Sinudenoids A–E, C₁₉-Norcembranoid Diterpenes with Unusual Scaffolds from the Soft Coral <i>Sinularia densa</i>

Abstract

Five new furanobutenolide-derived C₁₉-norcembranoid diterpenes, sinudenoids A-E (<b>1-5</b>, respectively), were isolated from the soft coral <i>Sinularia densa</i>. Sinudenoid A (<b>1</b>) possesses an uncommon 5/5/11-fused tricyclic ring system. Sinudenoids B-D (<b>2-4</b>, respectively) share the same tetracyclic 5/5/6/6 ring system but represent two kinds of new skeletons. Sinudenoid E (<b>5</b>) is the second compound with the rare 8/8 bicyclic carbon core. A plausible biosynthesis pathway for compounds <b>1-6</b> is proposed. Compound <b>5</b> exhibits strong anti-inflammatory activity in the zebrafish model.