New norditerpenoid alkaloids from Scutellaria barbata with cytotoxic activities.

Two new norditerpenoid alkaloids, named scutebarbatines M-N (1 and 2), were isolated from the whole plant of Scutellaria barbata D. Don. Their structures were established on the basis of detailed spectral analyses. In vitro, two 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 IC₅₀ values in the range of 3.5-6.3 µM.