Semisynthesis of Esters of Fraxinellone C4/10-Oxime and Their Pesticidal Activities

Design, Synthesis and Antifungal Activity of Nootkatone Derivatives Containing Acylhydrazone and Oxime Ester

In an attempt to search for new natural products-based antifungal agents, fifty-three nootkatone derivatives were designed, synthesized, and evaluated for their antifungal activity against Phytophthora parasitica var nicotianae, Fusarium oxysporum, Fusarium graminearum and Phomopsis sp. by the mycelium growth rate method. Nootkatone derivatives N17 exhibited good inhibitory activity against Phomopsis. sp. with EC50 values of 2.02 μM. The control effect of N17 against Phomopsis. sp. on kiwifruit showed that N17 exhibited a good curative effect in reducing kiwifruit rot at the concentration of 202 μM(100×EC50 ), with the curative effect of 41.11 %, which was better than commercial control of pyrimethanil at the concentration of 13437 μM(100×EC50 ) with the curative effect of 38.65 %. Phomopsis. sp. mycelium treated with N17 showed irregular surface collapse and shrinkage, and the cell membrane crinkled irregularly, vacuoles expanded significantly, mitochondria contracted, and organelles partially swollen by the SEM and TEM detected. Preliminary pharmacological experiments show that N17 exerted antifungal effects by altering release of cellular contents, and altering cell membrane permeability and integrity. The cytotoxicity test demonstrated that N17 showed almost no toxicity to K562 cells. The presented results implied that N17 may be as a potential antifungal agents for developing more efficient fungicides to control Phomopsis sp.

Expedient discovery of novel oxime ester derivatives of piperine/piperine analogs as potent pesticide candidates and their mode of action against Tetranychus cinnabarinus Boisduval

BACKGROUND

Nowadays, pest infestation and resistance have appeared as a consequence of repeated and extensive use of pesticides. Thus, development of new effective pesticide candidates in crop protection is highly desirable. Herein, a series of new piperine derivatives containing oxime ester scaffolds were regioselectively and stereoselectively prepared as pesticidal agents.

RESULTS

Steric configurations of compounds 2, 5z and 13e were definitively determined by single-crystal X-ray diffraction. Against Tetranychus cinnabarinus, notably, compounds 5f [median lethal concentration (LC50 ) = 0.14 mg mL-1 ] and 5v (LC50  = 0.13 mg mL-1 ) showed >107-fold greater acaricidal activity than piperine (LC50  = 15.02 mg mL-1 ), which were comparable to the commercial acaricide spirodiclofen. Against Aphis citricola, compound 5d (LD50  = 19.12 ng aphid-1 ) exhibited 6.1-fold more potent aphicidal activity than piperine (LD50  = 116.06 ng aphid-1 ). Additionally, through scanning electron microscopy, the toxicology study suggested that the acaricidal activity of piperine derivatives may be related to damage of the cuticle layer crest of T. cinnabarinus.

CONCLUSION

The structure-activity relationships suggested that 3,4-dioxymethylene of piperine was crucial for its acaricidal activity; and introduction of a certain length of aliphatic chain at the C-2 position was beneficial to the aphicidal and acaricidal activities. Compounds 5f and 5v are potential leads for further structural modification as acaricidal agents. © 2023 Society of Chemical Industry.

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.

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.

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.

Recent Advances on Biological Activities and Structural Modifications of Dehydroabietic Acid

Dehydroabietic acid is a tricyclic diterpenoid resin acid isolated from rosin. Dehydroabietic acid and its derivatives showed lots of medical and agricultural bioactivities, such as anticancer, antibacterial, antiviral, antiulcer, insecticidal, and herbicidal activities. This review summarized the research advances on the structural modification and total synthesis of dehydroabietic acid and its derivatives from 2015 to 2021, and analyzed the biotransformation and structure-activity relationships in order to provide a reference for the development and utilization of dehydroabietic acid and its derivatives as drugs and pesticides.

Construction of new oxime esters of cholesterol containing piperic acid-like fragments as insecticidal agents against Aphis citricola Van der Goot (Homoptera: Aphididae) and Plutella xylostella Linnaeus (Lepidoptera: Plutellidae)

In order to application of cholesterol as pesticidal agents, a series of oxime esters of cholesterol containing piperic acid-like fragments were semi-synthesized by modification of cholesterol at the C-3 and C-6 positions. Their structures were characterized by ¹H NMR, HRMS and mp, and their purity was determined by HPLC. Against Aphis citricola Van der Goot, derivatives Ib (R = 4-FPh) and In (R = 3,4-ethylenedioxystyryl) exhibited 5.0 and 4.8 folds more pronounced aphicidal activity of their precursor cholesterol. Against Plutella xylostella Linnaeus, compounds Ia (R = Ph) and If (R = 3,4-methylenedioxyphenyl) showed 2.2 and 2.0 folds more potent insecticidal activity of cholesterol. Their SARs were also observed.

