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

Four new neo-clerodane diterpenoid alkaloids, named scutebarbatines I-L (1-4), were isolated from the whole plant of Scutellaria barbata D. DON. Their structures were established on the basis of detailed spectral analyses. In vitro, the four new compounds showed significant cytotoxic activities against three human cancer lines (HONE-1 nasopharyngeal, KB oral epidermoid carcinoma, and HT29 colorectal carcinoma cells), and gave IC(50) values in the range 3.2-8.3 microM.