Pd-catalyzed regiocontrolled Sonogashira and Suzuki cross-coupling reaction of 3,6-dihalogenoimidazo[1,2-a]pyridines: one-pot double-coupling approach

New and efficient regioselective Sonogashira and Suzuki-Miyaura palladium-catalyzed coupling reactions of 3,6-dihalogenoimidazo[1,2-a]pyridines followed by another cross-coupling has been successfully developed. Various solvents, palladium species and bases were tested. Scope and limitations of this regiocontrolled palladium-catalyzed reaction were investigated. The synthesis of 3,6-disubstituted imidazo[1,2-a]pyridine derivatives using one-pot regioselective double-coupling approach was developed. This procedure affords convergent syntheses of polysubstituted compounds in high yields in a very few steps.     

Current perspectives and recommendations for the development of mass spectrometry methods for the determination of allergens in foods

Allergen detection and quantification is an essential part of allergen management as practiced by food manufacturers. Recently, protein MS methods (in particular, multiple reaction monitoring experiments) have begun to be adopted by the allergen detection community to provide an alternative technique to ELISA and PCR methods. MS analysis of proteins in foods provides additional challenges to the analyst, both in terms of experimental design and methodology: (1) choice of analyte, including multiplexing to simultaneously detect several biologically relevant molecules able to trigger allergic reactions; (2) choice of processing stable peptide markers for different target analytes that should be placed in publicly available databases; (3) markers allowing quantification (e.g., through standard addition or isotopically labeled peptide standards); (4) optimization of protease digestion protocols to ensure reproducible and robust method development; and (5) effective validation of methods and harmonization of results through the use of naturally incurred reference materials spanning several types of food matrix.     

Allosteric regulation of protein kinase PKCζ by the N-terminal C1 domain and small compounds to the PIF-pocket

Protein kinases are key mediators of cellular signaling, and therefore, their activities are tightly controlled. AGC kinases are regulated by phosphorylation and by N- and C-terminal regions. Here, we studied the molecular mechanism of inhibition of atypical PKCζ and found that the inhibition by the N-terminal region cannot be explained by a simple pseudosubstrate inhibitory mechanism. Notably, we found that the C1 domain allosterically inhibits PKCζ activity and verified an allosteric communication between the PIF-pocket of atypical PKCs and the binding site of the C1 domain. Finally, we developed low-molecular-weight compounds that bind to the PIF-pocket and allosterically inhibit PKCζ activity. This work establishes a central role for the PIF-pocket on the regulation of PKCζ and allows us to envisage development of drugs targeting the PIF-pocket that can either activate or inhibit AGC kinases.     

Cytochromes P450 as useful biocatalysts: addressing the limitations

Cytochrome P450 monooxygenases (P450s or CYPs) are a unique family of enzymes which are capable of catalysing the regio- and stereospecific oxidation of non-functionalised hydrocarbons. Despite the enormous synthetic potential of P450s, these enzymes have yet to be extensively employed for research purposes or in industry. Lack of stability, low activity, narrow substrate specificity, expensive cofactor requirements, limited solvent tolerance and electron supply are some of the main reasons why the academic and industrial implementation of these important biocatalysts remains a challenge. Considering the significance of P450s, many research groups have focused on improving their properties in an effort to make more robust catalysts with broad synthetic applications. This article focuses on some of the factors that have limited the exploitation of P450s and explores some of the significant steps that have been taken towards addressing these limitations.     

Propagation Kinetics of Isoprene Radical Homopolymerization Derived from Pulsed Laser Initiated Polymerizations

The propagation kinetics of isoprene radical polymerizations in bulk and in solution are investigated via pulsed laser initiated polymerizations and subsequent polymer analyses via size‐exclusion chromatography, the PLP‐SEC method. Because of low polymerization rate and high volatility of isoprene, the polymerizations are carried out at elevated pressure ranging from 134 to 1320 bar. The temperatures are varied between 55 and 105 °C. PLP‐SEC yields activation parameters of k_p (Arrhenius parameters and activation volume) over a wide temperature and pressure range that allow for the calculation of k_p at technically relevant ambient pressure conditions. The k_p values determined are very low, e.g., 99 L mol^?1 s^?1 at 50 °C, which is even lower than the corresponding value for styrene polymerizations. The presence of a polar solvent results in a slight increase of k_p compared to the bulk system. The k_p values reported are important for determining rate coefficients of other elemental reactions from coupled parameters as well as for modeling isoprene free‐radical polymerizations and reversible deactivation radical polymerization with respect to tailored polymer properties and optimizing the polymerization processes.     

