Preparation of Matrinic/Oxymatrinic Amide Derivatives as Insecticidal/Acaricidal Agents and Study on the Mechanisms of Action against Tetranychus cinnabarinus

Novel Flavonol Derivatives Containing 1,3,4-Thiadiazole as Potential Antifungal Agents: Design, Synthesis, and Biological Evaluation

In order to discover novel compounds with excellent agricultural activities, novel flavonol derivatives containing 1,3,4-thiadiazole were synthesized and evaluated for their antifungal activities. The bioassay results showed that some of the target compounds had good antifungal activities against Botrytis cinerea, Phomopsis sp. and Sclerotinia sclerotiorum in vitro. It is worth noting that the half-effective concentration (EC50) value of Y18 against B. cinerea was 2.4 μg/mL, which was obviously superior to that of azoxystrobin (21.7 μg/mL). The curative activity of Y18 at 200 μg/mL (79.9%) was better than that of azoxystrobin (59.1%), and its protective activity (90.9%) was better than that of azoxystrobin (83.9%). Morphological studies by using scanning electron microscopy and fluorescence microscopy revealed that Y18 could affect the normal growth of B. cinerea mycelium. In addition, the mechanism of action studies indicated that Y18 could affect the integrity of cell membranes by inducing the production of endogenous reactive oxygen species and the release of the malondialdehyde content, leading to membrane lipid peroxidation and the release of cell contents. The inhibitory activity of flavonol derivatives containing 1,3,4-thiadiazole on plant fungi is notable, offering significant potential for the development of new antifungal agents.

Three new quinolizidine alkaloids from the roots of Sophora tonkinensis

Three new quinolizidine alkaloids (1 - 3), including one new naturally isoflavone and cytisine polymer (3), along with 6 known ones were isolated from the ethanol extract of Sophora tonkinensis Gagnep. Their structures were elucidated by comprehensive spectroscopic data analysis (IR, UV, HRESIMS, 1D and 2D NMR), combined with ECD calculations. The antifungal activity against Phytophythora capsica, Botrytis cinerea, Gibberella zeae, and Alternaria alternata of the compounds was evaluated in a mycelial inhibition assay. Biological tests indicated that compound 3 exhibited strong antifungal activity against P. capsica with EC50 values of 17.7 μg/ml.

Eurycomanone (EN) Activates Transcription Factor FoxO by Inhibiting the Insulin Signaling Pathway to Suppress the Development of Spodoptera frugiperda

The insulin-like signaling (IIS) pathway is essential for insect growth and development. In this study, we showed that eurycomanone (EN) is an active compound with growth inhibitory activity against Spodoptera frugiperda larvae. Experiments in cells and RNA-seq analysis in the midgut showed that EN targeted the IIS pathway in S. frugiperda to activate the transcription factor SfFoxO (S. frugiperda forkhead boxO) to regulate mRNA levels associated with nutrient catabolism. Additionally, mass spectrometry imaging revealed that EN was distributed in the larval gut and enriched in the inner membrane of the gut. Immunofluorescence, western blotting, and quantitative reverse transcription-polymerase chain reaction (qRT-PCR) results showed that EN induced program cell death (PCD) in the larvae midgut. Thus, EN targeted the insulin receptor to inhibit the IIS signaling pathway, exerting inhibitory activity on the growth and development of S. frugiperda larvae. Our results suggest that EN has great potential as a botanical pesticide, and the IIS signaling pathway may be an effective target for botanical pesticides.

Design, Synthesis and Various Bioactivity of Acylhydrazone-Containing Matrine Analogues

