis chitinase (OfChtI). Their insecticidal activities against Plutella xylostella, Spodoptera frugiperda, and Ostrinia furnacalis larvae were evaluated. The results revealed that the insecticidal activity was not significantly enhanced when the heptacycle on the pyrazole ring was reduced to a hexacycle. However, the insertion of an additional methylene spacer between the substituted phenyl ring and the amide bond can improve the insecticidal activity. Among the derivatives, the most potent compound, 6j, exhibited promising insecticidal activities against P. xylostella and S. frugiperda. Further protein binding assays and molecular docking indicated that 6j could target both EcR and OfChtI, and is a potential lead compound for IGRs. The present work provides valuable clues for the development of new dual-target IGRs.

Discovery of Novel Isoxazoline Compounds that Incorporate a para-Diamide Moiety as Potential Insecticidal Agents against Fall Armyworm (Spodoptera frugiperda)

Spodoptera frugiperda is a major migratory agricultural pest, which seriously impedes agricultural production around the world. To discover potent compounds against S. frugiperda, a number of novel isoxazoline derivatives were designed and synthesized and created on account of the identified lead compound F32 (4-(5-(3,5-dichlorophenyl)-5-(trifluoromethyl)-4,5-dihydroisoxazol-3-yl)-2-methyl-N-(3-propionamidophenyl)benzamide). Based on the three-dimensional quantitative structure-activity relationship of those compounds, the compound G22 (N-(4-acetamidophenyl)-4-(5-(3,5-dichlorophenyl)-5-(trifluoromethyl)-4,5-dihydroisoxazol-3-yl)-2-methylbenzamide) was developed. A bioassay showed that G22 is highly lethal to S. frugiperda (LC₅₀ = 1.57 mg/L), a more effective control than insecticides fipronil (LC₅₀ = 78.8 mg/L) and chlorantraniliprole (LC₅₀ = 1.60 mg/L). Field trials were also implemented to identify candidate agents. Furthermore, from the insect γ-aminobutyric acid (GABA) enzyme-linked immunosorbent assay, it is obvious that G22 could up-regulate the expression of GABA of insects, which showed a similar result to fipronil. The analysis of molecular docking exhibited that the hydrophobic effect and hydrogen bonds play key roles in the combination between G22 with GABA receptors. This study provides a potent isoxazoline candidate compound for the S. frugiperda control.

Design, Synthesis, and Insecticidal Activity of Novel Isoxazoline Compounds That Contain Meta-diamides against Fall Armyworm (Spodoptera frugiperda)

Fall armyworm (Spodoptera frugiperda) is a major migratory pest around the entire world that causes severe damage to agriculture. We designed and synthesized a series of novel isoxazoline derivatives based on the previously discovered active compound H13 to find new and effective candidates against S. frugiperda. Most of them showed excellent insecticidal activity. In addition, a three-dimensional quantitative structure-activity relationship model was established, and compound F32 was designed and synthesized based on the results. The bioassay result showed that compound F32 exhibited excellent activity against S. frugiperda (LC₅₀ = 3.46 mg/L), which was substantially better than that of the positive control fipronil (LC₅₀ = 78.8 mg/L). Furthermore, an insect γ-aminobutyric acid (GABA) enzyme-linked immunosorbent assay indicated that F32 can upregulate the content of GABA in insects in a manner similar to that of fipronil. Molecular docking showed that the hydrophobic effect and hydrogen-bond interactions are vital factors between the binding of F32 and receptors. All of these results suggest that compound F32 could be employed as a novel isoxazoline lead compound to control S. frugiperda.

Design, Synthesis, and Bioactivity of Spiro Derivatives Containing a Pyridine Moiety

We designed and synthesized a series of pyridine spiro derivatives and evaluated their insecticidal and antiviral activities. Some compounds exhibited good insecticidal and antiviral activities. Notably, the E series of compounds displayed good insecticidal activity against Tetranychus urticae. Compounds E20 (EC₅₀ = 63.68 mg/L) and F4 (EC₅₀ = 47.81 mg/L) exhibited inactivation activities against the tobacco mosaic virus (TMV), which were similar to that of Ningnanmycin (EC₅₀ = 58.01 mg/L). Molecular docking showed that compounds E20 and F4 exhibited satisfactory affinities for the TMV coat protein (TMV-CP), with binding energies (-6.7 and -6.4 kcal/mol, respectively) slightly lower than that of Ningnanmycin (-6.3 kcal/mol). Further, molecular dynamics analysis revealed that compounds E20 and F4 exhibited better binding stability values than Ningnanmycin. Microscale thermophoresis showed that compounds E20 (K_d = 0.053 ± 0.016 μM) and F4 (K_d = 0.045 ± 0.022 μM) bound more strongly to TMV-CP than Ningnanmycin (K_d = 0.10 ± 0.029 μM). The results of transmission electron microscopy showed that these two compounds hindered the self-assembly and growth of TMV. In summary, we showed that these pyridine spiro derivatives could be used as a basis for the research and development of novel pesticides.

