Synthesis and biological activities of 2,3-dihydro-1,3,4-oxadiazole compounds and its derivatives as potential activator of ryanodine receptors

A series of novel 2,3-dihydro-1,3,4-oxadiazoles containing N-pyridylpyrazole carboxamides moieties were obtained by applying a new synthetic route. Their insecticidal tests against oriental armyworm (Mythimna separata) and diamondback moth (Plutella xylostella) indicated that most of the compounds showed moderate to excellent activities at the testing concentrations. In particular, compound 6a showed 40% larvicidal activities against oriental armyworm at 1 mg/L, while 7a against diamondback was 100% at 0.01 mg/L. Calcium imaging results demonstrated that 6a, 6d and 7a stimulated a transient elevation in [Ca²⁺]_i in the absence of external calcium after the central neurons dye loading with fluo-3 AM, implying that these novel compounds were potential activators of the ligand-gated calcium channel on the endoplasmic reticulum.     

Synthesis and insecticidal evaluation of novel anthranilic diamides containing N-substitued nitrophenylpyrazole

To cope with developing pest resistance and ecological problems associated with conventional insecticides and to search for potent insecticides targeting at ryanodine receptor (RyR), a series of novel anthranilic diamides containing N-substitued nitrophenylpyrazole were designed and synthesized. The insecticidal activities of target compounds against oriental armyworm (Mythimna separata) and diamondback moth (Plutella xylostella) were evaluated in our greenhouse by bio-assay tests and the relative structure–activity relationships were briefly discussed. Most compounds exhibited moderate to high activities, in which G₇ and K₅ showed high activity against oriental armyworm and K₂ and K₄ against diamondback moth even better than the control-chlorantraniliprole. The calcium imaging technique was used to investigate the effects of several typical title compounds on the [Ca²⁺]_i, especially the effects of G₇ on the intracellular calcium ion concentration ([Ca²⁺]_i) in neurons, which indicated that some title compounds were potent activators of the RyR.     

Anthranilic diamides derivatives as potential ryanodine receptor modulators: Synthesis,biological evaluation and structure activity relationship

A series of novel anthranilic diamides derivatives (7a–s) containing halogen, trifluoromethyl group and cyano group were designed, synthesized, and characterized by melting point, ¹H NMR, ¹³C NMR and elemental analyses. The bioactivity revealed that most of them showed moderate to excellent activities against oriental armyworm (Mythimna separata) and diamondback moth (Plutella xylostella). Above all, the larvicidal activity of 7o against oriental armyworm was 100% and 40% at 0.25 and 0.1?mg?L^?1, comparable to that of the standard chlorantraniliprole (100%, 0.25?mg?L^?1 and 20%, 0.1?mg?L^?1). What is more, 7o against diamondback moth displayed 90% insecticidal activity at 0.01?mg?L^?1, superior to chlorantraniliprole (45%, 0.01?mg?L^?1). The experiments 7o on the American cockroach (Periplaneta Americana) heart beating rates (Dorsal vessel) and contractile force were compared with chlorantraniliprole. In addition, 7o could affect the calcium homeostasis in the central neurons of the third larvae of oriental armyworm, which revealed that the ryanodine receptor is the potential target of 7o. The density functional theory (DFT) calculation results revealed the amide bridge, the benzene ring of anthraniloyl moiety and pyrazole ring might play an important role in the insecticidal activity through hydrophobic interactions and π-π conjugations.     

