Alkaloids bearing rare skeletons from Forsythia suspensa with anti-inflammatory and anti-viral activities in vitro

Abstract

Five alkaloids, including two previously undescribed alkaloids, named forsyshiyanines A and B, attributable to the rare skeletons 4b,5,6,7,8,8a,9,10-octahydrobenzo[f]quinoline and (6,7-dihydro-5H-cyclopenta[c]pyridin-7-yl)methyl, respectively, along with three known ones (3-5), were isolated from the ripe fruits of Forsythia suspensa. The chemical structures including absolute configurations of two undescribed compounds were established using integrated spectroscopic techniques, electronic circular dichroism calculations, and single-crystal x-ray diffraction analysis. In vitro, five alkaloids showed anti-inflammatory activities, with the inhibition rates of the release of β-glucuronidase from polymorphonuclear leukocytes of rats being in the range 47.9%-56.0% at a concentration of 10 μM. Moreover, five compounds exhibited anti-viral activities against influenza A virus and respiratory syncytial virus, with IC₅₀ values in the range of 7.3-32.5 μM and EC₅₀ values in the range 3.7-14.1 μM.

Keywords: Alkaloid; Anti-inflammatory; Anti-viral; Forsyshiyanines A and B; Forsythia suspensa; Oleaceae.