Compounds with acylhydrazone fragments contain amide and imine groups that can act as electron donors and acceptors, so they are easier to bind to biological targets and thus generally exhibit significant biological activity. In this work, acylhydrazone fragments were introduced to the C-14 or C-11 position of matrine, a natural alkaloid, aiming to enhance their biological activities. The result of this bioassay showed that many synthesized compounds exhibited excellent anti-virus activity against the tobacco mosaic virus (TMV). Seventeen out of 25 14-acylhydrazone matrine derivatives and 17 out of 20 11-butanehydrazone matrine derivatives had a higher inhibitory activity against TMV than the commercial antiviral agent Ribavirin (the in vitro activity, in vivo inactivation, curative and protection activities at 500 µg/mL were 40.9, 36.5 ± 0.9, 38.0 ± 1.6 and 35.1 ± 2.2%, respectively), and four 11-butanehydrazone matrine derivatives even had similar to or higher activity than the most efficient antiviral agent Ningnanmycin (55.4, 57.8 ± 1.4, 55.3 ± 0.5 and 60.3 ± 1.2% at 500 µg/mL for the above four test modes). Among them, the N-benzyl-11-butanehydrazone of matrine formed with 4-bromoindole-3-carboxaldehyde exhibited the best anti-TMV activity (65.8, 71.8 ± 2.8, 66.8 ± 1.3 and 69.5 ± 3.1% at 500 µg/mL; 29, 33.5 ± 0.7, 24.1 ± 0.2 and 30.3 ± 0.6% at 100 µg/mL for the above four test modes), deserving further investigation as an antiviral agent. Other than these, the two series of acylhydrazone-containing matrine derivatives were evaluated for their insecticidal and fungicidal activities. Several compounds were found to have good insecticidal activities against diamondback moth (Plutella xylostella) and mosquito larvae (Culex pipiens pallens), showing broad biological activities.

Optimization of Osthole in the Lactone Ring as an Agrochemical Candidate: Synthesis, Characterization, and Pesticidal Activities of Osthole Amide/Ester Derivatives and Their Effects on Morphological Changes of Mite Epidermis

Structural modification of natural products is one of the important ways in the discovery of novel pesticides. Based on a diversity-oriented synthesis strategy, herein, two series of amide/ester derivatives (52 compounds) were obtained by opening the lactone of osthole. Interestingly, the effect of different concentrations of aq. sodium hydroxide on the ratio of two isomers (cis- and trans-2) was investigated, and a magical phenomenon of ultraviolet (UV) light irradiation on intertransformation of two isomers (cis- and trans-2) was observed. Against Mythimna separata, when compared with the precursor osthole, compounds 4b, 4l, 5l, 5m, 7h, 7l, and 7m displayed more pronounced growth inhibitory activity with the final mortality rates of 62.0-68.9%. Compounds 4b, 4i, and 5m showed 5.7-6.6 times stronger acaricidal activity against Tetranychus cinnabarinus than osthole, and notably, control effects of compounds 4i and 5m were 2.4- and 2.7-fold that of osthole in the management of T. cinnabarinus in the greenhouse. Scanning electron microscopy (SEM) images of the epidermis of 5m-treated T. cinnabarinus indicated that compound 5m can destroy the mite cuticle layer. Compounds 4b and 5m can be used as leads to further explore more promising pesticidal agents.

Novel Sophoridine Derivatives as Potential Larvicidal Agents against Aedes albopictus: Synthesis, Biological Evaluation, Acetylcholinesterase Inhibition, and Morphological Study

Two series of novel sophoridine derivatives were designed, synthesized, and evaluated for their anti-mosquito activity. SOP-2g, SOP-2q, and SOP-2r exhibited potential larvicidal activity against Aedes albopictus larva with LC₅₀ values of 330.98, 430.53, and 411.09 ppm, respectively. Analysis of structure-activity relationships indicated that the oxime ester group was beneficial for improving the larvicidal biological activity, whereas the long-chain aliphatic group and fused-ring group were introduced. Furthermore, the larvicidal mechanism was also investigated based on the inhibition assay of acetylcholinesterase (AChE) and the morphological observation of dead larva treated with derivatives. Results indicated that the AChE inhibitory activity of the preferred three derivatives were 63.16%, 46.67%, and 35.11%, respectively, at 250 ppm concentration. Additionally, morphological evidence demonstrated that SOP-2q and SOP-2r induced changes in the larva's intestinal cavity, caudal gill, and tail, thereby displaying larvicidal action against Ae. albopictus together with AChE inhibition. Therefore, this study implied that sophoridine and its novel derivatives could be used to control the population of mosquito larva, which may also be effective alkaloids to reduce the mosquito population density.

