Triterpene Saponins in the Defensive Secretion of a Chrysomelid Beetle, Platyphora ligata

Abstract

The secretion of the defensive glands of adults of the chrysomelid beetle Platyphora ligata from Panama has been shown to contain, besides chlorogenic acid (1) and a mixture of phosphatidylcholines, two new oleanane triterpene saponins, named ligatosides A and B. Their structures were established as 3-O-beta-D-glucuronopyranosyl-16alpha,23-dihydroxyoleanol ic acid-28-O-2-(3,4-dimethoxybenzoyl)-beta-D-glucopyranoside (2) and 3-O-beta-D-glucopyranosyl-(1-->2)-beta-D-glucuronopyranosyl-16a lpha, 23-dihydroxyoleanolic acid-28-O-2-(3, 4-dimethoxybenzoyl)-beta-D-glucopyranoside (3), respectively, by a combination of extensive 1D and 2D NMR methods (COSY, HMQC, HMBC, and TOCSY) and FABMS. This is the first report of triterpene saponins in the defensive secretion of an insect.

The triterpene glycosides of Holothuria forskali: usefulness and efficiency as a chemical defense mechanism against predatory fish

“…Kubanek et al reported that the unpalatable nature of extracts from the sponge Erylus formosus was due to their triterpene glycoside content and that these molecules could thus protect the sponge from predatory reef fish (Kubanek et al, 2000). In this species, the triterpene glycosides appear to deter predation, microbial attachment, and fouling by invertebrates and algae; in another species, Ectyoplasia ferox, they were shown to be anti-predatory and allelopathic (Kubanek et al, 2002 (Plasman et al, 2000a;Plasman et al, 2000b). These secretions are produced by glands localized on the elytra and on the pronotum of adult beetles (Plasman et al, 2001).…”

Chemical defense in Platyphora kollari Baly and Leptinotarsa behrensi Harold (Coleoptera: Chrysomelidae). Hypotheses on the origin and evolution of leaf beetles toxins

“…Consequently, it is highly probable that the beetles find a precursor of these compounds in their diet. This must be a non-specific compound widely distributed in plants, since neither the secretion of P. ligata (Plasman et al 2000a), nor that of P. kollari (this study) changed in quality when the insects fed on different host plants. i-Amyrin found in the hexane extracts of three food plants (M. micrantha, I. batatas and C. ar6ensis) could be such a precursor.…”

“…Moreover, M. micrantha, the food plant of P. ligata, does not contain the oleanene glycosides found in this beetle (Plasman et al 2000a). Consequently, it is highly probable that the beetles find a precursor of these compounds in their diet.…”

“…An evolutionary scheme has been put forward (Pasteels et al 1989), which assumed that the synthesis of amino acid derivatives constituted the plesiomorphic condition, and that cardenolides and other steroid derivatives represent an apomorphic condition. Therefore, the discovery of triterpene glycosides in three chrysomelid species from Panama raises interesting questions about the origin of these compounds, since we have found that the host plant of Platyphora ligata is devoid of the triterpene glycosides and that the composition of the beetles defensive secretion is constant regardless as to its food plant among the Asteraceae (Plasman et al 2000a).…”

“…Mikania micrantha (Eupatoriae), host plant of P. ligata (Plasman et al 2000a), and I. batatas (Convolvulaceae), on which P. kollari was fed, showed the presence of both h-and i-amyrin in the hexane extract. No oleanolic acid could be detected in any of the extracts.…”