Angewandte Chemie International Edition

Fusicoccin, a naturally occurring compound, stabilizes a 14-3-3 protein–protein interaction and induces wilting of plants by opening the gas-exchanging stomatal pores (gray). C. Ottmann and co-workers describe in their Communication on page 4129 ff. how easily available small molecules have been identified that mimic the action of fusicoccin. Crystal-structure and functional biophysical analyses reveal the binding modes of these molecules.

The diastereoselective self-assembly of homochiral porous metal–organic tetrahedral M₄L₆ cages from enantiopure C₂-symmetric bridging ligands (H₂L) and C₃-symmetric octahedral trivalent metal ions is described by Cui and co-workers in their Communication on page 4121 ff. The cages can resolve small racemic alcohols with high enantioselectivity (up to 99.5% ee) by crystallization inclusion, although kinetically stable host–guest complexes were not formed with alcohols in solution.

“When I wake up I drink coffee. If I could be anyone for a day, I would be Lewis Carroll. He worked just down the road from here. But, only for a day. The most significant scientific advance of the last 100 years has been the human genome sequence through a wonderful amalgamation of biology, chemistry, engineering, computer hardware and software, and management skills. Plus some adroit politics …” This and more about Hagan Bayley can be found on page 4010.

John Wiley & Sons, Hoboken 2009. 266 pp., hardcover € 64.90.—ISBN 978-0470096031

The bigger, the better: In the last decade, the development of organic electronics, and particularly of organic field-effect transistors, carbon nanotubes, and graphene, has spurred efforts to prepare larger acenes. Stable, large acenes have been obtained and fully characterized. Developments in the synthesis of heptacenes, as well as the very recent synthesis of octacene and nonacenes, are highlighted.

David versus Goliath: Since the first synthesis of urea by F. Wöhler (see portrait) in 1828, chemistry has played a major role in the decline of vitalism through its reductionist approaches and has continuously provided remarkable contributions to the understanding of the nature of life. Future progress in the emerging postgenomic era resides in the balanced combination of chemistry and integrative biology.

Guanine-rich sequences of nucleic acids can assemble into tetrastranded structures. The resulting G-quadruplexes have been identified as potential targets for the development of anticancer drugs and have sparked great interest in the design of molecules that can stabilize quadruplex structures. This Review presents an overview of the interaction of metal complexes with G-quadruplex DNA, highlights their potential use as anticancer drugs and as molecular probes.

A cut and shut job: The highly selective title reaction proceeds, using O₂ as the oxidant, to afford tetrahydroquinoline derivatives. This chemistry offers a new approach to polysubstituted 4,5-dihydrocyclopenta[c]quinolines, and also valuable mechanistic insight into this ring-expansion reaction.

Size control: Sterically stabilized methacrylic nanolatexes are readily prepared by aqueous dispersion polymerization using RAFT reactions (see scheme; CTA=chain transfer agent). Varying the length of the poly(HPMA) chains allows precise size control of the nanolatex particles.

You′re having a lahf! The asymmetric hydroformylation (AHF) of allylic compounds, catalyzed by a rhodium–yanphos complex, is a direct and concise route to β²-amino aldehydes, acids, and alcohols with excellent enantioselectivity (see scheme; TON=turnover number, acac=acetylacetonate).

The CH borylation of simple alkenes catalyzed by palladium pincer complex 1 was performed in the presence of hypervalent iodine and bis(pinacolato)diboron compounds. The borylation reaction probably occurs by a Pd^II→Pd^IV oxidation–diboronate transmetalation sequence. TFA=trifluoroacetate.

A heterogeneous palladium catalyst, which is supported on a metal–organic framework, MIL-101, is highly efficient in water-mediated coupling reactions of chloroarenes. High yields are obtained in Suzuki–Miyaura cross-coupling and Ullmann homocoupling reactions of substituted aryl chlorides. Furthermore, the catalyst is easily recoverable and reusable (see picture; Cr blue, O red, C white).

Inorganic sheets: Graphene-like MoS₂ and WS₂ were prepared by three different chemical methods. Examination by microscopic techniques revealed that they consist of one or a few layers (see depicted TEM image of WS₂ layers), and an atomic-resolution TEM image showed that layered MoS₂ has a hexagonal arrangement of Mo and S atoms (see inset).

A chemical receptor specific to traces of organophosphorus agents (OPs) has been synthesized and grafted to a silicon nanoribbon field-effect transistor (SiNR-FET). X-ray structures illustrate the structural modifications of the receptor upon exposure to nerve agent simulants. A highly sensitive and selective detector of OPs can be obtained by monitoring the Drain-Source current of the SiNR-FET at an optimum back-gate voltage as a function of time.

Star-crossed lovers: The domino iododediazoniation/Sonogashira cross-coupling of terminal alkynes with arenediazonium salts has been developed. The arenediazonium salt synthesis/iododediazoniation/Sonogashira cross-coupling sequence can also be performed as a one-pot process, omitting the isolation of the arenediazonium salt.

Amazing ammonia: A new air-stable P,N-ligand (Mor-DalPhos) is reported that enables the palladium-catalyzed cross-coupling of ammonia to a variety of aryl chloride and aryl tosylate substrates with high chemoselectivity and, for the first time, at room temperature (see scheme; Ad=adamantyl, Ts=para-toluenesulfonyl).

Cross on UV light: A polymer bearing dithiocarbamate ester groups, linked to the polymer backbone through the dithiocarbamate nitrogen atom is capable of reversible cross-linking and de-linking through photochemical rearrangement of the pendant groups (see scheme).

