neo-Clerodane Diterpenoids from the Aerial Part of Scutellaria barbata

Three new neo-clerodane diterpenoids, barbatellarines C-E (1-3), were isolated from the CHCl(3)-soluble fraction of the aerial part of Scutellaria barbata. Their chemical structures were elucidated by detailed analysis of NMR and MS data. Compounds 1 and 2 were C(13) epimers, which was confirmed by an NOE difference experiment and the NOESY spectrum. The relative configuration was determined on the basis of the (1)H-NMR J-value and NOE data, while the absolute configuration of the previously isolated analogue, barbatellarine B (4), as a representative member of the group, was assigned by CD analysis.