Rhodium-Catalyzed Amination of Aromatic Olefins [1]

Summary.  The oxidative amination of styrene with secondary amines in the presence of cationic rhodium catalysts yields regiospecifically the corresponding anti-Markovnikov enamines. Styrene as the hydrogen acceptor gave concomitantly ethylbenzene. In the presence of 1,5-cyclooctadiene (cod) preferential reduction to cyclooctene takes place. The addition of cod reduces the rate of the reaction, but also the amount of ethylbenzene produced. Here, for the first time the ratio of enamine: ethylbenzene is > 1, which is favourable in case of more expensive styrene derivatives. A screening of various ligands for oxidative amination reveals that hemilabile 2-(ω-phosphino-n-alkyl)-pyridines are superior ligands for this reaction compared to simple alkyl and aryl phosphines. Received May 30, 2000. Accepted July 11, 2000     

Peels of buckyballs

The polymer analogous aromatization of double-stranded Diels-Alder polymers to give fully unsaturated, all-carbon ladder polymers by means of dehydration and dehydrogenation is described. The polymers obtained were characterized by solid state ¹³C NMR spectroscopy.     

Nucleosides and Nucleotides. Part 21. Synthesis of a Tridecanucleoside Dodecaphosphate Incorporating the Unnatural Base 2 (1 H)-Pyridone

The modified nucleoside Π_d (1) was used in the synthesis of the oligonucleotide d (TpTpΠpCpGpTpCpApApApApTpC). Diester methodology being unsatisfactory, the triester synthesis was investigated with the unnatural nucleoside. An improved method of nucleoside phosphorylation was developed for the synthesis of the fully-protected nucleotide 2e. This molecule could be cleanly and selectively deprotected, and allowed the efficient synthesis of the desired oligonucleotide.     

Screening Dyrk1A inhibitors by MALDI-QqQ mass spectrometry: systematic comparison to established radiometric,luminescence, and LC–UV–MS assays

Enzyme-catalyzed reactions play key roles in disease pathology, thus making them relevant subjects of therapeutic inhibitor screening experiments. Matrix-assisted laser desorption/ionization (MALDI) assays have been demonstrated to be able to replace established screening approaches. They offer increased sample throughput, but care must be taken to avoid instrumental bias from differences in ionization efficiencies. We compared a MALDI-triple-quadrupole (QqQ) method for the Dyrk1A peptide substrate woodtide to LC–MS, liquid chromatography with ultraviolet detection (LC–UV), luminescence, and radiometric assays. MALDI measurements were performed on a MALDI-QqQ instrument in the multiple-reaction monitoring mode. Different MALDI conditions were investigated to address whether matrix type, sample support, and MRM- or SIM-based detection conditions can be used to accommodate the molar responses of substrate peptide and its phosphorylated form. UV detection served as a reference method. The impact of MALDI matrix on IC₅₀ values was small, even considering that matrix preparations were used that are known to alleviate response differences. IC₅₀ values determined by MALDI were ca. 2-fold lower than those determined by LC–UV. Although MALDI generated lower ion yields for the phosphorylated peptide than for the peptide substrate, we found that a correction of compound potencies was readily possible using correction factors based on unbiased LC–UV results. A thorough method development delivered a robust assay with excellent performance (Z′ > 0.91) that was close to that seen for LC–UV.

Molecular surfaces: An advantageous starting point for the description of composition‐dependent viscosities applied to polymer solutions

The viscosity of polymer/solvent systems is modeled as a function of composition under the premises that the dissipation of energy is taking place at the molecular interfaces and that the friction between solvent and solute varies with composition due to a change in the flow mechanism (drainage of coils). The simple expression obtained in this manner contains three system‐specific parameters: a geometric factor γ, which accounts for the differences of the surface to volume ratios of the components; a hydrodynamic parameter α, which measures the friction between solute and solvent in the case of fully draining polymer coils; and β, which corrects for changes in the friction between unlike molecules resulting from collective motions owing to limited draining. Experimental data published for 12 poly(dimethylsiloxane)/pentamer mixtures can be represented quantitatively by this relation; moreover the knowledge of the three system‐specific parameters permits the calculation of intrinsic viscosities, and the molecular weight dependencies of γ and α yield the entangle molecular weight of the polymer. © 1999 John Wiley & Sons, Inc. J Polym Sci B: Polym Phys 37: 2221–2228, 1999     

Ce2Ti2SiO9 – das erste Titanat‐Silicat mit Cer – Präparation,Charakterisierung und Struktur

Ce₂Ti₂SiO₉ – the First Titanate‐Silicate with Cerium – Preparation, Characterization, and Structure Ce₂Ti₂SiO₉ was synthesized by chemical vapour transport in a temperature gradient (1050 °C → 900 °C) using Ce₂Ti₂O₇ as precursor and ammoniumchloride as transport agent. SiO₂ was provided from the wall of the used silica tubes. The chemical composition of the crystals was determined by EDX and EELS analysis. The structure of Ce₂Ti₂SiO₉ was determined and refined to R1 = 0.025, _wR2 = 0.067, respectively. The monoclinic phase crystallizes in the space group C2/m (No. 12) with a = 16.907(3) Å, b = 5.7078(8) Å, c = 7.574(2) Å, β = 111.38(2)° and Z = 4. Ti is octahedral, Si is tetrahedral surrounded by oxygen. Ce(1) is coordinated by eight, Ce(2) by ten oxygen atoms. There are edge connected chains of Ti(1)–O‐octahedra parallel [010] which are connected along [001] with each other by Ti(2)–O‐octahedra‐pairs and Si–O‐tetrahedra.     

Aluminiumorganyle mit pentakoordiniertem Aluminium-Atom: Synthese und Molekülstrukturen von [AlX2{2,6-(NEt2CH2)2C6H3}] (X = Cl,Et, H)

Aluminium Organyls with Pentacoordinate Aluminium: Syntheses and Molecular Structures of [AlX₂{2,6-(NEt₂CH₂)₂C₆H₃}] (X = Cl, Et, H) The reaction of [Li{2,6-(NEt₂CH₂)₂C₆H₃}]₂ with AlCl₃ or Et₂AlCl gives [AlX₂{2,6-(NEt₂CH₂)₂C₆H₃}] [X = Cl ( 1 ), Et ( 2 )] in good yield. 1 reacts with NaH in toluene to give [AlH₂{2,6-(NEt₂CH₂)₂C₆H₃}] ( 3 ). 1–3 were characterised spectroscopically (¹H, ¹³C, ²⁷Al n.m.r., i.r., mass spectroscopy). In solution at room temperature 1–3 exhibit dynamic behaviour. For 1 and 3 this can be frozen out below 278 K (¹H n.m.r.), indicating the presence of monomeric molecules with pentacoordinate Al at low temperature. Such species are also observed in the solid state as shown by an X-ray structure determination on 1 (monoclinic space group P2₁/n, a = 9.7325(14), b = 13.552(5), c = 28.858(7) Å, β = 99.57(2)°, V = 3753(2) ų, Z = 8, at 223(2) K) and 2 (monoclinic space group C2/c, a = 15.0045(12), b = 9.2986(8), c = 14.9955(12) Å, β =99.512(1)°, Z = 4, at 223(2) K).     

Polymer modified and stabilized cholesteric liquid crystal materials for flat panel application

Polymer dispersions, even in very low concentrations, can improve the performance of cholesteric liquid crystal materials necessary for their application in flat panel displays. Normal scattering mode, reverse scattering mode and reflective mode cholesteric liquid crystal materials are described. The roll of the polymer in each of these display modes is reviewed as are the unique electro-optic characteristics of the dispersions.