Helvetica Chimica Acta最新文献

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.

Atropisomeric scaffolds offer the possibility to predictably position donor and acceptor groups in specific spatial relationships. Herein, a configurationally stable 1,2’-binaphthyl linkage was employed to place a ruthenium(II) tris-(2,2’-bipyridine) complex in proximity to an anthracene moiety to explore how photoinduced triplet-triplet energy transfer can proceed across this type of molecular bridge. An efficient synthesis provided the ruthenium(II)-anthracene dyad with high yields, which allowed to determine characteristic features for the intramolecular energy transfer.

4-Aryl-1,4-dihydropyridines are prevalent pharmacophores and versatile building blocks in medicinal and synthetic chemistry. Herein, we demonstrated a mechanistically distinct radical-radical cross-coupling approach to 4-aryl-1,4-dihydropyridines, via direct C4−H arylation of 1,4-dihydropyridines with readily available cyanoarenes. This mild protocol is initiated by the direct photoexcitation of 1,4-dihydropyridines, eliminating the need for expensive photocatalysts and enabling operation under ambient air conditions.

A recurring misconception in some textbooks and research papers has led to an abandonment of fundamental physical laws when describing a subset of acid-base equilibria, especially regarding the role of the solvent. In the specific case of the autoprotolysis of water, experiments and theoretical calculations prove that the K_w of water at 25 °C, 1.00×10⁻¹⁴, is identical to its acid ionization constant, K_a. Nevertheless, several articles have been published erroneously purporting to give theoretical proof that the K_a of water is 10^−15.743 (1.81×10⁻¹⁶) and that the K_a of the aqueous proton (hydronium ion) is 55.3 rather than 1.00. Here we argue that using the incorrect numbers has pedagogical implications beyond those of a simple error. Arguments for the incorrect K_a and pK_a values require a misapplication of Henry's law and violate long-standing methods that use Raoult's law and the conservation of matter to describe the behavior of solutions. As a result, chemistry students may be asked to accept one set of physical principles in one course and another set in another course. Here we argue for adherence to fundamental physical laws governing solution equilibria as applied to the autoprotolysis of water and all aqueous acid base equilibria.

Chiral polycyclic aromatic hydrocarbons with monkey saddle topology are a fascinating class of negatively curved compounds. To make the monkey-saddles valuable building blocks for chirality-assisted synthesis (CAS) approaches, the inversion barriers between the two possible enantiomers need to be high enough to prevent interconversion under CAS conditions. By molecular editing, aza monkey saddles were converted to the corresponding chromene monkey saddles that are configurationally stable even at temperatures of 220 °C over a period of 47 days. Their structures were studied by single X-ray diffraction and enantiomers were separated to study the chiroptical properties. Furthermore, mechanistic assumptions of the formation of the chromene monkey saddles by DFT calculations are discussed.

Herein, we detail an extension of our research on the synthesis of a small library of furanoheliangolides and the characterization of the covalent interaction between goyazensolide and IPO5. Using a build-couple-pair strategy, we assembled a small library of germacrene-type lactones and diversified them into eight groups of structurally different analogues. The germacrene lactones were synthesized using Sonogashira coupling and Barbier-type macrocyclization, while the furanoheliangolides were further elaborated through gold-catalyzed transannulation followed by esterification. This synthetic approach enabled the generation of a goyazensolide alkyne-tagged cellular probe, which was used to identify the selective binding between goyazensolide and the oncoprotein importin-5 (IPO5). Mass spectrometry analysis of the proteolytic digest from the reaction between the goyazensolide probe and a recombinant IPO5 indicated a covalent engagement at Cys560 of IPO5, which was confirmed by site-directed mutagenesis.

Imido ligand is a ubiquitous motif in organometallic chemistry, serving roles spanning from ancillary ligands to reactive sites. The nature of M=N bond is highly depended on the metal centres and their d-electron configuration, with late transition metal (TM) imido complexes exhibiting contrasting features when compared to their early TM analogues. Envisioning to uncover general electronic descriptor for the nature of imido ligands, we computationally investigate the solid-state ¹⁵N NMR signatures of late TM imido complexes with various central metals, geometries and d-electron counts, and compare them against these of the corresponding early TM systems. The spectroscopic signatures are mostly driven by the presence of filled, π-symmetry orbitals in late TM imido complexes, suggesting the development of high-lying π(M=N) and low-lying σ/σ^*(M=N) orbitals. This contrasts with what is observed for the reported early TM systems, for which high-lying σ-type orbitals determine the NMR signature. Noteworthily, Ni- and Pd-imido complexes with formal d¹⁰ configurations exhibit highly asymmetric nitrogen-15 NMR signature with extremely deshielded principal components, because of the presence of filled, high-lying antibonding π^*(M=N) orbitals, consistent with their high reactivity. The sensitive response of ¹⁵N NMR signature to the nature of metal sites further highlights that chemical shift is a useful reactivity descriptor.