Wenjun Wu

Insecticidal and Feeding Deterrent Effects of Fraxinellone from Dictamnus dasycarpus against Four Major Pests

Fraxinellone, a well-known and significant naturally occurring compound isolated from Meliaceae and Rutaceae spp. has been widely used as a drug for the treatment of tumors. On the other hand, fraxinellone exhibited a variety of insecticidal activities including feeding-deterrent activity, inhibition of growth, and larvicidal activity. The present study focused on the antifeedant and larvicidal activities of fraxinellone against the larvae of Lepidoptera, including Mythimna separata, Agrotis ypsilon, Plutella xylostella, and one kind of sanitary pest, Culux pipiens pallens. Meanwhile, the ovicidal activities and the effects of fraxinellone on the larval development of M. separata were also observed. The LC50 values of fraxinellone against 3rd instar larvae of M. separata, 2nd instar larvae of P. xylostella and 4th instar larvae of C. pipiens pallens were 15.95/6.43/3.60 × 10−2 mg mL−1, and its AFC50 values against 5th instar larvae of M. separata, 2nd instar larvae of P. xylostella and 2nd instar larvae of A. ypsilon were 10.73/7.93/12.58 mg mL−1, respectively. Compared with the control group, fraxinellone obviously inhibited the pupation rate and the growth of M. separata. Once M. separata was treated with fraxinellone at concentrations of 5.0, 10.0, and 20.0 mg mL−1, respectively, the stages from the larvae to adulthood and the egg hatching duration were prolonged to 1/2/3, and 4/3/4 days, respectively. Additionally, fraxinellone strongly inhibited the development rate and the egg hatch proportion of M. separata.

Antibacterial Activity Composition of the Fermentation Broth of Streptomyces djakartensis NW35

The new compound Z-4-2 was isolated from the fermentation broth of Streptomyces djakartensis NW35, together with the known compound N-acetyltryptamine (Z-9-2) by bioassay-guided fractionation. Its chemical structure was elucidated as (E)-2-methoxy-1,4 naphthoquinone-1-oxime (Z-4-2) mainly by NMR analyses and MS spectral data. Their antibacterial activities against bacteria were evaluated by the filter paper method. The results of indicated that these compounds possess significant antibacterial activities.

Design and Synthesis of New 2-Aryl-4,5-Dihydro-thiazole Analogues: In Vitro Antibacterial Activities and Preliminary Mechanism of Action

Sixty 2-aryl-4,5-dihydrothiazoles were designed and synthesized in yields ranging from 64% to 89% from cysteine and substituted-benzonitriles via a novel metal- and catalyst-free method. The structures of the title compounds were confirmed mainly by NMR spectral data analysis. Antibacterial activity assays showed that the compounds (S)-2-(2′-hydroxyphenyl)-4-hydroxy-methyl-4,5-dihydrothiazole (7h) and (R)-2-(2′-hydroxyphenyl)-4-hydroxymethyl-4,5-dihydro-thiazole (7h′) exhibited significant inhibition against Ralstonia solanacearum, Pseudomonas syringae pv. actinidiae, Bacillus subtilis and Bacillus cereus, with minimum inhibitory concentrations (MICs) ranging from 3.91 to 31.24 μg·mL−1. The effect of substituents showed that not only electron-withdrawing groups, but also electron-donating groups could abolish the antibacterial activities unless a 2′-hydroxy group was introduced on the 2-aryl substituent of the 4,5-dihydrothiazole analogues. The results of scanning electron microscope (SEM) and fatty acid exposure experiments indicated that these antibacterial compounds influence fatty acid synthesis in the tested bacteria.

