Angewandte Chemie International Edition

A large number of superstructures with characteristic dimensions in the range of a few nanometers up to several micrometers are formed by the self-organization of block copolymers (see picture). Possible applications in the fields of materials science and molecular biology are currently being intensively investigated. Their range of application extends from the production of inorganic nanoparticles and mesoporous materials up to take-up/release systems in chemo- and gene therapy.

Chiral organolithium compounds are versatile intermediates with numerous applications in asymmetric synthesis. They range widely in their configurational stability and in the stereochemistry of their electrophilic substitution. Effective transfer of stereochemical information from the lithiated intermediate (C1 and epi-C1) to the final product (P1 and ent-P1) is dependent on the interplay between these two factors.

Has translation a central role in the present and future of science? After showing the importance of translating in the past, in the way the names of the chemical elements were transferred (from Dutch sources) to Japanese, the author tries to answer the above question. His conclusion is that today's dominance of English imposes an increased need for translation, as 1) the major portion of the secondary literature in any country is published in that nation's language, 2) in cases where English is the destination language for publication, scientists in many non-English speaking nations report their primary research in their mother tongue and then have to translate their results into English for submission, and 3) research has to be communicated to non-scientists, including the public, the mass media, educators, political leaders, and other decision makers.

That previously unattainable organolanthanide(II) complexes may be accessible through judicious manipulation of reaction conditions and supporting ligands is suggested by the recent isolation of the organothulium(II) compound [CpTm(thf)] [Eq. (1); Cp″=η⁵-C₅H₃-1,3-(SiMe₃)₂]. In light of the diverse reactions mediated by Sm^II compounds it seems likely that these new compounds will provide a useful addition to the armory of reagents available to the synthetic chemist.

Owing to their highly strained ring system and interesting functional group, β-lactones possess significant synthetic potential. Recently, novel methods have been developed to synthesize these valuable building blocks very efficiently by catalytic, enantioselective reactions, such as [2+2] cycloadditions, starting from simple precursors. These processes also offer an attractive alternative for the synthesis of optically active β-hydroxy and β-amino acids (see scheme).

A higher anticancer activity is observed in photodynamic tests with the first sterically bulky (nonplanar) perhalogenated zinc phthalocyanine (Pc), [F₆₄PcZn(acetone)₂] (see structure: F green, N blue, O red, C gray) in comparison with planar zinc perfluorophthalocyanine. The perfluoroisopropyl substituents enhance the solubility, stabilize axial ligands (such as the coordinated acetone molecules in the structure shown), narrow the HOMO–LUMO gap, shift redox potentials, and increase the lifetime of the excited triplet state of the new complex.

An enzyme-inspired phthalocyanine (Pc) complex [F₆₄PcCo(acetone)₂] is the first representative of a novel class of robust homogeneous catalysts. This complex couples aryl and alkyl phosphanes with acetone to catalytically produce ylides (the structure shows the ylide coordinated to the F₆₄PcCo unit: F green, N blue, O red, C gray, P yellow) and water under ambient conditions using only air, a route that avoids the classical use of halogenated intermediates.

A helix that expands on cooling: The crystal structure of TrpGly⋅H₂O consists of helical peptide nanotubes extending throughout the crystal. The thermal expansion is negative in the helical direction (see graph; a axis: red, c  axis: blue). This effect is believed to be linked to the increasing order of water molecules enclosed in the helices.

An unusual vertex-shared double-cubane [{Cu₃(μ₃-Cl)(μ₃-OH)₃}₂Cu]⁶⁺ core surrounded by a belt of hydrogen-bonded chloride ions is present in the title compound. Magnetic data show an S=1/2 ground state, which implies there is substantial spin-frustration within the heptacopper aggregate.

Perfectly adept for tumor treatment: With the seco-CBI-Q galactoside 1 a novel highly potent prodrug for the selective treatment of cancer using the ADEPT approach was developed, which shows very promising results in preclinical trials on a human bronchial carcinoma in SCID mice (see picture; lung tissue after (A) and before treatment (B)).

