6.2.2 6/6/5-Membered Ring System
Hyrtiosal (116), which possesses a 6/6/5-membered ring system, was isolated from
the Okinawan marine sponge Hyrtios erectus, collected at a coral reef off Ishigaki
Island, Okinawa, Japan (Fig. 80) [97]. Compound 116 has been shown to inhibit the
proliferation of KB cells. Its formation starting from geranylfarnesyl diphosphate (8)
is illustrated in Fig. 80.
OPP
8
OPP
OPP
H
+
H
+
8
114
OPP
OPP
115
OPP
a)
b)
Fig. 79 Proposed cyclization mechanisms for the formation of the 6/6/6-membered ring systems of
(a) 114 and (b) 115
OPP
OPP
116
O
O
H
OH
H
+
8
H
O
OPP
OPP
OPP
O
H
oxidation
Fig. 80 Structure of
hyrtiosal (116), and possible
cyclization mechanism for
the formation of the 6/6/5membered ring system
42
T. Mitsuhashi and I. Abe