BACKGROUND
Chemical pesticides are the main measures for pest control, but have caused growing resistance of pests and brought a series of environmental problems. Development of high‐efficient insecticidal molecules with novel scaffolds is therefore particularly urgent.
RESULTS
Based on a [5 + 1] annulation reaction with 5‐amino‐1H‐phenylpyrazole and dialkyl bromomalonate, 27 novel five‐substituted 4,5‐dihydropyrazolo[1,5‐a]quinazolines were designed following the intermediate derivatization method and synthesized. Bioassay results indicated that most of the test compounds displayed good insecticidal activities against Plutella xylostella, Spodoptera frugiperda, and Solenopsis invicta. In particular, the insecticidal activities of compounds 4a, 4f, and 4m against P. xylostella [median lethal concentration (LC50) values ranged from 3.87 to 5.10 mg L−1] were comparable to that of indoxacarb (LC50 = 4.82 mg L−1). In addition, compounds 4a and 9e showed similar high insecticidal activities against Spodoptera frugiperda (mortality rate = 79.63% and 72.12%) at 100 mg L−1, comparable to that of fipronil (mortality rate: 68.44%); compound 9a showed possible delayed toxicity against Solenopsis invicta (mortality rate: 95.66%) after 5 days of treatment at 1.0 mg L−1.
CONCLUSION
Due to their high insecticidal activities against P. xylostella, compound 4m, 4a, and 4f could be considered as qualified candidates for novel insecticide. Several other 4,5‐dihydropyrazolo[1,5‐a]quinazolines with relatively high bioactivity, such as compounds 9a and 9e, are also worth further optimization as potential insecticide or anticide candidates.
In searching for novel insecticidal leads, a series of N-pyridylpyrazolo-5-methyl amines and their derivatives were designed and synthesized. Among the 22 target compounds obtained, bioassays indicated that some of the target compounds exhibited good insecticidal activities against Plutella xylostella (P. xylostella) and Spodoptera frugiperda (S. frugiperda). In particular, compound 9j revealed the best insecticidal activity against P. xylostella, with a LC 50 value of 22.11 mg/L, and compound 9q had the best insecticidal activity against S. frugiperda which with 73.99% of mortality rate at 100 mg/L. Structure-activity relationship (SAR) analysis showed that 4-CF 3 at the position of R 1 linked with N-pyridylpyrazole via amide bond could enhance the insecticidal activity of the target compounds. This study provides valuable clues for the further design and optimization of N-pyridylpyrazole derivatives.
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