C17-Labdane diterpenoid alkaloids bearing a rare skeleton with anti-inflammatory and anti-oxidant activities from Forsythia suspensa.

Two undescribed C 17 -Labdane diterpenoid alkaloids, named forsylinfenines A and B (1 – 2) , attributable to a rare 4,4,10,13-tetramethyl-1(2),3(4),5(10),6(7)-octahydrobenzo[ f ]quinolin skeleton, along with three known β -carboline-type alkaloids (3 – 5), were isolated. The chemical structures including absolute configurations of two undescribed compounds were established by means of integrated spectroscopic techniques and electronic circular dichroism (ECD) calculations. In addition, a plausible biosynthetic pathway for the formation of compounds 1 and 2 was proposed. In vitro , five alkaloids (1 – 5), especially two undescribed alkaloids with rare skeleton (1 – 2), exhibited significant anti-inflammatory activities due to inhibiting the release of TNF- α , IL-6, and IL-1 β , as well as effective anti-oxidant activities owing to preventing the production of ROS in the LPS-induced RAW264.7 cells. [Display omitted] • Two undescribed alkaloids bearing a rare 4b,5,6,7,8,8a,9,10-octahydrobenzo[ f ]quinoline skeleton from Forsythia suspensa. • The absolute structures of two undescribed alkaloids were determined by ECD data. • The plausible biosynthetic pathway of two undescribed alkaloids was proposed. • Two undescribed alkaloids had significant anti-inflammatory activities by inhibiting the release of inflammatory factors. • Two undescribed alkaloids had effective anti-oxidant activities by inhibiting the production of ROS. [ABSTRACT FROM AUTHOR]