A Unified Synthesis of Diazenes from Primary Amines Using a SuFEx/Electrochemistry Strategy

The electrochemical synthesis of 1,2-disubsituted diazenes via anodic oxidation of bench stable symmetrical and unsymmetrical sulfamides is reported. This work capitalizes on the streamlined preparation of diverse N,N'-disubstituted sulfamides using Sulfur(VI) Fluoride Exchange (SuFEx) click chemistry that were subsequently subjected to electrochemical oxidation to afford the desired diazenes. The electrochemical nature of the reaction conditions obviated the need for chlorinating reagents, which considerably improved the sustainability of the overall process. Noteworthy, in addition to the synthesis of alkyl diazenes, these milder conditions were shown to be competent for the formation of azobenzenes, albeit in lower yields. Mechanistic experiments were conducted to delineate the reaction pathway and to rationalize the formation of side products observed during the electro-oxidation of N,N'-diarylsulfamides.

SuFEx Chemistry Enables Covalent Assembly of a 280-kDa 18-Subunit Pore-Forming Complex

Proximity-enhanced chemical cross-linking is an invaluable tool for probing protein-protein interactions and enhancing the potency of potential peptide and protein drugs. Here, we extend this approach to covalently stabilize large macromolecular assemblies. We used SuFEx chemistry to covalently stabilize an 18-subunit pore-forming complex, CsgG:CsgF, consisting of nine CsgG membrane protein subunits that noncovalently associate with nine CsgF peptides. Derivatives of the CsgG:CsgF pore have been used for DNA sequencing, which places high demands on the structural stability and homogeneity of the complex. To increase the robustness of the pore, we designed and synthesized derivatives of CsgF-bearing sulfonyl fluorides, which react with CsgG in very high yield to form a covalently stabilized CsgG:CsgF complex. The resulting pores formed highly homogeneous channels when added to artificial membranes. The high yield and rapid reaction rate of the SuFEx reaction prompted molecular dynamics simulations, which revealed that the SO2F groups in the initially formed complex are poised for nucleophilic reaction with a targeted Tyr. These results demonstrate the utility of SuFEx chemistry to structurally stabilize very large (here, 280 kDa) assemblies.

Highly Functionalized SuFEx-able Hub Bearing All-Carbon Quaternary Center via Rapid Brønsted Superbase Catalysis

A rapid Brønsted superbase catalysis for highly functionalized sulfur(VI)-fluoride exchange (SuFEx) hubs bearing all-carbon quaternary centers was developed. Remarkable functional group tolerance toward esters and nitriles was achieved by Michael addition of cyanoacetate derivatives to ethenesulfonyl fluoride with low catalyst loadings (∼0.5 mol %) within a short reaction time (0.5-30 min). Gram-scalability, water tolerance, and compatibility in polymeric catalysis showcase its unique practicability. SuFEx click conjugations were demonstrated using various amines, including DNA-tethered biomolecules.

Thionyl fluoride as a sulfur(IV) SuFEx hub for the efficient syntheses of sulfinamides and sulfinate esters

Herein, we demonstrate a method for the syntheses of sulfinamides and sulfinate esters using a novel sulfur(IV) fluoride exchange reaction with organometallic reagents. Our strategy involves the addition of an amine or alcohol nucleophile to thionyl fluoride, acting as a S(IV) SuFEx hub, followed by an organometallic reagent. This approach allows efficient access to sulfinamides (45-91% yields) and sulfinate esters (44-82% yields) in only 30 minutes. The sulfinamide and sulfinate esters also can be readily derivatized to the corresponding S(VI) sulfonamides, sulfonate esters, sulfonimidamides, and sulfonimidates without isolation of the intermediates.