Synthesis,insecticidal evaluation and mode of action of novel anthranilic diamide derivatives containing sulfur moiety as potential ryanodine receptor activators

Anthranilic diamide insecticide could control lepidopteran pests by selectively binding and activating insect ryanodine receptors (RyRs), and the unique mode of action is different from other conventional insecticides. In order to discover new anthranilic diamide insecticide as ryanodine receptors activators, a series of 11 novel anthranilic diamides derivatives (Ia-k) were synthesized and confirmed by melting point, ¹H NMR, ¹³C NMR and elemental analyses. The preliminary bioactivity revealed that most title compounds showed moderate to remarkable activities against oriental armyworm (Mythimna separata) and diamondback moth (Plutella xylostella). Especially, compounds Ia and If, which exhibited 100% larvicidal activity against oriental armyworm at 1.0?mg?L^?1, and comparable to that of chlorantraniliprole (100% at 1?mg?L^?1). If displayed 60% insecticidal activity against diamondback moth at 0.01?mg?L^?1, better than chlorantraniliprole (45% at 0.01?mg?L^?1). The preliminary structure activity relationships were discussed. In addition, the calcium imaging experiment indicated that the insect ryanodine receptor is the potential target of If.     

Additive effects on the improvement of insecticidal activity: Design,synthesis, and insecticidal activity of novel pymetrozine derivatives

A series of new pymetrozine analogues containing both methyl on the imine carbon and phenoxy group at the pyridine ring were designed and synthesized. Their insecticidal activities against bean aphid (Aphis craccivora), mosquito larvae (Culex pipiens pallens), cotton bollworm (Helicoverpa armigera), corn borer (Ostrinia nubilalis) and oriental armyworm (Mythimna separata) were evaluated. The results of bioassays indicated that most of the target compounds showed good insecticidal activity against bean aphid; especially, IIIf (80%) and IIIl (80%) exhibited higher aphicidal activity than pymetrozine (30%) at 5 mg/kg, and the two compounds still showed 20% and 30% mortality at 2.5 mg/kg, respectively, whereas pymetrozine displayed no activity at the same concentration. These compounds exhibited a completely different structure–activity relationship to that of known pymetrozine derivatives, in which it is thought introducing alkyl group on the imine carbon could be detrimental to the activities. Our new result suggested that the methyl on the imine carbon and phenoxy group at the pyridine ring of phenoxy group may play additive effects on the improvement of aphicidal activity. Besides this, compound IIIs, containing an allyl at the para position of phenoxy group, exhibited excellent insecticidal activity against mosquito larvae, lepidoptera pests cotton bollworm, corn borer and oriental armyworm.     

Synthesis and insecticidal activity studies of novel phenylpyrazole derivatives containing arylimine or carbimidate moiety

Phenylpyrazole insecticides are successful for crop protection and public hygiene by blocking gamma-aminobutyric acid (GABA)-gated chloride channels and glutamate-gated chloride (GluCl) channels. A series of novel phenylpyrazoles containing arylimine or 1-methoxyaryl groups were designed and synthesized. The addition reaction of methanol to the imines 1–11 was investigated and the cayno addition products 13–15 were obtained. The compounds 1–15 were confirmed by ¹H NMR and elemental analysis. The results of bioassay indicated that some compounds exhibited comparable bioactivity to fipronil against a broad spectrum of insects such as bean aphid (Aphis craccivora), mosquito (Culex pipiens pallens), diamondback moth (Plutella xylostella) and Oriental armyworm (Mythimna separata). Especially, the foliar contact activity against bean aphid of compound 7 at 10 µg mL⁻¹ was 68%, the larvacidal activity against mosquito of compounds 5, 13 and 15 at 0.0025 µg mL⁻¹ was 100%, the larvacidal activity against diamondback moth of compounds 9 and 11 at 0.05 µg mL⁻¹ was 100%, the larvacidal activity against Oriental armyworm of compound 9 at 1 µg mL⁻¹ was 100%. The 3-cayno moiety on pyrazole ring was essential for the high insecticidal activities against bean aphid, diamondback moth and Oriental armyworm, while the 3-carbimidate moiety on pyrazole ring was crucial to the excellent high insecticidal activities against mosquito.     

