Bioactive saponins from Microsechium helleri and Sicyos bulbosus

Abstract

Eleven oleanane-type saponins ( 1– 11) have been isolated from Microsechium helleri and Sicyos bulbosus roots and were evaluated for their antifeedant, nematicidal and phytotoxic activities. Saponins {3- O-β- d-glucopyranosyl (1 → 3)-β- d-glucopyranosyl-2β,3β,16α,23-tetrahydroxyolean-12-en-28-oic acid 28- O-α- l-rhamnopyranosyl-(1 → 3)-β- d-xylopyranosyl-(1 → 4)-[β- d-xylopyranosyl-(1 → 3)]-α- l-rhamnopyranosyl-(1 → 2)-α- l-arabinopyranoside} ( 1), and {3- O-β- d-glucopyranosyl-2β,3β,16α,23-tetrahydroxyolean-12-en-28-oic acid 28- O-α- l-rhamnopyranosyl-(1 → 3)-β- d-xylopyranosyl-(1 → 4)-[β- d-xylopyranosyl-(1 → 3)]-α- l-rhamnopyranosyl-(1 → 2)-α- l-arabinopyranoside} ( 2) were also isolated from M. helleri roots together with the two known compounds 3 and 4. Seven known structurally related saponins ( 5– 11) were isolated from S. bulbosus roots. The structures of these compounds were established as bayogenin and polygalacic glycosides using one- and two-dimensional NMR spectroscopy and mass spectrometry. Compounds 7, 10, bayogenin ( 12) and polygalacic acid ( 13) showed significant ( p < 0.05) postingestive effects on Spodoptera littoralis larvae, compounds 5– 11 and 12 showed variable nematicidal effects on Meloydogyne javanica and all tested saponins had variable phytotoxic effects on several plant species ( Lycopersicum esculentum, Lolium perenne and Lactuca sativa). These are promising results in the search for natural pesticides from the Cucurbitaceae family.