Antiplasmodial Sesquiterpenoid Lactones from Trichospira verticillata : Structure Elucidation by Spectroscopic Methods and Comparison of Experimental and Calculated ECD Data

A dichloromethane extract of Trichospira verticillata from the Natural Products Discovery Institute was discovered to have good antiplasmodial activity (IC50 ∼5 μg/mL). After purification by liquid–liquid partition and C18 reversed-phase HPLC, four new germacranolide-type sesquiterpenoid lactones named trichospirolides A–D (1–4) were isolated. The structures of the new compounds were elucidated by analysis of their 1D and 2D NMR and MS data. The relative and absolute configurations were assigned based on a comparison of calculated and experimental ECD and UV spectra, specific rotations, internuclear distances, and coupling constants for all possible diastereomers for each compound. Among these four compounds, the conjugated dienone 1 displayed the most potent antiplasmodial activity, with an IC50 value of 1.5 μM.