Synthesis of 18F‐Labelled β‐Lactams by Using the Kinugasa Reaction

Owing to their broad spectrum of biological activities and low toxicity, β‐lactams are attractive lead structures for the design of novel molecular probes. However, the synthesis of positron emission tomography (PET)‐isotope‐labelled β‐lactams has not yet been reported. Herein, we describe the simple preparation of radiofluorinated β‐lactams by using the fast Kinugasa reaction between ¹⁸F‐labelled nitrone [¹⁸F]‐ 1 and alkynes of different reactivity. Additionally, ¹⁸F‐labelled fused β‐lactams were obtained through the reaction of a cyclic nitrone 7 with radiofluorinated alkynes [¹⁸F]‐ 6 a , b . Radiochemical yields of the Kinugasa reaction products could be significantly increased by the use of different Cu^I ligands, which additionally allowed a reduction in the amount of precursor and/or reaction time. Model radiofluorinated β‐lactam‐peptide and protein conjugates ([¹⁸F]‐ 10 and ¹⁸F‐labelled BSA conjugate) were efficiently obtained in high yield under mild conditions (aq. MeCN, ambient temperature) within a short reaction time, demonstrating the suitability of the developed method for radiolabelling of sensitive molecules such as biopolymers.     

Thermotropic Properties and Molecular Packing of Discotic Tristriazolotriazines with Rigid Substituents

Tristriazolotriazines with a threefold dialkoxyaryl substitution have been prepared by Huisgen reaction of cyanuric chloride and the corresponding tetrazoles. Although these dyes show a negative or inverted solvatochromism of the UV/Vis absorption, their fluorescence is strongly positive solvatochromic. These discotic fluorophores are also emissive in their solid state and in their broad liquid‐crystalline mesophase. The structural study indicates that the thermotropic properties and organization of these systems can be well tuned by the steric demand of the aryl groups. Depending on the substituents, the compounds showed either a pure crystalline phase or a highly complex helical superstructure with a characteristic liquid‐crystalline phase at elevated temperatures. Changing the steric demand of the attached aryls allowed controlling the discs arrangement within the columnar helix, which is of great importance for the molecular orbital overlap.     

On the theory of porous elastic rods

We consider the direct approach to the theory of rods, in which the thin body is modelled as a deformable curve with a triad of rigidly rotating orthonormal vectors attached to every material point. In this context, we employ the theory of elastic materials with voids to describe the mechanical behavior of porous rods. First, we derive the dynamical nonlinear field equations of the model. Then, in the framework of linear theory, we prove the uniqueness of the solution to the associated boundary-initial-value problem. We identify the relevant field quantities from the theory of directed curves by comparison with the three-dimensional equations of straight porous rods. Finally, for orthotropic and homogeneous rods, we determine the constitutive coefficients in terms of the three-dimensional elasticity constants by solving several problems in the two different approaches.     

Properties of water in the interfacial region of a polyelectrolyte bilayer adsorbed onto a substrate studied by computer simulations

We study the static and dynamic properties of water near a poly(styrene sulfonate)/poly(diallyldimethylammonium) (PSS/PDADMA) bilayer adsorbed onto a substrate by atomistic molecular dynamics simulations. Qualitative changes in the dynamics of water in the proximity of the adsorbed bilayer are observed - such as in the lateral diffusion, residence time and hydrogen-bonding lifetime - as compared with water in the presence of the bare substrate. Static properties of water are similarly influenced, and a high polarization of water molecules is found to be present surprisingly far from the adsorbed bilayer.     

Modulation of protein-protein interactions with small organic molecules

Many proteins exert their biological roles as components of complexes, and the functions of proteins are often determined by their specific interactions with other proteins. Because of the central importance of protein-protein interactions for cellular processes, the ability to interfere with specific protein-protein interactions provides a powerful means of influencing the function of selected proteins within the cell. Cell-permeable small organic modulators of protein-protein interactions are thus highly desirable tools both for the study of physiological cellular processes and for the treatment of numerous diseased states. Herein a number of protein-protein interactions that are considered to be pharmaceutical targets are presented, which will familiarize the reader with the strategies that have been employed for the successful identification of small molecule modulators of these protein-protein interactions. These encouraging examples suggest that combined research efforts in the areas of functional proteomics, assay development, and organic synthesis will open up novel possibilities for the treatment of human diseases in the future.     

Enantioselective Visible‐Light‐Mediated Formation of 3‐Cyclopropylquinolones by Triplet‐Sensitized Deracemization

3‐Allyl‐substituted quinolones undergo a triplet‐sensitized di‐π‐methane rearrangement reaction to the corresponding 3‐cyclopropylquinolones upon irradiation with visible light (λ=420 nm). A chiral hydrogen‐bonding sensitizer (10 mol %) was shown to promote the reaction enantioselectively (88–96 % yield, 32–55 % ee). Surprisingly, it was found that the enantiodifferentiation does not occur at the state of initial product formation but that it is the result of a deracemization event. The individual parameters that control the distribution of enantiomers in the photostationary state have been identified.     

Improving GC-MS screening analysis by functional-group-related silica gel fractionation of industrial wastewater extracts

The separation of the components of complex industrial waste water extracts according to their functional groups has been accomplished by use of small silica gel columns eluted with a hexane – dichloromethane – methanol gradient. The six fractions obtained covered a polarity range from aliphatic fatty acids to (aromatic) polyhydroxy and polyether compounds. Recovery of model compounds was between 75 and 105%. Used prior to GC-MS analysis this fractionation substantially enhances chromatographic resolution and facilitates peak identification. The procedure was exemplarily applied to an extract of anaerobically treated tannery waste water. Phenols, aromatic acids, and aromatic and aliphatic (poly)hydroxy acids, in the low ppm range, were determined as main constituents. Since fractionation extends the range of detection, trace substances such as chlorocresol, dichlorobenzoic acid, mercaptobenzothiazole, and mercaptoacetic acid were also detectable at the ppb level.     

Spectroscopic fingerprints of amine and imide functional groups in self-assembled monolayers.

The electronic structures of naphthalene tetracarboxylic diimide (NTCDI) and 1,4-bis(4,6-diamino-1,3,5-triazin-2-yl)benzene (BDG) monolayer assemblies grown on Au(111) are investigated by photoemission spectroscopy, X-ray absorption, and density functional theory. The different spectroscopic features in the absorption and core-level photoemission spectra are understood in terms of contributions from different core and molecular levels at N- and O-atom sites. This study provides clear spectroscopic fingerprints for amine and imide functional end groups, which drive the self-organization process in a number of planar, pi-conjugated molecular structures.     

Hydrogen-bond-mediated enantio- and regioselectivity in a Ru-catalyzed epoxidation reaction

A chiral epoxidation catalyst based on a tricyclic octahydro-1H-4,7-methanoisoindol-1-one scaffold, in which a hydrogen bonding site and the catalytically active ruthenium center are spatially separated, was synthesized. It was shown that epoxidation reactions in such a supramolecular catalyst occur with high enantio- and regioselectivity because the hydrogen bonds expose the substrate to the ruthenium porphyrin complex with a clear conformational preference. The epoxidation of 3-vinylquinolone proceeded in up to 95% ee (71% yield).