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Dual‐Functionalisation of Fluorophores for the Preparation of Targeted and Selective Probes

Par / 14 septembre 2020 / Non classé
Dual‐Functionalisation of Fluorophores for the Preparation of Targeted and Selective Probes

The use of fluorescent probes for studying biological systems has been crucial to our understanding of health and disease, with targeted, selective sensors providing us with highly specific biological information. This Minireview gives an overview of the different methods used to functionalise commonly used fluorophores with both sensing and targeting groups. Key directions for future research in this field are also presented.

Abstract

A key current challenge in biological research is the elucidation of the that roles chemicals and chemical reactions play in cellular function and dysfunction. Of the available cellular imaging techniques, fluorescence imaging offers a balance between sensitivity and resolution, enabling the cost‐effective and rapid visualisation of model biological systems. Importantly, the use of responsive fluorescent probes in conjunction with ever‐advancing microscopy and flow cytometry techniques enables the visualisation, with high spatiotemporal resolution, of both specific chemical species and chemical reactions in living cells. Ideal responsive fluorescent probes are those that contain a fluorophore tethered to both a sensing unit, to ensure selectivity of response, and a targeting group, to control the sub‐cellular localisation of the probe. To date, probes that are both targeted and selective are relatively rare and most localised probes are discovered serendipitously rather than by design. A challenge in this field is therefore the identification of suitable fluorophore scaffolds that can be readily attached to both sensing and targeting groups. Here we review current strategies for dual‐functionalisation of fluorophores, highlighting key examples of targeted, responsive probes.

Wiley: Angewandte Chemie International Edition: Table of Contents
Authors: Natalie Trinh, Katrina A. Jolliffe, Elizabeth J. New
doi.org/10.1002/anie.202007673

Hetero‐Diels–Alder Cycloaddition with RAFT Polymers as Bioconjugation Platform

Par / 14 septembre 2020 / Non classé
Hetero‐Diels–Alder Cycloaddition with RAFT Polymers as Bioconjugation Platform

Already there: Polymers obtained by RAFT polymerization with thiocarbonylthio transfer agents possessing an electron‐deficient carbon–sulfur double bond undergo bioconjugation by hetero‐Diels–Alder cycloaddition, without the need for other reactive end groups. This ligation occurs over a few hours, at ambient temperature and near‐neutral pH, without any catalyst required.

Abstract

We introduce the bioconjugation of polymers synthesized by RAFT polymerization, bearing no specific functional end group, by means of hetero‐Diels–Alder cycloaddition through their inherent terminal thiocarbonylthio moiety with a diene‐modified model protein. Quantitative conjugation occurs over the course of a few hours, at ambient temperature and neutral pH, and in the absence of any catalyst. Our technology platform affords thermoresponsive bioconjugates, whose aggregation is solely controlled by the polymer chains.

Wiley: Angewandte Chemie International Edition: Table of Contents
Authors: Ana Beloqui, Shivshankar R. Mane, Marcel Langer, Mathias Glassner, Dennis M. Bauer, Ljiljana Fruk, Christopher Barner‐Kowollik, Guillaume Delaittre
doi.org/10.1002/anie.202005747

Bioinspired Divergent Oxidative Cyclizations of Geissoschizine: Total Synthesis of (–)‐17‐nor‐Excelsinidine, (+)‐16‐epi‐Pleiocarpamine, (+)‐16‐Hydroxymethyl‐Pleiocarpamine and (+)‐Taberdivarine H

Par / 14 septembre 2020 / Non classé
Bioinspired Divergent Oxidative Cyclizations of Geissoschizine: Total Synthesis of (–)‐17‐nor‐Excelsinidine, (+)‐16‐epi‐Pleiocarpamine, (+)‐16‐Hydroxymethyl‐Pleiocarpamine and (+)‐Taberdivarine H

To synthesize excelsinidines and mavacurans alkaloids, bio‐inspired oxidative cyclizations of (+)‐geissochizine and analogues mediated by KHMDS/I2 were studied. Applied to geissoschizine, the N4–C16 bond formation led to excelsinidines core. Quaternization of the aliphatic nitrogen was necessary to access the mavacurans core (N1–C16 bond). Alternatively, 17‐nor‐excelsinidine was synthetized via an intramolecular nucleophilic substitution of an α‐chlorolactam.

