Green Insecticides Research Articles

Synthesis and Insecticidal Activities of Novel Nitrogenous Derivatives of Celangulin-V

In order to develop new biorational pesticides and clarify the potential structural factors needed for the biological activity of celangulin-V analogues, thirty novel nitrogenous derivatives were designed and synthesized. The single crystal structure of celangulin-V is reported for the first time and provides a more accurate structure than that previously reported. The structures of all the new derivatives were confirmed by either NMR or ESI-MSn analysis. Insecticidal activities of these compounds were tested against the third-instar larvae of Mythimna separata. One derivative (1-6) showed higher insecticidal activity than celangulin-V, with a KD50 of 231.2 microg.g(-1), while two compounds (2-13 and 2-14) exhibited lower insecticidal activities; the others revealed no activity at a concentration of 20 mg mL(-1). The results support the view that celangulin-V has the potential to be a lead structure of semi-synthetic green insecticides.

Evaluation of some plant products for the management of Prostephanus truncatus (Horn) (Coleoptera: Bostrichidae) in stored maize (Zea mays) and their effect on nutritional composition of the kernels

The bioactivity of powder from the leaves of Aristolochia ringens, Dalbergia saxatilis, Dioclea reflexa, Ocimum gratissimum, Chrysophyllum albidum, Moringa oleifera, Citrus limon and Newbouldia laevis was tested against the larger grain borer (LGB) in maize kernels and the effect of the powder on the nutritional composition of the kernels was determined. A total of 72 glass bottles containing 100 g maize kernels was divided into four groups. In the first group of 32 glass bottles, 5 g powder of the experimental plants was admixed uniformly with the kernels (5% w/w). Ten 1–5-day-old LGB adults were introduced into each of the glass bottles. A second group of 32 glass bottles contains 100 g maize kernels admixed with the plant powder as described above, but LGB were not added. In the third group of four glass bottles, 100 g maize kernels received insects only, while in the fourth group of four glass bottles 100 g maize kernels were neither mixed with plant products nor infested with LGB. The treatments were arranged on worktables using completely randomised design and left for three months. The plant products-treated samples (insect free) were passed through a 30 mesh sieve to sieve out the powder and the clean kernels were analysed for proximate composition. The untreated maize kernel had a significantly (p < 0.05) higher % of grain weight loss (17.33), grain damage % (70.96), number (122.0) of adult LGB, weight (14.46 g) of grain dust and lower % of grain germination. The adsorption and absorption of some of the plant powder by the kernels had significant effect on the kernel composition of protein, fibre and carbohydrate, but not on moisture, dry matter and fat and ash content. Control of LGB with the powder of the test plants could be used as green insecticide for the management of LGB.

Synthesis and Insecticidal Activities of Novel Derivatives of 1β,4α,6α,9α-Tetrahydroxy-2β,12-epoxymethano-β-dihydroagarofuran

In order to develop novel biorational pesticides, twelve new ether derivatives of 1β,4α,6α,9α-tetrahydroxy-2β,12-epoxymethano-β-dihydroagarofuran (3) were synthesized. The structure of the important intermediate 3 was confirmed by X-ray crystallography, and the new derivatives (3.1–3.12) were elucidated by IR, 1H NMR, 13 C NMR and 2D NMR spectroscopic and ESI-MS analysis. Insecticidal activities of these derivatives were tested against the third-instar larvae of Mythimna separata. Though most of the derivatives (3.1–3.4, 3.6, 3.8, 3.9–3.12) revealed no obvious activities at the concentration of 10 mg/mL –1, two compounds 3.5 and 3.7, with KD50 values of 12.9 (μg/g-1 and 7.8 μg/g –1, respectively, showed much higher insecticidal activities than celangulin-V, with a KD50 of 321.4 μg·g–1, the main insecticidal component from the root bark of Chinese bittersweet, Celastrus angulatus Max. The results showed that β-dihydroagarofuran has the potential to be a lead structure for semi-synthetic green insecticides.

Synthesis and Insecticidal Activities of New Ester-Derivatives of Celangulin-V

In order to develop new biorational pesticides, ten new 6-substituted ester derivatives of Celangulin-V were designed and synthesized. The structures of the new derivatives were confirmed by IR, 1H-NMR, 13C-NMR and ESI-MS spectral analysis. Insecticidal activities of these compounds were tested against the third-instar larvae of Mythimna separata. Two derivatives (1.1, 1.2) showed higher insecticidal activities than Celangulin-V, with mortality of 75.0% and 83.3%, respectively. While four compounds (1.3, 1.4, 1.7, 1.8) denoted lower insecticidal activities, the others (1.5, 1.6, 1.9, 1.10) revealed no activities at a concentration of 10 mg.mL−1. The results suggest that C-6 substitutions of Celangulin-V are very important in determining the insecticidal activities of its ester-derivatives. That the acetyl (1.1) and propionyl (1.2) derivatives possessed much higher insecticidal activities than Celangulin-V itself supported the view that Celangulin-V has the potential to be a lead structure of semi-synthetic green insecticides.

Synthesis and Insecticidal Activities of New Ether-Derivatives of Celangulin-V

In order to find new biorational pesticides, eight new 6-substituted ether derivatives of Celangulin-V were synthesized. The structures were confirmed by IR, 1H NMR and 13C NMR spectroscopic and HRMS analyses. The insecticidal activities of these compounds were tested against third-instar larvae of Mythimna separata. Four derivatives (b, c, f, g) showed higher insecticidal activities than Celangulin-V, with KD50 values of 135.9, 101.33, 169.0 and 219.2 microg x g-1, respectively. However, two compounds (a, d) showed lower insecticidal activities and two (e, h) no activity. The results suggest that C-6 substitutions in these compounds are very important for their insecticidal activities. The insecticidal activities of the derivatives with two or three carbon substitutions at C-6 are higher than that of Celangulin-V showing that this compound has the potential to be a lead structure for semi-synthetic, green insecticides.