64
O
O
CHO
OH
65
66
67
O
O
O
OEt
O
O
O
HO
O
O
HO
Fig. 43 Structures of 64–67
68
OH
O
69
O
O
O
O
HO
HO
Fig. 44 Structures of
acantholide A (68) and
acantholide B (69)
8
OPP
OPP
H
+
H
H
OPP
OPP
Fig. 45 Cyclization
mechanism for the
formation of the
6-membered rings of 64–69
26
T. Mitsuhashi and I. Abe