Novel Matrine Derivatives as Potential Larvicidal Agents against Aedes albopictus: Synthesis, Biological Evaluation, and Mechanistic Analysis

A large number of studies have shown that matrine (MA) possesses various pharmacological activities and is one of the few natural, plant-derived pesticides with the highest prospects for promotion and application. Fifty-eight MA derivatives were prepared, including 10 intermediates and 48 target compounds in 3 series, to develop novel mosquitocidal agents. Compounds 4b, 4e, 4f, 4m, 4n, 6e, 6k, 6m, and 6o showed good larvicidal activity against Aedes albopictus, which is both a highly aggressive mosquito and an important viral vector that can transmit a wide range of pathogens. Dipping methods and a bottle bioassay were used for insecticidal activity evaluation. The LC50 values of 4e, 4m, and 6m reached 147.65, 140.08, and 205.79 μg/mL, respectively, whereas the LC50 value of MA was 659.34 μg/mL. Structure–activity relationship analysis demonstrated that larvicidal activity could be improved by the unsaturated heterocyclic groups introduced into the carboxyl group after opening the D ring. The MA derivatives with oxidized N-1 lost their mosquitocidal activities, indicating that the bareness of N-1 is crucial to maintain their anti-mosquito activity. However, the activity was not greatly influenced by introducing a cyan group at C-6 or a benzene sulfonyl group at N-16. Additionally, compounds 4e and 4m exhibited good inhibitory activities against acetylcholinesterase with inhibitory rates of 59.12% and 54.30%, respectively, at a concentration of 250 μg/mL, whereas the inhibitory rate of MA was 9.88%. Therefore, the structural modification and mosquitocidal activity of MA and its derivatives obtained here pave the way for those seeking strong mosquitocidal agents of plant origin.

Exploration of Synergistic Pesticidal Activities, Control Effects and Toxicology Study of a Monoterpene Essential Oil with Two Natural Alkaloids

With the increasing development of pest resistances, it is not easy to achieve satisfactory control effects by using only one agrochemical. Additionally, although the alkaloid matrine (MT) isolated from Sophora flavescens is now utilized as a botanical pesticide in China, in fact, its pesticidal activities are much lower in magnitude than those of commercially agrochemicals. To improve its pesticidal activities, here, the joint pesticidal effects of MT with another alkaloid oxymatrine (OMT) (isolated from S. flavescens) and the monoterpene essential oil 1,8-cineole (CN) (isolated from the eucalyptus leaves) were investigated in the laboratory and greenhouse conditions. Moreover, their toxicological properties were also studied. Against Plutella xylostella, when the mass ratio of MT and OMT was 8/2, good larvicidal activity was obtained; against Tetranychus urticae, when the mass ratio of MT and OMT was 3/7, good acaricidal activity was obtained. Especially when MT and OMT were combined with CN, the significant synergistic effects were observed: against P. xylostella, the co-toxicity coefficient (CTC) of MT/OMT (8/2)/CN was 213; against T. urticae, the CTC of MT/OMT (3/7)/CN was 252. Moreover, the activity changes over time of two detoxification enzymes, carboxylesterase (CarE) and glutathione S-transferase (GST) of P. xylostella treated with MT/OMT (8/2)/CN, were observed. In addition, by scanning electron microscope (SEM), the toxicological study suggested that the acaricidal activity of MT/OMT (3/7)/CN may be related to the damage of the cuticle layer crest of T. urticae.

Matrine-Type Alkaloids with Anti-Tomato Spotted Wilt Virus Activity from the Root of Sophora tonkinensis Gagnep

As a continuation of our research on the development of pesticide active quinolizidine alkaloids (QAs) from the family Fabaceae, the chemical constituents of the root of Sophora tonkinensis Gagnep. were systematically investigated. Seventeen new matrine-type alkaloids (1-17), including one new naturally occurring compound (17), along with 20 known ones were isolated from the EtOH extract of S. tonkinensis. Notably, compound 5 possessed an unprecedented 6/6/5/4/6/6 hexacyclic system. Their structures were confirmed via comprehensive spectroscopic data analysis (IR, UV, NMR, HRESIMS), ECD calculation, and X-ray crystallography. Biological tests indicated that compounds 1, 4, 10, 12, 13, and 30 displayed significant anti-tomato spotted wilt virus (TSWV) activities compared with the positive control ningnanmycin. Moreover, compound 12 strongly inhibited the expression of the TSWV N, NSs, and NSm genes and TSWV NSs protein in plant host. Furthermore, compounds 4, 10, 12, 20, and 22 exhibited moderate insecticidal activities against TSWV thrip vector (Frankliniella occidentalis).

