2.3.3 Other Notable Points
The examples shown in Sects. 2.3.1 and 2.3.2 suggest that not all compounds with
25 carbon atoms are sesterterpenoids. However, it should also be noted that the basic
carbon skeletons of some sesterterpenoids are composed of fewer than 25 carbons,
due to a degradation reaction during their biosynthesis. For example, even though
ircinin-3 (22) from the sponge Ircinia oros possesses only 21 carbon atoms, 22 is a
sesterterpenoid (Fig. 17) [17].
3 Linear Sesterterpenoids
The linear sesterterpenoids do not possess a carbocyclic moiety. Thus, the terpene
cyclases are not involved in their biosynthesis. The C 25 polyprenyl chain of GFPP
(8) is directly modified by tailoring enzymes to form a variety of linear
sesterterpenoids.
One of the simplest linear sesterterpenoids is geranylfarnesol (23), discovered
from the wax of the scale insect Ceroplastes albolineatus [18]. Another example of a
simple linear sesterterpenoid is geranylnerolidol (24) from the fungus Cochliobolus
heterostrophus [19]. The putative biosynthesis pathways of 23 and 24 should not be
complicated, since the elimination of the diphosphate moiety and the attack of H 2 O
should be sufficient to form 23 and 24 from 8 (Fig. 18).
Actually, 23 and 24 are the simplest examples, and in many cases, further
tailoring reactions occur to generate more functionalized linear sesterterpenoids. In
spite of their simple basic carbon skeletons, many kinds of linear sesterterpenoids,
especially from marine organisms, have been reported.
22
HOOC
OPP
8
C 25
C 21
– C 4
O
O
Fig. 17 Compound 22 is
considered to be generated
from 8. The C 4 partial
structure, which is shown by
bold blue lines in 8, is
removed by the degradation
reaction during the
biosynthesis of 22
12
T. Mitsuhashi and I. Abe
The examples shown in Sects. 2.3.1 and 2.3.2 suggest that not all compounds with
25 carbon atoms are sesterterpenoids. However, it should also be noted that the basic
carbon skeletons of some sesterterpenoids are composed of fewer than 25 carbons,
due to a degradation reaction during their biosynthesis. For example, even though
ircinin-3 (22) from the sponge Ircinia oros possesses only 21 carbon atoms, 22 is a
sesterterpenoid (Fig. 17) [17].
3 Linear Sesterterpenoids
The linear sesterterpenoids do not possess a carbocyclic moiety. Thus, the terpene
cyclases are not involved in their biosynthesis. The C 25 polyprenyl chain of GFPP
(8) is directly modified by tailoring enzymes to form a variety of linear
sesterterpenoids.
One of the simplest linear sesterterpenoids is geranylfarnesol (23), discovered
from the wax of the scale insect Ceroplastes albolineatus [18]. Another example of a
simple linear sesterterpenoid is geranylnerolidol (24) from the fungus Cochliobolus
heterostrophus [19]. The putative biosynthesis pathways of 23 and 24 should not be
complicated, since the elimination of the diphosphate moiety and the attack of H 2 O
should be sufficient to form 23 and 24 from 8 (Fig. 18).
Actually, 23 and 24 are the simplest examples, and in many cases, further
tailoring reactions occur to generate more functionalized linear sesterterpenoids. In
spite of their simple basic carbon skeletons, many kinds of linear sesterterpenoids,
especially from marine organisms, have been reported.
22
HOOC
OPP
8
C 25
C 21
– C 4
O
O
Fig. 17 Compound 22 is
considered to be generated
from 8. The C 4 partial
structure, which is shown by
bold blue lines in 8, is
removed by the degradation
reaction during the
biosynthesis of 22
12
T. Mitsuhashi and I. Abe