Helvetica Chimica Acta最新文献

Functional molecular electronics require molecular design that provides integrity and stability. In this work, we explored two types of single molecule devices differing in anchoring to the conducting leads. Single molecule conductance was measured by STM break junction method and the molecular conductor was composed of the redox active anthraquinone center (switching element) containing either 4-pyridyl or p-phenylene thioacetate anchoring groups. The experimental results were supported by quantum chemical charge transport calculations. Molecular junctions containing 4-pyridyl anchors displayed two stable configurations with conductance values of 4.9 nS and 20 pS, respectively. Molecules anchored via p-phenylene thioacetate groups led to one main junction configuration with conductance of 0.1 nS. Junctions employing 4-pyridyl anchoring groups had higher junction formation probability, which in combination with lower conductance makes them better candidates for switching purposes.

Oligoprolines adopt the well-defined polyproline II (PPII) helical conformation, even at a short chain length of six residues. These rigid peptides are versatile molecular rulers and scaffolds, yet there has been great difficulty in obtaining single crystals for X-ray crystal structure analysis to probe their conformation in the solid state. Here, we report a crystal structure of an oligoproline hexamer bearing an N-terminal terephthalic acid moiety. Comparison with that of a previously obtained crystal structure of a closely related hexaproline revealed influence of the terminal functional groups and the solvent on the crystal packing.

Pseudocontact shift NMR spectroscopy is a powerful tool in integrative structural biology. Conformationally rigid, enantiopure chelators with extremely high affinity to lanthanoids play a crucial role for this technique. In this context, we have synthesized enantiopure complexes of Y, Eu, Dy, Tm and Lu of (S)-H₂bbppn (H₂bbppn: N,N’-bis(2-hydroxybenzyl)-N,N’-bis(2-methylpyridyl)propylene-1,2-diamine) and investigated their NMR properties. Strongly paramagnetic ¹H-NMR spectra showing extremely large chemical shift ranges were obtained for Dy (2280 ppm), Tm (380 ppm) and Eu (68 ppm) and the anisotropy of the magnetic susceptibility was determined in all cases. The axial components of the susceptibility tensors for the (S)-bbppn complexes were determined as 225, −32 and 6×10⁻³² m³ for Dy, Tm and Eu. For (S)-[Y(bbppn)Cl], a single crystal structure was obtained providing atom coordinates for the isostructural series of lanthanoid compounds. It was demonstrated that in all cases rigid, enantiopure lanthanoid complexes were formed, providing an attractive new scaffold for potential conjugatable lanthanoid chelating tags.

The development of a safe, efficient and scalable continuous-flow-chemistry protocol for the O-difluoromethylation of two 3-hydroxypyridine building blocks is described. This example highlights that continuous flow chemistry has become firmly established within Novartis Biomedical Research, and when implemented appropriately can enable the continuous supply of material from the first realization of a potentially interesting intermediate within a discovery project all the way through to clinical evaluation.

We report herein an unprecedented and scalable synthetic method for the production of specific aminoquinoline compounds with potential applications as sweetness-enhancing agents. The first strategy involves the reaction of ortho-aminobenzonitriles with β-ketoesters in the presence of stoichiometric amounts of FeCl₃. Alternatively, the second strategy focuses on an enamine synthesis using alkyl acetoacetate and aminobenzonitrile. The resulting enaminonitrile is then converted into aminoquinoline under basic conditions. This newly developed process yields the desired compounds with an overall yield above 45 % over five steps with high purity.

The emergence of photoredox chemistry has enabled the development of previously inaccessible synthetic transformations. Despite the popularity of photoredox chemistry, commercial photoreactors remain expensive. As a result, most academic research groups resort to self-built, not easily replicable reactor designs, jeopardizing the reproducibility and accessibility of photochemical research. To address these issues, this work introduces an easily replicable and modular open-source photoreactor optimized for lab-scale photochemical synthesis. The reactor is operationally simple, operates consistently and reproducibly, and is inexpensive to manufacture. Our design integrates active temperature regulation, an exchangeable vial rack, and customizable light sources into a hybrid structure of machined aluminum, 3D-printed parts, and commercially available components. The open-source reactor with detailed 3D CAD files on GitHub is designed to make research in the field of photochemistry more accessible and reproducible.

Here we searched chemical space for small and novel diamond-like, 3D-shaped building blocks, which are very rare but highly valuable for medicinal chemistry because they can increase the natural product likeness of drug molecules and improve their selectivity, water solubility and metabolism. We explored the Generated DataBases (GDBs), which list all possible organic molecules up to a defined size, identified 162 norbornane containing ring systems related to the known trinorbornane, and took inspiration from its simpler substructure brexane to design brexazine as a new chiral and 3D-shaped piperazine analog. The synthesis of brexazine was realized in 11 steps and 11.5 % overall yield from a commercially available norbornene building block. These experiments illustrate the value of exploring chemical space from first principles to design new building blocks for drug discovery.

NanoLuc (NLuc) is one of the brightest luciferases and has been used in numerous reporter assays and sensor designs. However, its blue light emission (460 nm) is suboptimal for deep tissue imaging or some diagnostic application, and red shifting its emission is desirable. Here, we report the design and synthesis of novel furimazine and coelenterazine analogs conjugated with fluorophores to achieve red-shifted bioluminescence with NLuc and closely related H-Luc via a bioluminescence resonance energy transfer (BRET). Structural insights into NLuc-substrate interactions informed the functionalization of substrates. We report the synthesis of novel substrate-fluorophore conjugates. We show that red-shifted emission was achieved with high BRET ratios. The conjugates are less bright than the parent substrates, but our study highlights the importance of linker length and flexibility for optimizing bioluminescence emission reaching wavelength beyond 600 nm.

A highly soluble thiophene-based poly(tetrazine) polymer was prepared that can undergo inverse-electron-demand Diels-Alder (IEDDA) click reactions efficiently with different types of trans-cyclooctene (TCO) derivatives resulting in post-polymerization functionalization. The resulting pyridazines post-oxidation exhibited strong interactions with single-walled carbon nanotubes (SWNTs) and showed selectivity toward metallic SWNTs. The resulting dispersions were used to prepare thin films, whose sheet resistivity was measured. It was found that α-amino-ω-methoxy triethylene glycol (TEG) functionalized pyridazine dispersion film resulted in a lower sheet resistance by several orders of magnitude compared to the non-clicked tetrazine dispersion indicating better conductivity post-IEDDA. Furthermore, modification of the polymer backbone while bound to the SWNT was performed successfully, preserving the properties of the nanotubes.