2-Methylimidazole-1-(N-tert-octyl)sulfonimidoyl Fluoride: A Bench-Stable Alternative to SOF4 as Precursor to N,O-Substituted S(VI) Compounds

S(VI) compounds with multiple N or O substituents are often difficult to make and several crucial routes, such as multimodal SuFEx (Sulfur (VI) Fluoride Exchange) chemistry, rely on the highly useful but hazardous SOF4 gas. Safety issues and inaccessibility of SOF4 strongly hamper the developments of these organic compounds. Here we describe the synthesis and applications of 2-methylimidazole-1-(N-tert-octyl)sulfonimidoyl fluoride (ImSF), a novel bench-stable analogue of SOF4. ImSF is synthesized on a gram scale via a double fluorination of t-OctNSO. We show ImSF can undergo substitution reactions with phenols and amines, which lead to sulfurimidates and sulfuramidimidates, respectively, the intrinsically chiral analogous of medicinally relevant sulfates and sulfamates in which an S=O moiety is replaced by S=NR unit. Finally we demonstrate that such substitutions can occur enantiospecifically, providing the first entry to chiral sulfurimidates and sulfuramidimidates.

Dichlorotriazine-based multivalent probe for selective affinity labeling of carbohydrate-binding proteins

A new series of multivalent gold nanoparticle probes bearing different electrophilic groups were synthesized and their affinity labeling reactivities were evaluated. The dichlorotriazine group was identified as a useful protein-reactive label, allowing selective capture of a target protein at nanomolar probe concentrations.

In-Flow Generation of Thionyl Fluoride (SOF2) Enables the Rapid and Efficient Synthesis of Acyl Fluorides from Carboxylic Acids

Herein, we report an approach for generating thionyl fluoride (SOF2) from the commodity chemicals thionyl chloride (SOCl2) and potassium fluoride (KF). The methodology relies on a microfluidic device that can efficiently produce and dose this toxic gaseous reagent under extremely mild and safe conditions. Subsequently, the in situ-generated thionyl fluoride is reacted with an array of structurally and electronically differing carboxylic acids, leading to the direct and efficient synthesis of highly sought-after acyl fluorides. Importantly, our investigation also highlights the inherent modularity of this flow-based platform. We demonstrate the adaptability of this approach by not only synthesizing acyl fluorides but also directly converting carboxylic acids into a diverse array of valuable compounds such as esters, thioesters, amides, and ketones. This versatility showcases the potential of this approach for a wide range of synthetic applications, underscoring its significance in the realm of chemical synthesis.

Fe-Catalyzed Fluorosulfonylation of Alkenes via Sulfur Dioxide Insertion: Synthesis of Lactam-Functionalized Alkyl Sulfonyl Fluorides

A novel Fe-catalyzed fluorosulfonylation of alkenes with Na2S2O4 and N-fluorobenzenesulfonimide (NFSI) for assembling various lactam-functionalized alkyl sulfonyl fluorides is disclosed. In this reaction, Na2S2O4 acts as both an SO2 source and a reductant. Furthermore, the resulting products can be efficiently transformed into valuable chemicals, including sulfonyl esters and sulfonamides, via the sulfur(VI) fluoride exchange (SuFEx) click reaction. Preliminary mechanistic studies suggest that the transformation proceeds through intramolecular radical cyclization, SO2 insertion, sulfite anion formation, and fluorination.

Radical Fluorosulfonamidation: A Facile Access to Sulfamoyl Fluorides

Recently, the introduction of fluorosulfonyl (-SO2F) groups have attracted considerable research interests, as this moiety could often afford enhanced activities and new functions in the context of chemical biology and drug discovery. Herein, we report the design and synthesis of 1-fluorosulfamoyl-pyridinium (FSAP) salts, which could serve as an effective photoredox-active precursor to fluorosulfamoyl radicals and enable the direct radical C-H fluorosulfonamidation of a variety of (hetero)arenes. This method features mild conditions, visible light, broad substrate scope, good group tolerance, etc., and a metal-free protocol is also viable by using organic photocatalysts. Further, FSAP can also be applied to the radical functionalization of alkenes via 1,2-difunctionalization, radical distal migration, tandem radical-polar crossover reactions, etc. In addition, a formal C-H methylamination of (hetero)arenes by combining this radical C-H fluorosulfonamidation with subsequent hydrolysis as well as product derivatization are also demonstrated.

Synthesis of α-Bromo Arylethyl Sulfonyl Fluorides and β-Arylethenesulfonyl Fluorides via Copper-Catalyzed Meerwein Arylation

A practical copper-catalyzed process for the synthesis of the β-arylethenesulfonyl fluorides is described. A series of α-bromo arylethyl sulfonyl fluorides was prepared via Meerwein reaction from arenediazonium tetrafluoroborates and ethenesulfonyl fluoride (ESF) under mild conditions. The following β-arylethenesulfonyl fluorides were further obtained through a β-elimination reaction. This protocol features excellent regio- and stereoselectivity and broad substrate scope.

