Quinoline alkaloid featuring a rare 6/6/5/5-fused skeleton with anti-inflammatory and anti-oxidative activities from...

Numerous compounds were isolated from Forsythia suspensa, but only a few were found to simultaneously show effective anti-oxidant and anti-inflammatory activities, which inspired us to further explore active compounds from this plant. As a result, three undescribed quinoline alkaloids, named forsypenanhuines A-C (1-3), were isolated, of which 1 was a pair of enantiomers with a rare 6/6/5/5-fused skeleton and separated as an optically pure enantiomer (+)-1 by chiral HPLC. Their chemical structures including absolute configuration were elucidated via spectroscopic techniques, ECD calculation, and single crystal X-ray diffraction analysis. In addition, a plausible biosynthetic pathway for the formation of compounds 1-3 was proposed. In vitro, the three quinoline alkaloids [(+)-1, and 2-3] exhibited significant anti-inflammatory activities due to inhibiting the release of TNF-α, IL-6, and IL-1β, as well as effective anti-oxidative activities owing to preventing the generation of ROS in the LPS-induced RAW264.7 cells.