Structure-activity relationships of eugenol derivatives against Aedes aegypti (Diptera: Culicidae) larvae.

BACKGROUND: Dengue fever is a severe public health problem for several countries. In order to find effective larvicides to aid control programs, the structure-activity relationships of eugenol derivatives against Aedes aegypti (Diptera: Culicidae) larvae were evaluated. Additionally, the composition and larvicidal activity of Syzygium aromaticum essential oil was assessed. RESULTS: Four compounds representing 99.05% of S. aromaticum essential oil have been identified. The essential oil was active against Ae. aegypti larvae (LC(50) = 62.3 and 77.0 ppm, field-collected and Rockefeller larvae respectively). The larvicidal activity of eugenol, the major compound of the essential oil, was further evaluated (LC(50) = 93.3 and 71.9 ppm, field-collected and Rockefeller larvae respectively). The larvicidal activity and structure-activity relationships of synthetic derivatives of eugenol were also assessed. The larvicidal activity of the derivatives varied between 62.3 and 1614.9 ppm. Oxidation of eugenol allylic bond to a primary alcohol and removal of the phenolic proton resulted in decreased potency. However, oxidation of the same double bond in 1-benzoate-2-methoxy-4-(2-propen-1-yl)-phenol resulted in increased potency. CONCLUSION: Structural characteristics were identified that may contribute to the understanding of the larvicidal activity of phenylpropanoids. The present approach may help future work in the search for larvicidal compounds.

Toxic effects on and structure-toxicity relationships of phenylpropanoids, terpenes, and related compounds in Aedes aegypti larvae.

In the search for toxic compounds against Aedes aegypti L. (Diptera: Culicidae) larvae, a collection of commercially available aromatic and aliphatic diversely substituted compounds were selected and evaluated. p-Cymene exhibited the highest larvicidal potency LC50 = 51 ppm, whereas 1,8-cineole exhibited the lowest activity value LC50 = 1419 ppm. To aid future work on the search for larvicidal compounds, the structure-toxicity relationships of this collection have been evaluated. The presence of lipophilic groups results in an overall increase in potency. In general, the presence of hydroxyl groups resulted in less potent compounds. However, methylation of such hydroxyls led to an overall increase in potency. The most potent compounds showed comparably good larvicidal activity in A. aegypti larvae as other terpenes, which we assume to be the result of the increased lipophilicity.