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.

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.

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.

High Value-Added Use of Citrus Industrial Wastes in Agriculture: Semisynthesis and Anti-Tobacco Mosaic Virus/Insecticidal Activities of Ester Derivatives of Limonin Modified in the B Ring

Globally, the citrus industry produces various wastes, which contain a great deal of limonoids. In order for the sustainable development of the citrus industry, and considering the diverse bioactivities of limonoids, a series of ester derivatives were constructed by structural modification of limonin in the B ring. Furthermore, two seven-membered lactone derivatives of limonin and obacunone with a novel skeleton in the B ring were obtained by the Baeyer-Villiger oxidation rearrangement. The steric structures of six key compounds 3a, 3b, 4m, 4n, 6, and 7 were determined by X-ray crystallography. It demonstrated that the molar ratio of 3a (7α-isomer) and 3b (7β-isomer) depended on the mixed solvents in the reduction system. The anti-tobacco mosaic virus (TMV) activities under three different modes of action for most of the tested compounds were as the following sequence: inactivation effect > protection effect > curative effect. It was noteworthy that compound 4aa displayed the most potent anti-TMV/insect growth inhibitory activities, which indicated that the introduction of the phenylacryloyloxy group at the C-7β position of limonin could significantly improve its agricultural biological activities. This study will pave the way for future value-added application of citrus industrial wastes and provide strong evidence for the discovery of sustainable biopesticides based on limonoids.

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.

Fraxinellone: From pesticidal control to cancer treatment

Fraxinellone (FRA) is a degraded limonoid isolated from the root bark of Dictamnus plants. The potent insecticidal activity of FRA has led to the synthesis of numerous derivatives (presented here with the structure-activity relationships) active against the oriental armyworm Mythimna separata Walker. In addition to its pesticidal activity, the natural product displays potent anti-inflammatory and immuno-modulatory effects at the origin of hepatoprotective and anticancer properties. This mini-review provides an update of the mechanism of action of FRA to highlight the recently discovered capacity of the compound to deactivate cancer-associated fibroblasts and thus to limit the immunosuppressive tumor microenvironment. The anticancer mode of action of FRA raises new ideas to better understand its primary insecticidal activity. The relationship between drug-induced cancer cell death and insect cell death is discussed. A drug interaction with the insect cytokine growth-blocking peptide (GBP), a member of the large EGF family, is proposed, supported by preliminary molecular modeling data. Altogether, the review shed light on the pharmacological properties of fraxinellone as an antitumor agent and a natural insecticide.

Spectroscopy, Thermodynamics and Molecular Docking of Fraxinellone with DNA

Fraxinellone is an important botanical lactone compound and has been demonstrated to have insecticidal activity. To provide theoretical support to the assessment on the safety of utilizing fraxinellone as a natural insecticidal agent, the interactions between fraxinellone and armyworm DNA, salmon sperm DNA and calf thymus DNA were investigated using UV-Vis absorption spectroscopy, isothermal titration calorimetry, and molecular docking. Results showed that there were two types of combinations between fraxinellone and three kinds of DNA. Type I combination had an equilibrium constant of combination (Ka₁) of about 10⁵ and binding sites (n₁) of 0.40-0.70, while type II combination had an equilibrium constant of combination (Ka₂) of 10³ and binding sites (n₂) of 1.35-3.15. Results of molecular docking showed that there were non-classical embedding type interactions between fraxinellone and three kinds of DNA, with the reaction taking place in small groove areas of the DNA structure, resulting in relatively weak interactive forces.

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.

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

In continuation of our program to develop natural-product-based pesticidal candidates, matrinic/oxymatrinic amides were obtained through structural optimization of matrine. N'-(4-Fluoro)phenyl-N-(4-bromo)phenylsulfonyloxymatrinic amide (IIm) showed potent insecticidal activity against Mythimna separata. N-(Un)substituted phenylsulfonylmatrinic acids (3a-c) exhibited promising acaricidal activity against Tetranychus cinnabarinus. By qRT-PCR analysis of nAChR subunits and AChE genes and determination of AChE activity of (un)treated T. cinnabarinus, it suggested that the open lactam ring of matrine and carboxyl group and (4-methyl)phenylsulfonyl of N-(4-methyl)phenylsulfonylmatrinic acid (3b) were necessary for action with α2, α4, α5, and β3 nAChR subunits; compound 3b was an inhibitor of AChE in T. cinnabarinus, and AChE was one possible target of action in T. cinnabarinus against 3b; and compound 3b may be an antagonist of nAChR and AChE in T. cinnabarinus.

