Toxicity and Sublethal Effects of Phthalides Analogs to Rhyzopertha dominica.

Phthalides and their precursors have demonstrated a large variety of biological activities. Eighteen phthalides were synthesized and tested on the stored grain pest Rhyzopertha dominica. In the screening bioassay, compounds rac-(2R,2aS,4R,4aS,6aR,6bS,7R)-7-bromohexahydro-2,4-methano-1,6-dioxacyclopenta[cd]pentalen-5(2H)-one (15) and rac-(3R,3aR,4R,7S,7aS)-3-(propan-2-yloxy)hexahydro-4,7-methano-2-benzofuran-1(3H)-one (17) showed mortality similar to the commercial insecticide, Bifenthrin® (≥90 %). The time (LT50 ) and dose (LD50 ) necessary to kill 50 % of the R. dominica population were determined for the most efficacious phthalides 15 and 17. Compound 15 presented the lowest LD50 (1.97 µg g-1 ), being four times more toxic than Bifenthrin® (LD50 =9.11 µg g-1 ). Both compounds presented an LT50 value equal to 24 h. When applied at a sublethal dose, both phthalides (especially compound 15), reduced the emergence of the first progeny of R. dominica. These findings highlight the potential of phthalides 15 and 17 as precursors for the development of insecticides for R. dominica control.

Toxicity to Diaphania hyalinata, selectivity to non-target species and phytotoxicity of furanones and phthalide analogues.

BACKGROUND: Despite being of great importance to crop protection, the disadvantages of intensive and inappropriate use of pesticides have stimulated the search for more selective and less harmful agrochemicals. Thus, we have evaluated the effectiveness of 16 synthetic molecules (phthalides and precursors) to control the melonworm Diaphania hyalinata, a key pest in cucurbit crops of economic importance in Brazil. The selectivity to beneficial organisms Solenopsis saevissima and Tetragonisca angustula and the phytotoxicity to Cucumis sativus of the promising insecticides were also assessed. RESULTS: In the screening assay, compounds 1 and 6 provided 91 and 88% mortality of the melonworm. Compound 1 presented higher toxicity (median lethal dose LD50 = 15.99 µmol g(-1) ) and higher speed on pest control (median survival time LT50 = 420 min) than compound 6 (LD50 = 44.51 µmol g(-1) and LT50 = 840 min). Both compounds inhibited less than 11% of host-plant growth and caused ≤36 and ≥93% mortality of predator and pollinator respectively. CONCLUSION: Among the tested compounds, only compounds 1 and 6 were effective in melonworm control. Both compounds presented no considerable phytotoxicity and were selective to predator but non-selective to pollinator, which enables their application for pest control if the exposure of the bees is minimised. © 2015 Society of Chemical Industry.

Synthesis and insecticidal activity of an oxabicyclolactone and novel pyrethroids.

Deltamethrin, a member of the pyrethroids, one of the safest classes of pesticides, is among some of the most popular and widely used insecticides in the World. Our objective was to synthesize an oxabicyclolactone 6 and five novel pyrethroids 8–12 from readily available furfural and D-mannitol, respectively, and evaluate their biological activity against four insect species of economic importance namely A. obtectus, S. zeamais, A. monuste orseis, and P. americana. A concise and novel synthesis of 6,6-dimethyl-3-oxabicyclo[3.1.0]hexan-2-one (6) from furfural is described. Photochemical addition of isopropyl alcohol to furan-2(5H)-one afforded 4-(1'-hydroxy-1'-methylethyl)tetrahydro-furan-2-one (3). The alcohol 3 was directly converted into 4-(1'-bromo-1'-methylethyl)-tetrahydrofuran-2-one (5) in 50% yield by reaction with PBr(3) and SiO(2). The final step was performed by cyclization of 5 with potassium tert-butoxide in 40% yield. The novel pyrethroids 8–12 were prepared from methyl (1S,3S)-3-formyl-2,2-dimethylcyclopropane-1-carboxylate (7a) by reaction with five different aromatic phosphorous ylides. Compounds 6–12 presented high insecticidal activity, with 6 and 11 being the most active. Compound 6 killed 90% of S. zeamais and 100% of all the other insects evaluated. Compound 11 killed 100% of all insects tested.