Seconoriridone A: A C16-seco-noriridal derivative with a 5/5/7 tricyclic skeleton from Belamcanda chinensis

Abstract Seconoriridone A ( 1 ), a novel C 16 - seco -noriridal with a 5/5/7 tricyclic scaffold, was isolated from the rhizome of Belamcanda chinensis . Its structure and absolute configuration were determined by NMR spectroscopy and quantum chemical calculations. Notably, seconoriridone A featured a 2-butanonyl moiety with oxidative cleavage of the conventionally multisubstituted cyclohexane ring of iridals. Seconoriridone A was a mixture of C-14 epimers in the presence of hemiacetal. The plausible biosynthetic pathway for 1 was deduced.