α-Helical l- and D-polyalanines have magnetic properties when self-assembled as monolayers on gold surfaces. The properties depend on the chirality of the molecules and on the direction of their dipole moment relative to the substrate. They were investigated by IR spectroscopy, which determined the orientation of the molecules relative to the surface in the presence of a magnetic field, and by measuring the spin selectivity for electron transmission through the layers.

No interpenetration: The use of bulky phosphane ligands allows the preparation of a non-interpenetrating two-dimensional nanoporous structure with hexagonal channels (see picture). In the as-synthesized polymer these channels are saturated with solvent, however, this solvent can be exchanged for other solvents which in turn can be removed by heating under vacuum without collapse of the structure.

Photolyase-catalyzed repair of pyrimidine (6-4) photoadducts was modeled with synthetic, covalently linked flavin–oxetane 1. The repair reaction (oxetane splitting) requires the reduced flavin in its deprotonated form. The key step of the repair reaction involves an electron transfer from the flavin to the oxetane.

Formamidopyrimidine lesions (Fapy⋅dA; see scheme) are produced in greater yields than 8-oxopurines (OA) under O₂-deficient conditions from a common intermediate. OA give rise to low levels of A→C transversions. In vitro experiments show that Fapy⋅dA induces a DNA polymerase to misinsert nucleotides significantly more often than does OA, which suggests that the formamidopyrimidine may be a more potent premutagenic lesion.

Disulfide exchange leads to the attachment of phosphate ester 1 to a solid surface, which can then be used in turnover selection to screen a large library of proteins for phosphate monoester hydrolysis activity. This ester hydrolysis leads to formation of an electrophilic quinone methide 2, which bonds covalently to the protein catalyst and links it to the surface for selection.

Blocking the catalyst through the formation of Rh^I–η⁶-arene complexes (the complex [Rh((R,R)-Et-DuPHOS)(C₆H₆)]⁺ is shown; Et-DuPHOS = 2′,5′,2″,5″-tetraethyl-1,2-bis(phospholanyl)benzene) can decrease the activity of asymmetric hydrogenations. The inhibiting effects of aromatic compounds were quantified by means of kinetic measurements and confirmed by means of X-ray crystal structure analysis and ¹⁰³Rh NMR spectroscopy.

Based on information from the X-ray structure of the TMC-95A/proteasome complex, TMC-95A (A) was reduced to the minimum core structure (B). The inhibitory potency of the synthetic analogue confirms that the simplified ring structure may well serve as the lead for further improvement of affinity and selectivity of reversible proteasome inhibitors.

Bridging coordination of Mo₂P₂complexes between metal centers is a prerequisite for the formation of a one-dimensional polymer. The choice of counterion also has a deciding role in determining the polymer structure: while the complex [Cp₂Mo₂(CO)₄(μ,η²-P₂)] (1; Cp=C₅H₅) with AgNO₃ forms a zigzag polymer chain, with CuBr 1 forms a linear coordination polymer (see structure).

Accessible in one step each, tetra- and pentacyclopropylcyclopentadiene (3) can be prepared from dicyclopropylacetylene (1) and n-butyl formate (2 a) or methyl cyclopropanecarboxylate (2 b), respectively. The five cyclopropyl substituents in 3 b exert a significant donor effect on the cyclopentadienide core when this is bound to a metal center such as in 4.

Excellent mechanical properties make γ-Si₂AlON₃, one of the first spinel sialons and 4-3-spinels, a promising material for structural and abrasive applications. The hardness of this phase synthesized at 13 GPa/1800°C surpasses that of the low-pressure α- and β-sialons, which are used for metal-cutting and engineering applications. The picture shows a γ-Si₂AlON₃ surface that was used for Vickers hardness testing and indicates the structural relation between β- and γ-sialons and the corresponding phases of Si₃N₄.

A bulky binol-based ligand is the key structural feature of the ruthenium complex 1, which displays an unprecedented metathesis activity combined with high stability. For a range of dienes, ring-closing metathesis reactions catalyzed by 1 lead to near quantitative yields of cycloalkenes after a few minutes.

