Angewandte Chemie International Edition

The homochirality of life is still an unsolved mystery. Magneto-chiral dichroism (MChD, the dependence of the absorbance of a chiral molecule on the direction of a magnetic field) has attracted attention as a plausible way to explain this puzzle. Several examples of MChD of metal compounds are known, but MChD of biological organic compounds has not been reported. In their Communication on page 9133 ff., K. Ishii et al. describe the first observation of MChD in organic compounds by using porphyrin J-aggregates.

A mechano- and thermoresponsive luminescent liquid-crystalline material that has a single luminophore group and shows three distinct colors of reddish-orange, yellow, and green is described by Y. Sagara and T. Kato in their Communication on page 9128 ff. Mechanically induced isothermal and thermal phase transitions accompany the switching of the nanostructures formed by the liquid crystal and lead to a change in the intermolecular interactions.

Assembly of nanostructures by using DNA has the potential to realize new materials. In their Communication on page 9185 ff., J.-W. Kim et al. introduce a simple and sustainable strategy to place DNA linkers at 90° or 180° angles on nanoparticles, thus producing a nanoscale building block that allows control of the nanoassembly geometry. The picture depicts the iterative process of DNA attachment at maximal separation resulting in DNA linkers at well-defined orientations. (Artwork by Min Kim.)

“What I look for first in a publication is architecturally beautiful structures. My favorite piece of research is R. B. Woodward's total synthesis of reserpine …” This and more about Masayuki Inoue can be found on page 9016.

Wiley-VCH, Weinheim, 2011. 282 pp., hardcover, € 109.00.—ISBN 978-3527316694

The fundamental question of how silicon handles antiaromaticity in four-membered ring systems has been answered by the synthesis and characterization of the first tetrasilacyclobutadiene Si₄Ar₄ (1) and by the first dimeric silaisonitrile Si₂(NAr′)₂ (2). Compound 1 is best described by the charge-separated resonance structure 1′ and 2 by a structure with π-type lone pairs at the nitrogen atoms and vacant π orbitals at the silicon atoms.

The Stöber method is an authoritative approach for the synthesis of monodisperse colloidal silica spheres; this method has now been extended to the synthesisis of monodisperse resorcinol-formaldehyde resin polymer and carbon spheres.

Nature's bounty: Recent advances in analytical and synthetic tools are facilitating the development of materials inspired by nature. This Review highlights the history and the state-of-the-art in the quest to understand the molecular mechanisms behind nature's most remarkable peptide-based materials, as well as the attempts to apply that understanding to design biomimetic materials.

Singles only: DNA sequences can be induced to spontaneously adsorb to the surfaces of Ag colloids through their nucleotide side chains (see picture). The SERS spectra of these nonspecifically bound strands are sufficiently reproducible that they can be used to identify single-base mismatches in short (25-mer and 23-mer) strands. Subtracting the spectra of different DNA sequences results in difference spectra that contain features corresponding to the exchanged nucleotides.

Stereodefined: The title reaction provides an atom-economic route to benzonorcaradienes. The diastereoselectivity of the coupling relies upon the structure of the alkene; unsubstituted bicyclic alkenes afforded exclusively exo-benzonorcaradienes (see scheme) whereas the bicyclic alkenes with substituents at the bridgehead positions resulted in endo-benzonorcaradienes.

Cationic layers: Copper hydroxide ethanedisulfonate consists of cationic sheets (see structure of a [Cu₄(OH)₆]²⁺ layer; Cu green, O red, H white) with ethanedisulfonate as extraframework counteranion. This material shows excellent anion exchange properties for both organics and metal oxo anion pollutants, with over five times higher adsorption capacity for permanganate than hydrotalcite.

Vanadium oxide layers with homogeneous nanoporous nanotubular morphology (see picture) were successfully fabricated by direct anodization of vanadium in fluoride electrolytes such as [TiF₆]²⁻ or [BF₄]⁻. The pore size and layer thickness can easily be controlled by tailoring the electrochemical conditions. Such nanotubular or porous structures are promising for the fabrication of lithium-ion insertion electrodes.

A golden dig! Gold-catalyzed direct access to functionalized 2H-1-benzoxocines, eight-membered-ring ethers, is described. This unprecedented synthesis of benzoxocines occurs by an 8-endo-dig cyclization of the 1,7-enyne substrates.

Finally, a choice! A highly selective palladium(II)-catalyzed ortho-monofluorination reaction has been achieved for the first time through a weak coordination (see scheme; Ar=2,3,5,6-tetrafluoro-4-(trifluoromethyl)phenyl). Simple modification of this protocol allows for a choice between mono- and difluorination. The mono- and difluorinated benzoic acid derivatives are valuable in the pharmaceutical and agrochemical industries.

A trifluoromethylated symphony! A new transformation involving trifluoromethyl diazomethane generated in situ has been developed that allows direct access to trifluoroethyl ketone derivatives from aldehyde and cyclohexanone compounds (see scheme).

