Exploring insecticidal activity and SAR study of newly synthesized Benzo[h]quinoline-based heterocycles against Aphis craccivora Koch. and Culex pipiens L. Larvae.

The key material, 2-chlorobenzo[h]quinoline-3-carbaldehyde condensed with various active-methylene reagents to produce some benzo[h]quinoline-based heterocycles like pyrazolone, imidazolone, thiazolidine, pyrimidinone, and indolinone candidates. The insecticidal activities of synthesized substrates were evaluated against cowpea aphid, Aphis craccivora, adults and common house mosquito, Culex pipiens larvae. The results of toxicological bioassays demonstrated that compounds 9 and 11, containing 2-thioxoimidazolidine and 2-thioxothiazolidine core, exhibited high insecticidal activity against A. craccivora adults with LC50s of 3.54 and 3.87 µg/mL, and against C. pipiens larvae with LC50s of 1.61 and 1.83 µg/mL, respectively. Schiff base 7 and arylidene 5 (bearing pyrazolone scaffolds) achieved good potencies with low LC50 values of 4.40 and 5.25 µg/mL for A. craccivora adults, and 2.16 and 2.49 µg/mL for C. pipiens larvae, respectively. On the other hand, the bulky pyrimidinetrione 16 and indolone 18 showed low toxicities. Overall, the tested substrates were more effective against C. pipiens larvae than A. craccivora adults. The current study highlighted the effect of the inserted function groups on 2-chlorobenzo[h]quinoline core on the compounds’ activity through the structure-activity relationship (SAR) study. This study presents promising results for the development of novel and effective insecticides to be integrated into pest control programs.