Synthesis of Redshifted Azobenzene Photoswitches by Late‐Stage Functionalization

Azobenzenes are versatile photoswitches that can be cycled between their trans‐ and cis‐configuration with light. The wavelengths required for this isomerization are substantially shifted from the UV to the visible range through tetra‐ortho‐chlorination. These halogenated azobenzenes display unique photoswitching characteristics, but their syntheses remain limited and inefficient. A new general method for the synthesis of tetra‐ortho‐chloro azobenzenes has been developed, which relies on direct palladium(II)‐catalyzed C?H activation of pre‐existing standard azobenzenes. This late‐stage functionalization has a broad substrate scope and can be used to create a variety of useful building blocks for the construction of more elaborate redshifted photopharmaceuticals. This method is used to prepare red‐ AzCA‐4 , a photoswitchable vanilloid that enables optical control of the cation channel TRPV1 with visible light.     

Total Synthesis of the Biphenyl Alkaloid (−)‐Lythranidine

A sequence comprising a ring‐closing alkyne metathesis of a propargyl alcohol derivative, followed by a ruthenium‐catalyzed redox isomerization of the derived cycloalkyne and a transannular aza‐Michael addition allowed the formation of the distinguishing piperidine‐metacyclophane framework of the Lythraceum alkaloid lythanidine in a few high‐yielding steps. This application attests to the excellent functional‐group tolerance of a molybdenum alkylidyne complex endowed with triphenylsilanolate ligands, which enabled the macrocyclization even in the presence of protic functionalities, and thus illustrates the power of contemporary catalytic acetylene chemistry for target‐oriented synthesis.     

Catalyst Activation,Deactivation, and Degradation in Palladium‐Mediated Negishi Cross‐Coupling Reactions

Pd‐mediated Negishi cross‐coupling reactions were studied by a combination of kinetic measurements, electrospray‐ionization (ESI) mass spectrometry, ³¹P NMR and UV/Vis spectroscopy. The kinetic measurements point to a rate‐determining oxidative addition. Surprisingly, this step seems to involve not only the Pd catalyst and the aryl halide substrate, but also the organozinc reagent. In this context, the ESI‐mass spectrometric observation of heterobimetallic Pd–Zn complexes [L₂PdZnR]⁺ (L=S‐PHOS, R=Bu, Ph, Bn) is particularly revealing. The inferred presence of these and related neutral complexes with a direct Pd–Zn interaction in solution explains how the organozinc reagent can modulate the reactivity of the Pd catalyst. Previous theoretical calculations by González‐Pérez et al. (Organometallics­ 2012 , 31, 2053) suggest that the complexation by the organozinc reagent lowers the activity of the Pd catalyst. Presumably, a similar effect also causes the rate decrease observed upon addition of ZnBr₂. In contrast, added LiBr apparently counteracts the formation of Pd–Zn complexes and restores the high activity of the Pd catalyst. At longer reaction times, deactivation processes due to degradation of the S‐PHOS ligand and aggregation of the Pd catalyst come into play, thus further contributing to the appreciable complexity of the title reaction.     

Development of a Multimatrix UHPLC-MS/MS Method for the Determination of Paracetamol and Its Metabolites in Animal Tissues

Paracetamol/acetaminophen (APAP) is one of the most popular pharmacologically active substances used as an analgesic and antipyretic agent. The metabolism of this drug occurs in the liver and leads to the formation of two main metabolites—glucuronic acid and sulfate derivate. Despite the wide use of paracetamol in veterinary medicine, a handful of analytical methods were published for the determination of paracetamol residues in animal tissues. In this paper, a multimatrix method has been developed for the determination of paracetamol and two metabolites—paracetamol sulfate (PS) and p-Acetamidophenyl β-D-glucuronide (PG). A validation procedure was conducted to verify method reliability and fit purpose as a tool for analyzing acetaminophen and metabolites in muscle, liver, lung, and kidney samples from different species of animals. Established validation parameters were in agreement with acceptable criteria laid by the European legislation. The initial significant matrix effect was successfully reduced by implementing an internal standard—4-Acetamidophenyl β-D-glucuronide-d3 (PG-d3, IS). The usefulness of the developed method was verified by analyzing samples from an experiment in which paracetamol was administrated to geese.     

The Role of Formamidine Groups in Dextran Based Nonviral Vectors for Gene Delivery on Their Physicochemical and Biological Characteristics

Dextran‐formamidine esters (dextran‐N‐[(dimethylamino)methylene]‐β‐alanine ester) with different degrees of substitution (0.45–0.92) are synthesized in an one‐pot reaction. Dextran (Mw 60 000 g mol^?1) is allowed to react with unprotected beta‐alanine and iminium chloride and investigated regarding the potential as gene delivery system for the transfer of plasmid DNA. With degrees of substitution ≥ 0.63 improved DNA binding with formation of enzymatically stable complexes of about 130–160 nm with negative surface charges are obtained. These physicochemical characteristics correlated with increasing transfection rates in CHO‐K1 cells determined by a luciferase reporter gene assay in dependency of the number of formamidine residues, N/P ratios and amount of DNA. The role of the number of formamidine groups is also highlighted by in vitro cyto‐ and hemotoxicity tests under the chosen conditions. These results indicate that dextran‐formamidine esters are a very promising material for the safe and efficient gene delivery.     

Thin liquid droplet on top of a rotating non-isothermal liquid layer

Wafers are usually coated by using spin-coating, where centrifugal forces are used to spread a droplet on the rotating wafer. This flow is unstable to the fingering instability, where several segments of the wetting front spread faster than the average, resulting in several fingers. The liquid flows via the existing fingers while the area in between does not get coated. A precise experimental investigation is problematic, as the droplet has to be placed quite exactly in the center of the rotation. Replacing the wafer by a second liquid should lead to a parabolic-shaped free interface and the droplet should center itself due to gravity. Here, we derive a model for the free interfaces of a thin droplet on top of a rotating liquid by taking gravity, centrifugal forces, friction, (thermo-)capillary and line forces into account. Additionally, this setup is the simplest example of multiple coating, where several free interfaces and contact lines influence each other. (© 2017 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim)