Schwefel(VI)-fluorid-Austausch (SuFEx): Eine weitere gute Anwendung für die Click-Chemie

SuFEx-Based Polysulfonate Formation from Ethenesulfonyl Fluoride-Amine Adducts

The SuFEx-based polycondensation between bisalkylsulfonyl fluorides (AA monomers) and bisphenol bis(t-butyldimethylsilyl) ethers (BB monomers) using [Ph₃ P=N-PPh₃ ]⁺ [HF₂ ]^- as the catalyst is described. The AA monomers were prepared via the highly reliable Michael addition of ethenesulfonyl fluoride and amines/anilines while the BB monomers were obtained from silylation of bisphenols by t-butyldimethylsilyl chloride. With these reactions, a remarkable diversity of monomeric building blocks was achieved by exploiting readily available amines, anilines, and bisphenols as starting materials. The SuFEx-based polysulfonate formation reaction exhibited excellent efficiency and functional group tolerance, producing polysulfonates with a variety of side chain functionalities in >99 % conversion within 10 min to 1 h. When bearing an orthogonal group on the side chain, the polysulfonates can be further functionalized via click-chemistry-based post-polymerization modification.

Palladium-Catalyzed Fluorosulfonylvinylation of Organic Iodides

A palladium-catalyzed fluorosulfonylvinylation reaction of organic iodides is described. Catalytic Pd(OAc)₂ with a stoichiometric amount of silver(I) trifluoroacetate enables the coupling process between either an (hetero)aryl or alkenyl iodide with ethenesulfonyl fluoride (ESF). The method is demonstrated in the successful syntheses of eighty-eight otherwise difficult to access compounds, in up to 99 % yields, including the unprecedented 2-heteroarylethenesulfonyl fluorides and 1,3-dienylsulfonyl fluorides.

Multidimensional SuFEx Click Chemistry: Sequential Sulfur(VI) Fluoride Exchange Connections of Diverse Modules Launched From An SOF4 Hub

Sulfur(VI) fluoride exchange (SuFEx) is a new family of click chemistry based transformations that enable the synthesis of covalently linked modules via S^VI hubs. Here we report thionyl tetrafluoride (SOF₄ ) as the first multidimensional SuFEx connector. SOF₄ sits between the commercially mass-produced gases SF₆ and SO₂ F₂ , and like them, is readily synthesized on scale. Under SuFEx catalysis conditions, SOF₄ reliably seeks out primary amino groups [R-NH₂ ] and becomes permanently anchored via a tetrahedral iminosulfur(VI) link: R-N=(O=)S(F)₂ . The pendant, prochiral difluoride groups R-N=(O=)SF₂ , in turn, offer two further SuFExable handles, which can be sequentially exchanged to create 3-dimensional covalent departure vectors from the tetrahedral sulfur(VI) hub.

Reengineering Antibiotics to Combat Bacterial Resistance: Click Chemistry [1,2,3]-Triazole Vancomycin Dimers with Potent Activity against MRSA and VRE

Vancomycin has long been considered a drug of last resort. Its efficiency in treating multiple drug-resistant bacterial infections, particularly methicillin-resistant Staphylococcus aureus (MRSA), has had a profound effect on the treatment of life-threatening infections. However, the emergence of resistance to vancomycin is a cause for significant worldwide concern, prompting the urgent development of new effective treatments for antibiotic resistant bacterial infections. Harnessing the benefits of multivalency and cooperativity against vancomycin-resistant strains, we report a Click Chemistry approach towards reengineered vancomycin derivatives and the synthesis of a number of dimers with increased potency against MRSA and vancomycin resistant Enterococci (VRE; VanB). These semi-synthetic dimeric ligands were linked together with great efficiency using the powerful CuAAC reaction, demonstrating high levels of selectivity and purity.

A Heck-Matsuda Process for the Synthesis of β-Arylethenesulfonyl Fluorides: Selectively Addressable Bis-electrophiles for SuFEx Click Chemistry

A Heck-Matsuda process for the synthesis of the otherwise difficult to access compounds, β-arylethenesulfonyl fluorides, is described. Ethenesulfonyl fluoride (i.e., vinylsulfonyl fluoride, or ESF) undergoes β-arylation with stable and readily prepared arenediazonium tetrafluoroborates in the presence of the catalyst palladium(II) acetate to afford the E-isomer sulfonyl analogues of cinnamoyl fluoride in 43-97 % yield. The β-arylethenesulfonyl fluorides are found to be selectively addressable bis-electrophiles for sulfur(VI) fluoride exchange (SuFEx) click chemistry, in which either the alkenyl moiety or the sulfonyl fluoride group can be the exclusive site of nucleophilic attack under defined conditions, making these rather simple cores attractive for covalent drug discovery.

