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DBL%20Hendrix%20small.png College chemistry, 1983

Derek Lowe The 2002 Model

Dbl%20new%20portrait%20B%26W.png After 10 years of blogging. . .

Derek Lowe, an Arkansan by birth, got his BA from Hendrix College and his PhD in organic chemistry from Duke before spending time in Germany on a Humboldt Fellowship on his post-doc. He's worked for several major pharmaceutical companies since 1989 on drug discovery projects against schizophrenia, Alzheimer's, diabetes, osteoporosis and other diseases. To contact Derek email him directly: Twitter: Dereklowe

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June 16, 2002

A Strange Compound, In Strange Places

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Posted by Derek

A recent paper (Ang. Chem. Int. Ed.41 1740, for those with chemistry libraries at hand) illustrates some interesting things about "natural" and "unnatural" compounds.

It's well known that polychlorinated molecules (DDT, PCBs and others) are quite stable and persistent. Glenn Reynolds over at Instapundit stirred up some folks a few days ago with a reference to DDT, but no matter whose views you subscribe to, there's no denying that the stuff hangs around. One reason is that the compounds are quite lipophilic - they don't sit in aqueous solution waiting to react with things, and they tend to accumulate in lipid tissues of animals, which takes them out of circulation. Another reason is that polychlorinated compounds just aren't all that reactive in general; they're poor substrates for many standard reactions.

(As an aside, that's one of the reasons that the atmospheric effects of chlorofluorocarbons took such a long time to be recognized. These compounds are almost completely unreactive under biological conditions, and not much more lively under even forcing artificial ones. But no one had thought much about what would happen if they got into the upper atmosphere, where they could be hit by hard ultraviolet, the sort that doesn't make it to the ground. . .)

At any rate, there's been a clear distinction between polychlorinated man-made compounds and others which occur in nature. There are thousands of them, actually, many made by marine organisms (who have plenty of chlorine, bromine, and iodine to play around with in seawater.) These tend to be more water-soluble and reactive, though, and haven't been found to persist in tissues.

Until now, it seems. The paper I referred to gives leading references to an odd compound called Q1. It's been found in biological samples all over the world, and sometimes in some seriously large concentrations. Analysis showed it to have an empirical formula that doesn't correspond to any compound that's ever been reported. The paper has the real structure, confirmed by two different syntheses, and it's a rather odd-looking chlorinated bipyrrole.

The thing is, no one knows where the stuff comes from. And (for once) it doesn't appear to be us, since the compound was completely unknown until now. Nothing even that close to it is produced industrially. The closest things are some other halogenated pyrroles found in some marine bacteria, lending credence to the theory that this is a biogenic material. No one's found one like this, though.

As I've spoken to people about this, reactions have been interesting. Most of my fellow chemists have found the structure intruiging, and the idea that it's a natural product pretty weird. But I've had a couple of colleagues react by saying "That has to be coming from people." When I point out the features mentioned in the paragraph above, it doesn't seem to convince them. "It'll turn out to be from us," I've been told.

Well, I'm with the authors of the paper in not thinking so. Nature's got a lot of surprises, and making something that looks just like a synthetic pollutant doesn't seem like too much of a stretch. Think of it as a polychlorinated prank, pulled off by some dinoflagellate or red algae.

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