The five binary species Ga(μ-H)₂Ga, In(μ-H)₂In (see left structure), HGaGaH, HInInH (center), and GaGaH₂ (right) were prepared by matrix isolation and characterized unambiguously by IR spectroscopy and quantum-chemical calculations. Investigations of the photochemical properties reveal that each of the isomers can be interconverted by photolysis.

By hydrolysis of a single CF₃group in concentrated sulfuric acid, the new boron carbonyl (CF₃)₃B−CO compound (see molecular structure) is obtained from K[B(CF₃)₄]. (CF₃)₃B−CO exhibits rather unusual properties and bears an electrophilic carbonyl carbon atom.

The novel dideoxyosones 1 and 2 were shown to be precursors of the important in vivo crosslinks glucosepane and pentosidine. In 1 and 2, the lysine N^ε atom is directly bonded to C1 of the original sugar group. The formation of these compounds proceeds through carbonyl shifts along the entire carbohydrate backbone.

ARTS in chemistry: Aryloxymethyl hyponitrites provide the first aryloxyl radical thermal sources (ARTS) which generate a well-defined flux of aryloxyl radicals (ArO^.) at room temperature [Eq. (1)]. These novel compounds can be used for quantitative studies on reactions of ArO^. with biomolecules, as exemplified by the PhO^.-mediated oxidation of human low-density lipoprotein.

Reactive reagents can be prepared by means of olefin cross-metathesis. A wide variety of functionalized allyl boronates were synthesized and were found to react cleanly with aldehydes to afford homoallylic alcohols, without prior purification (see scheme). Olefins that bear allylic ethers, halides, protected aldehydes, and sterically encumbering groups are viable substrates for this reaction.

When four conditions are met redox polymers can be electrodeposited by ligand exchange: the film must be electron- or hole-conducting; the redox centers of the deposited polymer that are based on transition metal complexes must contain a labile ligand in their inner coordination sphere; the redox polymer must contain a strongly coordinating but yet uncoordinated ligand; and the surface density of the adsorbed redox polymer must be high. By taking care of these points, the authors also succeeded in co-depositing enzymes and electroreducing/oxidizing their substrates with the electrodes obtained.

Nine epoxide rings are formed sequentially when A2E is irradiated with blue light in the presence of oxygen [Eq. (1)]. Mechanistically, A2E generates singlet oxygen and reacts with it to give the polyoxiranes. An understanding of the reaction of A2E with oxygen is important as blue light induces the apoptotic death of A2E-laden retinal pigment epithelium cells, which are typical of age-related macular degeneration.

Reversible Diels–Alder reaction of C₆₀ with an anthracenyl dendron bearing a poly(amidoamine) substituent forms the fullerodendrimer depicted. It is readily soluble in water and acts as a photosensitizer for the generation of singlet oxygen.

A double inversion of configuration and episulfonium ion intermediates are at the heart of a method for the stereospecific interconversion between cis and trans 2,3-epoxysulfides (see scheme). This method can be used in the stereoselective synthesis of epoxides.

A heterogeneous version of the Sharpless epoxidation: a chiral tartaric acid derivative is grafted onto the surface of silica and in the mesopores of MCM-41 (see picture). The hybrid chiral catalyst is as effective as the homogeneous complex in terms of turnover number and enantioselectivity, and the product is easily separated by simple filtration.

The regiospecific cycloaddition of an o-quinone imine and a highly reactive enamine, which are electrogenerated simultaneously, can be carried out at ambient temperature in the absence of catalyst. This reaction is a powerful tool for the one-pot synthesis of new polyfunctionalized 1,4-benzoxazine derivatives (see scheme).

Junction function: Molecule-controlled devices based on metal–semiconductor junctions can exhibit negative differential resistance (NDR) at room temperature. The active component is a self-assembled monolayer of molecular dipoles (see schematic representation; X=CF₃, CN, H, OMe). A systematic change in the dipole moment of these molecules results in a corresponding systematic change in the NDR effect, thus establishing for the first time molecularly tunable NDR.

