Labdane diterpenoids from Forsythia suspensa with anti-inflammatory and anti-viral activities.

Five previously undescribed labdane diterpenoids, named Forsypensins A-E, were isolated from the fruits of Forsythia suspensa. The structures and relative configurations of the compounds were elucidated via extensive spectroscopic methods, and their absolute configurations were fully confirmed by single crystal X-ray diffraction analyses using Cu Kα radiation and electronic circular dichroism data. The five labdane diterpenoids showed in vitro anti-inflammatory activity in rat polymorphonuclear leukocytes, inhibiting the rates of β-glucuronidase release by 43.6%-49.2% at concentrations of 10 μM. The compounds also had anti-viral activity against influenza A (H1N1) virus and respiratory syncytial virus (RSV), with IC₅₀ values in the range 21.8-27.4 μM, and EC₅₀ values in the range 10.5-15.4 μM, respectively.