Palladium-catalyzed non-directed C–H bond arylation of difluorobenzenes and dichlorobenzenes bearing benzoxazole or benzothiazole

International audienceWe report, herein, on palladium-catalyzed direct arylation of difluorobenzenes and dichlorobenzenes bearing benzoxazole or benzothiazole moieties, which don't act as directing groups. With moderate electron-withdrawing substituents on the aryl bromides as coupling partners, the reaction proceeds nicely using phosphine-free PdCl2 catalyst, and potassium pivalate/dimethylacetamide (PivOK/DMA) as catalytic system. The reaction was regioselective and occurred at the less hindered ortho-positions of fluorine or chlorine atom

Toxicity of the active fraction of Pergularia tomentosa and the aggregation pheromone phenylacetonitrile on Schistocerca gregaria fourth-instar nymph: effects on behavior and acetylcholinesterase activity

Chemical insecticides remain the most used approach in locust control although they present a serious menace to human health and the environment. The search for alternative control methods, efficient and environmentally friendly, has become indispensable. The aim of this work is to study the effect of the aggregation pheromone, phenylacetonitrile, alone or in combination with the active fraction of Pergularia tomentosa on Schistocerca gregaria fourth-instar nymph. Toxicity bioassays showed that the combination of phenylacetonitrile with the active fraction of P. tomentosa significantly increased nymph mortality. Results also showed that the aggregation pheromone caused significant mortality especially after 6 hours of exposure. The pheromone also caused neurotoxic effects on S. gregaria nymph due to the disturbance of the acetylcholinesterase activity. We also noted the presence of cannibalism phenomenon. Phenylacetonitrile seems to have an effect on phase ployphenism of S. gregaria imagos that exhibit specific traits to the solitarious phase

A Simple and Efficient Synthesis of (Hetero)Aryl-Substituted Benzothiazolyl or Benzoxazolyl Furan, Thiophene and N-methylpyrrole Derivatives through a Palladium-Catalyzed Regioselective C–H Bond Arylation

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Repellency and toxicity of the crude ethanolic extract of Limoniastrum guyonianum against Tribolium castaneum. Acheuk, F., Belaid, M., Lakhdari, W., Abdellaoui, K., Dehliz, A., and Mokrane, K. (Algeria/Tunisia)

In nature, the interaction between plants and insects has led to the production of a set of secondary compounds. Many plant secondary metabolites have significant insecticidal activity. The aim of this study is to evaluate the repellent and insecticidal effect of the crude ethanolic extract of Limoniastrum guyonianum against adults of the red flour beetle Tribolium castaneum. For the insecticidal activity, five doses (100, 200, 400, 600, and 800 µg/insect) were tested and were topically applied onto insect thorax. An area preference method was adopted to assess the repellent activity. A phytochemical study and measurement of two enzymatic biomarkers: acetylcholinesterase (AChE) and gluthatione Stransferase (GST) were made to understand the mechanisms of toxic action of the tested extract. Phytochemical study showed the presence of various groups of natural products. The plant is rich in flavonoids, tannins, alkaloids, and glycosides. Low amount of saponins was noted. The study also showed that this plant does not contain iridoids. For repellent activity, the results showed that the highest dose (800 µg/insect) exhibited obvious repellent effect against T. castaneum. The repellency percentage was 90.14 ± 2.5% after 4 h of exposure. The crude extract was found to be toxic to T. castaneum and the corresponding LD50value was 218.3 μg/insect. Moreover, the extract inhibits the activity of the acetylcholinesterase (IC50: 205.7 µg/insect)

Effects of Latex from Pergularia tomentosa and the Aggregation Pheromone, Phenylacetonitrile, on Locusta migratoria Larvae

Despite being a serious risk to human health and environment, chemical insecticides remain the most used for locust control. Searching for alternative control methods, effective and compatible with the environment, has become of increasing interest. Plant latex is an endogenous fluid secreted from highly specialized laticifer cells and has been suggested to act as a plant defense system. The aim of the present investigation was to study the insecticidal potentialities of Pergularia tomentosa latex at different concentrations, alone or in combination with the penylacetonitrile (PAN), on the 4th instar larvae of Locusta migratoria. The obtained results showed that the latex revealed an interesting insecticidal activity against L. migratoria larvae, resulting in a mortality reaching 96.49 %, 6 days after treatment. Toxicity bioassays revealed that PAN, associated with the latex, is able to accelerate and to increase the mortality rate. Pheromone-based treatment affected the health of treated insects by significantly reducing their respiratory rhythms. PAN was shown able to alter, quantitatively and qualitatively, the larval blood cells as expressed by the significant decrease in the number of the differential haemocyte counts (prohemocyte, plasmatocytes and granulocytes) and the important cell lysis

Antifeedant and antigonadotropic effects of Ruta chalepensis methanolic extract against Locusta migratoria. Abdellaoui, K., Miladi, M., Ben Marzouk, I., Bahloul, N., Acheuk, F., Chaira, N., and Ben Halima-Kamel, M. (Tunisia / Algeria)

The migratory locust Locusta migratoria is one of the most important pests due to its extensive and serious damage to crops in large parts of Africa and Asia. To identify novel new environment friendly products for the management of the migratory locust, experiments were conducted to assess the effect of a methanolic extract of Ruta chalepensis (ME-Rc) on feeding activity and different reproductive phases of L. migratoria. The results showed that ME-Rc caused a significant decline in food intake and insect digestibility. The treatment applied to adult females caused a significant lengthening of the preoviposition period and a significant reduction in both fecundity and fertility. ME-Rc also affected growth and development of oocytes as evidenced by measurements of ovarian weight, length and volume of terminal oocytes and ovarian index. In addition, ME-Rc based-treatments led to disturbances in the incorporation of haemolymph metabolites (proteins and carbohydrates) in oocytes resulting in a significant decrease in their concentrations in ovaries

Palladium-Catalyzed Regioselective C–H Bond Arylations of Benzoxazoles and Benzothiazoles at the C7 Position

We report herein, a very simple catalytic system for the direct arylation of benzoxazole and benzothiazole derivatives at C7 position, namely, phosphine-free PdCl₂ associated with PivOK in NMP at 150 °C. (Thio)­phenoxy chelation-assisted Pd-catalyzed C–H bond cleavage, from an opened intermediate, was proposed to explain this unique regioselectivity. This reaction allows the synthesis of 2-amino-6-arylphenols through the ring opening of the benzoxazole