We report a full account of our efforts towards bioinspired oxidative cyclizations of geissochizine and analogs to mimic the biosynthesis of the mavacuran, akuammilan, and excelsinidine groups of monoterpene indole alkaloids. The construction of the A,B,C,D ring system of geissoschizine was first achieved by merging two known syntheses of this alkaloid. Modified Ma’s oxidative conditions (KHMDS/I2) applied directly to geissoschizine induced formation of the N4–C16 bond encountered in the excelsinidines core. Identical conditions applied to C16‐dimethylmalonate‐containing N4‐quaternized substrates ended in the formation of the mavacurans core (N1–C16 bond). With this unified oxidative cyclization strategy: (–)‐17‐nor‐excelsinidine, (+)‐16‐epi‐pleiocarpamine, (+)‐16‐hydroxymethyl‐pleiocarpamine, 16‐formyl‐pleiocarpamine and (+)‐taberdivarine H were synthetized. We also report a shortened total synthesis of 16‐epi‐pleiocarpamine compared to our preliminary communication from a C16‐monoester analog. Alternatively, 17‐nor‐excelsinidine was synthesized via an intramolecular nucleophilic substitution of a 7‐membered ring α‐chlorolactam prepared from 16‐desformyl‐geissoschizine.

Wiley: European Journal of Organic Chemistry: Table of Contents
Authors: Maxime Jarret, Aurélien Tap, Victor Turpin, Natacha Denizot, Cyrille Kouklovsky, Erwan Poupon, Laurent Evanno, Guillaume Vincent
doi.org/10.1002/ejoc.202000962

Biosynthetically Relevant Reactivity of Polyneuridine Aldehyde

Par / 14 septembre 2020 / Non classé
Biosynthetically Relevant Reactivity of Polyneuridine Aldehyde

The reactivity of polyneuridine aldehyde, the first biosynthetic member of the sarpagan‐type alkaloids, was studied. Retro‐biomimetic formation of corynan‐type alkaloids (e.g. geissoschizine) and the biomimetic formation of quebrachidine, the first biosynthetic parent of the ajamalan‐type alkaloids were performed. In addition, an unusual intramolecular carbonyl‐ene‐reaction involving the indole nucleus delivered an original polycyclic scaffold.

Polyneuridine aldehyde is a key intermediate in the biosynthetic routes of monoterpene indole alkaloids family of natural products. The molecule is the first biosynthetic member of the sarpagan‐type alkaloids and is an entry to the ajmalan‐type and alstophyllan‐type alkaloids. Complementary to the recent description of polyneuridine aldehyde, its reactivity was studied. Retro‐biomimetic formation of corynan‐type alkaloids (e.g., geissoschizine) and the biomimetic formation of quebrachidine, the first biosynthetic parent of the ajamalan‐type alkaloids, were performed. In addition, an unusual intramolecular carbonyl‐ene‐reaction involving the indole nucleus delivered an original polycyclic scaffold.

Wiley: European Journal of Organic Chemistry: Table of Contents
Authors: Victor Turpin, Erwan Poupon, Jean‐Christophe Jullian, Laurent Evanno
doi.org/10.1002/ejoc.202000963

Mass‐Spectrometric Imaging of Electrode Surfaces—a View on Electrochemical Side Reactions

Par / 14 septembre 2020 / Non classé
Mass‐Spectrometric Imaging of Electrode Surfaces—a View on Electrochemical Side Reactions

In‐depth understanding of electrochemical side reactions is essential for the optimization of new electrode materials or electrochemical cell geometry. The presented MALDI‐MS imaging approach offers a fast and elegant way to detect electrochemical byproducts on the electrode surface and provides additional information about molecular mass and spatial distribution.

Abstract

Electrochemical side reactions, often referred to as “electrode fouling”, are known to be a major challenge in electro‐organic synthesis and the functionality of modern batteries. Often, polymerization of one or more components is observed. When reaching their limit of solubility, those polymers tend to adsorb on the surface of the electrode, resulting in a passivation of the respective electrode area, which may impact electrochemical performance. Here, matrix‐assisted laser‐desorption/ionization mass spectrometry (MALDI‐MS) is presented as valuable imaging technique to visualize polymer deposition on electrode surfaces. Oligomer size distribution and its dependency on the contact time were imaged on a boron‐doped diamond (BDD) anode of an electrochemical flow‐through cell. The approach allows to detect weak spots, where electrode fouling may take place and provides insight into the identity of side‐product pathways.

