Novel Antioxidant neo‐Clerodane Diterpenoids from Scutellaria barbata

Abstract Four new neo ‐clerodane diterpenoids, barbatines A–D ( 1 – 4 ), have been isolated from the whole plant of Scutellariabarbata (Lamiaceae), along with the known scutebarbatine A ( 5 ), and their structures determined by spectral analysis, including mass spectrometry and 2D NMR spectroscopy. The absolute configurations of 2 and 5 were established from their CD spectra by using the exciton chirality rule. A biogenetic pathway for these compounds is proposed based on their structures. Barbatine A ( 1 ) and scutebarbatine A ( 5 ) showed a significant ability to protect cells against H 2 O 2 with ED 50 values of 16.8 and 5.0 μ M , respectively.(© Wiley‐VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2009)