Abstract: Two new neo-clerodane diterpenoids, 6,7-dibenzoyloxybarbatin C (1, named barbatin D) and 6-(2-acetoxy-3-methylbutanoloxy)-7-(2-carbonyl-3-methylbutanoyloxy) barbatin C (2, named barbatin E) 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 1–2 showed cytotoxic activities against three human cancer lines, namely, HONE-1 nasopharyngeal, KB oral epidermoid carcinoma, and HT29 colorectal carcinoma cells, and with IC50 values in the range of 3.5–6.7 μM.

Key words: barbatin D, barbatin E, cytotoxic activity, neo-clerodane diterpenoid, Scutellaria barbata.