Defense sesterterpenoid lactones from Leucosceptrum canum

Area of Science:

• Natural Product Chemistry
• Organic Chemistry
• Chemical Ecology

Background:

• Leucosceptrum canum, a woody Labiatae plant, is a source of diverse secondary metabolites.
• Sesterterpenoids are a class of terpenoids with potential biological activities.
• Insect antifeedant compounds play a crucial role in plant defense mechanisms.

Purpose of the Study:

• To isolate and characterize novel sesterterpenoids from Leucosceptrum canum.
• To investigate the structural elucidation of these compounds, including relative stereochemistry.
• To evaluate the insect antifeedant activity of the isolated sesterterpenoids.

Main Methods:

• Isolation of compounds using chromatographic techniques.
• Structure determination through comprehensive 1D and 2D Nuclear Magnetic Resonance (NMR) spectroscopy and Mass Spectrometry (MS).
• Confirmation of structures and stereochemistry for specific compounds via single crystal X-ray diffraction analysis.

Main Results:

• Ten sesterterpenoids, designated leucosceptroids E-N (1-10), were isolated.
• All compounds possess a characteristic α,β-unsaturated γ-lactone moiety.
• Leucosceptroid G (3) and leucosceptroid N (10) demonstrated potent antifeedant activity against Helicoverpa armigera.

Conclusions:

• The novel class of sesterterpenoids was named leucosceptrane sesterterpenoids.
• The identified leucosceptroids may function as defensive compounds for Leucosceptrum canum against insect herbivory.
• Further research into the ecological role and potential applications of these sesterterpenoids is warranted.