Design, Synthesis, and Insecticidal Evaluation of Neonicotinoids with Conjugated Diene

Discovery of Novel Isoxazoline Derivatives Containing Pyrazolamide Fragment as Insecticidal Candidates

Lepidopteran species cause significant harm to agricultural yields and food quality. In this study, a series of innovative isoxazoline derivatives incorporating pyrazolamide moieties were carefully designed and synthesized as potential insecticidal agents. Among these, compound F16 demonstrated an LC50 value of 0.01 mg/L against Plutella xylostella, surpassing that of the lead compound fluxametamide (LC50 = 0.15 mg/L). Furthermore, F16 exhibited broad-spectrum insecticidal activity against Pyrausta nubilalis, Spodoptera frugiperda, Chilo suppressalis, Aphis craccivora, and Sogatella furcifera. Notably, F16 possessed low toxicity against Danio rerio, whereas fluxametamide displayed moderate toxicity. Furthermore, molecular docking analysis demonstrated that the potent insecticidal activity of F16 is likely mediated by its specific interactions with γ-GABA receptors primarily through the formation of hydrogen bonds with key residues. Density functional theory calculations and molecular electrostatic potentials were also performed to gain insights into the insecticidal behavior of F16. These findings suggest that F16 is a promising candidate for further investigation as a novel pesticide.

Discovery of Novel Neonicotinoids with Conjugated Diene Enabled by Cascade Allylation/Isomerization Synthetic Methodology

As one of the most significant insecticides, neonicotinoids have played a pivotal role in crop protection and public sanitation. However, the high resistance and bee toxicity of neonicotinoid insecticides have attracted considerable attention. Herein, a series of neonicotinoid compounds with conjugated diene moieties were synthesized through the cascade allylation/isomerization reaction. Most of the target compounds exhibited excellent insecticidal activities against Aphis craccivora, and some compounds exhibited good insecticidal activities against Mythimna separata. In particular, compound A15 showed outstanding insecticidal activity against A. craccivora (LC50 = 0.15 mg/L), which was superior to that of imidacloprid (LC50 = 0.36 mg/L). In addition, this candidate exhibited minimal cross-resistance to imidacloprid. The acute contact toxicity tests on Apis mellifera suggested that compound A15 was 10 times less toxic than imidacloprid. Electrophysiological experiments and molecular docking studies indicated that compound A15 exerted its insecticidal effects by interfering with nicotinic acetylcholine receptors. This work identifies a novel conjugated diene neonicotinoid candidate with significant potential for further development.

Ecological risks caused by neonicotinoid pesticides in sediments: A case study of freshwater basins in China

Neonicotinoid insecticides (NNIs) are extensively used in agricultural production in China due to their selective neurotoxicity towards target insects. In recent years, the rapid development of agriculture has increased the use and residue of NNIs. Consequently, the sediment environment, serving as the ultimate sink, is significantly impacted by NNIs. Upon release into the environment, NNIs can enter the human body through the food chain, posing potential ecological and human health risks. This study analyzed 79 sediment samples from two major river basins in North and South China, the Liaohe River basin in Liaoning Province and the Jianjiang River basin in Guangdong Province. The content, composition, distribution, and source of eight NNIs were analyzed, and assess the ecological and human health risks of the target compounds in these regions. The results indicated that the average concentration of NNIs in the sediments of the Jianjiang River basin (2.34 μg/kg) is slightly higher than that of the Liaohe River basin (2.32 μg/kg), and the sources of NNIs in the two areas were different, with differences in the sources of NNIs likely attributable to varying types of agricultural production. The risk assessment revealed that the ecotoxicological and public health risks were more pronounced in the Jianjiang River basin compared to the Liaohe River basin, underscoring the critical need for surveillance and management of hazardous substances like NNIs. The insights findings from this study can provide scientific guidance for the risk evaluation and environmental management of NNIs.