It takes two to tango: A domino multicatalytic synthesis of dihydroquinolines is realized, wherein the products of a rhodium-catalyzed arylation of alkynes are cyclized by a palladium-promoted CN cross-coupling (see scheme). The combination of catalysts with potentially exchangeable ligands is remarkable as each metal–ligand combination affords specific reactivity and selectivity.

We just clicked: A convergent approach consisting of two successive copper(I)-catalyzed azide–alkyne cycloaddition “click” reactions leads to a diblock copolymer in which the two blocks are linked by a rotaxane-type mechanical bond (see scheme). Rotaxane formation is templated by a square-planar Pd^II complex.

Direct access: The title reaction has been developed under mild reaction conditions (see scheme; DMSO=dimethyl sulfoxide). This reaction can be effectively scaled up and offers not only a green and attractive approach to β-ketophosphonates, but also a useful example of direct incorporation of an oxygen atom from dioxygen into organic frameworks.

How low can you go? The natural substrate for the epigenetic regulators PHF8, JmjD2A, and JmjD2C (lysine demethylases), a peptide consisting of 39 amino acid residues, can be truncated to 14, 8, and 4 amino acids, respectively, while maintaining catalytic activity (see picture). Inhibitors were prepared by attaching small molecules to the truncated substrates. Selective inhibition of JmjD2C over JmjD2A and PHF8 was possible.

Sultam of swing: Both enantiomers of 1,2-thiazetidin-3-one oxides were obtained in very good yields with excellent enantioselectivities when using N-heterocyclic carbene catalysts (see scheme; M.S.=molecular sieves, TBS=tert-butyldimethylsilyl). The products were easily converted into 3-oxo-β-sultams, α-mercapto amides, and β-mercapto amines through oxidation or reduction.

Keeping tabs on tyrosine: A three-component Mannich-type reaction extends the scope of site-directed spin labeling by selectively labeling the unique tyrosine residue of CP12 protein (see picture), as was confirmed by mass spectrometry. EPR spectroscopy of the labeled protein showed a very high mobility of the probe, which remained very mobile after complex formation with GAPDH.

Three become one: The title compound can be prepared in 26 steps by employing a unified Prins cyclization strategy to construct both tetrahydropyran rings (see scheme). The route combines two similar dioxinone fragments and one aldehyde component to generate the core structure. (−)-Exiguolide selectively inhibits the growth of A549 cancer cells at low concentrations; the triene side chain and the Z-enoate geometry are both necessary for this cytotoxicity.

The power of palladium: The total synthesis of the alkaloid hodgkinsine B has been achieved with just six isolated intermediates and only four chromatographic operations. The route involves a palladium-catalyzed enantioselective desymmetrizing N-allylation of meso- chimonanthine to establish the absolute configuration and elaboration of the desymmetrized core by a diastereoselective palladium-catalyzed α-oxindole arylation.

Activating the inactive: A copper-catalyzed allylic trifluoromethylation of unactivated terminal olefins proceeds under mild conditions to produce linear allylic trifluoromethylated products with high E/Z selectivity (see scheme). The reaction can be applied to a range of substrates bearing numerous functional groups. Furthermore, the reaction is scalable and amenable to a benchtop setup.

A-spiro-ing: The title reaction of α-isothiocyanato imides and methyleneindolinones has been realized for the first time using 1 as the catalyst. This newly developed synthetic method provides a simple, efficient, and environmentally friendly way to access, in an enantioselective manner, densely functionalized spirooxindoles having three contiguous stereogenic centers.

A glowing image: The photoluminescent colors reddish-orange, yellow, and green, are generated from a single liquid-crystalline mixture containing one luminophore (see picture). The colors are easily distinguished by the naked eye and can be reversibly written and erased. Moreover, these luminescent colors can be switched by mechanical and thermal stimuli.

Direction decides: Magneto-chiral dichroism describes the dependence of the absorbance of a chiral molecule on the direction of a magnetic field to which it is exposed, and it may help to explain the homochirality of life. This phenomenon was now observed in organic compounds using porphyrin J-aggregates.

Morning light: In vivo photodissociation of CO from bacterial c-type cytochromes yields a redox-active Fe²⁺ form, which can be oxidized at an electrode surface to the Fe³⁺ form. Reduction by electrons from the metabolic pathway regenerates the Fe²⁺ form (see picture). Spectroscopic monitoring of this process yields information on the in vivo respiratory electron-transport dynamics.

Structure matters: Owing to the structure and arrangement of the [Be₃B₃O₁₂F]¹⁰⁻ group (see picture, left, Be blue, B olive, F green, O red), the mixed-cation fluorine beryllium borate NaSr₃Be₃B₃O₉F₄ (right) exhibits a large second harmonic generation effect and a short UV absorption edge. Its crystals show no layering tendency, making it promising for applications in deep-UV nonlinear optics.

