2.3.2 Highly Branched Isoprenoids
Compound 21 is a highly branched isoprenoid produced by the diatom
Rhizosolenia setigera [16]. Five isoprene units are found readily in its structure
(Fig. 15). Thus, 21 is a member of the terpenoids, and 25 carbon atoms exist in
its basic carbon skeleton. However, 21 is not a sesterterpenoid, since 21 is not
derived from the C 25 polyprenyl diphosphate 8, but from (C 10 ) 5 and (C 15 )
6 (Fig. 16).
21
Fig. 15 Structure of 21. The structure of 21 has five isoprene units, but 21 is not a sesterterpenoid.
The isoprene units are shown by bold lines
21
OPP
OPP
6
5
OPP
8
C 15
C 10
C 25
C 25
Fig. 16 Putative biosynthesis pathway of 21. Compound 21 is biosynthesized from 5 and 6, but not
from 8
Sesterterpenoids
11