Photoredox-Catalysis Fluorosulfonyldifluoromethylation of Unactivated Alkenes and (Hetero)arenes with ICF2SO2F

The fluorosulfonyldifluoromethylation of unactivated alkenes and (hetero)arenes with iododifluoromethanesulfonyl fluoride (ICF2SO2F) under visible light photoredox catalysis was successfully developed. Key to the successful fluorosulfonyldifluoromethylation of aromatic compounds was the usage of AgOTf as an additive to promote the formation of the CF2SO2F radical. The protocol provided a straightforward way to introduce the interesting and useful CF2SO2F group on sp3 and sp2 carbons.

Intramolecular chalcogen bonding activated SuFEx click chemistry for efficient organic-inorganic linking

SuFEx click chemistry demonstrates remarkable molecular assembly capabilities. However, the effective utilization of alkyl sulfonyl fluoride hubs in SuFEx chemistry, particularly in reactions with alcohols and primary amines, presents considerable challenges. This study pioneers an intramolecular chalcogen bonding activated SuFEx (S-SuFEx) click chemistry employing alkyl sulfonyl fluorides with γ-S as the activating group. The ChB-activated alkyl sulfonyl fluorides can react smoothly with phenols, alcohols, and amines, exhibiting enhanced reactivity compared to SO2F2. Excellent yields have been achieved with all 75 tested substrates. Pioneering the application of S-SuFEx chemistry, we highlight its immense potential in organic-inorganic linking, considering the critical role of interfacial covalent bonding in material fabrication. The S-SuFEx hub 1c, incorporating a trialkoxy silane group has been specifically designed and synthesized for organic-inorganic linking. In a simple step, 1c efficiently anchors various organic compounds onto surfaces of inorganic materials, forming functionalized surfaces with properties such as antibacterial activity, hydrophobicity, and fluorescence.

Activation of SO2F2 at a Rhodium PNP Pincer Complex: Ligand Supported S-F Bond Cleavage to Generate NSO2F Derivatives

The κ2-(P,N)-phosphine ligand precursor NH(CH2CH2PCy2)2 can be used for the synthesis of the rhodium(I) complex [Rh(CO){ĸ3-(P,N,P)-Cy2PC2H4NHC2H4PCy2}][Cl] (1). The deprotonated complex [Rh(CO){ĸ3-(P,N,P)-Cy2PC2H4NC2H4PCy2}] (2) shows a cooperative reactivity of the PNP ligand in the activation reaction of SO2F2 to yield the rhodium fluorido complex trans-[Rh(F)(CO){ĸ2-(P,P)-Cy2PC2H4N(SO2F)C2H4PCy2}]2 (3) by S-F bond cleavage. It is remarkable that no reaction was observed when 3 was treated with hydrogen sources e. g. dihydrogen, organosilicon compounds such as triethylsilane or TMS-CF3 and different fluorine sources such as SF4 or Selectfluor®. However, the treatment of complex 3 with XeF2 in the presence of CsF resulted in the formation of the unique fluorido rhodium(III) complex cis,trans-[Rh(F)3(CO){ĸ2-(P,P)-Cy2PC2H4N(SO2F)C2H4PCy2}]2 (4). In the presence of pyridine(HF)X or BF3 the fluorido complex 3 converted into the dicationic complexes [Rh(CO){ĸ2-(P,P)-Cy2PC2H4N(SO2F)C2H4PCy2}]2[XF]2, X=HF (5) or BF3 (6), respectively.

