Anti-inflammatory and anti-viral labdane diterpenoids from the fruits of Forsythia suspensa.

• Eight labdane diterpenoids, including two new ones, were isolated from the fruits of Forsythia suspensa. • The absolute structures of two new labdane diterpenoids were determined by single crystal X-ray diffraction analysis and ECD data. • Eight labdane diterpenoids showed anti-inflammatory, with the inhibition rates of release of β -glucuronidase from polymorphonuclear leukocytes of rats being in the range 46.8–51.0%. • Eight labdane diterpenoids showed anti-viral activities against influenza A (H1N1) virus with the IC 50 values in the range 18.4–26.2 μM, and against respiratory syncytial virus (RSV) with the EC 50 values in the range 10.5–14.4 μM. Eight labdane diterpenoids, including two new labdane diterpenoids, named forsyshiyanins A-B (2 – 3), along with six known ones (1 , 4 – 8), were isolated from the fruits of Forsythia suspensa. The new structures including their absolute configurations were elucidated by extensive spectroscopic analyses, X-ray diffraction and computational calculation. In vitro , eight labdane diterpenoids showed anti-inflammatory activities, with the inhibition rates of release of β -glucuronidase from polymorphonuclear leukocytes of rats being in the range 46.8–51.0% at concentrations of 10 µM, as well as anti-viral activities against influenza A (H1N1) virus and respiratory syncytial virus (RSV), with the IC 50 values in the range 18.4–26.2 μM and EC 50 values in the range 10.5–14.4 μM, respectively. [ABSTRACT FROM AUTHOR]