Atropurpuran, a novel diterpene with an unprecedented pentacyclic cage skeleton, from Aconitum hemsleyanum var. atropurpureum

A novel diterpene with an unprecedented pentacyclic skeleton, designated as atropurpuran (1), featuring a unique motif to fuse two bicyclo[2.2.2]octane units, was isolated from the roots of Aconitum hemsleyanum var. atropurpureum. Its structure and relative configuration were established by NMR techniques and single-crystal X-ray diffraction. The biosynthetic origin of 1 was proposed to be Hetidane-type diterpenoid.