Synthesis and Evaluation of 11-Butyl Matrine Derivatives as Potential Anti-Virus Agents

Matrine derivatives were reported to have various biological activities, especially the ester, amide or sulfonamide derivatives of matrine deriving from the hydroxyl or carboxyl group at the end of the branch chain after the D ring of matrine is opened. In this work, to investigate whether moving away all functional groups from the C-11 branch chain could have an impact on the bioactivities, such as anti-tobacco mosaic virus (TMV), insecticidal and fungicidal activities, a variety of N-substituted-11-butyl matrine derivatives were synthesized. The obtained bioassay result showed that most N-substituted-11-butyl matrine derivatives had obviously enhanced anti-TMV activity compared with matrine, especially many compounds had good inhibitory activity close to that of commercialized virucide Ningnanmycin (inhibition rate 55.4, 57.8 ± 1.4, 55.3 ± 0.5 and 60.3 ± 1.2% at 500 μg/mL; 26.1, 29.7 ± 0.2, 24.2 ± 1.0 and 27.0 ± 0.3% at 100 μg/mL, for the in vitro activity, in vivo inactivation, curative and protection activities, respectively). Notably, N-benzoyl (7), N-benzyl (16), and N-cyclohexylmethyl-11-butyl (19) matrine derivatives had higher anti-TMV activity than Ningnanmycin at both 500 and 100 μg/mL for the four test modes, showing high potential as anti-TMV agent. Furthermore, some compounds also showed good fungicidal activity or insecticidal activity.

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.

Discovery of evodiamine derivatives as potent insecticide candidates

In the search for novel more effective insecticides, natural products could be used as ideal template compounds due to their good environmental compatibility, various bioactivities, unique scaffolds and mode of action. We have found that natural product evodiamine, the main active component from the fruits of Evodia rutaecarpa (Juss.) Benth, displayed obvious insecticidal activities against lepidoptera pests. To continue our research, a series of evodiamine derivatives 3a-3aa were rationally designed and synthesized. The larvicidal activities results indicated that most of target compounds displayed better efficacy than evodiamine, matrine, and rotenone against Mythimna separata, Plutella xylostella and Helicoverpa armigera, among which 3z exhibited excellent larvicidal activities (65% at 2.5 mg/L against M. separata, 75% at 1.0 mg/L against P. xylostella, and 85% 10 mg/L against H. armigera, respectively), much better than evodiamine (0%), matrine (0%), and rotenone (0%). The preliminary structure activity relationships demonstrated that the fluorine atom at the E ring of evodiamine had a positive influence on the larvicidal activity. The calcium imaging experiment studies indicated that 3z could act on the ryanodine receptor (RyR) of M. separata and was an effective calcium activator for RyR.

Development of Botanical Pesticides: Exploration on the Phenotype of Vestigial Wings of Insect Pests Induced by Plant Natural Products or Their Derivatives by Blocking Tyrosine Phosphorylation of Insulin Receptor 1

Unlike faster-acting conventional insecticides, some botanical insecticides exhibit growth inhibitory activity against some insect pests. One of the distinguishing features of growth inhibitory activity appears to be in malformed moths with vestigial wings. However, the molecular mechanism underlying vestigial wings of insect pests induced by plant natural products or their derivatives is still elusive. In this work, based upon the phenotype of the vestigial wings of Mythimna separata Walker (as a model pest) induced by a podophyllotoxin derivative 2a (as a model compound), we found that compound 2a not only resulted in 22.1% of malformed moths with vestigial wings but also significantly decreased the fecundity of vestigial-winged female moths in the P generation; the trait of vestigial wings caused by 2a in the P generation can be inherited by the F1 generation; compound 2a may target insulin receptor 1 (InR1), suppress the InR1 mRNA level, and block InR1-pY1229 and InR1-pY1233/1234 phosphorylation levels in a tissue-specific manner "head/thorax/wing tissues". Notably, compound 2a can also induce the vestigial wings of Spodoptera frugiperda (another seriously harmful migratory lepidoptera pest). It is noteworthy that this insect insulin receptor can be used as a new kind of target receptors for the design of novel green insecticides.