Out-of-plane steric bulk furnished by a cyclophane substituent on iodine(III) strongly destabilizes the transition state in the reductive elimination from diaryliodonium salts and leads to regiochemical control (dubbed SECURE), as is demonstrated by computational and experimental studies. This approach should be general for high-valent main-group and transition metal ions. X=N₃, OAc, PhO, CF₃CH₂O, SCN, PhS.

The first enol silenolates, (tBuMe₂Si)₂SiC(OLi)Ad and (tBu₂MeSi)₂SiC(OLi)Ad, were synthesized and characterized by X-ray spectroscopy. Calculations show that, in contrast to organic enolates, which exist predominantly in the enol form regardless of solvation, the enol form of silenolates (left) is favored in nonpolar solvents, and the keto form (right) when strongly solvated. Ad=1-adamantyl.

Radically complex: Well-defined mononuclear Ru^I and Os^I complexes (see scheme) have metalloradical character, as indicated by EPR spectroscopy and DFT calculations. The Ru^I and Os^I metalloradicals exhibit both one-electron and two-electron redox reactivity. The latter process affords unusual imido complexes with substantial radical character on the {ArN} moiety.

Cyclohexyne steps into the ring! Cyclohexyne is used for the facile synthesis of polycyclic, medium sized rings. Its insertion into cyclic ketones enables rapid access to densely functionalized building blocks.

In harmony: Nanoparticles of Mn₃O₄ and core/shell-structured Rh/Cr₂O₃ as cocatalysts on the surface of a solid solution of GaN and ZnO as catalyst promote O₂ and H₂ evolution, respectively, under visible light (λ>420 nm), thereby achieving enhanced water-splitting activity compared to analogues modified with either Mn₃O₄ or Rh/Cr₂O₃.

Protein crystals turned to stone: Protein-mediated aggregation of microemulsion water droplets is used to prepare discrete ferritin nanocrystals with periodically arranged close packed structures. Addition of tetramethoxysilane (TMOS) to the microemulsion produces silica-ferritin hybrid nanoparticles with well-ordered mesostructured interiors (see scheme).

A buried polar bilayer interface composed of interdigitated peptide ends and a high density of CF₃COO⁻ counterions passifying lysine amines are identified in nanotubes obtained by self-assembly of short peptides. The structure reveals distinct characteristics that differentiate peptide bilayers and lipid bilayers that can now be exploited for the construction of lipid-like nanomaterials with protein functionality.

Functionalization of quantum dots (QDs) was achieved by controlling the surface density of functional groups by electrostatic repulsion. These QDs were conjugated with His-tagged proteins in vitro and in live cells by self-assembly without requiring further fractionation, and dual-color tracking of cell surface receptors was possible.

Molecular plug: On-bead screening of a combinatorial library of 216 tetravalent oligopeptides reveals highly specific, noncompetitive inhibitors of the serine protease β-tryptase with nanomolar affinity. The ligands most likely bind to the protein surface and act as a molecular plug that blocks access to the active sites, which are buried inside a central cavity (see picture).

Heteroatom control in the assembly of nanoscale gigantic heteropolyoxotungstates was accomplished by using SeO₃²⁻ to give [H₂W₄₃Se₃O₁₄₈]²⁴⁻ {W₄₃Se₃}, [H₄W₇₇Se₅O₂₆₅]⁴⁴⁻ {W₇₇Se₅}, [H₆W₆₃Se₆O₂₂₁]³⁴⁻ {W₆₃Se₆}, and [H₈W₁₀₀Se₁₆O₃₆₄]⁵⁶⁻ {W₁₀₁Se₁₆} cluster anions. The clusters are all derived from a common {W₂₂Se₂} building block and are constructed without the need to employ addition heterometallic linkers; the three smaller clusters incorporate pentagonal W(W₄) units.

Cage rage: Chiral tetrahedral cages are diastereoselectively self-assembled from enantiopure C₂-symmetric biphenyl bis(β-diketonate) linkers and C₃-symmetric octahedral Fe³⁺ or Ga³⁺ ions (see picture; Fe purple, C blue, O red; cavity shown as an orange sphere). The porous polyhedra exhibit metal-dependent chiroptical behavior and act as hosts for the crystallization separation of racemic alcohols with up to 99.5 % ee.

Take it to the limit: Parent acenes larger than heptacene have eluded synthesis for decades. When 1,2-diketone bridges in suitably designed tetraketone precursors were removed by irradiation under matrix-isolation conditions (see scheme), the parent systems of the two next higher acenes were accessible experimentally.

Two structurally unrelated small molecules that stabilize the interaction of a 14–3–3 protein with the proton pump PMA2 have been identified. The compounds are selective among different 14–3–3 protein–protein interactions and are active in vivo. Crystal structures of ternary complexes revealed that the molecules bind to different sites in the interface of the 14–3–3 protein and PMA2 (see picture), thus explaining the different binding kinetics.

Downsizing: A pocket-size permanent magnet has been constructed that is suitable for measuring ¹H NMR spectra of samples in standard NMR tubes. The new shimming approach implemented to overcome the inherent inhomogeneity of permanent magnets opens the door to compact high-resolution NMR spectrometers for conventional samples.

Naturally synthetic: Acid/base catalyst (S)-1 can be used in highly enantioselective alcoholytic desymmetrizations of meso anhydrides. For example, the methanolysis of cyclobutane anhydride derivative 2 gave hemiester 3 in 99:1 e.r. (see scheme). Ester 3 was used in a short enantioselective synthesis of (+)-grandisol.