Chemistry Reference
In-Depth Information
OH
HO
2
C
CHO
8
9
O
O
O
O
O
O
OH
110
one is possibly siphonarienal (
9
) isolated from
Siphonaria grisea
, whereas such
unusual pyrone-containing metabolites as siphonarin A (
10
) were isolated from
S. zelandica
. Marine polypropionates not only play defensive roles in mollusks,
but also they show antimicrobial, antivial, and cytotoxic activities.
2.1.4 Polyethers
Dinoflagellates, which are unique, aquatic photosynthesizing eukaryotes, are clas-
sified in the kingdom Protoctista. They produce a variety of unusual polyketides
with potent bioactivities (14). The most unique metabolites are “ladder-shaped”
polyethers; brevetoxin B (
11
), which was isolated from
Gymnodinium breve
(currently,
Karenia brevis
), was the first example of this group, and more than
15 brevetoxins have been isolated from the same source. Ciguatoxin (
12
)isa
causative agent of ciguatera, a fish poisoning in subtropical and tropical regions,
first isolated from a moray eel. It was later found to be originated from the
dinoflagellate
Gambierdiscus toxicus
that contains a more complex polyether,
maitotoxin (
13
), which is also involved in ciguatera (5, 14).
G. toxicus
produces
a variety of polyether compounds, namely highly antifungal gambieric acid (
14
).
Maitotoxin, which is the most toxic natural product (LD
50
value of 50 ng/kg
in mice), increases membrane permeability to Ca
2+
, but the detailed mechanism
remains unknown. Ciguatoxin is also highly toxic (1/10 potency of maitotoxin)
and activates voltage-gated Na
+
channels, whereas brevetoxins are much less
toxic, although their mode of action is similar to that of ciguatoxin.
HO
CHO
H
H
O
O
H
H
O
H
O
O
H
O
O
O
H
H
O
O
H
O
H
H
H
H
O
H
H
111
