Forsyqinlingines C (1) and D (2), two C 9 -monoterpenoid alkaloids bearing a rare skeleton, were isolated from the ripe fruits of Forsythia suspensa. Their structures, including absolute configurations, were fully elucidated by extensive spectroscopic data and ECD experiments. The plausible biogenetic pathway for compounds 1 and 2 was also proposed. In vitro, two C 9 -monoterpenoid alkaloids showed anti-inflammatory activity performed by the inhibitory effect on the release of β-glucuronidase in rat polymorphonuclear leukocytes (PMNs), as well as antiviral activity against influenza A (H1N1) virus and respiratory syncytial virus (RSV).

Two unique trinorlabdane diterpenoid alkaloids, forsyqinlingines A (1) and B (2), were isolated from the ripe fruits of Forsythia suspensa, and found to show significant anti-inflammatory activities and anti-viral activities.