Angewandte Chemie International Edition

Cover image for Vol. 43 Issue 22

May 24, 2004

Volume 43, Issue 22

Pages 2865–2975

    1. Cover Picture: The First Account of a Structurally Persistent Micelle (Angew. Chem. Int. Ed. 22/2004) (page 2865)

      Michael Kellermann, Walter Bauer, Andreas Hirsch, Boris Schade, Kai Ludwig and Christoph Böttcher

      Article first published online: 19 MAY 2004 | DOI: 10.1002/anie.200490066

      The exceptional structure of the first reconstructed micelles is formed by the self-assembly of amphiphilic dendrocalixarenes in aqueous solution. A. Hirsch, C. Böttcher, and co-workers report in their Communication on page 2959 ff. that the relatively rigid T-shaped structure of the molecule allows efficient backfolding and thus the formation of aggregates with high curvature. Structural determination of the nanocontainers permits characterization of the micellar architecture at the molecular level.

    2. Statistical Analysis of Single-Molecule Junctions (pages 2882–2884)

      Marcel Mayor and Heiko B. Weber

      Article first published online: 30 APR 2004 | DOI: 10.1002/anie.200301733

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      Establishing contact: Recent progress in the investigation of single-molecule contacts established in an electrochemical scanning tunneling experiment are described (see picture). The setup allows for the successive formation of many hundreds of junctions and a statistical analysis of the voltage dependence of the electrical current. This method is a new reliable tool to characterize molecular junctions and contributes to elucidating the potential of molecular electronics.

    3. Taking Snapshots of Photoexcited Molecules in Disordered Media by Using Pulsed Synchrotron X-rays (pages 2886–2905)

      Lin X. Chen

      Article first published online: 28 APR 2004 | DOI: 10.1002/anie.200300596

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      Snapshots of excited-state molecular structures in solution during chemical reactions serve as the basis for understanding reaction intermediates. The method of choice for obtaining such structures is photo-chemical excitation by a laser pulse and subsequent analysis by time-resolved X-ray absorption spectroscopy. (X-rays generated by third-generation synchrotron sources; see picture of the Advanced Photon Source of the Argonne National Laboratory, Illinois).

    4. Putting tert-Butyl Cation in a Bottle (pages 2908–2911)

      Tsuyoshi Kato and Christopher A. Reed

      Article first published online: 6 MAY 2004 | DOI: 10.1002/anie.200453931

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      Usually viewed as intermediates that become long-lived at low temperatures in superacidic media, simple alkyl carbocations such as the tert-butyl cation can be isolated as stable salts at room temperature when partnered with inert carborane anions. The X-ray crystal structures of tert-butyl (depicted), tert-pentyl, and methylcyclopentyl cations have been determined with CHB11Me5X6 counterions (X=Br or Cl). C blue; H white; B yellow; X green.

    5. An Efficient and General Method for the Synthesis of α,ω-Difunctional Reduced Polypropionates by Zr-Catalyzed Asymmetric Carboalumination: Synthesis of the Scyphostatin Side Chain (pages 2911–2914)

      Ze Tan and Ei-ichi Negishi

      Article first published online: 19 MAY 2004 | DOI: 10.1002/anie.200353429

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      A decrease in the number of linear synthetic steps and an increase in efficiency have been realized in the synthesis of the side chain of scyphostatin. An efficient and selective synthesis of α,ω-difunctional reduced polypropionates from methyl 3-hydroxy-2-methylpropionate through the use of a Zr-catalyzed asymmetric carboalumination has been developed (see scheme, TBS=tert-butyldimethylsilyl).

    6. A Double Ring-Closing Metathesis Approach for the Synthesis of β-C-Trisaccharides (pages 2915–2918)

      Maarten H. D. Postema, Jared L. Piper, Venu Komanduri and Lei Liu

      Article first published online: 19 MAY 2004 | DOI: 10.1002/anie.200353478

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      Good things come in threes: A variety of β-C-trisaccharides have been successfully synthesized by double ring-closing metathesis, which provides the products in excellent overall yield after functionalization of the newly formed double bonds (see scheme). The precursor olefin–enol ethers were prepared by Takai methylenation of the appropriate diesters.

    7. Ethylene Epoxidation on Ag: Identification of the Crucial Surface Intermediate by Experimental and Theoretical Investigation of its Electronic Structure (pages 2918–2921)

      Suljo Linic, Hong Piao, Kaveh Adib and Mark A. Barteau

      Article first published online: 19 MAY 2004 | DOI: 10.1002/anie.200353584

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      Intermediate success: A combination of high-resolution X-ray photoelectron spectroscopy and density functional theory allows the electronic structures of adsorbates to be probed to an unprecedented level of detail. By using these techniques, the adsorption of ethylene oxide onto an Ag(111) surface has been shown to result in the formation of an unsymmetrical surface oxametallacycle structure (see picture).

