Phyllanacidins A-C, three new cleistanthane diterpenoids from Phyllanthus acidus and their cytotoxicities

Phytochemical investigation on the nonpolar extracts of P. acidus leaves afforded three new cleistanthane diterpenoids, named phyllanacidins A-C (1-3) 5 in addition to three known ones (4-6). Among them, compounds 2 and 3 represent the first examples of 17-nor cleistanthane diterpenoids. Their structures including absolute configurations were elucidated on the basis of extensive spectroscopic data and single crystal X-ray diffraction analysis. All the isolated cleistanthane diterpenoids were evaluated for their cytotoxic activities against five human cancer cell lines. Compounds 4-6 exhibited moderate cytotoxicity with IC50 values ranging from 16.11 to 30.82 mu M.