New Clerodane diterpenes from Zuelania guidonia

We studied the content of cytotoxic compounds from Zuelania guidonia (Flacourtiaceae) leaves collected in Santa Rosa, Guanacaste (Costa Rica). We isolated two labdanes (1,2) and twenty clerodanes (3–22), sixteen of which have not been previously reported. Interestingly, clerodane glycosides are described for the first time in this family. The isolation was carried out using HPLC techniques and the structural elucidation was performed with 1D and 2D NMR and mass spectrometric techniques. The absolute stereochemistry of the elucidated clerodanes was proposed to be 5S, 8R, 9R and 10S based on previous X-ray studies for compounds from this family. The relative stereochemistry of the remaining chiral carbons was determined using NOE and 13C-NMR spectroscopy.