Histopathological effects and immunolocalization of periplocoside NW from Periploca sepium Bunge on the midgut epithelium of Mythimna separata Walker larvae

Periplocoside NW (PSNW) with pregnane glycoside skeleton is a novel insecticidal compound isolated from the root bark of Periploca sepium Bunge. This compound has a potent stomach poisoning activity against several insect pests. In this study, we observed the intoxication symptoms, investigated the histopathological effects and carried out immuno-electron microscopic localization of PSNW on the midgut epithelium of oriental armyworm Mythimna separata Walker larvae for better understanding its action mechanism against insects. Ultrastructural observations showed that cell damages caused by PSNW in the midgut of M. separata larvae are related to the degeneration of brush border microvilli. The dissolution of cytoskeletal structures in the interior and on the surface of microvilli was responsible for the decrease in size and eventual disappearance of microvilli when bubbles of cytoplasmic substances protrude into the midgut lumen of M. separata, thus resulting in cell death. The immuno-electron microscopic localization research showed that gold particle appeared on the microvilli layer of the midgut of M. separate larvae firstly. The density of gold particle gradually added with the time, and finally microvilli layer was destructed severely. Meantime, the gold particles were also presented to the intracellular organelle membrane and the organelles also were destructed. Therefore, we proposed that this membrane system on insect midgut epithelium cells is the initial acting site of PSNW against insects.

Isolation of the Binding Protein of Periplocoside E from BBMVs in Midgut of the Oriental Amyworm Mythimna separata Walker (Lepidoptera: Noctuidae) through Affinity Chromatography

Periplocosides, which are insecticidal compounds isolated from the root bark of Periploca sepium Bunge, can affect the digestive system of insects. However, the mechanism though which periplocosides induces a series of symptoms remains unknown. In this study, affinity chromatography was conducted by coupling periplocoside E-semi-succinic acid ester with epoxy amino hexyl (EAH) sepharose 4B. Sodium dodecyl sulfonate-polyacrylamide gelelectrophoresis (SDS-PAGE) was performed to analyze the fraction eluted by periplocoside E. Eight binding proteins (luciferin 4-monooxygenase, aminopeptidase N, aminopeptidase N3, nicotinamide adenine dinucleotide health (NADH) dehydrogenase subunit 5, phosphatidylinositol 3-phosphate 3-phosphatase myotubularin, actin, uncharacterized family 31 glucosidase KIAA1161, and 2OG-Fe(2) oxygenase superfamily protein) were obtained and identified through liquid chromatography/quadrupole-time of flight-mass spectrometry (LC/Q-TOF-MS) analysis of the midgut epithelium cells of Mythimna separata larvae. Aminopeptidase N and N3 are potential putative targets of periplocosides. This study establishes the foundation for further research on the mechanism of action and target localization of periplocosides in agricultural pests.

Modulation of the Ca2 + signaling pathway by celangulin I in the central neurons of Spodoptera exigua

Celangulin I is an insecticidal component isolated from Chinese bittersweet Celastrus angulatus. The present study explored the possible effects of celangulin I on the calcium signaling pathway, especially on the L-type Ca(2+) 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 celangulin I could activate the high voltage-gated calcium channel at the concentration of 150μM. The peak currents were increased by 17% of the initial value at the end of the 10-min recording after treated with celangulin I. The rises of intracellular calcium ion concentration ([Ca(2+)]i) in neurons treated by celangulin I showed that the effects of celangulin I were concentration-dependent. Activation of the RyRs by ryanodine decreased the calcium release induced by celangulin I, indicating that celangulin I exerts effect on insect RyRs. Furthermore, we also provided evidence for the first time that celangulin I activates inositol 1,4,5-trisphosphate (IP3) sensitive intracellular calcium release channels in the endoplasmic reticulum third instar larvae neurons of S. exigua. Plausibly, these experimental results can explain the characteristic symptoms of anesthesia and paralysis in celangulin I treated insects.

