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February 05, 2006

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Doug M.

Why three-rings, I wonder. IMS (and it may not) there are four- and five-rings too: easier to synthesize, and ought to screw up the herbivore's chemistry just as well.

Ginkgoes -- another very old plant family with just a few modern representatives -- also produce some very strange compounds. Makes you wonder what a Cretaceous pharmocopeia would have looked like.

Also if plant life has gotten better, worse, or about the same in terms of synthesizing weird stuff. No way to ever know that, of course. (Though I can come up with a Just So Story: dinosaurs, huge and hard-mouthed, ignored mechanical defenses like thorns. So plants were forced to come up with ever more bizarre and brilliant chemicals.)

Doug M.

Carlos

Doug, the three-membered rings are in very specific places. There seem to be two main types of cyclopropyl variants, ones that mimic the amino acid proline, and ones that mimic the amino acid glutamic acid.

In the proline analogs, the cyclopropane ring actually shares an edge with the five-membered ring which makes up the proline molecule's "backbone". Proline is the only amino acid to incorporate a ring in its backbone, and because of the rigidity this introduces to proteins, it's widely used when the protein needs to make a sharp bend. Collagen, in fact, is about one-third proline, because it winds in the opposite direction of most proteins, left-handed versus right-handed.

The variant proline seems to completely disrupt proline intake and metabolism. The extra carbon on the side causes the molecule to bind better to enzymes which normally bind proline than proline itself.

The cyclopropyl glutamate variants work in a somewhat different way. Glutamate is an amino acid, but it also has an extra acidic group on its "side chain". In shape, but not in charge, the cyclopropyl group is a relatively close mimic of this acidic group. So for the enzymes and receptors that don't use the acidic properties of the glutamate side chain when they bind to a molecule, the cyclopropyl variants are excellent mimics.

In neither case would four-membered (or larger) ring variants be useful.

(Which is not to say that strained rings are not biologically useful, because they are. The strained beta-lactam four-membered ring in penicillin is what gets the job done.)

There are other plants which produce the proline variants -- the horse chestnut, for instance -- but very few seem to produce the glutamate variants.

The go-to paper for this is Caveney et al., "New observations on the secondary chemistry of world Ephedra (Ephedraceae)", American Journal of Botany 88(7): 11991208. 2001.

Graeme

Interesting.

Also, the Wikipedia page on Ephedra, which I found from your gnetophytes link above, has this line: "The Chinese name is , ma huang, which means "yellow hemp"". I assume for the medicinal properties, since it doesn't seem to look much like hemp.

Carlos

This is a slight nitpick, but "ma huang" actually means "hemp yellow" or "numbing yellow". There's no word order inversion as in English in classical Chinese, and the word for hemp has both nominal and verbal qualities.

It might have had a similar meaning to what English-speakers would call "yellow hemp" -- probably does, in my amateur opinion -- but it might not've.

Syd Webb

Carlos,

I showed this piece to Beatrix. It appealled to her on so many levels. She spent the next half-hour Googling a variety of sites offering varying perspectives on 'Mormon tea.'

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