Thermlanseedlines A-G, seven thermopsine-based alkaloids with antiviral and insecticidal activities from the seeds of Thermopsis lanceolata R. Br

Seven undescribed thermopsine-based alkaloids (1-7), including one undescribed biogenetically related intermediate (7), were isolated from the seeds of Thermopsis lanceolata R. Br. Compound 1 possessed a 6/6-6 tricyclic skeleton, while compounds 2-6 represented three rare dimerization patterns constructed by quinolizidine alkaloids. Their structures were elucidated by comprehensive spectroscopic data analysis as well as ECD calculations. Biologically, compound 6 displayed significant anti-Tomato spotted wilt virus (TSWV) activity compared with the positive control ningnanmycin. Moreover, compound 1 exhibited good insecticidal activity against Aphis fabae with LC₅₀ value of 25.2 mg/L.

The Advances on Bioactivities, Mechanisms of Action, and Structural Optimizations of Matrine and Its Derivatives

Matrine, a tetracyclo-quinolizidine alkaloid, is isolated from the industrial crop plant Sophora flavescens. Due to a wide range of pharmacological and agricultural properties, the research on the phytochemistry, pharmacology, toxicology and mechanisms of action of matrine and its derivatives has received much attention. On the other hand, to improve their biological activities, the study on structural optimizations and structure-activity relationships of matrine and its derivatives has also attached more and more importance. In this review article, the update advances on bioactivities, mechanisms of action, structural modifications and structure-activity relationships of matrine and its derivatives from 2017 to 2020 are presented. We hope that this review will provide a reference for the development and application of matrine and its derivatives as drugs or pesticides in the future.

High Value-Added Application of Natural Products in Crop Protection: Semisynthesis and Acaricidal Activity of Limonoid-Type Derivatives and Investigation of Their Biocompatible O/W Nanoemulsions as Agronanopesticide Candidates

The increasingly serious resistance of Tetranychus cinnabarinus Boisduval to a wide range of insecticides/acaricides poses a major challenge to their control. The citrus processing industry generates a huge quantity of various wastes that contain many limonoids. To effectively utilize these byproducts and discover more potent green acaricidal molecules as sustainable alternatives for traditional resistant pesticides, various limonoid-type derivatives (halogenated/seven-membered lactam derivatives of obacunone and halogenated/oxime esters/oxime ethers/seven-membered lactam derivatives of limonin) were synthesized based on a diversity-oriented synthetic strategy. The key steric configurations of 10 derivatives were further confirmed by X-ray crystallography. Compound 9m, which displayed greater than 9.7-fold potent acaricidal activity of limonin, was of preeminence. In addition, some interesting structure-activity relationships were observed. Moreover, a biocompatible O/W nanoemulsion delivery system was used to prepare the limonin-based agronanoacaricide, which exhibited pronounced control efficiency against T. cinnabarinus Boisduval in the greenhouse. This systematic investigation will provide valuable information and guidance for future value-added applications of novel eco-friendly natural product-based nanopesticides.

Natural-product-based pesticides: Semisynthesis, structural elucidation, and evaluation of new cholesterol-matrine conjugates as pesticidal agents

To develop new potential pesticide candidates from low value-added natural bioactive products, a series of new cholesterol-matrine conjugates (I(a-e)-IV(a-e)) were prepared from two lead compounds cholesterol and matrine. Against Mythimna separata Walker, compound IVa exhibited 3.0 and 2.6 folds promising insecticidal activity of cholesterol and matrine, respectively; against Aphis citricola Van der Goot, compound IVd showed 4.3 and 2.2 folds potent aphicidal activity of their precursors; notably, it also showed good control effects in the greenhouse; against Plutella xylostella Linnaeus at a dose of 20 μg/nymph, compound IIIe exhibited 2.8 and 2.0 folds oral toxicity of cholesterol and matrine, respectively. Compounds IIIe, IVd and IVe can be used as the leads for further structural optimization as the insecticidal and aphicidal agents.