Synthesis and insecticidal evaluation of novel N-pyridylpyrazolecarboxamides containing cyano substituent in the ortho-position

In an attempt to search for potent insecticides targeting the ryanodine receptor (RyR), a series of novel N-pyridylpyrazolecarboxamides containing cyano substituent in the ortho-position were designed and synthesized. Their insecticidal activities of target compounds against oriental armyworm (Mythimna separata) and diamondback moth (Plutella xylostella) indicated that most of the compounds showed moderate to high activities at the tested concentrations. In particular, compound 6l and 6o showed 86% larvicidal activities against Plutella xylostella at the concentration of 0.1 mg/L, while the activity of compound 6h against Mythimna separate was 80% at 1 mg/L. The calcium imaging technique was applied to investigate the effects of some title compounds on the intracellular calcium ion concentration ([Ca²⁺]_i), experimental results demonstrated that compound 6h stimulates a transient elevation in [Ca²⁺]_i in the absence of external calcium after the central neurons dye loading with fluo-3 AM. However, when the central neurons were dyed with fluo-5 N and incubated with 2-APB, [Ca²⁺]i decreased transiently by treated of compound 6h. All of the calcium imaging technique experiments demonstrated that these novel compounds deliver calcium from endoplasmic reticulum to cytoplasm, which proved that the title compounds were the possible activators of insect RyR.     

Novel chlorantraniliprole derivatives as potential insecticides and probe to chlorantraniliprole binding site on ryanodine receptor

The lepidopteran pests such as diamondback moth are the regularly harmful pests of crops in the world, which brings enormous losses in crop production. Chlorantraniliprole is an anthranilic diamide insecticide registered for the control of lepidopteran pests with high insecticidal activity, however with uncertain binding site action target of chlorantraniliprole on ryanodine receptor, a series of new chlorantraniliprole derivatives were synthesized and the insecticidal activities of these compounds against diamondback moth were evaluated with chlorantraniliprole and indoxacarb as control. All compounds except 8h, 8p and 8t exhibited varying degree of activities against diamondback moth. Especially, compounds 8c, 8i, 8k and 8l displayed good insecticidal activities against diamondback moth and the activities are even better than that of indoxacarb during 72 h period. The K_i values of all synthesized compounds were calculated through autodocking program respectively. The relationship between calculation value of molecular docking and results of insecticidal activities indicated that the proposed specific receptor, the membrane-spanning domain protein of diamondback moth ryanodine receptor in our study might have chlorantraniliprole binding sites.     

Synthesis and insecticidal activities of 2,3-dihydroquinazolin-4(1H)-one derivatives targeting calcium channel

A series of compounds containing dihydroquinazolinone moiety was designed and synthesized. Amine bridge part was changed in comparison with known anthranilic diamides insecticides. Their insecticidal activities against oriental armyworm (Mythimna separata) indicated that most of the compounds showed moderate to high activities at the tested concentrations. In particular, compounds 5a and 5k showed 80% larvicidal activities against oriental armyworm at the concentration of 5 mg/L. The present study also explored the possible effects of target compounds on the high voltage-gated calcium channel and the calcium channels in the endoplasmic reticulum in the central neurons isolated from the third instar larvae of Spodoptera exigua using whole-cell patch clamp and calcium imaging technique. The results showed that compound 5a activated the high voltage-gated calcium channel in the central neurons of S. exigua weakly. The peak currents only increased by 6% of the initial value at the end of the 10-min recording after treated with 0.22 μM 5a, while chlorantraniliprole has an opposite effect. The effects of 5a on the intracellular calcium ion concentration ([Ca²⁺]_i) in neurons were well investigated. The experimental results indicated that these novel compounds have different mechanism compared with chlorantraniliprole.     

Synthesis,insecticidal activities and SAR of novel phthalamides targeting calcium channel

In order to find novel and environmental friendly insecticides targeting the ryanodine receptor, three series of novel phthalamides containing heptafluoroisopropyl group, low fluorine atoms group and non-fluorine group were designed and synthesized. 35 novel structures of three series were obtained. Insecticidal activities of title compounds against oriental armyworm (Mythimna separata) and diamondback moth (Plutella xylostella) indicated that most of title compounds showed moderate to high activities at the tested concentration. The structure–activity relationship (SAR) was discussed in detail. During synthesizing title compounds B₈, C₇, D₁, D₉ and D₁₂, their corresponding positional isomers (B₈′, C₇′, D₁′, D₉′ and D₁₂′) were afforded, and their structures were confirmed by 2D NMR. The calcium-imaging technique was also applied to investigate the effects of compounds B₂, B₁₀, C₄ and C₅ on the intracellular calcium ion concentration ([Ca²⁺]_i), which indicated that they released stored calcium ions from endoplasmic reticulum, which denoted that some compounds are potential modulators of the insect ryanodine receptor (RyR).     

