Larvicidal Activity of Geranylacetone Derivatives against Culex quinquefasciatus Larvae and Investigation of Environmental Toxicity and Non-Target Aquatic Species

A grindstone method based on Mannich condensation was used to synthesize geranylacetone derivatives (1a–1f). The method showed a high yield under milder reaction conditions. Analyses of the synthesized compounds were carried out by FTIR, 1H, 13C NMR, mass spectrometry, and elemental analysis. We synthesized and evaluated the larvicidal and ichthyotoxic activities of six compounds (1a–1f) in this study. Compound 1f (5,9-dimethyl-1-phenyl-3-(2-(3-phenylallylidene)hydrazinyl)deca-4,8-dien-1-one) was more active (LD50: 14.1 µg/mL) against the second instar larvae of Culex quinquefasciatus than geranylacetone (67.2 µg/mL), whereas the former caused 13.9% mortality at 100 µg/mL. Geranylacetone, in an antifeedant screening test, showed 53.1% against Oreochromis mossambicus within 24 h. The compound 1f showed high larvicidal activity against C. quinquefasciatus and was non-toxic to non-target aquatic species.