Trinorlabdane Diterpenoid Alkaloids Featuring An Unprecedented Skeleton With Anti-Inflammatory And Anti-Viral Activities From Forsythia Suspensa

Two unique trinorlabdane diterpenoid alkaloids, forsyqinlingines A (1) and B (2), were isolated from the ripe fruits of Forsythia suspensa. Their structures, including absolute stereochemical configurations, were fully elucidated from extensive spectroscopy experiments, single-crystal X-ray diffraction, and electronic circular dichroism (ECD). In addition, a plausible biosynthetic pathway for the formation of compounds 1 and 2 in Forsythia suspensa was also proposed. In vitro, the two C-17-labdane diterpenoid alkaloids exhibited anti-inflammatory activities by inhibiting the release of beta-glucuronidase in rat polymorphonuclear leukocytes (PMNs), and antiviral activities against influenza A (H1N1) virus and respiratory syncytial virus (RSV).