Synthesis and insecticidal activity of some pyrazole, pyridine, and pyrimidine candidates against Culex pipiens L. larvae

The expansion of the Culex pipiens population has increased the spread of arboviruses, due to the ineffectiveness of several traditional insecticides available to control this vector. Some heterocycles bearing a benzoquinoline moiety, such as pyrazoline, pyridine, pyridone, and pyrimidine derivatives, were synthesized from the reaction of 3-(3-chlorobenzo[f]quinolin-2-yl)-1-(4-chlorophenyl)prop-2-en-1-one with some nitrogen and carbon nucleophiles. The synthesized compounds were investigated against laboratory and field strains of C. pipiens larvae. The activities of prepared derivatives were varied, where compounds 7, 5, and 9 showed good toxicities with LC₅₀ of 180.35, 222.87, and 235.25 µg/mL, respectively, for the lab strain. At the same time, their potencies decreased to 242.44, 265.83, and 280.84 µg/mL, respectively, for the field strain. In contrast, pyridone 10 was the least effective compound with an LC₅₀ of 336.93 and 346.60 µg/mL for the lab and field strain, respectively. The field strain exhibited low resistance levels against all tested compounds. Structure-activity relationship was studied to demonstrate the effect of each substitution on activity against C. pipiens. Therefore, more substitutions should be inserted to enhance the activity of chalcone to be used in the mosquito larvae control programs, especially the field strain showed low resistance levels.