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CONCENTRATES Another natural Diels-Alder reaction Although synthetic chemists regularly employ the DielsAlder reaction to create rings, unambiguous examples of its use in nature are rare (C&EN, Dec. 4 , 2 0 0 0 , page 72). Now, bioorganic chemistry professor Olov Sterner at Lund University, in Sweden, and coworkers provide evidence that an intramolecular cyclization (shown) in the biosynthesis ofa fungal metabo lite is an enzyme-catalyzed Diels-Alder reac tion [Angew. Chem. Int. Ed., 41,2158 (2002)}. The formation of the tricyclic product from the monocyclic precursor proceeds sponta neously, if slowly, in organic solvents, the re searchers note. The reaction yields only one isomer and is accelerated in water—key evi dence that it is indeed a Diels-Alder reaction. Compared to the spontaneous abiotic cycliza tion, the rate is eight times faster in the pres ence of live Galiella rufa. But fungi that have been heated do not affect the rate. Unlike the two previously reported cases of bio logically catalyzed Diels-Alder reactions, the function of the pre sumed enzyme in the new example appears to be solely to speed the reaction, not to affect the nature of the products. The re searchers have not yet isolated the purported Diels-Alderase.
Tree root fungi tap into new soil calcium pool Acid rain depletes calcium from forest soils and may choke the growth of trees, which use calcium from the soil to form and maintain their cell walls. Bioavailable calcium in the soil is known to come from atmospheric deposition and from slow weathering of calci um-containing silicate miner als. Researchers led by geology professor Joel D. Blum of the University of Michigan have now shown that some trees are bypassing these sources and obtaining their calcium direct ly from the calcium phosphate mineral apatite {Nature, 4Y7, 729 (2002)}. They analyzed calcium/strontium ratios and strontium isotope abundances in trees, soil, and water in the Hubbard Brook experimental forest in northern New Hamp shire. The symbiotic mycorrhizal fungi that live on the 26
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roots ofthese trees are likely to help the trees access this alter native calcium pool, Blum says. These fungi can send out fila ments that extract calcium ions directly from apatite. 'This ad ditional source of calcium will affect our estimates of how much acidity a forest soil can withstand and may help explain why some trees are more sus ceptible than others to acid rain," Blum tells C&EN.
Metal phosphide changes crystal structure in solid "An unusual example of facile covalent bond breaking within the crystalline solid state that can be reversed by the in put of electrochemical energy" has been reported by a team led by chemistry professor Linda F. Nazar of the University of Waterloo, in Canada [Science, 296,2012 (2002)}. The team found that when manganese phosphide (MnP^ is exposed
to lithium ions at low potential in an electrochemical cell, lithi um ions intercalate into the lat tice and Ρ—Ρ bonds are cleaved (reduced), yielding Li 7 MnP 4 . In the reverse electrochemical ox idation process, lithium is ex tracted and the Ρ—Ρ bonds are reformed to give M n P 4 . The Ρ—Ρ bonds thus serve as an electron storage reservoir, the researchers write. The cry stal structures of M n P 4 and Li 7 MnP 4 are different but re lated: T h e former contains chains of M n P 6 octahedra linked by phosphorus atoms, and the latter has edge-shared M n P 4 and LiP 4 tetrahedra. That the structural transfor mation occurs reversibly in the solid state at room temperature "must be a consequence of sim ilarity in phosphorus packing in the two structures," the chemists conclude. They be lieve these results are of inter est both fundamentally and with respect to possible appli cations in lithium-ion batteries.
Total synthesis of plicamine The alkaloid (+)-plicamine (shown) is a recendy discovered member of a family of natural products that exhibits a wide range of biological activities. Chemistry professor Steven V Ley and postdocs Ian R. Baxendale and Claudia Piutti at the University of Cambridge have pulled off (+)-plicamine,s first total synthesis with an unusu al twist: All the synthetic trans formations were carried out using a combination of sup ported reagents and scavengers {Angew. Chem. Int. Ed., 4 1 , CH-,0,
2194 (2002)}. The immobi lized systems allowed them to work up reactions by simple fil tration followed by evapora tion and to avoid chromatog raphy, crystallization, and distillation. "Given the relative complexity of the molecule, the synthesis is a powerful demonstration of the ability to achieve multistep transforma tions without conventional chromatographic methods," the researchers write.
Virulence genes in bacteria that are resistant to vancomycin The genes that cause viru lence in vancomycin-resistant Enterococcusfaecalis form a clus ter known as a pathogenicity is land, according to researchers at the University of Oklahoma Health Sciences Center [Na irn, 417,746 (2002)}. Michael S. Gilmore of the departments of ophthalmology and of mi crobiology and immunology and Nathan Shankar and Arto S. Baghdayan of the depart ment of pharmaceutical sci ences believe that this is the first time a true pathogenicity island has been found in a gram-po sitive organism. The patho genicity island is very similar across strains. This region is ap proximately 150 kilobases, has a lower guanine and cytosine content than the rest of the genome, and is flanked by re peated sequences at the edges. The island includes a number of genes with no assignable function and which are not found in nonpathogenic strains. The team also found within the pathogenicity island a cluster of new genes, which could be in vestigated as targets for drug therapy The pathogenicity is land could also be useful for identifying particularly virulent strains of E.faecalis. HTTP://PUBS.ACS.ORG/CEN