Wiley: Angewandte Chemie International Edition: Table of Contents
Authors: Jens Fangmeyer, Arne Behrens, Barbara Gleede, Siegfried R. Waldvogel, Uwe Karst
doi.org/10.1002/anie.202010134

Synthesis of Diverse Aromatic Ketones through C−F Cleavage of Trifluoromethyl Group

Par / 17 septembre 2020 / fluorine, Non classé
Synthesis of Diverse Aromatic Ketones through C−F Cleavage of Trifluoromethyl Group

Make the cut: An efficient synthetic method of aromatic ketones through C−F cleavage of trifluoromethyl group is disclosed. The high functional group tolerance of the transformation and the remarkable stability of trifluoromethyl group in various reactions enabled multi‐substituted aromatic ketone synthesis in an efficient route involving useful transformations such as ortho‐lithiation, aryne chemistry, and cross‐couplings.

Abstract

An efficient synthetic method of aromatic ketones through C−F cleavage of trifluoromethyl group is disclosed. The high functional group tolerance of the transformation and the remarkable stability of trifluoromethyl group in various reactions enabled multi‐substituted aromatic ketone synthesis in an efficient route involving useful transformations such as ortho‐lithiation, aryne chemistry, and cross‐couplings.

Wiley: Chemistry – A European Journal: Table of Contents
Authors: Mai Ikeda, Tsubasa Matsuzawa, Takamoto Morita, Takamitsu Hosoya, Suguru Yoshida
chemistry-europe.onlinelibrary.wiley.com/doi/abs/10.1002/chem.202001816

Nickel‐Catalyzed Amination of (Hetero)aryl Halides Facilitated by a Catalytic Pyridinium Additive

Par / 14 septembre 2020 / Non classé
Nickel‐Catalyzed Amination of (Hetero)aryl Halides Facilitated by a Catalytic Pyridinium Additive

Pyridinium gives a hand to Ni: A Ni‐catalyzed amination has been developed as an efficient synthetic tool of promising potential for application in industry. A diverse selection of (hetero)aryl halides were coupled successfully with primary and secondary alkyl amines, and anilines in good to excellent yields. This coupling features low NiCl2‐dtbbpy loadings, catalytic amounts of Zn metal and a pyridinium additive, and an organic base (see scheme).

Abstract

An efficient and operationally simple Ni‐catalyzed amination protocol has been developed. This methodology features a simple NiII salt, an organic base and catalytic amounts of both a pyridinium additive and Zn metal. A diverse number of (hetero)aryl halides were coupled successfully with primary and secondary alkyl amines, and anilines in good to excellent yields. Similarly, benzophenone imine gave the corresponding N‐arylation product in an excellent yield.

Wiley: Chemistry – A European Journal: Table of Contents
Authors: Dongyang Han, Sasa Li, Siqi Xia, Mincong Su, Jian Jin
chemistry-europe.onlinelibrary.wiley.com/doi/abs/10.1002/chem.202002800

HFO‐1234yf as a CF3‐Building Block: Synthesis and Chemistry of CF3‐Ynones

Par / 14 septembre 2020 / Non classé
HFO‐1234yf as a CF3‐Building Block: Synthesis and Chemistry of CF3‐Ynones

Reaction of the inexpensive refrigerant gas HFO‐1234yf with strong base leads to elimination of HF to give an alkynide that can be trapped to form CF3‐ynones, which are highly reactive electrophiles for rapid and clean Michael‐type additions. With dinucleophiles, various CF3‐heterocycles can be synthesised including the blockbuster drug celecoxib.

