7 Tetracarbocyclic Sesterterpenoids
7.1 Tetracarbocyclic Sesterterpenoids Constructed by
the Type 1 Terpene Cyclases
7.1.1 7/6/6/5-Membered Ring System
Aspergilloxide (120), isolated from a fungus, Aspergillus sp., has a 7/6/6/5membered ring system (Fig. 86) [103]. A possible cyclization reaction to form
the basic carbon skeleton starting from geranylfarnesyl diphosphate (8) is also
shown in Fig. 86.
7.1.2 5/8/6/6-Membered Ring System
Asperterpenol A (121) and a derivative have been reported from a mangrove
endophytic fungus, Aspergillus sp. 085242 (Fig. 87) [104]. Compound 121 is an
acetylcholinesterase inhibitor. Their tetracarbocyclic skeletons would be formed
starting from geranylfarnesyl diphosphate (8) as shown in Fig. 87.
OH
OH
O
120
PPO
8
H H
Fig. 86 Structure of
aspergilloxide (120), and
possible cyclization reaction
for the formation of the 7/6/
6/5-membered ring system
46
T. Mitsuhashi and I. Abe