Selective Ring-Opening Polymerization of Silyl Glycidyl Ether through Organocatalysis

Silyl ether constitutes a multipurpose (macro)molecular functionality for being, e.g., SuFEx-clickable and easily cleavable as a hydroxyl precursor. Its direct incorporation by anionic polymerization is challenged by its base susceptibility. In this study, a two-component organocatalyst shows strict epoxy-selectivity in the anionic ring-opening polymerization (ROP) of commercially available tert-butyldimethylsilyl (R)-(-)-glycidyl ether (TBSGE). The silyl ether pendant groups are fully preserved in the resultant polyether and readily undergo acidic hydrolysis to yield well-defined linear polyglycerol (PGC). Combination of the ROP with mechanistically distinct polymerization chemistries delivers PGC-based polyurethane and a hybrid amphiphilic block copolymer. The SuFEx reaction with sulfonyl fluoride shows effective tuning of polyTBSGE into a sulfonate-functionalized polyether. We have thus exploited the chemoselectivity of organocatalysis to facilitate access to polymers carrying reactive pendant functionalities.

Radical Ring-Opening Fluorosulfonylation of Methylenecyclobutanols via Electron Donor-Acceptor Photoactivation

A visible-light-mediated catalyst- and additive-free method for radical ring-opening fluorosulfonylation of methylenecyclobutanols is reported. Sulfuryl chlorofluoride acts as a FSO2 radical precursor as well as an electron acceptor to form electron donor-acceptor complexes with various methylenecyclobutanol substrates. This method shows fully regioselective and (E)-stereoselective ring-opening processes, providing a variety of FSO2-functionalized γ,δ-unsaturated carbonyls in 38-77% yields. A selection of product diversifications has been studied to demonstrate the versatility of these sulfonyl fluoride products.

Enabling Modular Click Chemistry Library through Sequential Ligations of Carboxylic Acids and Amines

High-throughput synthesis and screening of chemical libraries play pivotal roles in drug discovery. Click chemistry has emerged as a powerful strategy for constructing highly modular chemical libraries. However, the development of new click reactions and unlocking new clickable building blocks remain exceedingly challenging. Herein, we describe a double-click strategy that enables the sequential ligations of widely available carboxylic acids and amines with fluorosulfuryl isocyanate (FSO2NCO) via a modular amidation/SuFEx (sulfur-fluoride exchange) process. This method provides facile access to chemical libraries of N-fluorosulfonyl amides (RCONHSO2F) and N-acylsulfamides (RCONHSO2NR'R'') in near-quantitative yields under simple and practical conditions. The robustness and efficiency of this double click strategy is showcased by the facile construction of chemical libraries in 96-well microtiter plates from a large number of carboxylic acids and amines. Preliminary biological activity screening reveals that some compounds exhibit high antimicrobial activities against Gram-positive bacterium S. aureus and drug-resistant MRSA (MIC up to 6.25 μg ⋅ mL-1). These results provide compelling evidence for the potential application of modular click chemistry library as an enabling technology in high-throughput medicinal chemistry.

Design of a covalent protein-protein interaction inhibitor of SRPKs to suppress angiogenesis and invasion of cancer cells

Serine-arginine (SR) proteins are splicing factors that play essential roles in both constitutive and alternative pre-mRNA splicing. Phosphorylation of their C-terminal RS domains by SR protein kinases (SRPKs) regulates their localization and diverse cellular activities. Dysregulation of phosphorylation has been implicated in many human diseases, including cancers. Here, we report the development of a covalent protein-protein interaction inhibitor, C-DBS, that targets a lysine residue within the SRPK-specific docking groove to block the interaction and phosphorylation of the prototypic SR protein SRSF1. C-DBS exhibits high specificity and conjugation efficiency both in vitro and in cellulo. This self-cell-penetrating inhibitor attenuates the phosphorylation of endogenous SR proteins and subsequently inhibits the angiogenesis, migration, and invasion of cancer cells. These findings provide a new foundation for the development of covalent SRPK inhibitors for combatting diseases such as cancer and viral infections and overcoming the resistance encountered by ATP-competitive inhibitors.

The Modular Synthesis of Sulfondiimidoyl Fluorides and their Application to Sulfondiimidamide and Sulfondiimine Synthesis

A modular synthesis of sulfondiimidoyl fluorides-the double aza-analogues of sulfonyl fluorides-allowing variation of the carbon and both nitrogen-substituents is reported. The chemistry uses readily available organometallic reagents, commercial sulfinylamines, simple electrophiles, and N-fluorobenzenesulfonimide (NFSI), as the starting materials. The reactions are broad in scope, efficient, and scalable. We show that the sulfondiimidoyl fluoride products can be combined with amines to provide sulfondiimidamides, and with organolithium reagents to provide sulfondiimines, and that reactivity in these transformations can be modulated by variation of the N-substituents.