Semisynthesis of novel N-acyl/sulfonyl derivatives of 5(3,5)-(di)halogenocytisines/cytisine and their pesticidal activities against Mythimna separata Walker, Tetranychus cinnabarinus Boisduval, and Sitobion avenae Fabricius

BACKGROUND

To discover novel natural product-based pesticidal agents for crop protection, a series of N-acyl/sulfonyl derivatives of 5(3,5)-(di)halogenocytisines/cytisine were prepared by structural modifications of cytisine. Their pesticidal activities were evaluated against three typically crop-threatening agricultural pests, Mythimna separata Walker, Tetranychus cinnabarinus Boisduval, and Sitobion avenae Fabricius.

RESULTS

Compound 5f exhibited the promising pesticidal activities against three tested pests. All N-phenylsulfonylcytisine derivatives showed potent acaricidal activity. Compound 5j exhibited 2.5-fold more potent acaricidal activity than cytisine, and showed good control effects. Intermediates 2, and 3/3' displayed pronounced aphicidal activity. Some interesting results of structure-activity relationships were also obtained.

CONCLUSION

These results demonstrate that compounds 5f and 5j could be further modified as pesticidal agents. © 2019 Society of Chemical Industry.

Semisynthesis of Matrinic Acid/Alcohol/Ester Derivatives, Their Pesticidal Activities, and Investigation of Mechanisms of Action against Tetranychus cinnabarinus

To discover new natural-product-based potential pesticides, 85 matrinic acid/alcohol/ester derivatives were synthesized by structural modifications of a quinolizidine alkaloid matrine. N-(4-Methyl)benzylmatrinyl n-decylate (76) and N-(2-chloro)benzylmatrinyl n-undecylate (86) exhibited greater than seven-fold more pronounced acaricidal activity than matrine against Tetranychus cinnabarinus; N-(2-chloro)benzylmatrinyl benzoate (80) showed the most promising insecticidal activity against Mythimna separata. The carboxyl group of matrinic acids and introduction of n-decyl/ n-undecylcarbonyl into matrinic alcohols were important for the acaricidal activity; introduction of alkyloxy into the carboxyl of matrinic acids and introduction of the electron-withdrawing groups on the N-benzyl of matrinic esters were necessary for the insecticidal activity. Through RT-PCR and qRT-PCR analysis, it was shown that the lactam ring of matrine was vital for action on VGSC; opening the lactam ring of matrine and the alkylcarbonyl of side-chain were two important factors for acting with α1, α2, and α4 nAChR subunits; α1, α2, α4, and β3 subunits may be the target of action of compound 86 against T. cinnabarinus.

Synthesis of Piperine Analogs Containing Isoxazoline/Pyrazoline Scaffold and Their Pesticidal Bioactivities

In continuation of our program to discover new potential pesticidal agents, thirty-one piperine analogs containing isoxazoline/pyrazoline scaffold were prepared, and confirmed by infrared spectra, proton/carbon-13 nuclear magnetic resonance spectra, and high-resolution mass spectra. The structures of compounds VIIb and VIIIc were further determined by ¹H-¹H COSY spectra. Especially the configuration of compound VIIIc was unambiguously confirmed by single-crystal X-ray diffraction. Their pesticidal activities were evaluated against three serious and typically crop-threatening agricultural pests, Tetranychus cinnabarinus Boisduval (spider mite), Mythimna separata Walker (Oriental armyworm), and Plutella xylostella Linnaeus (diamondback moth). Compounds VIIIb and VIIIc exhibited greater than 40-fold more potent acaricidal activity than the lead compound piperine against T. cinnabarinus. Notably, compounds VIa-c exhibited more pronounced oral toxicity against P. xylostella than toosendanin; compounds VIb and VIc displayed more promising growth inhibitory activity against M. separata than toosendanin. It demonstrated that the methylenedioxy and isoxazoline scaffolds were important for the oral toxicity and growth inhibitory activity against P. xylostella and M. separata, respectively; the ethylenedioxy and isoxazoline scaffolds were vital for the acaricidal activity against T. cinnabarinus. Moreover, compounds VIb, VIIf, and VIIIc showed very low toxicity against NRK-52E cells.

Furan-Site Bromination and Transformations of Fraxinellone as Insecticidal Agents Against Mythimna separata Walker

Furan ring of limoninoids is critical in exhibiting insecticidal activity. Herein, fraxinellone (1) was used as a template of furan-containing natural products and a series of its derivatives was synthesized by selective bromination in good yields on gram-scale and following Suzuki-Miyaura or Sonogashira coupling reactions in moderate to good yields. Bromination of limonin (9) was also accomplished without altering other functional groups in high yield. Furthermore, an evaluation of insecticidal activity against the instar larvae of Mythimna separata showed that derivatives 2, 3b, 3g, 5a, 5d and 5h displayed more potent insecticidal activity than 1 and toosendanin.

