Machaerium acutifolium compounds with larvicidal activity against Aedes aegypti

Plant extracts and isolated compounds are known for their insecticidal activity. The Aedes aegypti mosquito has a significant medical impact as it transmits a number of arboviruses and is able to develop resistance to the commercially available insecticides. This study investigates larvicidal compounds isolated from Machaerium acutifolium, designated by the Brazilian Forest Service as a sustainable species.

A M. acutifolium trunk ethyl acetate extract was fractionated using chromatographic methods with full structural elucidation by mass spectrometry (MS), nuclear magnetic resonance and specific rotation analyses revealing: one new 3-arylcoumarin derivative 1; two flavonoids 2 and 3; a trans-stilbene 4, and an unprecedented natural indene 5. The larvicidal activity against Ae. aegypti after 24 h exposure was: crude extract (median lethal dose, LC₅₀ 205 mg L^-1 ), fraction C (LC₅₀ 27 mg L^-1 ) and 5 (LC₅₀ 24 mg L^-1 ).

A M. acutifolium extract showed larvicidal activity, which increased with prolonged exposure, demonstrating LC₅₀ 75 mg L^-1 after 72 h. Although the flavonoids 2 and 3 and trans-stilbene 4 were deemed inactive according to the adopted mortality limit, additional tests revealed their ability to cause 65% Ae. aegypti larvae mortality, suggesting they could contribute to the larvicidal activity. Compound 5, identified by liquid chromatography-MS, was over eight-fold more toxic to larvae than the crude extract after 24 h. Therefore, 5 constitutes a structural model for new prototypes to control Ae. aegypti. These data reinforce the potential of natural products as a source of commercial alternatives for vector control strategies, respecting both sustainability and eco-friendly principles. © 2020 Society of Chemical Industry.