Genetically Enabling Phosphorus Fluoride Exchange Click Chemistry in Proteins

Phosphorus Fluoride Exchange (PFEx), recently debuted in small molecules, represents the forefront of click chemistry. To explore PFEx's potential in biological settings, we developed amino acids PFY and PFK featuring phosphoramidofluoridates and incorporated them into proteins through genetic code expansion. PFY/PFK selectively reacted with nearby His, Tyr, Lys, or Cys in proteins, both in vitro and in living cells, demonstrating that proximity enabled PFEx reactivity without external reagents. The reaction with His showed unique pH-dependent properties and created thermally sensitive linkages. Additionally, Na2SiO3 enhanced PFEx reactions with Tyr and Cys. PFEx, by generating defined covalent P-N/O linkages, extends the utility of phosphorus linkages in proteins, aligning with nature's use of phosphate connectors in other biomolecules. More versatile and durable than SuFEx, PFEx in proteins expands the latent bioreactive arsenal for covalent protein engineering and will facilitate the broad application of this potent click chemistry in biological and biomedical fields.

Host-Guest Stimuli-Responsive Click Chemistry

Click chemistry has reached its maturity as the weapon of choice for the irreversible ligation of molecular fragments, with over 20 years of research resulting in the development or improvement of highly efficient kinetically controlled conjugation reactions. Nevertheless, traditional click reactions can be disadvantageous not only in terms of efficiency (side products, slow kinetics, air/water tolerance, etc.), but also because they completely avoid the possibility to reversibly produce and control bound/unbound states. Recently, non-covalent click chemistry has appeared as a more efficient alternative, in particular by using host-guest self-assembled systems of high thermodynamic stability and kinetic lability. This review discusses the implementation of molecular switches in the development of such non-covalent ligation processes, resulting in what we have termed stimuli-responsive click chemistry, in which the bound/unbound constitutional states of the system can be favored by external stimulation, in particular using host-guest complexes. As we exemplify with handpicked selected examples, these supramolecular systems are well suited for the development of human-controlled molecular conjugation, by coupling thermodynamically regulated processes with appropriate temporally resolved extrinsic control mechanisms, thus mimicking nature and advancing our efforts to develop a more function-oriented chemical synthesis.

Perfluorooxosulfate Salts as SOF4-Gas-Free Precursors to Multidimensional SuFEx Electrophiles

Sulfur(VI) Fluoride Exchange (SuFEx) chemistry stands as a well-established method for swiftly constructing complex molecules in a modular fashion. An especially promising segment of this toolbox is reserved for multidimensional SuFEx hubs: three or more substituents pluggable into a singular SVI centre to make 'beyond-linear' clicked constructions. Sulfurimidoyl difluorides (RNSOF2) stand out as the prime example of this, however their preparation from the scarcely available thionyl tetrafluoride (SOF4) limits this chemistry to only a few laboratories with access to this gas. In this work, we identify silver pentafluorooxosulfate (AgOSF5) as a viable SuFEx hub with reactivity equal to SOF4. The AgF2-mediated oxidation of SOCl2 gives rise to the hexacoordinate AgOSF5 adduct, which in contact with primary amines produces the sulfurimidoyl fluorides in high yields. In addition, we have found this workflow to be fully extendable to the trifluoromethyl homologue, AgOSF4CF3, and we propose the use of AgOSF4X salts as a general route to azasulfur SuFEx electrophiles from commercial starting materials.

Iterative click reactions using trivalent platforms for sequential molecular assembly

A facile synthesis of multi(triazole)s by iterative click reactions is disclosed. Good functional group tolerance of sequential click assembly by sulfur-fluoride exchange (SuFEx), copper-catalyzed azide-alkyne cycloaddition (CuAAC), and thia-Michael reaction realizes the iterative click reactions. Diverse multi(triazole)-type mid-molecules can be synthesized easily from readily available modules through good chemoselective reactions without functional group transformation steps.

