Cytotoxic Neoclerodane Diterpenoids from Scutellaria barbata

Seven new neoclerodane diterpenoids, scutebatas A-G (1-7), have been isolated from Scutellaria barbata. Compounds 1-3 possess a rare alpha-hydroxy group in their alpha,beta-unsaturated lactone rings. Their structures were elucidated by spectroscopic analysis, and the relative configuration of scutebata A was deduced using ROESY data and the computational DFT method. Compounds 1, 2, 4, 5, and 6 were evaluated for in vitro cytotoxicity against six human cancer cell lines: HL-60, SMMC-7721, A-549, SK-BR-3, CACO-2, and PANC-1. Scutebata A (1) showed weak cytotoxicity against SK-BR-3 with an IC(50) value of 15.2 muM.