Discovery of (5-(Benzylthio)-4-(3-(trifluoromethyl)phenyl)-4H-1,2,4-triazol-3-yl) Methanols as Potent Phytoene Desaturase Inhibitors through Virtual Screening and Structure Optimization

Phytoene desaturase (PDS) is not only an important enzyme in the biosynthesis of carotenoids but also a promising target for herbicide discovery. However, in recent years, no expected PDS inhibitors with new scaffolds have been reported. Hence, a solution for developing PDS inhibitors is to search for new compounds with novel chemotypes based on the PDS protein structure. In this work, we integrated structure-based virtual screening, structure-guided optimization, and biological evaluation to discover some PDS inhibitors with novel chemotypes. It is noteworthy that the highly potent compound 1b, 1-(4-chlorophenyl)-2-((5-(hydroxymethyl)-4-(3-(trifluoromethyl)phenyl)-4H-1,2,4-triazol-3-yl)thio)ethan-1-one, exhibited a broader spectrum of post-emergence herbicidal activity at 375-750 g/ha against six kinds of weeds than the commercial PDS inhibitor diflufenican. Surface plasmon resonance (SPR) assay showed that the affinity of our compound 1b (K_D = 65.9 μM) to PDS is slightly weaker but at the same level as diflufenican (K_D = 38.3 μM). Meanwhile, determination of the phytoene content and PDS mRNA quantification suggested that 1b could induce PDS mRNA reduction and phytoene accumulation. Moreover, 1b also caused the increase of reactive oxygen species (ROS) and the change of ROS-associated enzyme activity in albino leaves. Hence, all these results indicated the feasibility of PDS protein structure-based virtual screen and structure optimization to search for highly potent PDS inhibitors with novel chemotypes for weed control.

Structure-Based Bioisosterism Design, Synthesis, Biological Activity and Toxicity of 1,2,4-Oxadiazole Substituted Benzamides Analogues Containing Pyrazole Rings

In order to discover pesticidal lead compounds with high activity and low toxicity, a series of novel benzamides substituted with pyrazole-linked 1,2,4-oxadiazole were designed via bioisosterism. The chemical structures of the target compounds were confirmed via ¹H NMR, ¹³C NMR and HRMS analysis. The preliminary bioassay showed that most compounds exhibited good lethal activities against Mythimna separate, Helicoverpa armigera, Ostrinia nubilalis and Spodoptera frugiperda at 500 mg/L. Particularly in the case of Mythimna separate, compound 14q (70%) exhibited obvious insecticidal activity. In addition, compound 14h demonstrated good fungicidal activity against Pyricularia oryae with an inhibition rate of 77.8%, and compounds 14e, 14k, 14n and 14r also showed certain antifungal activities (55.6–66.7%). The zebrafish toxicity test showed that the LC₅₀ of compound 14h was 14.01 mg/L, which indicated that it may be used as a potential leading compound for further structural optimization.

Rational Design, Synthesis, and Biological Investigations of N-Methylcarbamoylguanidinyl Azamacrolides as a Novel Chitinase Inhibitor

Chitinase is one of the most important glycoside hydrolyases, widely existing in bacteria, fungi, insects, and plants. It is involved in fungal cell wall remodeling and insect molting. Chitinase inhibitors are an effective means of controlling pathogens and pests. Natural product argifin is a 17-membered pentapeptide that exhibits efficient chitinase inhibitory activity. However, the complexity of the synthetic process results in a lot of restrictions for wide range of applications. In this work, we designed a series of azamacrolide chitinase inhibitors based on the structural features of argifin that have high inhibitory activities against bacterial and insectile chitinase. The most potent chitinase inhibitor compound 19c exhibited IC₅₀ values of 56 nM and 110 nM against OfChi-h and SmChiB, respectively. The molecular docking and molecular dynamics simulations revealed that all inhibitors were bound to the -1 subsite of chitinases via N-methylcarbamoylguanidinyl as well as argifin. Finally, a bioactivity assay against pests was carried out. Compound 18a showed 80% mortality for Mythimna separata at a concentration of 50 mg/L. Besides, insecticides 19b and 19c exhibited high mortality against Plutella xylostella (76 and 73% mortalities at 50 mg/L, respectively).

Crystal structure of 3-(difluoromethyl)-1-methyl-N-(4,11,11-trimethyl-1,2,3,4-tetrahydro-1,4-methanoacridin-9-yl)-1H-pyrazole-4-carboxamide monohydrate, C23H26F2N4O3

C23H26F2N4O3, orthorhombic, P212121 (no. 19), a = 11.6524(10) Å, b = 11.9777(10) Å, c = 15.9058(13) Å, V = 2220.0(3) Å3, Z = 4, R gt (F) = 0.0305, wR ref (F 2) = 0.0751, T = 296(2) K.

