7.1.4 5/5/6/5- and 5/6/6/5-Membered Ring Systems
The 5/5/6/5-membered ring system is exemplified by mangicol A (125) [111], while
the 5/6/6/5-membered ring system is found in the structure of neomangicol A (126)
(Fig. 90) [112]. A proposed cyclization mechanism for the formation of the 5/5/6/5membered ring systems is shown in Fig. 91. Since both 125 and 126 were isolated
from the same fungus, Fusarium heterosporum, it is proposed that the 5/6/6/5membered ring system of 126 is generated starting from geranylfarnesyl diphosphate
(8) by the conversion of a precursor possessing the 5/5/6/5-membered ring
system [111].
OH
HO
OH
OH
OH
HO
OH
OH
Cl
125
126
Fig. 90 Structures of
mangicol A (125) and
neomangicol A (126)
H
H H
OPP
8
125
Fig. 91 Possible
cyclization reaction for the
formation of the 5/5/6/5membered ring system of
mangicol A (125)
Sesterterpenoids
49
The 5/5/6/5-membered ring system is exemplified by mangicol A (125) [111], while
the 5/6/6/5-membered ring system is found in the structure of neomangicol A (126)
(Fig. 90) [112]. A proposed cyclization mechanism for the formation of the 5/5/6/5membered ring systems is shown in Fig. 91. Since both 125 and 126 were isolated
from the same fungus, Fusarium heterosporum, it is proposed that the 5/6/6/5membered ring system of 126 is generated starting from geranylfarnesyl diphosphate
(8) by the conversion of a precursor possessing the 5/5/6/5-membered ring
system [111].
OH
HO
OH
OH
OH
HO
OH
OH
Cl
125
126
Fig. 90 Structures of
mangicol A (125) and
neomangicol A (126)
H
H H
OPP
8
125
Fig. 91 Possible
cyclization reaction for the
formation of the 5/5/6/5membered ring system of
mangicol A (125)
Sesterterpenoids
49