Megalanthine, a Bioactive Sesquiterpenoid from Heliotropium megalanthum, its Degradation Products and their Bioactivities

The new bioactive sesquiterpenoid (3R,6E)-2,6,10-trimethyl-3-(3-p-hydroxyphenylpropanoyloxy)-dodeca-6,11-diene-2,10-diol, named megalanthine, was isolated from the resinous exudates of Heliotropium megalanthum. The degradation products of this compound were identified. Several plant-defensive properties (insecticidal, antifungal, and phytotoxic) were evaluated after obtaining positive results in a preliminary etiolated wheat coleoptile bioassay. This bioassay showed the need to have both the phenolic and sesquiterpene moieties of the natural product present to achieve a biological effect. This result was confirmed in phytotoxicity bioassays. Megalanthine was ruled out as a significant plant-plant defense agent because of its lack of stability. The positive results recorded in the antifungal and antifeedant tests suggest, however, that this chemical is relevant in several ecological interactions involving H. megalanthum.