151 possesses a 5/4/5-membered ring system, while 152 has a 4/5/5-membered ring
system (Fig. 107).
10.6 6/8/6/5-Membered Ring System
Astellifadiene (153) is a sesterterpenoid with a 6/8/6/5-membered ring system
(Fig. 108) [138]. The formation of the 6/8/6/5-membered ring system from
geranylfarnesyl diphosphate (8) requires two cyclization reactions. In the first
cyclization, an 11/6/5-membered ring is generated, and then deprotonation finalizes
the reaction. Next, protonation occurs to initiate the second round of cyclization, and
the basic carbon skeleton of 153 is formed. The gene for the biosynthesis of 153 has
been found in the genome of the fungus Emericella variecolor NBRC 32302.
OPP
H
H
+
H
H
8
151
152
Fig. 107 Structures and formation of prenylspata-13,17-diene (151) and geranylkelsoene (152)
Sesterterpenoids
61
system (Fig. 107).
10.6 6/8/6/5-Membered Ring System
Astellifadiene (153) is a sesterterpenoid with a 6/8/6/5-membered ring system
(Fig. 108) [138]. The formation of the 6/8/6/5-membered ring system from
geranylfarnesyl diphosphate (8) requires two cyclization reactions. In the first
cyclization, an 11/6/5-membered ring is generated, and then deprotonation finalizes
the reaction. Next, protonation occurs to initiate the second round of cyclization, and
the basic carbon skeleton of 153 is formed. The gene for the biosynthesis of 153 has
been found in the genome of the fungus Emericella variecolor NBRC 32302.
OPP
H
H
+
H
H
8
151
152
Fig. 107 Structures and formation of prenylspata-13,17-diene (151) and geranylkelsoene (152)
Sesterterpenoids
61