wistarii from the Great Barrier Reef, Australia [69], while 87 was isolated from a
sponge, Ircinia sp., collected at Hurghada, Red Sea, Egypt [71].
A proposed biosynthesis of 86 is shown in Fig. 63. Actually, 86 seems to be
biosynthesized via a linear sesterterpenoid 88, and the Diels–Alder reaction might
occur to form the bicarbocyclic moiety of 86. In the same manner, 87 should be
formed via ent-88.
The biosynthesis pathway of ircinianin sulfate (89) (Fig. 64) [72] should be
similar to that of 86. Compound 89 is an unstable metabolite from the sponge Ircinia
wistarii, collected from the Great Barrier Reef, Australia.
O
O
O
O
87
O
O
O
O
86
Fig. 62 Structures of (þ)wistarin (86) and (À)wistarin (87)
O
OH
O
O
O
OH
O
O
(S)
(S)
OH
O
O
O
88
86
Diels–Alder
Fig. 63 Proposed
mechanism to generate the
basic carbon skeleton of 86
OSO 3 Na
O
O
O
89
Fig. 64 Structure of
ircinianin sulfate (89)
34
T. Mitsuhashi and I. Abe