Spirodiclofen ether derivatives: semisynthesis, structural elucidation, and pesticidal activities against Tetranychus cinnabarinus Boisduval, Aphis citricola Van der Goot and Mythimna separata Walker

Diversifying the benzenesulfonamide scaffold for potential V-ATPase inhibitors: synthesis and insecticidal activity evaluation

Celangulin V is a natural β-dihydroagarofuran derivative isolated from Celastrus angulatus which shows insecticidal activity in many agricultural pests. Using celangulin V as a molecular probe, we find out a new pesticide target: subunit H of V-ATPase. To explore the potential application of this novel target, lead sulfonamides have been found through virtual screening. Combined with the previous work, 46 sulfonamide derivatives are designed and synthesized. All target compounds are first screened for their insecticidal activities against Mythimna separata. The results of bioassay reveal that most of the designed compounds exhibit significant insecticidal activities against third-instar larvae of M. separata under the concentration of 10 mg/mL, and compound 8.4 shows the highest activity with LC50 value of 1.72 mg/mL, 15-fold smaller than that of celangulin V (25.89 mg/mL). Molecular docking results further indicated that compound 8.4 might serve as a potential inhibitor of the subunit H of V-ATPase. This study provides a potential sulfonamide candidate compound for the M. separata control.

Plant natural product-based pesticides in crop protection: semi-synthesis, mono-crystal structures and agrochemical activities of osthole ester derivatives, and study of their toxicology against Tetranychus cinnabarinus (Boisduval)

BACKGROUND

Owing to large amounts of synthetic pesticides being extensively and unreasonably used for crop protection, currently, resistance and negative impacts on human health and environment safety have appeared. Therefore, development of potential pesticide candidates is highly urgent. Herein, a series of ester derivatives of osthole were designed and synthesized as pesticidal agents.

RESULTS

Six spatial configurations of 4'-(p-toluenoyloxy)osthole (4b), 4'-(m-fluorobenzoyloxy)osthole (4f), 4'-(p-fluorophenylacetyloxy)osthole (4m), 4'-(3'',4''-methylenedioxybenzoyloxy)osthole (4q), 4'-formyloxyosthole (4u) and 4'-acetyloxyosthole (4v) were determined by X-ray mono-crystal diffraction. Compounds 4b, 4'-(p-chlorobenzoyloxy)osthole (4g), 4'-(m-chlorobenzoyloxy)osthole (4h), 4'-(p-bromobenzoyloxy)osthole (4i) and 4'-(2''-chloropyridin-3''-ylcarbonyloxy)osthole (4p) showed higher insecticidal activity than toosendanin against Mythimna separata Walker; notably, compound 4b displayed 1.8 times insecticidal activity of the precursor osthole. Against Tetranychus cinnabarinus Boisduval, compounds 4g and 4h showed 3.3 and 2.6 times acaricidal activity of osthole, and good control effects in the glasshouse. Scanning electron microscopy assay demonstrated that compound 4g can damage the cuticle layer of T. cinnabarinus resulting in death.

CONCLUSION

Compounds 4g and 4h can be further studied as lead pesticidal agents for the management of M. separata and T. cinnabarinus. These results will pave the way for application of osthole derivatives as agrochemicals. © 2024 Society of Chemical Industry.

Synergistic action and mechanism of scoparone, a key bioactive component of Artemisia capillaris, and spirodiclofen against spider mites

BACKGROUND

Plants have numerous defensive secondary metabolites to withstand insect attacks. Scoparone, which is extracted from the medicinal plant Artemisia capillaris, has potent acaricidal effects on Tetranychus cinnabarinus. Spirodiclofen, derived from a tetronic acid derivative, is a potent commercial acaricide that is extensively used globally. However, whether scoparone has synergistic effects when used in conjunction with spirodiclofen and the underlying synergistic mechanism remains unclear.

RESULTS

Scoparone exhibited a potent synergistic effect when it was combined with spirodiclofen at a 1:9 ratio. Subsequently, cytochrome P450 monooxygenase (P450) activity, RNA-Seq and qPCR assays indicated that the enzyme activity of P450 and the expression of one P450 gene from T. cinnabarinus, TcCYP388A1, were significantly inhibited by scoparone and spirodiclofen + scoparone; conversely, P450 was activated in spirodiclofen-exposed mites. Importantly, RNAi-mediated silencing of the TcCYP388A1 gene markedly increased the susceptibility of spider mites to spirodiclofen, scoparone and spirodiclofen + scoparone, and in vitro, the recombinant TcCYP388A1 protein could metabolize spirodiclofen. Molecular docking and functional analyses further indicated that R117, which is highly conserved in Arachnoidea species, may be a vital specific binding site for scoparone in the mite TcCYP388A1 protein. This binding site was subsequently confirmed using mutagenesis data, which revealed that this binding site was the sole site selected by scoparone in spider mites over mammalian or fly CYP388A1.

CONCLUSIONS

These results indicate that the synergistic effects of scoparone and spirodiclofen on mites occurs through the inhibition of P450 activity, thus reducing spirodiclofen metabolism. The synergistic effect of this potent natural product on the detoxification enzyme-targeted activity of commercial acaricides may offer a sustainable strategy for pest mite resistance management. © 2024 Society of Chemical Industry.