Synthesis,larvicidal activity,and SAR studies of new benzoylphenylureas containing oxime ether and oxime ester group

A series of new structural benzoylphenylureas (BPUs) containing oxime ether and oxime ester group were designed and synthesized. The larvicidal activities against Oriental armyworm and mosquito of these benzoylphenylureas were evaluated and the result of bioassay displayed specific structure–activity relationship (SAR). Most of the compounds exhibited excellent larvicidal activities against Oriental armyworm and mosquito. Interestingly, some compounds showed different structure–activity relationship towards diamondback moth, beet armyworm, and corn borer although three tested insects all belong to the same insect order.     

Thioether-bridged arylalkyl-linked N-phenylpyrazole derivatives: Design,synthesis, insecticidal activities,structure-activity relationship and molecular-modeling studies

Owing to thioether diverse physicochemical properties by non-covalent interactions with bio-macromolecules, thioether derivatives containing heterocyclic moiety are known for their interesting insecticidal bioactivities and attracting considerable attention as neuroactive insecticides. Here we synthesis a series of novel thioether bridged N-phenylpyrazole derivatives incorporating various (hetero)aromatic substituents into 4-position of the pyrazole ring. Structure-activity relationship (SAR) studies resulted in compounds 6d and 7d with the most potent insecticidal activity among the series containing various substituted benzene substituents (LC₅₀?=?13.70–25.47?μg/g). Further optimization to increase the lipophilicity and charge density of aromatic substituents of compounds 6d and 7d resulted in compounds 12d, 14d and 16d with sulfur-containing heterocycle substituents possessing good insecticidal activity against Musca domestica L. among the series (LC₅₀?=?0.67–1.30?μg/g). The thioether bridge N-phenylpyrazole derivatives, which exhibit different length of the spacer arm introduced between N-phenylpyrazole moiety and the (hetero)aromatic substituents, were also prepared and evaluated. By contrast, the insecticidal activities of compounds containing the short thioether bridge, 1,2-bis((hetero)aromatic thio) ethane, are higher than that containing the long thioether bridge, 1,3-bis((hetero)aromatic thio) propane. The results of molecular docking and pharmacophore analyses indicated A299, T303, and L306 of a subunit were essential to form non-covalent interactions contacts with the ligands. Specially, the sulfur-containing heterocycle substituent derivatives 12d and 14d as the sterically favored areas could form the important hydrophobic interactions with the deeper residue P295.     

Synthesis of 4β-acyloxypodophyllotoxin analogs modified in the C and E rings as insecticidal agents against Mythimna separata Walker

To discover the new natural-product-based insecticidal agents, four series of sixty novel 4β-acyloxypodophyllotoxin analogs modified in the C and E rings were prepared, and their insecticidal activity was tested against the pre-third-instar larvae of oriental armyworm, Mythimna separata (Walker) in vivo at the concentration of 1 mg/mL. It demonstrated that the position of the dioxo group on the E-ring of 4′-demethylepipodophyllotoxin was regioselectively controlled by the chlorine atom at its C-2′ position when 2′-chloro-4′-demethylepipodophyllotoxin was oxidized by sodium periodate. Among all the derivatives, IIIi exhibited the best potent insecticidal activity with the final mortality rate of 63.3%. To alkylacyloxy series, the proper length of the side chain at the C-4 position of Ia–g, IIa–g and IIIa–g was important for their insecticidal activity.     