Discovery of Potent Selective HDAC6 Inhibitors with 5-Phenyl-1H-indole Fragment: Virtual Screening, Rational Design, and Biological Evaluation

Among the HDACs family, histone deacetylase 6 (HDAC6) has attracted extensive attention due to its unique structure and biological functions. Numerous studies have shown that compared with broad-spectrum HDACs inhibitors, selective HDAC6 inhibitors exert ideal efficacy in tumor treatment with insignificant toxic and side effects, demonstrating promising clinical application prospect. Herein, we carried out rational drug design by integrating a deep learning model, molecular docking, and molecular dynamics simulation technology to construct a virtual screening process. The designed derivatives with 5-phenyl-1H-indole fragment as Cap showed desirable cytotoxicity to the various tumor cell lines, all of which were within 15 μM (ranging from 0.35 to 14.87 μM), among which compound 5i had the best antiproliferative activities against HL-60 (IC50 = 0.35 ± 0.07 μM) and arrested HL-60 cells in the G0/G1 phase. In addition, 5i exhibited better isotype selective inhibitory activities due to the potent potency against HDAC6 (IC50 = 5.16 ± 0.25 nM) and the reduced inhibitory activities against HDAC1 (selective index ≈ 124), which was further verified by immunoblotting results. Moreover, the representative binding conformation of 5i on HDAC6 was revealed and the key residues contributing 5i's binding were also identified via decomposition free-energy analysis. The discovery of lead compound 5i also indicates that virtual screening is still a beneficial tool in drug discovery and can provide more molecular skeletons with research potential for drug design, which is worthy of widespread application.

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.

Design, synthesis, and evaluation of novel arecoline-linked amino acid derivatives for insecticidal and antifungal activities

A series of arecoline derivatives with amino acid moieties were designed and synthesised using an acylamide condensation strategy, taking arecoline as the foundational structure. The insecticidal efficacy of these compounds against Aphis craccivora and Tetranychus cinnabarinus was evaluated. Notably, derivatives 3h and 3i demonstrated superior insecticidal activity compared with arecoline. Additionally, 3h and 3i showed good fungicidal effectiveness against two types of plant fungi. Moreover, molecular docking analyses suggested that 3h and 3i could affect the nervous systems of A. craccivora and T. cinnabarinus by binding to neuronal nicotinic acetylcholine receptors. These findings suggest that compounds 3h and 3i represent promising leads for further development in insecticide and fungicide research.

Design, synthesis and insecticidal activity of novel Isoxazoline Acylhydrazone compounds

BACKGROUND

Nowadays, the diamondback moth has ascended to become one of the most formidable pests plaguing cruciferous vegetables. Consequently, the exigency for the development of efficacious pesticide candidates for crop protection has never been more paramount. In response to this pressing need, this study presents a compendium of novel isoxazoline derivatives, incorporating acylhydrazone moieties, synthesized with the express purpose of serving as potential insecticides.

RESULTS

The structures of these derivatives were confirmed using Proton nuclear magnetic resonance (1 H NMR), Carbon-13 nuclear magnetic resonance (13 C NMR), and high-resolution mass spectrometry (HR-MS). Most of these derivatives demonstrated effective insecticidal activities against Plutella xylostella. Notably, compound E3 exhibited exceptional insecticidal activity against Plutella xylostella (LC50  = 0.19 mg L-1 ), surpassing the effectiveness of ethiprole (LC50  = 3.28 mg L-1 ), and comparable to that of fluxametamide (LC50  = 0.22 mg L-1 ). Interestingly, compound E3 also displayed potent insecticidal activity against Pyrausta nubilalis (LC50  = 0.182 mg L-1 ) and Chilo suppressalis (LC50  = 0.64 mg L-1 ), and the LC50 values of fluxametamide were 0.23 mg L-1 (P. nubilalis) and 2.26 mg L-1 (C. suppressalis), respectively. The molecular docking results revealed that the compound E3 can form a hydrogen bond and two Pi-Pi bonds with the active sites of GABA receptors. In addition, the DFT calculations were also performed to study the relationship between insecticidal activities. The structure-activity relationships suggested that the identity of the R substituent was crucial for their pesticidal activities.

CONCLUSION

The results of the present study suggest that isoxazoline acylhydrazone derivatives could be promising candidates against P. xylostella and other Lepidopteran pests. © 2023 Society of Chemical Industry.