6.1.2 5/12/5-Membered Ring System
Sesterterpenoids with 5/12/5-membered ring systems have been found in both a
fungus and a plant. Variculanol (108) was isolated from the fungus Aspergillus
variecolor [91], while nitinol (109) was reported from the plant Gentianella nitida,
which is used in Peruvian folk medicine (Fig. 71) [92]. Compound 109 exhibits
activity to enhance IL-2 gene expression in a human T cell line. A possible
cyclization mechanism for the formation of the 5/12/5-membered ring system
starting from geranylfarnesyl diphosphate (8) is shown in Fig. 72.
HO
OH
OH
108
109
Fig. 71 Structures of
variculanol (108) and nitinol
(109)
H
H
H
H
OPP
H
H
108
109
8
Fig. 72 Proposed
cyclization mechanism for
the formation of the 5/12/5membered ring system
38
T. Mitsuhashi and I. Abe
Sesterterpenoids with 5/12/5-membered ring systems have been found in both a
fungus and a plant. Variculanol (108) was isolated from the fungus Aspergillus
variecolor [91], while nitinol (109) was reported from the plant Gentianella nitida,
which is used in Peruvian folk medicine (Fig. 71) [92]. Compound 109 exhibits
activity to enhance IL-2 gene expression in a human T cell line. A possible
cyclization mechanism for the formation of the 5/12/5-membered ring system
starting from geranylfarnesyl diphosphate (8) is shown in Fig. 72.
HO
OH
OH
108
109
Fig. 71 Structures of
variculanol (108) and nitinol
(109)
H
H
H
H
OPP
H
H
108
109
8
Fig. 72 Proposed
cyclization mechanism for
the formation of the 5/12/5membered ring system
38
T. Mitsuhashi and I. Abe