    8. New Clathrate Hydrate Structure: High-Pressure Tetrahydrofuran Hydrate with One Type of Cavity (pages 2922–2924)

      Alexander V. Kurnosov, Vladislav Yu. Komarov, Vladimir I. Voronin, Alexander E. Teplykh and Andrej Yu. Manakov

      Article first published online: 19 MAY 2004 | DOI: 10.1002/anie.200453712

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      Water cages: A water framework consisting of uniform space-filling polyhedral cages containing tetrahydrofuran molecules has been detected in a new clathrate hydrate formed under a pressure of 0.8 GPa. Topologically the cage represents a space-filling tetradecahedron with four tetra-, four penta-, and six hexagonal faces (see picture).

    9. Synthesis of Dendritic Polyoxometalate Complexes Assembled by Ionic Bonding and Their Function as Recoverable and Reusable Oxidation Catalysts (pages 2924–2928)

      Lauriane Plault, Andreas Hauseler, Sylvain Nlate, Didier Astruc, Jaime Ruiz, Sylvain Gatard and Ronny Neumann

      Article first published online: 19 MAY 2004 | DOI: 10.1002/anie.200453870

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      Regenerable and reusable dendritic catalysts have been synthesized by the ionic assembly of polyammonium dendrimers and polyoxometalate (POM) trianionic units. These dendrimers (see example depicted, in which the POM is [PO4{WO(O2)2}4]3−) are found to catalyze, at ambient temperature, the quantitative epoxidation of olefins by H2O2 in water/CDCl3 and the selective and quantitative oxidation of thioanisole to its sulfone.

    10. Polysulfones: Catalysts for Alkene Isomerization (pages 2928–2930)

      Dean Marković and Pierre Vogel

      Article first published online: 19 MAY 2004 | DOI: 10.1002/anie.200453897

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      A radical intermediate is generated when methylidenecyclopentane (1) is isomerized by SO2 into 1-methylcyclopentene (3) through the formation of a polysulfone polymer (PS), which first abstracts a hydrogen atom from the alkene. The allyl radical intermediate 2 abstracts a hydrogen atom from another alkene molecule 1, to yield the isomerized alkene and regenerating the allyl radical. Polysulfones are organic catalysts.

    11. A Concise Asymmetric Synthesis of the Marine Hepatotoxin 7-Epicylindrospermopsin (pages 2930–2933)

      Ryan E. Looper and Robert M. Williams

      Article first published online: 6 MAY 2004 | DOI: 10.1002/anie.200454208

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      Born from a simple amino acid … the potent hepatotoxic cyanobacterial alkaloid 7-epicylindrospermopsin (see picture) has been synthesized through a concise asymmetric eighteen-step route. An intramolecular 1,3-dipolar cycloaddition and a nitroaldol reaction are key steps in the construction of the natural product from a precursor with a single stereogenic center.

    12. Luminescent 2D Macrocyclic Networks Based on Starburst Molecules: [{Ag(CF3SO3)}1.5(tdapb)] and [{Ag(NO3)}3(tdapb)] (pages 2933–2936)

      Corey Seward, Wen-Li Jia, Rui-Yao Wang, Gary D. Enright and Suning Wang

      Article first published online: 19 MAY 2004 | DOI: 10.1002/anie.200353126

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      The impact of the anion on the assembly of extended 2D structures has been demonstrated by two distinct luminescent 2D lattices. Shown here is the macrocyclic cloverleaf-shaped cavity obtained from the reaction of a starburst ligand with Ag(NO3). Use of the triflate salt instead results in a honeycomb-shaped cavity.

    13. A Peptidomimetic HIV-Entry Inhibitor Directed against the CD4 Binding Site of the Viral Glycoprotein gp120 (pages 2937–2940)

      Axel T. Neffe and Bernd Meyer

      Article first published online: 19 MAY 2004 | DOI: 10.1002/anie.200353271

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      Barring infection: A new CD4-binding peptidomimetic (see ball-and-stick structure; CD4 is shown in green) has been designed and synthesized as an entry inhibitor of the HIV virus. The binding affinity of the peptidomimetic for CD4 is 40 μM, which is 150-fold better than that of the lead peptide NMWQKVGTPL. The mimetic also has a lower molecular weight and a higher proteolytic stability than the lead peptide.

    14. A Genetically Encoded Fluorescent Reporter of Histone Phosphorylation in Living Cells (pages 2940–2943)

      Chi-Wang Lin and Alice Y. Ting

      Article first published online: 19 MAY 2004 | DOI: 10.1002/anie.200353375

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      An increase in FRET indicates phosphorylation of histone H3 at serine 28. The protein-based reporter (see picture) responds to phosphorylation through intramolecular complexation between a substrate domain derived from histone H3 and a linked phosphoserine-recognition domain. The reporter is also effective inside living mammalian cells. FRET=fluorescence resonance energy transfer.

    15. Photoluminescence Properties of Discrete Conjugated Wires Wrapped within Dendrimeric Envelopes: “Dendrimer Effects” on π-Electronic Conjugation (pages 2943–2947)

      Wei-Shi Li, Dong-Lin Jiang and Takuzo Aida

      Article first published online: 19 MAY 2004 | DOI: 10.1002/anie.200353519

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      Third-generation dendrimers have been used to enable the synthesis and isolation of a series of spatially isolated, discrete conjugated wires G3-n (where n is the number of repeating monomer units, see schematic representation), including 147-nm long G3-64, which contains 192 aromatic rings and 256 triple bonds in the backbone. Photochemical studies show there is enhanced π-electronic conjugation in these systems.