A surface-assisted fabrication scheme enables direct surface coverage control of functionalized DNA nanostructures on centimeter-scaled silica (SiO₂) substrates from 0 to 100 % (see picture). Electrostatic interactions between the DNA structures and the surface lead to dramatic topological changes of the structures, thereby creating novel formations of the crystals.

Interconvertible host: Extended cavitands and capsules that recognize n-alkanes were generated using N-methyl glycoluril as a chiral spacer. The two host assemblies were interconverted by factors such as temperature, concentration, and guest length (see scheme).

Three's a charm: The title compound (see picture, right, WO₆ purple polyhedra, Mn orange and brown, Si green, O red) contains an embedded mixed-valence {Mn₅O₆} cubane core, which is structurally similar to the active site in photosystem II. Solid-, solution-, and gas-phase studies indicate the presence of three lacunary Keggin fragments, thereby giving insight into the complex solution chemistry of plenary POM fragments.

Combed to perfection: Fully aromatic comb-shaped copolymers based on a poly(arylene ether sulfone) (PAES) backbone with highly sulfonated (SA) poly(phenylene oxide) (PPO) graft chains have a nanochannel morphology (see picture) for efficient proton transport. These molecular structures show a dramatic enhancement in proton conductivity under partially hydrated conditions compared with typical hydrocarbon polymer electrolytes.

The best of both worlds: A novel amphiphilic homopolymer synthesized from a monomer consisting of a hydrophobic group (see picture, red) and a hydrophilic moiety (green) self-assembles in aqueous solution. The resulting micelles have a multi-core/shell structure and exhibit smart redox-responsive properties, thus providing a favorable drug delivery platform for cancer therapy.

One reagent for two techniques: Compound [¹¹¹In]1 provides a platform for sequential radionuclide and optical imaging of prostate cancer through targeting of the prostate-specific membrane antigen. Because the same subject can be dual-imaged after one injection of the agent, these findings support rapid clinical translation.

Layered catalyst: The attachment of α-amino acid ligands to inorganic nanosheets for use as ligands to vanadium, resulted in a catalyst that enhanced the enantioselectivity of the epoxidation of allylic alcohols (see picture) . The catalyst can be colloidized, allowing for the catalytic reactions to be carried out under pseudo-homogeneous reaction conditions and also the catalysts to be directly recycled by simple liquid/liquid separation.

Masked talent: A tetracyclo[5.3.3.0^4,9.0^4,12]tridecane skeleton can be accessed by an intramolecular reverse-electron-demand Diels–Alder (REDDA) reaction of masked ortho-benzoquinone (MOB; see scheme). This reaction gives access to the pentacyclic framework of atropurpuran, and also enables the construction of other anti-Bredt and cage-like complex molecules.

Fluoride's new role: Selective and efficient monoreductions of imides can be achieved with polymethylhydrosiloxane (PMHS) and tetra-n-butylammonium fluoride (TBAF) as catalyst (see scheme). The system is characterized by good chemoselectivity, operational simplicity, and functional-group tolerance; a concise mechanistic proposal was possible from in situ spectroscopic investigations.

One step at a time: DNA linkers were placed at defined locations and in defined 3D orientations on a colloidal nanoparticle. Because the implemented ligand-replacement strategy was carried out sequentially, DNA linkers maximally segregated, producing a nanoparticle with linkers at 90 or 180° angles (see picture). These building blocks should enable assembly of anisotropic nanostructures with precisely designed geometry and complex functionality.

Cores and effect: A biomimetic [2 Fe-2 S] cluster is characterized crystallographically in both the [Fe^IIIFe^III] and the mixed-valent [Fe^IIIFe^II] forms—the [2 Fe-2 S] cores show only minor geometric differences. The reduced form has an S=1/2 ground state and the unpaired electron is partially delocalized over the cluster core. The experimental effective coupling constant predicts the position of the intervalence charge transfer band in the IR regime.

The family of iron arsenide superconductors is expanded by the new iron platinum compounds (CaFe_1−xPt_xAs₁₀)Pt_4−yAs₈ with novel crystal structures. Layers of FeAs_4/4 tetrahedra and of nearly planar PtAs_4/2 squares with (As₂)⁴⁻ dumbbells are stacked in different ways, resulting in polytypes with triclinic or tetragonal symmetry. Superconductivity up to 35 K is induced either by Pt doping of the Fe site or by electron transfer from PtAs to FeAs layers.

The enzyme DrrA of the human pathogen Legionella pneumophila adenylylates specifically a tyrosine of the GTPase Rab1. An efficient synthesis route using Fmoc solid phase peptide synthesis led to Tyr-adenylylated peptides and allowed the generation of mono-selective polyclonal antibodies against this post-translational modification.

Powdered organozinc reagents: Various aryl and heteroaryl bromides as well as benzylic chlorides react with Mg and Zn(OPiv)₂⋅2 LiCl (OPiv=pivalate) to provide solid organozinc reagents after solvent evaporation. These powders can be stored at room temperature under argon for months and can be manipulated in air for a short time. They undergo smooth Negishi cross-coupling and carbonyl addition reactions (see scheme).