Synthesis and insecticidal activity of new deoxypodophyllotoxin derivatives modified in the D-ring

In continuation of our program aimed at the discovery of new natural-product-based insecticidal agents, twenty-six deoxypodophyllotoxin derivatives modified in the D-ring were synthesized and evaluated as insecticidal agents against the pre-third-instar larvae of oriental armyworm, Mythimna separata (Walker) in vivo at 1 mg/mL. The configuration of three compounds 3, 4, and IIIi was unambiguously determined by single-crystal X-ray diffraction. It demonstrated that aminolysis of deoxypodophyllotoxin in the presence of pyrrolidine and piperidine could result in complete inversion of the configuration of the carbonyl group at its C-2 position. Five compounds IIa, IIi–k, and IIIh showed the equal or higher insecticidal activity than toosendanin. Especially IIj displayed the most potent insecticidal activity with the final mortality rate of 65.5%.     

Synthesis and insecticidal activity of novel hydrazone compounds derived from a naturally occurring lignan podophyllotoxin against Mythimna separata (Walker)

In continuation of our program aimed at the discovery and development of natural-product-based insecticidal agents, a series of novel hydrazone derivatives of podophyllotoxin, which is a naturally occurring aryltetralin lignan and isolated as the main secondary metabolite from the roots and rhizomes of Podophyllum species, were synthesized and evaluated as insecticidal agents against the pre-third-instar larvae of oriental armyworm, Mythimna separata (Walker) in vivo at 1 mg/mL. Especially compounds 8i, 8j, 8t, and 8u showed the more potent insecticidal activity with the final mortality rates greater than 60%.     

Engineered Bacillus thuringiensis GO33A with broad insecticidal activity against lepidopteran and coleopteran pests

A recombinant plasmid pSTK-3A containing cry3Aa7 gene encoding a coleopteran-specific insecticidal protein was constructed and introduced into wild Bacillus thuringiensis subsp. aizawai G03, which contained cry1Aa, cry1Ac, cry1Ca, and cry2Ab genes and was highly toxic to lepidopteran insect pests. The genetically engineered strain were named G033A. Sodium dodecyl sulfate-polyacrylamide gel electrophoresis and Western blot analysis demonstrated that the cry3Aa7 gene was expressed normally and produced a 67 kDa protein in G033A, and the flat rectangular crystals of Cry3Aa7 toxin protein was observed under scanning electron microscope. The recombinant plasmid was maintained in bacteria cultured for 180 generations in culture media containing no antibiotics. Synthesis of the Cry3Aa7 toxin conferred high and broad toxicity to the recombinant strain G033A against coleopteran order, elm leaf beetle (Pyrrhalta aenescens) (LC₅₀ 0.35 mg/ml), for which the parental strain G03 was not toxic. Both the parental strain G03 and recombinant strain G033A showed strong insecticidal activity to lepidopteran pests, beet armyworm (Spodoptera exigua), diamondback moth (Plutella xylostella), and cotton bollworm (Helicoverpa amigera), respectively. The lethal concentration 50% (LC₅₀) of G033A against S. exigua, P. xylostella, and H. amigera was 4.26, 0.86, and 1.76 μg/ml, respectively.     

Comparative virulence of Beauveria bassiana isolates against lepidopteran pests of vegetable crops

