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May 2, 2006
Things I'm Glad I Don't Do: Isolating Ciguatoxin
The natural products topic (which I'll return to in a couple of days) has me starting up a companion to the "Things I Won't Work With" category. This is the first in the new category of "Things I'm Glad I Don't Do".
I mentioned ciguatoxin, and I notice that one of the comments to that post was from someone who'd had a brush with the stuff. My sympathies - it's supposed to be really awful. A number of warm-water fish species can have dangerous concentrations of the compound in them, and it's probably one of the most common non-bacterial sources of food poisoning. The thing is, the fish themselves don't make the stuff. They concentrate it from marine algae, who produce a lot of extravagantly crazy molecules.
So if you want some ciguatoxin yourself, you fool, you, a good source is an organism near the top of the food chain. Moray eels turn out to be a good bet. But you don't just turn one of them upside down over a beaker and squeeze his tail. No, the isolation is a bit more involved:
The moray eels (ca. 4000 kg) were collected from the Tuamotu Archipelago and from the Island of Tahiti in French Polynesia. The viscera (125 kg) were homogenized and extracted with two volumes of acetone twice. After filtration, the extract was left at -20 "C for 1 day to precipitate oily residue. The supernatant was evaporated to dryness and partitioned between diethyl ether and water. The ether layer was condensed and suspended in aqueous 80% MeOH, followed by defatting with hexane. The methanolic layer was condensed, dissolved in acetone. . .
The prep goes on in this vein, through six different columns, one after the other. Now, imagine joining this research group (which was Yasumoto's, in Japan). It's your first day in the lab, and here comes one of the post-docs carrying a couple of blenders in his arms. Behind him, another one is wheeling in the bags of frozen eel guts. It's moray margarita time, and will be for some time to come.
One other aspect of this isolation deserves comment, because I don't think you could do it like this today. In the final column or two, the paper outlines a brutal but effective method for cutting fractions to get the ciguatoxin: take a sample from each cut of the column and inject it into a mouse. If it doesn't die immediately, that fraction doesn't have any ciguatoxin in it. Gloves recommended.
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