science/ technology
concentrates Infrared transitions of very hot water assigned Scientists have known since 1995 that very hot water molecules exist in sunspots. They made the discovery by comparing infrared spectra of sunspots— where temperatures are about 3,200 K— with that of water at 1,800 K (C&EN, May 29, 1995, page 9). But researchers really didn't understand the complicated IR spectra because they didn't know the transitions that give rise to the dense absorption lines. Now, through a simulation of the IR spectrum of very hot water, accurate assignments of these absorption lines have been made. The simulation, based purely on theoretical calculations, was the work of a team including Russian theoretician Oleg L. Polyansky and physicist Jonathan Tennyson at University College, London, and Peter F. Bernath, a chemist at the University of Waterloo, Ontario [Science, 277, 346 (1997)]. The spectroscopic data not only provide further proof that water molecules exist on the sun but also will be useful in modeling systems such as forest fires and rocket plumes.^
ic residue into the active site of Ras, which provides an explanation for how the mutations found in tumor cells can lock the Ras switch into a permanent "on" position. The structure may provide clues that will aid in the design of small molecules that can switch off these mutant forms of Ras in tumors, the researchers suggest.^
Cell-membrane protein displays glycolipid antigen
drofuroic and Omethyllactic acids and lactate, (3-phenyllactate, malate, and mandelate esters. The oc-oxygen is essential for chelation of calcium.^
Making organozinc reagents more useful Organozinc reagents that transfer all of the desired alkyl substituent to aldehyde and ketone substrates have been developed at the University of Marburg, Germany [Angew. Chem. Int. Ed. Engl, 36, 1496 (1997)]. The new reagents are of the type R(TMSM)Zn, where R is a transferable alkyl group and TMSM is a nontransferable trimethylsilylmethyl group. This type of organozinc reagent is superior to R2Zn reagents, which transfer only one of the two R groups—often a waste of elaborate and valuable substituents. An example of the new reagent type is w-pentyl(TMSM)zinc, which is prepared by reacting dipentylzinc with bis(trimethylsilylmethyl)zinc. Organic chemistry professors Paul Knochel and Stefan Berger and their Marburg coworkers demonstrate the new reagents by Michael additions to 2-cyclohexenone. Furthermore, they show an asymmetric version by reacting the pentyl(TMSM)zinc reagent with benzaldehyde in the presence of 15 mole-% of either enantiomer of 7V,A^-bis(trifluoromethanesulfonyl)-^r^W51,2-diaminocyclohexane to get 92% of 1-phenyl-1-hexanol in 97% enantiomeric excess.^
The crystal structure of a molecule distantly related to the proteins encoded by the major histocompatibility complex (MHQ—the proteins that elicit an immune response by displaying peptide antigens on the cell surface—has been determined at Scripps Research Institute, La Jolla, Calif. Led by molecular bioloj gist Ian A. Wilson, \ the team determined the structure of the antigen-presenting molecule CD1 at a resolution of 2.8 A [Science, 277, 339 (1997)]. Their result strengthens the notion that CD1 can display glycolipid antigens and shows that the overall structure of CD1 is similar to that of MHC and related proteins. The general Crystal structure similarity of the binding domains of CD1 shows how to turn off (red), MHC proteins (yellow and light Ras protein signal green), and a related fetal protein (purple) is shown in the ribbon diagram. CDl's bind- Efficient synthesis of The crystal structure of an important sig- ing groove is deep and almost completely /V-acyl amino acids naling protein, human H-Ras, bound to the hydrophobic, the team says, making it suitChemists in Germany have perfected a critical domain of a protein that switches able for binding lipids.^ synthesis of TV-acyl amino acids by highit off, pl20GAP, has been solved by strucpressure, palladium-catalyzed reaction of tural biologists Klaus Scheffzek and Alfred aldehydes, amides, and carbon monoxide Wittinghofer at Max Planck Institute for Calcium tartrates [Angew. Chem. Int. Ed. Engl, 36, 1494 Molecular Physiology, Dortmund, Germa(1997)]. The method may lead to largeny, and their colleagues [Science, 277, 333 used to resolve scale production of such compounds for (1997)]. GAP proteins such as pl20GAP in- carboxylic acids use as chelating agents, detergents, and activate Ras by accelerating by several orders of magnitude the protein's slow, in- Chemists at the Technical University of machining oils, or of enantiomeric nonnattrinsic ability to hydrolyze GTP. Exacdy Budapest, Hungary, have devised resolu- ural amino acids to make drugs and feed how they accomplish this acceleration is tions of racemic cc-oxygenated carboxylic additives. For example, inorganic chemisparticularly important because about 25% acids and esters by crystallization of their try professor Matthias Beller at the Univerof human tumor cells contain mutant complexes with either enantiomer of cal- sity of Munich in Garching and coworkers forms of Ras that do not respond to GAP cium 0,0'-dibenzovltartrate [Angew. use isovaleraldehyde and acetamide to proteins and are permanently switched Chem. Int. Ed. Engl, 36, 1534 (1997)]. make 7V-acetylleucine in 99% yield. From on. The structure reveals that the interac- The method avoids use of toxic and costly benzaldehyde and acetamide they obtain tion between Ras and pl20 GAP has both alkaloids on a large scale. Organic chemi- TV-acetylphenylglycine in 85% yield. They hydrophilic and hydrophobic compo- cal technology professor Elemer Fogassy note that other workers reported a conents, which explains why the interaction and coworkers at Budapest Tech and crys- balt-catalyzed amidocarbonylation 25 is sensitive to both salts and lipids. It also tallographer Zsolt Bocskei at Chinoin Phar- years ago, but poor selectivity discourshows that the GAP protein puts a catalyt- maceuticals, Budapest, resolved tetrahy- aged commercialization.^ 28 JULY 21, 1997 C&EN
