Bioassay-guided isolation of neo-clerodane diterpenoids from Scutellaria barbata

Bioassay-guided isolation of the aerial part of Scutellaria barbata yielded three new neo-clerodane diterpenoids scutebatas P-R (1-3), together with two known ones: scutebata E (4) and scutebarbatine B (5). The chemical structures of the isolated compounds were elucidated by spectroscopic methods (NMR and MS) and by comparison with the spectroscopic data reported in the literature. All compounds except 3 showed weak cytotoxicity with IC50 values ranging from 35.11 to 42.73 μM against K562 cell lines, and compounds 1, 2, and 5 also displayed weak activities against HL60 cell lines.