NEWS OF THE WEEK CHEMICAL
ECOLOGY
OF PUSHY WEEDS AND TOXIC FROGS Weeds invade using small molecule; frogs defend with beefed-up toxin
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rare case (C&EN, April 15,2002, page 39). Now, they show that frogs of the genus Dendrobates (shown) that are fed pumiliotoxin (PTX) (+)-251D metabolize up to 80% of the alkaloid to allopumiliotoxin (aPTX) (+)-267A [Proc. Natl. Acad Set. USA, 100, 11092 (2003)}. But if the enantiomer— the nonnatural compound PTX (-)-251D - i s fed to the same frogs, it is unchanged. The hydroxylation that occurs in Dendrobates does not occur in other genera, such as Epipedobates and Phyllobates. aPTX( + )-267Aisfive times more toxic than PTX (+)-251D.The metabolism may be viewed as an adaptation to enhance ** the protective value of defensive compounds from the diet, the researchers suggest. The two studies "show the dynamic role of organic chemistry in natural interactions," commentsJerrold Meinwald, a chemistry professor at Cornell University and a pioneer of chemical ecology It is not enough to know the structures of natural compounds and how to synthesize them, he says. "What's really interesting is what these structures
chemical warfare is highFROG CHEMISTRY lighted in two newly pubMetabolic hydroxylation lished studies. The first reveals yields more potent toxin the role of a small molecule in helping an invasive plant occupy new territory The second shows that certain frogs can make dietderived toxins more potent by chemical transformation. Jorge M. Vivanco, assistant professor of horticultural biotechnology at Colorado State University, Fort Collins, and coworkers have laid out evidence of chemical warfare by the spotted knapweed (Centaurea maculosa, shown). According to Vivanco, this invaAllopumiliotoxin (+I-267A sive plant spreadfromEurasia to North America at the beginning whole root dies within one hour. of the 20th century, causing huge Meanwhile, in the labs ofJohn problems in some states. W Daly at NIH, the alkaloids in The weed's chemical weapon poison frogs continue to surprise. is (—)-catechin, a well-known Daly and coworkers have essecondary plant metabolite. Pre- tablished that the alkaloids are viously, Vivanco and others derived from diet, except in one d o . " — MAUREEN R0UHI showed that this compound and its enantiomer are produced by CHEMICAL TESTING the weed but that only (—)-catechin is phytotoxic. Now, they complete the case The ruling settles part of the case, for its role in the weed's prolifervoluntary chemical testing program has brought by the Physicians Committee for Reation. They find that (—)-catesurvived the first round of a legal attack sponsible Medicine and People for the Ethiby animal rights groups. chin is present in infested U.S. cal Treatment of Animals, that threatens to soils at levels that are highly toxA federal judge in New York City ruled on halt the HPV Challenge Program. ic to native North American Aug. 25 that EPA did not violate a law govHowever, the judge is allowing another argrasses but not to the weed itself erning federal advisory groups when it gument by the animal rights groups to go to [Science, 301,1377 (2003)}. Vi- helped establish the High Production Volume trial. They say that by selecting the chemivanco suspects that the weed re(HPV) Challenge Program. Under this initiacals for the program, EPA determined that it leases (—)-catechin to the soil as tive, chemical companies are voluntarily proneeded toxicity data for these compounds. it is produced and that some kind ducing basic toxicity data on some 2,800 subThis determination, they contend, required of pump prevents its reentry stances manufactured in or imported into the EPA to issue a regulation under the Toxic U.S. in quantities of more than 1 million lb In addition, the researchers Substances Control Act to force chemical per year. Environmental Defense, the Amerifind that (—)-catechin initiates companies to produce the data—rather than can Chemistry Council, and EPA set up the a cascade of events in susceptiset up a voluntary program. A trial date has program in 1998. The deadline for this effort ble plants leading to altered not been set.—CHERYL H0GUE is 2005 (C&EN, June 9, page 19). gene expression in the roots and culminating in cell death. The
Voluntary Program Passes Legal Hurdle
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C & E N / S E P T E M B E R 8. 2003
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