Water-soluble matrine-type alkaloids with potential anti-neuroinflammatory activities from the seeds of Sophora alopecuroides

A phytochemical investigation on the alkaloids from water-soluble part of Sophora alopecuroides led to obtain forty matrine-type alkaloids (1-40) including eighteen new ones (1-18), which covers almost all positions of the oxygen substitution in matrine-type structure. Notably, eight compounds (1-8) belong to rare bis-amide matrine-type alkaloid. The new structures were determined based on extensive spectroscopic data, electronic circular dichroism (ECD) calculations, and six instances, verified by X-ray crystallography. Most of isolates showed anti-neuroinflammatory activities based on the expression of tumor necrosis factor (TNF)-α and interleukin (IL)-6 in BV2 microglia cells. Especially, compound 39 can suppress those two mediator secretions in a dose-dependent manner with IC₅₀ values of 21.6 ± 0.5 and 16.7 ± 0.8 μM, respectively. Further mechanistic study revealed that 39 suppressed the phosphorylation of IκBα and p65 subunit to regulate the NF-κB signaling pathway.

Design, Synthesis, Antibacterial Activity, and Mechanisms of Novel 1,3,4-Thiadiazole Derivatives Containing an Amide Moiety

To discover novel antibacterial agents, a series of novel 1,3,4-thiadiazole derivatives containing an amide moiety were designed and synthesized, and their antibacterial activities were tested. Compound 30 was designed and synthesized according to the CoMFA model. Compound 30 exhibited higher antibacterial activities against Xanthomonas oryzae pv. oryzicola and Xanthomonas oryzae pv. oryzae, with EC₅₀ values of 2.1 and 1.8 mg/L, respectively, which were superior to those of thiodiazole copper (99.6 and 92.5 mg/L). The protective and curative activities of compound 30 against rice bacterial leaf blight were 51.3 and 46.1%, respectively, which were better than those of thiodiazole copper (37.8 and 38.5%). The protective and curative activities of compound 30 against rice bacterial leaf streak were 45.9 and 40.5%, respectively, which were better than those of thiodiazole copper (36.2 and 31.1%). In addition, the protective activity of compound 30 against rice bacterial leaf streak was related to increased activities of related defense enzymes and upregulated the differentially expressed proteins of the glycolysis/gluconeogenesis pathway.

Construction of Cholesterol Oxime Ether Derivatives Containing Isoxazoline/Isoxazole Fragments and Their Agricultural Bioactive Properties/Control Efficiency

To explore natural-product-based pesticidal candidates and high value-added application of cholesterol in agriculture, oximinoether derivatives of cholesterol-containing isoxazoline/isoxazole fragments (I-1∼I-16 and II-1∼II-18) were semiprepared by structural optimization of cholesterol. Their structures were characterized by optical rotation, high-resolution mass spectrometry (HRMS), IR, and ¹H NMR spectroscopy. Particularly, the Z configurations of oxime fragments at the C-7 position of target compounds were undoubtedly determined by X-ray crystallography. Against Mythimna separata Walker, compounds 3e, I-8, I-14, and II-3 showed 2.4-2.7-fold growth inhibitory activity of the precursor cholesterol. Against Plutella xylostella Linnaeus, compounds I-6, I-7, and I-9 showed 2.4-2.7-fold oral toxicity of cholesterol. Against Aphis citricola Van der Goot, compounds 2e and II-15 exhibited 4.9 and 5.8-fold aphicidal activity of cholesterol, respectively. Notably, they showed good control effects (3.0-5.0-fold promising control efficiency of 1) against A. citricola in the greenhouse. Structure-activity relationships (SARs) suggested that the C-3 hydroxyl group and the C-7 position of cholesterol are two important modification sites. It will pave the way for future structural optimization and application of cholesterol derivatives as potential pesticidal agents in agriculture.

Optimization of Osthole in the Lactone Ring: Structural Elucidation, Pesticidal Activities, and Control Efficiency of Osthole Ester Derivatives

