2.4. Germacrane
The traditional Chinese medicine Anisodus tanguticus , usually
used for promoting blood circulation, contain four novle
norsesquiterpenoids anisotanols A−D
(15 −18 ) with a
congested tricyclic 6/3/5 ring system, which have been assumed to be
biosynthesized by W−M 1,4-hydride shift and cyclization of
germacane-type carbon skeleton (Fig. 6).[38]Another unusual germacrane derivative tomenphantadenine (19 ),
with an adenine-substituted unit, has been isolated from the whole plant
of Elephantopus tomentosus L, and 19 showed potent
antibacterial activity against the gram-positive Staphylococcusaureus .[39]
Four rearranged sesquiterpenoids eugenunilones C−F
(20 −23 ), possibly originated from the carbon skeleton
of germacrane, have been isolated from the fruits of Eugenia
uniflora ,[40] an evergreen shrub native to South
America.[41-43] Structurally, eugenunilones C and
D (20 and 21 ) possess new skeletons assembled on caged
tricyclo[4.3.1.03,7]decane and
bicyclo[3.2.1]octane scaffolds, respectively, while eugenunilones E
and F (22 and 23 ) possess a rare
tricyclo[4.4.0.02,10]decane ring system.
Fig. 6. Proposed biosynthetic pathway for15 −18.