Reaction of low cost, readily available 4th generation refrigerant gas 2,3,3,3‐tetrafluoropropene (HFO‐1234yf) with lithium diisopropylamide (LDA) leads to formation of lithium 3,3,3‐trifluoropropynide, addition of which to a range of aldehydes formed CF3‐alkynyl alcohol derivatives on multigram scale, which were oxidised using Dess–Martin periodinane (DMP) to give substituted CF3‐ynones with minimal purification required. Michael‐type additions of alcohol and amine nucleophiles to CF3‐ynones are rapid and selective, affording a range of CF3‐enone ethers and enaminones in excellent yields with high stereoselectivity for the Z‐isomer. By analogous reactions with difunctional nucleophiles, a wide range of CF3‐substituted pharmaceutically relevant heterocyclic structures can be accessed, exemplified in the simple synthesis of the anti‐arthritis drug celecoxib from HFO‐1234yf in just three steps.

Wiley: European Journal of Organic Chemistry: Table of Contents
Authors: Ben J. Murray, Thomas G. F. Marsh, Dmitri S. Yufit, Mark A. Fox, Antal Harsanyi, Lee T. Boulton, Graham Sandford
doi.org/10.1002/ejoc.202001071

Radical‐Cation Cascade to Aryltetralin Cyclic Ether Lignans Under Visible‐Light Photoredox Catalysis

Par / 14 septembre 2020 / Non classé
Radical‐Cation Cascade to Aryltetralin Cyclic Ether Lignans Under Visible‐Light Photoredox Catalysis

Under blue LED irradiation, dicinnamyl ether derivatives undergo double cyclization to afford tricyclic lignans. Six natural products are synthesized from the corresponding monolignols in two or three steps.

Abstract

The development of concise, sustainable, and cost‐effective synthesis of aryltetralin lignans, bearing either a fused lactone or cyclic ether, is of significant medicinal importance. Reported is that in the presence of Fukuzumi’s acridinium salt under blue LED irradiation, functionalized dicinnamyl ether derivatives are converted into aryltetralin cyclic ether lignans with concurrent generation of three stereocenters in good to high yields with up to 20:1 diastereoselectivity. Oxidation of an alkene to the radical cation is key to the success of this formal Diels–Alder reaction of electronically mismatched diene and dienophile. Applying this methodology, six natural products, aglacin B, aglacin C, sulabiroin A, sulabiroin B, gaultherin C, and isoshonanin, are synthesized in only two to three steps from readily available biomass‐derived monolignols. A revised structure is proposed for gaultherin C.

Wiley: Angewandte Chemie International Edition: Table of Contents
Authors: Jia‐Chen Xiang, Qian Wang, Jieping Zhu
doi.org/10.1002/anie.202007548

Enantiospecific Solid Solution Formation Triggers the Propagation of Homochirality

Par / 14 septembre 2020 / Non classé
Enantiospecific Solid Solution Formation Triggers the Propagation of Homochirality

An enantiomerically pure additive can direct chiral symmetry breaking towards opposite outcomes, depending on the relative contributions of kinetic and thermodynamic processes. Kinetic growth inhibition directs symmetry breaking towards the enantiomer of the opposite configuration to the additive, whereas thermodynamic solid solution formation favors the same absolute configuration, thus offering a mechanism for the propagation of homochirality.

Abstract

Propagation of homochirality plays a crucial role in the discussion on the origin of life. We investigated the role of structurally related enantiopure additives in chiral symmetry breaking during reactive crystallizations. We demonstrate that symmetry breaking can be driven towards the same absolute configuration as the additive if this additive forms an enantiospecific solid solution with the racemate. We observe two antagonistic processes: enantiospecific growth inhibition directs symmetry breaking to the opposite enantiomer following “the rule of reversal”, and enantiospecific solid solution formation that favors homochiral outcome. During continuous grinding, contributions of solid solution formation override contributions of enantiospecific growth inhibition, directing the process towards the absolute configuration of the additive. Collectively, our findings offer a potential mechanism for the propagation of homochirality.

Wiley: Angewandte Chemie International Edition: Table of Contents
Authors: Iaroslav Baglai, Michel Leeman, Klaus Wurst, Richard M. Kellogg, Willem L. Noorduin
doi.org/10.1002/anie.202009719

Synthesis of Highly Enantioenriched Sulfonimidoyl Fluorides and Sulfonimidamides by Stereospecific Sulfur–Fluorine Exchange (SuFEx) Reaction

Par / 14 septembre 2020 / Non classé
Synthesis of Highly Enantioenriched Sulfonimidoyl Fluorides and Sulfonimidamides by Stereospecific Sulfur–Fluorine Exchange (SuFEx) Reaction

S–F exchange: Stereocontrolled synthesis provides highly enantioenriched sulfonimidoyl fluorides for SuFEx chemistry. Enantiospecific S−N bond formation is achieved with inversion by preventing fluoride promoted racemisation. A diverse array of sulfonimidamides is synthesised by using primary and secondary amines including complex amine‐containing drugs.