Forty-three isolates of the entomopathogenic fungus Beauveria bassiana were screened for virulence against second-instar larvae of diamondback moth (Plutella xylostella) (DBM), European corn borer (Ostrinia nubilalis) (ECB), corn earworm (Helicoverpa zea) (CEW), and fall armyworm (Spodoptera frugiperda) (FAW); 30 of these isolates were tested against beet armyworm (Spodoptera exigua) (BAW). Highly virulent isolates were also tested against black cutworm (Agrotis ipsilon) (BCW), and the most virulent isolate was also assayed against imported cabbage worm (Pieris rapae) (ICW) and cabbage looper (Trichoplusia ni) (CL). All lepidopteran species tested were susceptible to B. bassiana. Corn earworm and beet armyworm were most susceptible to fungal infection, and fall armyworm was least susceptible. Limited testing suggested low susceptibility of black cutworm and cabbage looper. B. bassiana isolate 1200 exhibited virulence against all pest species greater than or equal to commercial strain GHA of B. bassiana currently registered in the USA as BotaniGard®. In assays in which larvae were topically sprayed and maintained on the treated substrate for 24 h at 100% relative humidity, 6-day (25 °C) median lethal concentrations (LC₅₀s) of this isolate against CEW, BAW, DBM, FAW, ICW, ECB, CL, and BCW were 4, 5, 7, 11, 12, 98, 125, and 273 conidia/mm², respectively. The respective LC₅₀s of commercial strain GHA against these pest species were 9, 67, 97, 1213, 29, 1668, 541, and 3504 conidia/mm². Use of LC₅₀ versus median lethal concentration ratios (comparing LC₅₀s of each isolate to a “standard” strain) generated similar rankings of isolate virulence. Results from parametric ANOVAs of log LC₅₀ values followed by Tukey HSD multiple comparisons tests and those from Kruskal-Wallis nonparametric analyses followed by sequential Bonferroni tests for means comparisons were nearly identical.     

Synthesis and insecticidal activity of new oxime derivatives of podophyllotoxin-based phenazines against Mythimna separata Walker

To discover new natural-product-based insecticidal agents, a series of novel oxime derivatives of podophyllotoxin-based phenazines modified in the C, D and E rings of podophyllotoxin were prepared and tested as insecticidal agents against the pre-third-instar larvae of oriental armyworm, Mythimna separata (Walker) in vivo at 1 mg/mL. The steric configuration of IIIc was unambiguously confirmed by single-crystal X-ray diffraction analysis. Compounds IIIa–d, and IIIi exhibited an equal or higher insecticidal activity than toosendanin.     

The trifluoromethyl transformation synthesis,crystal structure and insecticidal activities of novel 2-pyrrolecarboxamide and 2-pyrrolecarboxlate

Two series of 2-phenylpyrroles: 3-bromo-5-(4-chlorophenyl)-4-cyanopyrrole-2-carboxamide (5a–5d) and 3-bromo-5-(4-chlorophenyl)-4-cyanopyrrole-2-carboxylate (6a–6c) were synthesized by a novel trifluoromethyl transformation. The result of insecticidal bioassays indicated that 6a–6c had moderate larvicidal activity against oriental armyworm and 6b also had good acaricidal activity, so 3-bromo-5-(4-chlorophenyl)-4-cyanopyrrole-2-carboxylate derivatives were expected to become lead compounds for new pesticides.     

Sublethal effects of hexaflumuron on development and reproduction of the diamondback moth,Plutella xylostella (Lepidoptera: Yponomeutidae)

Abstract Effects of hexaflumuron at 10% lethal concentration (LC₁₀) and LC₂₅ on development and reproduction parameters of the diamondback moth, Plutella xylostella (Linnaeus, 1753) (Lep.: Yponomeutidae) were investigated. Estimated LC₅₀, LC₁₀ and LC₂₅ values of leaf dip bioassay of hexaflumuron on the third instar larvae of the P. xylostella were 1.48, 0.59 and 0.91 mg/L, respectively. Hexaflumuron decreased pupal weight in the parent generation at sublethal concentrations but in the offspring generation, this effect was not observed. Sublethal concentrations increased egg, first and second larval instar and pupa developmental time and shortened life span of adults, but did not change the third and fourth larval instars and pre‐pupa developmental period. Also fecundity of females reduced significantly but hatchability of treatments and control were similar. Survival rate of pre‐adult stages declined significantly at LC₂₅ concentration. Reproduction parameters such as reproductive rate (R₀) and intrinsic rate of increase in sublethal concentrations were significantly lower compared with control, but gross reproduction rate (GRR) at the LC₁₀ concentration was increased and it could be hormoligosis. Also hexaflumuron significantly increased doubling time (Dt). We conclude that the sublethal effects of hexaflumuron might exhibit significant effects on the population dynamics of P. xylostella.