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

Five new neo-clerodane diterpenoid alkaloids, named scutebarbatine G (1), 6,7-di-O-nicotinoylscutebarbatine G (2), 6-O-nicotinoyl-7-O-acetylscutebarbatine G (3), scutebarbatine H (4) and 7-O-nicotinoylscutebarbatine H (5) were isolated from the whole plant of Scutellaria barbata D. DON. Their structures were elucidated by spectroscopic methods including extensive 1D and 2D NMR analyses. In vitro, compounds 1-5 showed significant cytotoxic activities against three human cancer lines, namely, HONE-1 nasopharyngeal, KB oral epidermoid carcinoma, and HT29 colorectal carcinoma cells, and gave IC(50) values in the range 3.4-8.5 microM.