neo-Clerodane Diterpenoids from Scutellaria barbata and Their Inhibitory Effects on LPS-Induced Nitric Oxide Production

Three new neo-clerodane diterpenoids (1–3) along with 12 known compounds (4–15) were isolated from a methanol extract of the aerial parts of Scutellaria barbata. The structures of 1–3 were determined by interpretation of their 1D and 2D NMR spectroscopic data as well as HRESIMS values. All isolated compounds were tested for their inhibitory effects on LPS-induced nitric oxide production in RAW 264.7 macrophages. Compounds 1–4, 7, and 10–12 were found to inhibit nitric oxide production with IC50 values ranging from 20.2 to 35.6 μM.