Liriogerphines A–D, a Class of Sesquiterpene–Alkaloid Hybrids from the Rare Chinese Tulip Tree Plant

Abstract

Liriogerphines A-D (<b>1-4</b>, respectively), an unprecedented class of hybrids of germacranolide-type sesquiterpenoids and aporphine-type alkaloids, were isolated from the rare medicinal plant <i>Liriodendron chinense</i>. Their structures were elucidated by comprehensive spectroscopic analyses combined with electronic circular dichroism calculations and X-ray crystallographic data. Biosynthetically, an aza-Michael addition reaction is proposed to be involved in the assemblies of this class of hybrids. Compound <b>4</b> exhibited cytotoxicity against leukemia cells via inducing apoptosis and inhibiting Bcl-2 expression.