Intramolecular Borylation via Sequential B−Mes Bond Cleavage for the Divergent Synthesis of B,N,B‐Doped Benzo[4]helicenes

New symmetric and unsymmetric B,N,B‐doped benzo[4]helicenes 3 – 6 a/b have been achieved in good yields, using a three‐step process, starting from N(tolyl)₃ in a highly divergent manner (7 examples). A borinic acid functionalized 1,4‐B,N‐anthracene 1 was found to display unprecedented reactivity, acting as a convenient and highly effective precursor for selective formation of bromo‐substituted B,N,B‐benzo[4]helicenes 2 a / 2 b via intramolecular borylation and sequential B?Mes bond cleavage in the presence of BBr₃. Subsequent reaction of 2 a / 2 b with Ar‐Li provided a highly effective toolbox for the preparation of symmetrically/unsymmetrically functionalized B,N,B‐helicenes. Their high photoluminescence quantum yields along with the small ΔE_ST suggest their potential as thermally activated delayed fluorescence (TADF) emitters for organic light‐emitting diodes (OLEDs).     

Making and Breaking Leupeptin Protease Inhibitors in Pathogenic Gammaproteobacteria

Leupeptin is a bacterial small molecule that is used worldwide as a protease inhibitor. However, its biosynthesis and genetic distribution remain unknown. We identified a family of leupeptins in gammaproteobacterial pathogens, including Photorhabdus, Xenorhabdus, and Klebsiella species, amongst others. Through genetic, metabolomic, and heterologous expression analyses, we established their construction by discretely expressed ligases and accessory enzymes. In Photorhabdus species, a hypothetical protein required for colonizing nematode hosts was established as a new class of proteases. This enzyme cleaved the tripeptide aldehyde protease inhibitors, leading to the formation of “pro‐pyrazinones” featuring a hetero‐tricyclic architecture. In Klebsiella oxytoca, the pathway was enriched in clinical isolates associated with respiratory tract infections. Thus, the bacterial production and proteolytic degradation of leupeptins can be associated with animal colonization phenotypes.     

Enantioselective Synthesis of N–C Axially Chiral Compounds by Cu-Catalyzed Atroposelective Aryl Amination

N−C axially chiral compounds have emerged recently as appealing motifs for drug design. However, the enantioselective synthesis of such molecules is still poorly developed and surprisingly no metal-catalyzed atroposelective N-arylations have been described. Herein, we disclose an unprecedented Cu-catalyzed atroposelective N−C coupling that proceeds at room temperature. Such mild reaction conditions, which are a crucial parameter for atropostability of the newly generated products, are operative thanks to the use of hypervalent iodine reagents as a highly reactive coupling partners. A large panel of the N−C axially chiral compounds was afforded with very high enantioselectivity (up to >99 % ee) and good yields (up to 76 %). Post-modifications of thus accessed atropisomeric compounds allows further expansion of the diversity of these appealing compounds.     

Recent advances in the development of graphene-based surface plasmon resonance (SPR) interfaces

Surface plasmon resonance (SPR) is a powerful technique for measurement of biomolecular interactions in real-time in a label-free environment. One of the most common techniques for plasmon excitation is the Kretschmann configuration, and numerous studies of ligand–analyte interactions have been performed on surfaces functionalized with a variety of biomolecules, for example DNA, RNA, glycans, proteins, and peptides. A significant limitation of SPR is that the substrate must be a thin metal film. Post-coating of the metal thin film with a thin dielectric top layer has been reported to enhance the performance of the SPR sensor, but is highly dependent on the thickness of the upper layer and its dielectric constant. Graphene is a single-atom thin planar sheet of sp2 carbon atoms perfectly arranged in a honeycomb lattice. Graphene and graphene oxide are good supports for biomolecules because of their large surface area and rich π conjugation structure, making them suitable dielectric top layers for SPR sensing. In this paper, we review some of the key issues in the development of graphene-based SPR chips. The actual challenges of using these interfaces for studying biomolecular interactions will be discussed and the first examples of the use of graphene-on-metal SPR interfaces for biological sensing will be presented.     

High-resolution atmospheric pressure infrared laser desorption/ionization mass spectrometry imaging of biological tissue

An atmospheric pressure laser desorption/ionization mass spectrometry imaging ion source has been developed that combines high spatial resolution and high mass resolution for the in situ analysis of biological tissue. The system is based on an infrared laser system working at 2.94 to 3.10 μm wavelength, employing a Nd:YAG laser-pumped optical parametrical oscillator. A Raman-shifted Nd:YAG laser system was also tested as an alternative irradiation source. A dedicated optical setup was used to focus the laser beam, coaxially with the ion optical axis and normal to the sample surface, to a spot size of 30 μm in diameter. No additional matrix was needed for laser desorption/ionization. A cooling stage was developed to reduce evaporation of physiological cell water. Ions were formed under atmospheric pressure and transferred by an extended heated capillary into the atmospheric pressure inlet of an orbital trapping mass spectrometer. Various phospholipid compounds were detected, identified, and imaged at a pixel resolution of up to 25 μm from mouse brain tissue sections. Mass accuracies of better than 2 ppm and a mass resolution of 30,000 at m/z?=?400 were achieved for these measurements.