A new sphingoid derivative from Acacia hockii De Wild (Fabaceae) with antimicrobial and insecticidal properties

Abstract

In Cameroon, several species of the genus Acacia are traditionally used for protection in granaries of stored foodstuffs such as cowpeas, maize and millet. The literature review on Acacia hockii made it possible to detect that few studies were carried out on this plant which would traditionally have the properties we seek. The objective of this work is to extract and isolate the active principles and then evaluate the insecticidal and antifungal activities of the extracts and compounds isolated from the fruits of A. hockii. The maceration method was used to obtain hexane, acetone and methanol extracts of A. hockii fruits which were used against adults of Callosobruchus maculatus (Coleoptera: Bruchidae), a pest of cowpea (Vigna unguiculata). The most active extract was fractionated by column chromatography and the compounds were elucidated by 1D and 2D NMR spectroscopy. The well-scattering method was used for evaluating the antifungal activity. The results show that all extracts were active against adults of C. maculatus and that the acetone extract was the most active with a 100% mortality rate at the concentration of 0.500 mg/mL and an LD50 of 0.06 g per gram of cowpea. The antifungal activity test of the acetone extract showed sensitivity against all tested strains Fusarium solani, Aspergillus flavus and Penicillium citrinum with MIC of 0.0625; 0.500 mg/mL, respectively. Fractionation of this extract led to the isolation of four compounds, among β-stigmasterol and β-sitosterol, β-stigmasterol-3β-O-D-glucopyranoside and N-((2S,3S,4R,14E)-1,3,4-trihydroxyicos-14-en-2-yl)palmitamide, a new sphingolipid with insecticidal and moderate antibacterial activities. A. hockii fruits can be considered a potential source for the production of biopesticides.