Efficient Synthesis and Antibacterial Evaluation of (±)-Yanglingmycin and Its Analogues

An efficient synthetic route was developed for the large-scale preparation of (±)-Yanglingmycin and its analogues. Three series of derivatives of (±)-Yanglingmycin were synthesized and the structures of all compounds were elucidated by analyses of NMR and ESI-MS spectra data. Moreover, their antibacterial activities against seven species of bacteria were systematically evaluated by the micro-broth dilution method, most of which displayed considerable activity. It was worth noting that compounds 5b, 5c, 5d, 6g, and 7 were found to be the most promising leading candidates, with peak MIC values of 0.98 μg·mL−1 for Bacillus subtilis, which is superior to positive controls (MIC = 3.91 μg·mL−1). The above results might lay the firm foundation for the design and synthesis of novel antibacterial drugs based on (±)-Yanglingmycin.

Bioassay-Guided Isolation of Antifungal Compounds from Disporopsis aspersa (Hua) Engl. ex Diels against Pseudoperonospora cubensis and Phytophthora infestans

Oomycetes are one type of the most highly destructive of the diseases that cause damage to some important crop plants, such as potato late blight, cucumber downy mildew, and grape downy mildew. As main approach of the ongoing search for new botanical fungicide from plant, the secondary metabolites of D. aspersa were investigated. Through efficient bioassay‐guided isolation, two new (1 and 2) and 12 known compounds (3 – 14) were isolated, and their structures were determined via extensive NMR, HR‐ESI‐MS, and IR. They were isolated from this genus for the first time except for compounds 11 and 12. The biological properties of 1 – 14 were evaluated against Pseudoperonospora cubensis and Phytophthora infestans. Compounds 1 – 8 showed potent antifungal activity in vitro. Additionally, compound 3 has preferable control effect on cucumber downy mildew, showing dual effect of protection and treatment in vivo.

Molecular Insights into the Potential Insecticidal Interaction of β-Dihydroagarofuran Derivatives with the H Subunit of V-ATPase

Celangulin V (CV), one of dihydroagarofuran sesquiterpene polyesters isolated from Chinese bittersweet (Celastrus angulatus Maxim), is famous natural botanical insecticide. Decades of research suggests that is displays excellent insecticidal activity against some insects, such as Mythimna separata Walker. Recently, it has been validated that the H subunit of V-ATPase is one of the target proteins of the insecticidal dihydroagarofuran sesquiterpene polyesters. As a continuation of the development of new pesticides from these natural products, a series of β-dihydroagarofuran derivatives have been designed and synthesized. The compound JW-3, an insecticidal derivative of CV with a p-fluorobenzyl group, exhibits higher insecticidal activity than CV. In this study, the potential inhibitory effect aused by the interaction of JW-3 with the H subunit of V-ATPase c was verified by confirmatory experiments at the molecular level. Both spectroscopic techniques and isothermal titration calorimetry measurements showed the binding of JW-3 to the subunit H of V-ATPase was specific and spontaneous. In addition, the possible mechanism of action of the compound was discussed. Docking results indicated compound JW-3 could bind well in ‘the interdomain cleft’ of the V-ATPase subunit H by the hydrogen bonding and make conformation of the ligand–protein complex become more stable. All results are the further validations of the hypothesis, that the target protein of insecticidal dihydroagarofuran sesquiterpene polyesters and their β-dihydroagarofuran derivatives is the subunit H of V-ATPase. The results also provide new ideas for developing pesticides acting on V-ATPase of insects.

Insight into the Mode of Action of Haedoxan A from Phryma leptostachya

Haedoxan A (HA) is a major active ingredient in the herbaceous perennial plant lopseed (Phryma leptostachya L.), which is used as a natural insecticide against insect pests in East Asia. Here, we report that HA delayed the decay rate of evoked excitatory junctional potentials (EJPs) and increased the frequency of miniature EJPs (mEJPs) on the Drosophila neuromuscular junction. HA also caused a significant hyperpolarizing shift of the voltage dependence of fast inactivation of insect sodium channels expressed in Xenopus oocytes. Our results suggest that HA acts on both axonal conduction and synaptic transmission, which can serve as a basis for elucidating the mode of action of HA for further designing and developing new effective insecticides.