Here, we prepared a series of novel osthole-type ester derivatives modified in the lactone ring of osthole, which is isolated from Cnidium monnieri. The positions of H-3 and H-4 of the representative compound 4z were determined by a ¹H-¹H COSY spectrum. By opening the lactone ring of osthole, the double bonds at the C-3 and C-4 positions of diol 3 and esters 4a-4z, 4a', and 4b' were still retained as a Z configuration. That is, H-3 and H-4 of compounds 3 and 4a-4z, 4a', and 4b' were all in the cis relationship. The steric configurations of 4k, 4v, and 4z were further undoubtedly determined by single-crystal X-ray diffraction. Against Tetranychus cinnabarinus Boisduval, four aliphatic esters 4c (R = n-C₃H₇; LC₅₀: 0.31 mg/mL), 4d (R = CH₃(CH₂)₁₀; LC₅₀: 0.24 mg/mL), 4a' (R = CH₃(CH₂)₉; LC₅₀: 0.28 mg/mL), and 4b' (R = CH₃(CH₂)₁₂; LC₅₀: 0.32 mg/mL) showed the most promising acaricidal activity, and compounds 4c, 4d, and 4a' also exhibited a potent control efficiency. Especially, compound 4d exhibited greater than fivefold acaricidal activity of the precursor osthole (LC₅₀: 1.22 mg/mL). Against Mythimna separata Walker, compounds 4g, 4l, and 4m displayed 1.6-1.8-fold potent insecticidal activity of osthole. It demonstrated that the lactone ring of osthole is not necessary for the agricultural activities, thiocarbonylation of osthole was not beneficial for the agricultural activities, introduction of R as an aliphatic chain is vital for the acaricidal activity, notably, the length of the aliphatic chain is related to the acaricidal activity, 4d could be further studied as a lead acaricidal agent, and to the aromatic series, R containing the fluorine atom(s) is important for the insecticidal activity.

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

BACKGROUND

Spirodiclofen is a spirocyclic tetronic acid-type acaricidal agent. Nowadays, serious pests resistance to spirodiclofen and cross-resistance to other acaricides has appeared. To overcome pests resistance and discover new potential agrochemicals, a series of ether derivatives were prepared based on spirodiclofen as a lead compound. Their pesticidal activities were investigated against three typically agricultural pests, Mythimna separata Walker, Aphis citricola Van der Goot and Tetranychus cinnabarinus Boisduval.

RESULTS

Four steric structures of compounds 5e, 5f, 5i and 5j were determined by single-crystal X-ray diffraction. Against T. cinnabarinus, compounds 5b, 5f and 5l exhibited potent acaricidal activity, and their good control effects in the glasshouse were observed when compared with spirodiclofen, especially the control efficiency of compound 5b was comparable to that of spirodiclofen; against M. separata, compound 5j showed > 1.8-fold potent insecticidal activity of spirodiclofen; against A. citricola, compounds 5d and 5j displayed > 2.0-fold potent aphicidal activity of spirodiclofen. The relationships between their structures and agricultural activities were also discussed.

CONCLUSION

Compounds 5b and 5d could be further studied as acaricidal and aphicidal agents, respectively; compound 5j can be considered as a lead compound for the insecticidal and aphicidal activities. This will pave the way for future application of these derivatives as pesticide substitutes for spirodiclofen. © 2021 Society of Chemical Industry.

Regioselective hemisynthesis and insecticidal activity of C8-hydrazones/acylhydrazones/sulfonylhydrazones coumarin-type derivatives of osthole

Osthole, a coumarin-type natural product, is isolated from Chinese traditional herbal medicine Cnidium monnieri. In order to improve the pesticidal activity of osthole, and high value-added application of the plant Cnidium monnieri, a series of new derivatives containing hydrazone/acylhydrazone/sulfonylhydrazone skeletons at the C-8 position of osthole were regioselectively semi-prepared. The steric structure of 3c was determined by the X-ray crystal structure. Against Mythimna separata Walker, benzoylhydrazone 3b (R¹ = 4-CH₃Ph) showed 1.6 folds potent insecticidal activity of the precursor osthole. Introduction of the acylhydrazones on the 3'-methyl-2'-butylenyl fragment at the C-8 position of osthole can improve the insecticidal activity. These will provide a foundation for future structural modifications of osthole as pesticidal agents.

