Four new neo-clerodane diterpenoid alkaloids from Scutellaria barbata with cytotoxic activities

Four new neo-clerodane diterpenoid alkaloids, named scutebarbatines C-F (1-4), were isolated from the whole plants of Scutellaria barbata D. DON. Their structures were elucidated by spectral analyses (UV, IR, FAB-MS, 1D-NMR and 2D-NMR). In vitro, compounds 1-4 showed significant cytotoxic activities against three human cancer cell lines, namely, HONE-1 nasopharyngeal, KB oral epidermoid carcinoma, and HT29 colorectal carcinoma cells, and gave IC(50) values in the range 3.9-7.8 muM.