Liriogerphines
A–D (1–4, respectively),
an unprecedented class of hybrids of germacranolide-type sesquiterpenoids
and aporphine-type alkaloids, were isolated from the rare medicinal
plant Liriodendron chinense. 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 4 exhibited
cytotoxicity against leukemia cells via inducing apoptosis and inhibiting
Bcl-2 expression.