Quinolizidine Alkaloids with Antiviral and Insecticidal Activities from the Seeds of Sophora tonkinensis Gagnep

The discovery of novel, effective, and botanical pesticides is one of the main strategies for modern plant protection and insect pest control. During the search for novel botanical pesticides from natural sources, the seeds of Sophora tonkinensis were systematically investigated to obtain 11 new matrine-type alkaloids (1-11), including one novel matrine-type alkaloid featuring an unprecedented 5/6/6/6 tetracyclic skeleton (1), along with 16 known compounds (12-27). Their structures were elucidated by comprehensive spectroscopic data analysis (IR, UV, NMR, and HRESIMS), ECD calculations, and single-crystal X-ray diffraction. The anti-tobacco mosaic virus (TMV) activity and insecticidal activities against Aphis fabae and Tetranychus urticae of the compounds were also respectively screened using the half-leaf method and spray method. Biological tests indicated that compounds 2, 4, 6, and 26 displayed significant anti-TMV biological activities compared with the positive control ningnanmycin. Compounds 7, 17, and 26 presented moderate activities against A. fabae with LC₅₀ values of 38.29, 18.63, and 23.74 mg/L, respectively. Moreover, compounds 13 and 26 exhibited weak activities against T. urticae.

Construction of oxime ester derivatives of osthole from Cnidium monnieri, and evaluation of their agricultural activities and control efficiency

BACKGROUND

In order to discover natural-product-based pesticidal candidates, a series of coumarin-like derivatives containing oxime ester fragments at the C-8 position were prepared by structural modification of osthole, a natural plant product isolated from Cnidium monnieri. Their pesticidal activities were evaluated against two typically fruit trees/crop-threatening agricultural pests, Mythimna separata Walker and Tetranychus cinnabarinus Boisduval.

RESULTS

Osthole was regioselectively oxidized by selenium dioxide to give the E-isomer, (2'E)-3'-formaldehydylosthole (2). Four key steric structures of 2, (2'E, 4'E)-(o-chloropyrid-3-ylcarbonyl)oximinylosthole (4o), (2'E, 4'E)-(styrylcarbonyl)oximinylosthole (4t), and (2'E, 4'E)-(acetyl)oximinylosthole (4w) were undoubtedly confirmed by X-ray crystallography. Against T. cinnabarinus, it is noteworthy that (2'E, 4'E)-(p-chlorophenylcarbonyl)oximinylosthole (4c) exhibited over three-fold more potent acaricidal activity of the precursor osthole, with especially good control efficiency observed in the glasshouse. Against M. separata, compounds 4c and (2'E, 4'E)-(p-nitrophenylcarbonyl)oximinylosthole (4f) showed the most pronounced growth inhibitory activity. The relationships between their structures and agricultural activities also were studied.

CONCLUSION

These results demonstrate that compound 4c could be further structurally modified as pesticidal agents. It will lay the foundation for future application of osthole derivatives as pesticides. © 2020 Society of Chemical Industry.

Semisynthesis and Pesticidal Activities of Derivatives of the Diterpenoid Andrographolide and Investigation on the Stress Response of Aphis citricola Van der Goot (Homoptera: Aphididae)

To discover natural-product-based pesticides, 7β-oxycarbonylandrographolide derivatives were stereoselectively constructed from a labdane diterpenoid andrographolide. Among them, 2'-(n)Pr-1',3'-dioxin-7β-oxy(m-Cl)benzoylandrographolide (IIc), 2'-(n)Pr-1',3'-dioxin-7β-oxyacetylandrographolide (IIf), 2'-(p-Me)Ph-1',3'-dioxin-7β-oxy(o-Cl)benzoylandrographolide (Vb), and 2'-(p-Me)Ph-1',3'-dioxin-7β-oxy(m-Cl)benzoylandrographolide (Vc) against Mythimna separata displayed the most promising growth inhibitory activity; 2'-(n)Pr-1',3'-dioxin-7β-oxy(o-Cl)benzoylandrographolide (IIb: LC₅₀ = 0.406 mg/mL) and IIc (LC₅₀ = 0.415 mg/mL) exhibited the most pronounced acaricidal activity (andrographolide; LC₅₀: 5.106 mg/mL) and good control effects against Tetranychus cinnabarinus; compounds Ic, IIe, and Va-c (LD₅₀ = 0.035-0.039 μg/nymph) showed potent aphicidal activity (andrographolide: LD₅₀ = 0.178 μg/nymph), and compounds IIe and Vb showed good control effects against Aphis citricola. Moreover, it was found that Hsp70 of A. citricola was an important gene involved in stress response to andrographolide and its derivatives.