LongLarf

A novel microfluidic system for the cell-free production and screening of antimicrobial peptides for their membrane specificity is introduced. On the device, the peptides are cell-free produced within water-in-oil-in-water double emulsion droplets. Within each droplet, the peptides can interact with different liposomes, generating a membrane-specific fluorescent signal. The droplets can be analyzed via fluorescence microscopy of flow cytometry.

Abstract

The global surge in bacterial resistance against traditional antibiotics triggered intensive research for novel compounds, with antimicrobial peptides (AMPs) identified as a promising candidate. Automated methods to systematically generate and screen AMPs according to their membrane preference, however, are still lacking. We introduce a novel microfluidic system for the simultaneous cell-free production and screening of AMPs for their membrane specificity. On our device, AMPs are cell-free produced within water-in-oil-in-water double emulsion droplets, generated at high frequency. Within each droplet, the peptides can interact with different classes of co-encapsulated liposomes, generating a membrane-specific fluorescent signal. The double emulsions can be incubated and observed in a hydrodynamic trapping array or analyzed via flow cytometry. Our approach provides a valuable tool for the discovery and development of membrane-active antimicrobials.

Synlett
DOI: 10.1055/s-0041-1737323

Because of the versatility of chiral 1,5-dicarbonyl structural motifs, the development of stereoselective Michael additions of arylacetic acid derivatives to electron-deficient alkenes is an important challenge. Over recent decades, an array of enantio- and diastereoselective methods of this type have been developed through the use of chiral organocatalysts. In this article, three distinct strategies in this research area are highlighted. Catalytic generation of either a chiral iminium electrophile (iminium catalysis) or a chiral enolate nucleophile (Lewis­ base catalysis) has allowed the efficient construction of stereogenic C–C bonds. We also introduce a synergistic catalytic approach involving the merger of these two catalytic cycles that provides selective access to all four stereoisomers of products with vicinal stereocenters.1 Introduction2 Iminium Catalysis3 Lewis Base Catalysis4 Synergistic Organocatalysis5 Summary
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Georg Thieme Verlag KG Rüdigerstraße 14, 70469 Stuttgart, Germany

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Nature Chemistry, Published online: 05 January 2022; doi:10.1038/s41557-021-00834-8

Synthesis
DOI: 10.1055/a-1679-8205

Trifluoromethanesulfonic anhydride (Tf2O) is utilized as a strong electrophilic activator in a wide range of applications in synthetic organic chemistry, leading to the transient generation of a triflate intermediate. This versatile triflate intermediate undergoes nucleophilic trapping with diverse nucleophiles to yield novel compounds. In this review, we describe the features and applications of triflic anhydride in organic synthesis reported in the past decade, especially in amide, sulfoxide, and phosphorus oxide chemistry through electrophilic activation. A plausible mechanistic pathway for each important reaction is also discussed.1 Introduction2 Amide Chemistry2.1 Carbon Nucleophiles2.2 Hydrogen Nucleophiles2.3 Nitrogen Nucleophiles2.4 Oxygen and Sulfur Nucleophiles2.5 hosphorus Nucleophiles2.6 A Vilsmeier-Type Reagent2.7 Umpolung Reactivity in Amides3 Sulfoxide Chemistry3.1 Oxygen Nucleophiles3.2 Carbon Nucleophiles3.3 Nitrogen Nucleophiles3.4 Thionium Reagents4 Phosphorus Chemistry4.1 Hendrickson’s Reagent4.2 Diaryl Phosphine Oxides4.3 Phosphonates, Phosphates and Phosphinates5 Conclusion and Outlook
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Georg Thieme Verlag KG Rüdigerstraße 14, 70469 Stuttgart, Germany

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Synthesis
DOI: 10.1055/a-1684-5552

In recent years, borane-based frustrated Lewis pairs have proved to be efficient hydrogenation catalysts and they have become an alternative to transition-metal-based systems. The hydrogen activation by classic FLPs leads to a protonated Lewis base and a borohydride. Consequently, hydrogenations catalyzed by classic FLPs consist of stepwise hydride transfer reactions and protonations (or vice versa). More recently, systems that operate via an initial hydroboration have allowed the substrate scope for FLP-catalyzed hydrogenations to be extended. In this review, hydrogenations of organic substrates catalyzed by borane­-based frustrated Lewis pairs are discussed. Emphasis is given to the mechanistic aspects of these catalytic reactions.1 Introduction2 FLP-Catalyzed Hydrogenation of Polarized Double Bonds2.1 Hydrogenation of Michael Acceptors by FLPs2.2 Asymmetric Hydrogenation of Polarized Double Bonds2.3 Hydrogenation of Arenes and N-Heterocycles3 Hydrogenation of Unactivated Olefins and Alkynes3.1 Hydrogenation of Olefins and Alkynes by an Initial Hydroboration4 Summary and Outlook
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Georg Thieme Verlag KG Rüdigerstraße 14, 70469 Stuttgart, Germany

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The big reveal: Hydrodehalogenation of 35 different aryl halides (Ar−I, Ar−Br, and Ar−Cl) is performed using a heterogeneous nickel catalyst (Ni-phen@TiO₂-800) and molecular hydrogen. This work represents an effective strategy for converting thermally and chemically inert hazardous compounds into their less noxious congeners. Characterization of the catalyst reveals nickel nanoparticles covered with N-doped carbon layers.

Abstract

Hydrodehalogenation is an effective strategy for transforming persistent and potentially toxic organohalides into their more benign congeners. Common methods utilize Pd/C or Raney-nickel as catalysts, which are either expensive or have safety concerns. In this study, a nickel-based catalyst supported on titania (Ni-phen@TiO₂-800) is used as a safe alternative to pyrophoric Raney-nickel. The catalyst is prepared in a straightforward fashion by deposition of nickel(II)/1,10-phenanthroline on titania, followed by pyrolysis. The catalytic material, which was characterized by SEM, TEM, XRD, and XPS, consists of nickel nanoparticles covered with N-doped carbon layers. By using design of experiments (DoE), this nanostructured catalyst is found to be proficient for the facile and selective hydrodehalogenation of a diverse range of substrates bearing C−I, C−Br, or C−Cl bonds (>30 examples). The practicality of this catalyst system is demonstrated by the dehalogenation of environmentally hazardous and polyhalogenated substrates atrazine, tetrabromobisphenol A, tetrachlorobenzene, and a polybrominated diphenyl ether (PBDE).

By the combination of DABCO and acetic acid under solvent-free conditions, the Morita-Baylis-Hillman reaction rate of both activated and non-activated aldehydes increased significantly. The disclosed procedure is operationally simple and is compatible with a wide array of both nucleophilic and electrophilic reaction partners.

Abstract

The Morita-Baylis-Hillman (MBH) reaction has been stablished as an important C−C bond-forming transformation between carbonyl-containing compounds and activated olefins. However, the slow reaction rate usually observed with electron-rich electrophilic partners hinders a more widespread use of this reaction. In order to overcome this drawback, the effects of several Brønsted acids on the rate of DABCO-catalyzed MBH reactions were evaluated. The protocol is operationally simple, involving neat and open-flask conditions, and is compatible with a wide range of reagents. We suggest a general acid catalysis mechanism to be responsible for the rate increase. The synthetic versatility of the MBH adducts is exemplified with a two-steps diastereoselective synthesis of the natural product (±)-sitophilure. We hope this acid-mediated protocol to have potential use as a general methodology for the MBH reaction.