Toxins in Nature - Natural Products Chemistry: Sources, Separations, and Structures - page 161

(a)
(b)
FIGURE 14.7 Structures of polytoxin (a) and brevitoxin (b); complex cyclic polyether
compounds.
remove the unwanted lipids, and the brevitoxins remaining in aqueous methanol are
purified further by chromatography.
The structure of the most potent component of the PSP toxins is called saxitoxin
and referred to as STX (Figure 14.8). Saxitoxin is a low molecular weight, water-
soluble, nitrogen-containing compound. The key feature is the carbamoyl moiety
leading to making saxitoxin a carbamate derivative, which is quite toxic to humans.
Various isomers exist (different groups attached to the basic STX molecule) that
form a very potent suite of toxins.
14.4 MARINE TOXINS: FISH
Two of the most well-known and most deadly fish poisons are known as ciguatoxin
and tetrodotoxin, both of which affect the nervous system. Ciguatoxin (Figure 14.9)
is the most potent sodium channel toxin known, and ciguatera poisoning is associ-
ated with reef dwelling fish such as barracuda, grouper, and snapper. Tetrodotoxin
(Figure 14.10) is associated with the puffer ish/blowish, known in Japan as “fugu,”
considered a delicacy but if improperly prepared by not removing the toxic “sac”
can lead to death. Chemically, these two toxins are wonderful examples of polyether
compounds, requiring extensive and careful spectroscopic and structure determi-
nation. In the case of polytoxin, Kishi et al. at Harvard University came up with a
remarkable total synthesis to confirm the stereochemistry.