Abstract

Sulfonimidamides present exciting opportunities as chiral isosteres of sulfonamides, with potential for additional directional interactions. Here, we present the first modular enantioselective synthesis of sulfonimidamides, including the first stereoselective synthesis of enantioenriched sulfonimidoyl fluorides, and studies on their reactivity. A new route to sulfonimidoyl fluorides is presented from solid bench‐stable, N‐Boc‐sulfinamide (Boc=tert‐butyloxycarbonyl) salt building blocks. Enantioenriched arylsulfonimidoyl fluorides are shown to be readily racemised by fluoride ions. Conditions are developed, which trap fluoride and enable the stereospecific reaction of sulfonimidoyl fluorides with primary and secondary amines (100 % es, es=enantiospecificity) generating sulfonimidamides with up to 99 % ee. Aryl and alkyl sulfonimidoyl fluoride reagents are suitable for mild late stage functionalisation reactions, exemplified by coupling with a selection of complex amines in marketed drugs.

Wiley: Chemistry – A European Journal: Table of Contents
Authors: Stephanie Greed, Edward L. Briggs, Fahima I. M. Idiris, Andrew J. P. White, Ulrich Lücking, James A. Bull
chemistry-europe.onlinelibrary.wiley.com/doi/abs/10.1002/chem.202002265

Altering Charges on Heterobimetallic Transition‐Metal Carbonyl Clusters

Par / 14 septembre 2020 / Non classé
Altering Charges on Heterobimetallic Transition‐Metal Carbonyl Clusters

Anything is possible! [Agm{M(CO)6}n]x clusters (M=Nb, Ta; m=1, 2, 6; n=2, 3, 4, 5; x=1−, 1+, 2+) were synthesized by the reaction of [NEt4][M(CO)6] and Ag[Al(ORF)4] (RF=C(CF3)3) and the structure determined by single‐crystal X‐ray diffraction methods. The [M(CO)6] fragments serve as ligands in the obtained clusters. DFT‐based AIM calculations were performed to provide an understanding of the bonding situation and the cores of the cations were interpreted as superatoms.

Abstract

The homoleptic group 5 carbonylates [M(CO)6]− (M=Nb, Ta) serve as ligands in carbonyl‐terminated heterobimetallic AgmMn clusters containing 3 to 11 metal atoms. Based on our serendipitous [Ag6{Nb(CO)6}4]2+ (4 a2+) precedent, we established access to such AgmMn clusters of the composition [Agm{M(CO)6}n]x (M=Nb, Ta; m=1, 2, 6; n=2, 3, 4, 5; x=1−, 1+, 2+). Salts of those molecular cluster ions were synthesized by the reaction of [NEt4][M(CO)6] and Ag[Al(ORF)4] (RF=C(CF3)3) in the correct stoichiometry in 1,2,3,4‐tetrafluorobenzene at −35 °C. The solid‐state structures were determined by single‐crystal X‐ray diffraction methods and, owing to the thermal instability of the clusters, a limited scope of spectroscopic methods. In addition, DFT‐based AIM calculations were performed to provide an understanding of the bonding within these clusters. Apparently, the clusters 3+ (m=6, n=5) and 42+ (m=6, n=4) are superatom complexes with trigonal‐prismatic or octahedral Ag6 superatom cores. The [M(CO)6]− ions then bind through three CO units as tridentate chelate ligands to the superatom core, giving overall structures related to tetrahedral AX4 (42+) or trigonal bipyramidal AX5 molecules (3+).

Wiley: Chemistry – A European Journal: Table of Contents
Authors: Wiebke Unkrig, Konstantin Kloiber, Burkhard Butschke, Daniel Kratzert, Ingo Krossing
chemistry-europe.onlinelibrary.wiley.com/doi/abs/10.1002/chem.202002339