Synthesis, toxicological and in silico evaluation of novel spiro pyrimidines against Culex pipiens L. referring to chitinase enzyme

The exponential development of resistance to conventional chemical insecticides adds another important motive for the creation of novel insecticidal active agents. One of the keys to meeting this challenge is the exploration of novel classes of insecticidal molecules with different modes of action. Herein, a novel series of spiro pyrimidine derivatives was prepared using some green synthetic methodologies such as microwave irradiation, and sonication under ultrasound waves. Spiro pyrimidine aminonitrile 1 is a key starting material for the synthesis of targets 2-9 by reaction with different carbon electrophiles and nitrogen nucleophiles. The structures of all the newly synthesized compounds were approved using spectral data. The toxicological efficiency and biological impacts of the synthesized spiro pyrimidine derivatives were assessed against Culex pipiens L. larvae. The toxicity of synthesized compounds showed remarkable variations against the C. pipiens larvae. Where, 3, 4 and 2 were the most efficient compounds with LC50 values of 12.43, 16.29 and 21.73 µg/mL, respectively. While 1 was the least potent compound with an LC50 value of 95.18 µg/mL. As well, other compounds were arranged according to LC50 values as follows 5 > 7 > 6 > 9 > 8. In addition, 3 and 4 exhibited significant prolongation of the developmental duration and greatly inhibited adult emergence. Moreover, many morphological deformities were observed in all developmental stages. Furthermore, cytotoxicity of the most effective compounds was assessed against the normal human cells (WI-38) as non-target organisms, where compounds 2, 4 and 3 showed weak to non-toxic effects. The study of binding affinity and correlation between chemical structure and reactivity was carried out using molecular docking study and DFT calculations to investigate their mode of action. This study shed light on promising compounds with larvicidal activity and biological impacts on the C. pipiens life cycle.

Synthesis of Piperine-Based Ester Derivatives with Diverse Aromatic Rings and Their Agricultural Bioactivities against Tetranychus cinnabarinus Boisduval, Aphis citricola Van der Goot, and Eriosoma lanigerum Hausmann

Exploration of plant secondary metabolites or by using them as leads for development of new pesticides has become one of the focal research topics nowadays. Herein, a series of new ester derivatives of piperine were prepared via the Vilsmeier−Haack−Arnold (VHA) reaction, and their structures were characterized by infrared spectroscopy (IR), melting point (mp), proton nuclear magnetic resonance spectroscopy (1H NMR), and carbon nuclear magnetic resonance spectroscopy (13C NMR). Notably, the steric configurations of compounds 6 and 7 were confirmed by single-crystal analysis. Against T. cinnabarinus, compounds 9 and 11 exhibited 47.6- and 45.4-fold more pronounced acaricidal activity than piperine. In particular, compounds 9 and 11 also showed 2.6-fold control efficiency on the fifth day of piperine. In addition, compound 6 (>10−fold higher than piperine) displayed the most potent aphicidal activity against A. citricola. Furthermore, some derivatives showed good aphicidal activities against E. lanigerum. Moreover, the effects of compounds on the cuticles of T. cinnabarinus were investigated by the scanning electron microscope (SEM) imaging method. This study will pave the way for future high value added application of piperine and its derivatives as botanical pesticides.

A New Strain of Lecanicillium uredinophilum Isolated from Tibetan Plateau and Its Insecticidal Activity

A new strain QHLA of Lecanicillium uredinophilum was isolated from a Chinese caterpillar fungus complex and its optimum growth temperature and fermentation conditions were studied. Its insecticidal activity was tested against larvae of seven different insect pests, including Henosepilachna vigintioctopunctata, Spodoptera exigua, Plutella xylostella, Spodoptera frugiperda, Sitobion avenae, Hyalopterus perikonus, and Aphis citricola. The optimum growth temperature was 21–24 °C. The highest spore production of the strain QHLA was 4.08 × 10⁶ spore/mL on solid medium with a nitrogen source of NH₄Cl. However, the highest mycelial growth rate of the strain QHLA was on solid medium with a nitrogen source from yeast extract (4.63 ± 0.03 mm/d). When the liquid medium contained peptone, yeast extract, and glucose, the water content of the mycelia was the lowest, while the spore production was the highest until day 12. When the liquid medium contained glucose, tussah pupa powder, KH₂PO₄, and MgSO₄, the mycelia production was highest until day 8. The bioassay for insecticidal activity indicated that the LC₅₀ values of QHLA were 6.32 × 10³ spore/mL and 6.35 × 10³ spore/mL against Sitobion avenae and Aphis citricola, respectively, while the LC₉₀ values of the strain QHLA against Aphis citricola and Sitobion avenae were 2.11 × 10⁷ spore/mL and 2.36 × 10⁸ spore/mL, respectively. Our results demonstrated that the strain QHLA was a high virulence pathogenic fungus against insect pests, with the potential to be developed as a microbial pesticide.

Spiro Derivatives in the Discovery of New Pesticides: A Research Review

Spiro compounds are biologically active organic compounds with unique structures, found in a wide variety of natural products and drugs. They do not readily lead to drug resistance due to their unique mechanisms of action and have, therefore, attracted considerable attention regarding pesticide development. Analyzing structure-activity relationships (SARs) and summarizing the characteristics of spiro compounds with high activity are crucial steps in the design and development of new pesticides. This review mainly summarizes spiro compounds with insecticidal, bactericidal, fungicidal, herbicidal, antiviral, and plant growth regulating functions to provide insight for the creation of new spiro compound pesticides.