Anti-inflammatory diterpenes from the seeds of Vitex negundo

Phytochemical investigation of a dichloromethane-soluble extract of Vitex negundo seeds led to the isolation of five labdane diterpenes, negundoins A–E (1–5), a 9,10-seco-abietane diterpene, negundoin F (6), a sandaracopimara-7,15-diene diterpene, negundoin G (7), and two known diterpene derivatives (8, 9). Their chemical structures were elucidated by detailed spectroscopic analyses on the basis of NMR, IR, and MS data. The anti-inflammatory effects of metabolites 1–7 were also evaluated in vitro. Compounds 3 and 5 were among the most potent inhibitors on nitric oxide production by LPS-stimulated RAW 264.7 macrophages, with IC₅₀ values of 0.12 and 0.23 μM, respectively. Further studies revealed that compounds 3 and 5 (5 μM) significantly reduced the levels of the iNOS protein to 0.40 ± 0.13% and 41.02 ± 6.02%, respectively, and COX-2 protein to 2.06 ± 0.53% and 26.40 ± 7.43%, respectively.