To overcome the limitations of using unstable imines in Staudinger cycloadditions to ketenes, aldehyde N,N-dialkylhydrazones 1 were used as stable imines. This strategy and a fine tuning of the auxiliary result in a straightforward synthesis of cycloadducts 2, deprotected β-lactams 3, and isoserines 4 (see scheme: a) Et₃N, toluene, ▵; b) 1. magnesium monoperoxyphthalate, 2. H₂, Pd/C; c) H⁺).

An increasingly targeted functional motif in organic synthesis is the ubiquitous chiral β-amino alcohol. A novel two-step approach for the regio- and stereoselective synthesis of a wide variety of 1,2-amino alcohols 4 involves the initial construction of chiral sulfamidates 3 from enantiopure diols 1, mediated by Burgess reagent (2, R = Me), followed by mild treatment with aqueous acid. Furthermore, the development of several new Burgess-type reagents 2 (R = CH₂Ph, CH₂-o-NO₂Ph, CH₂CH=CH₂, CH₂CCl₃) greatly extends the applications of this protocol.

Bucky balls and chains: The quadruple hydrogen-bonded fullerene array 1 was synthesized and fully characterized. In the highly dynamic polymeric state, the chemical integrity of the monomeric moiety is fully preserved, also with respect to its redox and UV/Vis behavior. Hence, 1 can potentially serve as a building block in supramolecular electronics.

A series of highly stereospecific reactions were used in the total synthesis of callipeltoside A (1), thus allowing the assignment of its absolute and relative configuration. a) Schmidt glycosylation, b) Ru Alder–ene coupling, c) Emmons–Wadsworth–Horner olefination, d) chiral auxiliary directed alkylation, e) asymmetric allylic Pd alkylation.

Synthesis in molten gallium provides access to a new class of boron-rich quaternary phases. Its first member, Tb_1.8C₂Si₈(B₁₂)₃, represents a new structure type in which B₁₂ icosahedra, eight Si atoms in a staggered ethane-like arrangement, and C₂ units are interconnected (see picture; red: Si, blue: B, black: C). The Tb sites have a partial occupation of about 60 %.

Appropriate gauche steric interactions between the N-substituents and the phosphanylmethyl groups (see picture, top right) in the novel 1,4-diphosphane ligands 1 having an imidazolidin-2-one backbone affect the conformational flexibility of the seven-membered chelate ring formed by coordination to a metal atom. Thus, Rh complexes of 1 are excellent catalysts for enantioselective hydrogenation of enamides (bottom, cod=cyclooacta-1,5-diene).

An intramolecular OH group can become much more effective in promoting phosphate hydrolysis when combined with multiple interactions in a model for the metallophosphatase active site (see picture; tacn=1,4,7-triazacyclononane).

Elaborate transcription of unimolecular stacks or helically bundled fibers of sugar-appended porphyrin gelators into silica by sol–gel polycondensation of tetraethoxysilane gives unique hollow silica fibers with a monodispersed 4-nm inner diameter (left picture) and huge helical silica bundles (right picture), respectively.

A nine-membered transition state characterizes the regioselective abstraction of the proton at C_5′ that leads to the orthoacetate 2 as the product. The alkoxy radical intermediate is obtained from the Glc-α1→4-Glc derivative 1 with (diacetoxyiodo)benzene (DIB) and iodine. A similar 1,8-hydrogen abstraction results when the alkoxy radical intermediate is generated under reductive conditions.

A niobium and pyridine salt of molybdo(vanado)phosphoric acid (see formula) leads to a catalyst that achieves excellent yield and productivity for both the conversion of propane into acrylic acid and n-butane into maleic acid. The catalyst is active under either hydrocarbon-rich or -lean reaction conditions.

A high level of enantioselectivity (78–93 % ee) and high yields (58–90 %) are obtained in the enantioselective nitroaldol reaction of nitromethane with several aldehydes when a novel dinuclear zinc catalyst is employed (see scheme).