Chemoselective Preparation of Clickable Aryl Sulfonyl Fluoride Monomers: A Toolbox of Highly Functionalized Intermediates for Chemical Biology Probe Synthesis

Sulfonyl fluoride (SF)-based activity probes have become important tools in chemical biology. Herein, exploiting the relative chemical stability of SF to carry out a number of unprecedented SF-sparing functional group manipulations, we report the chemoselective synthesis of a toolbox of highly functionalized aryl SF monomers that we used to quickly prepare SF chemical biology probes. In addition to SF, the monomers bear an embedded click handle (a terminal alkyne that can perform copper(I)-mediated azide-alkyne cycloaddition). The monomers can be used either as fragments to prepare clickable SF analogues of drugs (biologically active compounds) bearing an aryl ring or, alternatively, attached to drugs as minimalist clickable aryl SF substituents.

Chemoselective Synthesis of Polysubstituted Pyridines from Heteroaryl Fluorosulfates

A selection of heteroaryl fluorosulfates were readily synthesized using commercial SO2F2 gas. These substrates are highly efficient coupling partners in the Suzuki reaction. Through judicious selection of Pd catalysts the fluorosulfate functionality is differentiated from bromide and chloride; the order of reactivity being: -Br> -OSO2 F> -Cl. Exploiting this trend allowed the stepwise chemoselective synthesis of a number of polysubstituted pyridines, including the drug Etoricoxib.

Synthesis of Sulfotyrosine-Containing Peptides by Incorporating Fluorosulfated Tyrosine Using an Fmoc-Based Solid-Phase Strategy

Tyrosine O-sulfation is a common protein post-translational modification that regulates many biological processes, including leukocyte adhesion and chemotaxis. Many peptides with therapeutic potential contain one or more sulfotyrosine residues. We report a one-step synthesis for Fmoc-fluorosulfated tyrosine. An efficient Fmoc-based solid-phase peptide synthetic strategy is then introduced for incorporating the fluorosulfated tyrosine residue into peptides of interest. Standard simultaneous peptide-resin cleavage and removal of the acid-labile side-chain protecting groups affords the crude peptides containing fluorosulfated tyrosine. Basic ethylene glycol, serving both as solvent and reactant, transforms the fluorosulfated tyrosine peptides into sulfotyrosine peptides in high yield.

SuFEx on the Surface: A Flexible Platform for Postpolymerization Modification of Polymer Brushes

Polymer brushes present a unique architecture for tailoring surface functionalities due to their distinctive physicochemical properties. However, the polymerization chemistries used to grow brushes place limitations on the monomers that can be grown directly from the surface. Several forms of click chemistry have previously been used to modify polymer brushes by postpolymerization modification with high efficiency, however, it is usually difficult to include the unprotected moieties in the original monomer. We present the use of a new form of click chemistry known as SuFEx (sulfur(VI) fluoride exchange), which allows a silyl ether to be rapidly and quantitatively clicked to a polymer brush grown by free-radical polymerization containing native -SO2F groups with rapid pseudo-first-order rates as high as 0.04 s(-1). Furthermore, we demonstrate the use of SuFEx to facilely add a variety of other chemical functional groups to brush substrates that have highly useful and orthogonal reactivity, including alkynes, thiols, and dienes.

N-Heterocyclic Carbene Catalyzed Synthesis of δ-Sultones via α,β-Unsaturated Sulfonyl Azolium Intermediates

A limited array of reactive intermediates have enabled a wealth of discoveries in N-heterocyclic carbene organocatalysis. In this study, the viability of α,β-unsaturated sulfonyl azoliums as double electrophiles in new reactions is examined. Specifically, the (3+3) annulation of such species with the trimethylsilyl enol ethers of various 1,3-dicarbonyl compounds has been developed. This reaction provides access to a range of novel unsaturated δ-sultones (18 examples) in good yields (40-88 %) under mild reaction conditions. Mechanistic studies and the development of an enantioselective variant (55 % yield, 73:27 e.r.) support the intermediacy of an α,β-unsaturated sulfonyl azolium species.

Late-stage fluorination: fancy novelty or useful tool?

Charming fluorine: This Essay examines the recent surge in late-stage fluorination reactions and outlines challenges that need to be overcome to increase the impact of modern fluorination methods on the synthesis of complex organofluorine compounds. It is outlined how an improved understanding of the bonding interactions of fluoride could lead to a new class of mild fluorinating reagents and a range of functional-group-tolerant reactions.