Cinnamomols A and B, Immunostimulative Diterpenoids with a New Carbon Skeleton from the Leaves of Cinnamomum cassia

Two diterpenoids with an unprecedented diterpene carbon skeleton, cinnamomols A (1) and B (2), were isolated from the leaves of Cinnamomum cassia. 1 and 2 feature a cage-like, rigid, 5/5/5/5/5/6-fused hexacyclic ring system. The structures of 1 and 2 were established by extensive spectroscopic techniques and single-crystal X-ray diffraction, and their plausible biosynthetic pathways were proposed. 1 and 2 exhibited significant in vitro immunostimulative activity, and the mode of action of 1 was investigated.