Munronin O, a potential activator for plant resistance

A series of limonoids (1-8) were isolated from the whole plant of Munronia henryi and antiviral activities of the compounds were evaluated. The bioassay results demonstrated that Munronin O (1) showed remarkable protective activity and compounds 7 and 8 showed significant inactivating, protective, and curative activities against tobacco mosaic virus (TMV). With a 50% effective concentration (EC50) value of 91.5 μg/mL, compound 1 exhibited the best protective activity compared with ningnanmycin (192.3 μg/mL). The potential for these compound of inducing systemic acquired resistance (SAR) was also evaluated, and compound 1 showed excellent induction activities. Furthermore, it was found that potentiation of defense-related enzyme activity and the contents of SA was increased. Compound 1 could also inhibit the expression of TMV CP and up-regulate the expression of defense-related genes. This work revealed that compound 1 can induce resistance and enhance plant tolerance to TMV infection. Hence, compound 1 can be considered as a potential activator for inducing plant resistance.

Synthesis and insecticidal activities of 5-deoxyavermectin B2a oxime ester derivatives

Three series of avermectin B2a oxime ester derivatives were synthesized using avermectin B2a as starting material. All of the compounds were characterized by 1H NMR, 13C NMR, and HRMS. Bioassay results indicated that some of the derivatives (8b, 8c, 8d, 8f, 11k, 11l, 14c, 14j) showed potent insecticidal activities against Myzus persicae, Caenorhabditis elegans, or Tetranychus cinnabarinus. As shown by initial insecticidal activity data, compound 8d showed excellent activities (>90%) against M. persicae and C. elegans, which were more potent than that of avermectin B2a. Compound 8d might be a lead compound for designing new avermectin B2a derivatives.

Synthesis and Antifungal Activity of Novel 3-Caren-5-One Oxime Esters

A series of novel 3-caren-5-one oxime esters were designed and synthesized by multi-step reactions in an attempt to develop potent antifungal agents. Two E-Z stereoisomers of the intermediate 3-caren-5-one oxime were separated by column chromatography for the first time. The structures of all the intermediates and target compounds were confirmed by UV-Vis, FTIR, NMR, ESI-MS, and elemental analysis. The antifungal activity of the target compounds was preliminarily evaluated by the in vitro method against Fusarium oxysporum f. sp. cucumerinum, Physalospora piricola, Alternaria solani, Cercospora arachidicola, Gibberella zeae,Rhizoeotnia solani, Bipolaris maydis, and Colleterichum orbicalare at 50 µg/mL. The target compounds exhibited best antifungal activity against P. piricola, in which compounds (Z)-4r (R = β-pyridyl), (Z)-4q (R = α-thienyl), (E)-4f′ (R = p-F Ph), (Z)-4i (R = m-Me Ph), (Z)-4j (R = p-Me Ph), and (Z)-4p (R = α-furyl) had inhibition rates of 97.1%, 87.4%, 87.4%, 85.0%, 81.9%, and 77.7%, respectively, showing better antifungal activity than that of the commercial fungicide chlorothanil. Also, compound (Z)-4r (R = β-pyridyl) displayed remarkable antifungal activity against all the tested fungi, with inhibition rates of 76.7%, 82.7%, 97.1%, 66.3%, 74.7%, 93.9%, 76.7% and 93.3%, respectively, showing better or comparable antifungal activity than that of the commercial fungicide chlorothanil. Besides, the E-Z isomers of the target oxime esters were found to show obvious differences in antifungal activity. These results provide an encouraging framework that could lead to the development of potent novel antifungal agents.

Recent progress in the chemistry and biology of limonoids

Significant limonoids: new isolated limonoids, and recent developments in the total chemical synthesis, and structural modifications of limonoids regarding the bioactivities have been summarised.

Semisynthesis of some matrine ether derivatives as insecticidal agents

Compounds 4i and 4k exhibited more potent insecticidal activities than matrine against Plutella xylostella and Mythimna separata. These matrine derivatives may be considered as promising insecticidal candidates.

Semisynthesis of esters and oxime esters/sulfonates from furyl-ring-based acetylation derivatives of fraxinellone as insecticidal agents

Two compounds 9a and 10i exhibited the most promising pesticidal activity against early 3rd-instar larvae of Mythimna separata. Their structure–activity relationships were also observed.

Design, synthesis, antibacterial and insecticidal activities of novel N-phenylpyrazole fraxinellone hybrid compounds

A series of 20 novelN-phenylpyrazole fraxinellone hybrid compounds were prepared and evaluated for their antibacterial and insecticidal activities.