2.3.1 Meroterpenoids
One example of natural products that could be confused with the sesterterpenoids is a
group of meroterpenoids containing a C 10 polyketide moiety (e.g., preterretonin A
(18), protoaustinoid A (19), and andrastin E (20)) (Fig. 14) [15]. There are 25 carbon
atoms in the basic carbon skeletons of these compounds. However, they are not
biosynthesized via 8, but are generated from a C 15 terpenoid moiety and a C 10
polyketide moiety. These C 15 and C 10 moieties are combined in their biosynthesis to
form the C 25 basic carbon skeleton.
18
O
OH
CO 2 CH 3
O
H
+
HO
CO 2 CH 3
O
OH
H
HO
CO 2 CH 3
O
OH
H
HO
CO 2 CH 3
O
OH
H
O
HO
CO 2 CH 3
OH
HO
CO 2 CH 3
O
O
O
HO
CO 2 CH 3
OH
OH
OH
CO 2 H
OPP
19
20
6
+
C 15 terpenoid
condensation
oxidation
O-methylation
C 10 polyketide
cyclization
C 25 basic carbon skeleton
Fig. 14 Biosynthesis of 18–20. In their basic carbon skeletons, there are 25 carbons. However,
they are not sesterterpenoids
10
T. Mitsuhashi and I. Abe