Defensive sesterterpenoids with unusual antipodal cyclopentenones from the leaves of Leucosceptrum canum.

Two novel sesterterpenoids, leucosceptroids C (1) and D (2), possessing unusual antipodal cyclopentenones while maintaining the stereochemistry and functionality of the tricyclic cores, were discovered from the leaves of Leucosceptrum canum (Labiatae). Their structures including absolute stereochemistries were determined by comprehensive NMR, MS, and single-crystal X-ray diffraction analyses. The potent antifeedant activity of 1 against the generalist plant-feeding insect Helicoverpa armigera (EC(50) = 0.017 μmol/cm(2)) suggested them to be new defensive sesterterpenoids of L. canum.