Bioassay-guided isolation and identification of Aedes aegypti larvicidal and biting deterrent compounds from Veratrum lobelianum

Abstract

An ethanol extract from Veratrum lobelianum Bernh. rhizomes showed larvicidal activity with LC50 values of 11.79 ppm and 89.9 ppm against 1st and 4th instar larvae, respectively, at 24 h post-treatment. The extract also showed proportion not biting (PNB) value of 0.76 at 100 μg/cm2 against females of Ae. aegypti. Systematic bioassay-guided fractionation of V. lobelianum extract resulted in the isolation of five compounds that were identified as ethyl palmitate (1), ethyl linoleate (2), β-sitosterol (3), resveratrol (4) and oxyresveratrol (5) by GC-MS, 1H-NMR, and 13C-NMR techniques, comparison with literature data, and confirmation with authentic compounds. Compound 2 exhibited larvicidal activity with an LC50 value of 24.1 (22.0-26.2) ppm whereas 1 was inactive. β-Sitosterol (3) displayed the highest larvicidal activity with LC50= 1.7 (1.3-12.3) ppm and LC90= 5.1 (3.4-13.8) ppm. Compounds 4 and 5 had larvicidal activity with LC50 values of 18.5 (15.3-23.3) and 22.6 (19.0-26.8) ppm, respectively, and had an equivalent PNB values of 0.75 at 25 nmol/cm2. In addition, 4 and 5 were explored for their human-based repellency against Ae. aegypti, attractiveness against male medflies Ceratitis capitata, and also evaluated against series of human carcinoma cells (A549, HEK293, HeLa, SH-SY5Y); however, no significant activity was found.

Keywords

• fatty ethyl esters
• phytosterol
• stilbenoids
• pest control
• natural products