Larvicidal properties of the three major furostanol saponins of Balanites aegyptiaca fruit mesocarp against Aedes agypti mosquito larvae

Among various biological activities, saponin-rich extracts have been found to be larvicidal against mosquito larvae; however, no study so far has reported using pure furostanol saponins. In this study, three major furostanol saponins: 26-(O-β-D-glucopyranosyl)-3β,22,26-trihydroxyfurost-5-ene 3-O-β-D-glucopyranosyl-(l→4)-[α-L-rhamnopyranosyl-(1→2)] -β-D-glucopyranoside (1), 26-(O-β-D-glucopyranosyl)-22-O-methylfurost- 5-ene-3β,26-diol 3-O-β-D-xylopyranosyl-(l→3)-β-D- glucopyranosyl-(1→4)-[α-L-rhamnopyranosyl-(1→2)] -β-D-glucopyranoside (2), and 26-(O-β-D-glucopyranosyl)-22-O- methylfurost-5-ene.3β,26-diol 3-O-β-D-glucopyranosyl-(1→4)- [α-L-rhamnopyranosyl-(1→2)]-β-D-glucopyranoside (3) were isolated from methanol extracts of the fruit mesocarp of Balanites aegyptiaca (L.) Del. (desert date). Their identification was carried out by ESI-MS ⁿ and structures were elucidated by 800 MHz ¹H NMR spectroscopy. The larvicidal properties of these saponins against the Aedes aegypti mosquito larvae were evaluated. Results suggest that all three saponins possess larvicidal activity, but the activity was found to be related to the structure of the saponins, basically in the C-22 position of the aglycone and in the oligosaccharide chain. A furostanol saponin that presents -OCH₃ at the C-22 position compared to an -OH group, and the lack of a xylose molecule compared to its presence is found to be more larvicidal.