10.1 5/5/5/6/5-Membered Ring System
A genome-based approach generated quiannulatene (140), with a 5/5/5/6/5membered ring system (Fig. 101) [128]. The gene responsible for the production
of 140 was found from the genomic data of the fungus Emericella variecolor NBRC
32302. Notably, the 5/5/5/6/5-membered ring system of 140 is different from those
of 134–137 (Figs. 97 and 98). It is proposed that 140 is generated by the
deprotonation of the intermediate A in Fig. 100. The detailed cyclization mechanism
leading to the formation of 140 has been investigated by both computational
approaches [129, 130] and isotope labeling experiments [128]. From the plant
Arabidopsis thaliana, a gene for the biosynthesis of ent-140 has also been found
[131]. In addition, from the plant Brassica oleracea, a gene for the production of
boleracene (141) has been identified (Fig. 101) [131]. The stereochemistry of 141 is
different from those of 140 and ent-140.
10.2 5/8/6/5-Membered Ring System
Compound Bm2 (142) [132] and sesterfisherol (143), with a 5/8/6/5-membered ring
system, were also discovered by the genome-based approach (Fig. 102)
[133, 134]. The genes responsible for the production of 142 and 143 were found
in the genomes of the fungi Bipolaris maydis ATCC48331 and Neosartorya fischeri,
respectively. In fact, 123 and 124, which were mentioned in Sect. 7.1.3, also possess
similar 5/8/6/5-membered ring systems (Figs. 89 and 102). However, the stereochemistry and positions of the double bonds of 142, 143, 123, and 124 are different
from each other. A possible cyclization reaction starting from geranylfarnesyl
diphosphate (8) leading to the formation of 142 and 143 is shown in Fig. 103.
A
H
140
ent-140
141
Fig. 101 Structures of quiannulatene (140), ent-140, and boleracene (141), and formation of 140.
The formation of intermediate A is shown in Fig. 100
Sesterterpenoids
57
A genome-based approach generated quiannulatene (140), with a 5/5/5/6/5membered ring system (Fig. 101) [128]. The gene responsible for the production
of 140 was found from the genomic data of the fungus Emericella variecolor NBRC
32302. Notably, the 5/5/5/6/5-membered ring system of 140 is different from those
of 134–137 (Figs. 97 and 98). It is proposed that 140 is generated by the
deprotonation of the intermediate A in Fig. 100. The detailed cyclization mechanism
leading to the formation of 140 has been investigated by both computational
approaches [129, 130] and isotope labeling experiments [128]. From the plant
Arabidopsis thaliana, a gene for the biosynthesis of ent-140 has also been found
[131]. In addition, from the plant Brassica oleracea, a gene for the production of
boleracene (141) has been identified (Fig. 101) [131]. The stereochemistry of 141 is
different from those of 140 and ent-140.
10.2 5/8/6/5-Membered Ring System
Compound Bm2 (142) [132] and sesterfisherol (143), with a 5/8/6/5-membered ring
system, were also discovered by the genome-based approach (Fig. 102)
[133, 134]. The genes responsible for the production of 142 and 143 were found
in the genomes of the fungi Bipolaris maydis ATCC48331 and Neosartorya fischeri,
respectively. In fact, 123 and 124, which were mentioned in Sect. 7.1.3, also possess
similar 5/8/6/5-membered ring systems (Figs. 89 and 102). However, the stereochemistry and positions of the double bonds of 142, 143, 123, and 124 are different
from each other. A possible cyclization reaction starting from geranylfarnesyl
diphosphate (8) leading to the formation of 142 and 143 is shown in Fig. 103.
A
H
140
ent-140
141
Fig. 101 Structures of quiannulatene (140), ent-140, and boleracene (141), and formation of 140.
The formation of intermediate A is shown in Fig. 100
Sesterterpenoids
57