A Piperine-Based Scaffold as a Novel Starting Point to Develop Inhibitors against the Potent Molecular Target OfChtI

The insect chitinase OfChtI from the agricultural pest Ostrinia furnacalis (Asian corn borer) is a promising target for green insecticide design. OfChtI is a critical chitinolytic enzyme for the cuticular chitin degradation at the stage of molting. In this study, piperine, a natural amide compound isolated from black pepper, Piper nigrum L., was discovered for the first time to have inhibitory activity toward OfChtI. The compound-enzyme interaction was presumed to take place between the piperine benzo[d][1,3] dioxole skeleton and subsite -1 of the substrate-binding pocket of OfChtI. Hence, on the basis of the deduced inhibitory mechanism and crystal structure of the substrate-binding cavity of OfChtI, compounds 5a-f were designed and synthesized by introducing a butenolide scaffold into the lead compound piperine. The enzymatic activity assay indicated that compounds 5a-f (K_i = 1.03-2.04 μM) exhibited approximately 40-80-fold higher inhibitory activity than the lead compound piperine (I) (K_i = 81.45 μM) toward OfChtI. The inhibitory mechanism of the piperonyl butenolide compounds was elucidated by molecular dynamics, which demonstrated that the introduced butenolide skeleton improved the binding affinity to OfChtI. Moreover, the in vivo activity assay indicated that these compounds also displayed moderate insecticidal activity toward O. furnacalis. This work introduces the natural product piperine as a starting point for the development of novel insecticides targeting OfChtI.

Highly Efficient Synthesis and Acaricidal and Insecticidal Activities of Novel Oxazolines with N-Heterocyclic Substituents

Nitrogen heterocycles are found in numerous natural products, pharmaceuticals, and pesticides. Herein, we report the design and synthesis of a series of novel 2,4-diphenyl-1,3-oxazolines bearing various N-heterocyclic substituents via a 4-(4-(chloromethyl)phenyl)-2-(2,6-difluorophenyl)-4,5-dihydrooxazole intermediate generated by a modified Ritter reaction. Evaluation of the activities of the oxazolines against carmine spider mites (Tetranychus cinnabarinus) by means of a leaf-dipping method showed that most of the compounds exhibited good to excellent larvicidal and ovicidal activities. In particular, five compounds (one with a phthalimidyl group and four with a substituted indolyl group) have lower LC₅₀ values than the commercial acaricide etoxazole (0.088 mg/L against larvae and 0.128 mg/L against eggs). This work lays a foundation for the development of novel acaricides.

Design, Synthesis, and Molecular Mechanism Studies of N-Phenylisoxazoline-thiadiazolo[3,4-a]pyridazine Hybrids as Protoporphyrinogen IX Oxidase Inhibitors

Protoporphyrinogen oxidase (PPO, EC 1.3.3.4) is an important target for green agrochemical discovery. Herein, a novel N-phenylisoxazoline-thiadiazolo[3,4-a]pyridazine herbicidal active scaffold was designed by the scaffold hybridization strategy. Systematic structural optimization enabled the discovery of a series of derivatives with excellent weed control at 9.375-150 g ai/ha by the post-emergent application. Some derivatives exhibited improved Nicotiana tabacum PPO (NtPPO)-inhibitory activity than fluthiacet-methyl. Of these, 2b, with K_i = 21.8 nM, displayed higher weed control than fluthiacet-methyl at the rate of 12-75 g ai/ha, and selective to maize at 75 g ai/ha. In planta, 2b was converted into a bioactive metabolite 5 (K_i = 4.6 nM), which exhibited 4.6-fold more potency than 2b in inhibiting the activity of NtPPO. Molecular dynamics simulation explained that 5 formed stronger π-π interaction with Phe392 than that of 2b. This work not only provides a promising lead compound for weed control in maize fields but is also helpful to understand the molecular mechanism and basis of the designed hybrids.

New lead discovery of insect growth regulators based on the scaffold hopping strategy

Insect growth regulators (IGRs), which can interrupt or inhibit pest life cycles, are low-toxicity pesticides widely used in integrated pest management (IPM). Ecdysone analogues and chitinase inhibitors are familiar IGRs that have attracted considerable attention because of their unique modes of action and low toxicity to non-target organisms. To find new and highly effective candidate IGRs with novel mechanisms, D-08 (N-(4-(tert-butyl)phenyl)-2-phenyl-2,4,5,6,7,8-hexahydrocyclohepta[c]pyrazole-5-carboxamide) was chosen as a lead compound, and a series of novel heptacyclic pyrazolamide derivatives were designed and synthesized using the scaffold hopping strategy. The bioassay showed that III-27 (N-(2-methylphenethyl)-1-phenyl-1,4,5,6,7,8-hexahydrocyclohepta[c]pyrazole-5-carboxamide) had excellent activity against Plutella xylostella. Protein verification and molecular docking indicated that III-27 could act on both the ecdysone receptor (EcR) and Ostrinia furnacalis chitinase (Of ChtI) and is a promising new lead IGRs. The interaction mechanism of III-27 with EcR and Of ChtI was then studied by molecular docking. These results provide important guidance for the study of new dual-target IGRs.