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 similar to 5 mu g/mL), After purification by liquid liquid partition and C-18 reversed-phase HPLC, four new germacranolide-type sesquiterpenoictlacones named trichospirolides A I) (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-Sour compounds, the conjugated dienone 1 displayed the most potent antiplasmodial activity, with an IC50 value of 1.5 mu M.