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

Two new neo-clerodane diterpenoid alkaloids, scutebarbatine O (1) and 6-O-nicotinoylscutebarbatine G (2), were isolated from the whole plant of Scutellaria barbata. Their structures were elucidated by spectroscopic methods including extensive 1D and 2D NMR analyses. In vitro, compounds 1 and 2 showed cytotoxic activities against three human tumor cell lines, namely, HONE-1 nasopharyngeal, KB oral epidermoid carcinoma, and HT29 colorectal carcinoma cells, and with IC(50) values in the range of 2.1-5.7 microM.