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      A New Type of Material for the Recovery of Hydrogen from Gas Mixtures (pages 2948–2950)

      Jerry L. Atwood, Leonard J. Barbour and Agoston Jerga

      Article first published online: 19 MAY 2004 | DOI: 10.1002/anie.200353559

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      Molecular gas works:p-tert-Butylcalix[4]arene crystals possess large interstitial cavities when grown by sublimation and, although nonporous, are able to absorb and retain gases such as O2, N2, and CO2 under near-ambient conditions. H2 is not retained and thus the material can be used to effect the separation of H2 from gas mixtures. The gas can be removed by evacuation or immersion of the crystals in nitrobenzene (see picture).

    17. Doubly N-Confused Pentaphyrins (pages 2951–2955)

      Alagar Srinivasan, Tomoya Ishizuka, Hiromitsu Maeda and Hiroyuki Furuta

      Article first published online: 19 MAY 2004 | DOI: 10.1002/anie.200453732

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      Adding to the confusion: [3+2] coupling of confused tripyrrane and confused dipyrromethane dicarbinol, followed by oxidation, results in the synthesis of meso-pentafluorophenyl-substituted, doubly N-confused, oxo-substituted pentaphyrins (see X-ray crystal structure; green: F, blue: N, red: O). The oxopyrrole moieties have been shown to readily form intra- and intermolecular hydrogen bonds.

    18. A Carbon Material as a Strong Protonic Acid (pages 2955–2958)

      Michikazu Hara, Takemi Yoshida, Atsushi Takagaki, Tsuyoshi Takata, Junko N. Kondo, Shigenobu Hayashi and Kazunari Domen

      Article first published online: 19 MAY 2004 | DOI: 10.1002/anie.200453947

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      Incomplete carbonization of sulfoaromatic hydrocarbons results in a carbon material that consists of small polycyclic aromatic carbon sheets with attached SO3H groups (see picture). This insoluble solid acid exhibits remarkably high activity in the formation of ethyl acetate, the hydrolysis of cyclohexyl acetate, and the hydration of 2,3-dimethyl-2-butene.

    19. The First Account of a Structurally Persistent Micelle (pages 2959–2962)

      Michael Kellermann, Walter Bauer, Andreas Hirsch, Boris Schade, Kai Ludwig and Christoph Böttcher

      Article first published online: 2 APR 2004 | DOI: 10.1002/anie.200353510

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      Defined micelles: A completely uniform and structurally precise micelle spontaneously formed by exactly seven amphiphilic dendro-calixarene molecules in aqueous solution has been determined by cryo-TEM and 3D reconstruction techniques. The picture shows seven calixarene head groups, which have been fit visually into the reconstructed density map of the micelle.

    20. The Glycosyltransferase UrdGT2 Catalyzes Both C- and O-Glycosidic Sugar Transfers (pages 2962–2965)

      Clemens Dürr, Dirk Hoffmeister, Sven-Eric Wohlert, Koji Ichinose, Monika Weber, Ursula von Mulert, Jon S. Thorson and Andreas Bechthold

      Article first published online: 19 MAY 2004 | DOI: 10.1002/anie.200453758

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      Sweet success: A natural product glycosyltransferase, UrdGT2 from Streptomyces fradiae Tü2717, is the first glycosyltransferase able to catalyze both C-glycosidic and O-glycosidic sugar transfers. These results shed new light on the mechanisms of C-glycosylation of aromatic compounds, which is significant for chemoenzymatic drug lead derivatization as well as for enzymology.

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      A Silicon Analogue of Vinyllithium: Structural Characterization of a Disilenide (pages 2965–2967)

      David Scheschkewitz

      Article first published online: 19 MAY 2004 | DOI: 10.1002/anie.200353347

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      The reduction of Tip2SiCl2 by finely dispersed lithium powder directly affords the disilenide 1 (see picture), the structure of which could be characterized by X-ray crystallography. The reaction of 1 with Me3SiCl leads to the corresponding asymmetrical disilene. The ready availability of 1 is expected to open new possibilities for the synthesis of disilenes in general. Tip=2,4,6-iPr3C6H2

    22. An Efficient Synthesis of Diaryl Ketones by Iron-Catalyzed Arylation of Aroyl Cyanides (pages 2968–2970)

      Christophe Duplais, Filip Bures, Ioannis Sapountzis, Tobias J. Korn, Gérard Cahiez and Paul Knochel

      Article first published online: 19 MAY 2004 | DOI: 10.1002/anie.200453696

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      An alternative to acyl chlorides: Iron(III)-catalyzed arylation of aroyl and heteroaroyl cyanides with aryl magnesium reagents (see example in scheme) provides an easy and mild approach to polyfunctionalized diaryl ketones in yields up to 98 %.

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      Preview: Angew. Chem. Int. Ed. 22/2004 (page 2975)

      Article first published online: 19 MAY 2004 | DOI: 10.1002/anie.200490068

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