Sulfur(VI) Fluoride Exchange Chemistry in Solid-Phase Synthesis of Compound Arrays: Discovery of Histone Deacetylase Inhibitors

Multistep synthesis performed on solid support is a powerful means to generate small-molecule libraries for the discovery of chemical probes to dissect biological mechanisms as well as for drug discovery. Therefore, expansion of the collection of robust chemical transformations amenable to solid-phase synthesis is desirable for achieving chemically diverse libraries for biological testing. Here, we show that sulfur(VI) fluoride exchange (SuFEx) chemistry, exemplified by pairing phenols with aryl fluorosulfates, can be used for the solid-phase synthesis of biologically active compounds. As a case study, we designed and synthesized a library of 84 hydroxamic acid-containing small molecules, providing a rich source of inhibitors with diverse selectivity profiles across the human histone deacetylase enzyme family. Among other discoveries, we identified a scaffold that furnished inhibitors of HDAC11 with exquisite selectivity in vitro and a selective inhibitor of HDAC6 that was shown to affect the acetylation of α-tubulin over histone sites H3K18, H3K27, as well as SMC3 in cultured cells. Our results encourage the further use of SuFEx chemistry for the synthesis of diverse small-molecule libraries and provide insight for future design of selective HDAC inhibitors.

Ultrafast Flow Synthesis of o-Functionalized Benzenesulfonyl Fluorides and Subsequent SuFEx Connections via Lithiated Chemistry

Herein we present a flow-based, rapid, and straightforward approach to synthesize diverse functionalized sulfonyl fluorides by harnessing an aryllithium intermediate. The aryllithium intermediate was fully utilized under optimized conditions (0.016 s, -18 °C) to afford various functionalized sulfonyl fluorides and also intramolecular SuFEx cyclization products in high yields (27-94%). Furthermore, the integrated synthesis incorporating subsequent SuFEx connections with even unstable organolithium nucleophiles facilitated one-flow molecular assembly in high yields (42-72%).

Mild Strategy for the Preparation of Alkyl Sulfonyl Fluorides from Alkyl Bromides and Alcohols Using Photoredox Catalysis and Flow Chemistry

Facile access to sp3-rich scaffolds containing a sulfonyl fluoride group is still limited. Herein, we describe a mild and scalable strategy for the preparation of alkyl sulfonyl fluorides from readily available alkyl bromides and alcohols using photoredox catalysis. This approach is based on halogen atom transfer (XAT), followed by SO2 capture and fluorination. The method features mild conditions enabling fast access to high-value derivatives and has been scaled up to 5 g using a continuous stirred tank reactor cascade.

SuFEx-Enabled Direct Deoxy-Diversification of Alcohols

We introduce a new use of sulfonyl fluoride as a bifunctional reagent that facilitates the one-step deoxy-diversification of complex alcohol libraries. Our reaction design features a Sulfur(VI) Fluoride Exchange (SuFEx) mediated activation of alcohols and fluoride-induced activation of silicon-bound nucleophiles. This method enables the direct conversion of alcoholic C-O bonds in complex molecules into diverse analogues via C-C, C-N, C-Cl, and C-Br bond formation while suppressing any elimination side-products.

Fluorosulfonyl Arylation of Alkynes via Electron Donor-Acceptor Photoactivation

A radical fluorosulfonyl arylation of alkynes with sulfuryl chlorofluoride as the FSO2 radical precursor via electron donor-acceptor photoactivation driven by daylight or a blue light-emitting diode is disclosed. A series of valuable benzo-fused carbocycles and heterocycles have been produced with simple operation under mild conditions in the absence of any external catalysts or additives. The synthetic potential of this protocol has further demonstrated excellent scalability, as well as diverse postderivatizations, including SuFEx reactions and other useful cascade reactions.

A Mild Method for the Activation of Cation Exchange Membranes Used in Tubular PEM Electrolyzers

Co-extrusion of both half-cells in tubular PEM water electrolyzers can lower the costs for hydrogen production, since the number of components is reduced and the production process is simplified. However, after co-extrusion of the inner half-cell and the ion exchange membrane, the membrane is in its fluoride sulfonyl form and must be hydrolyzed to achieve the proton conductive sulfonic acid to be ready for use. Common practice is the hydrolysis using concentrated alkaline solutions, which causes a corrosion of the laminated anode electrode. We developed a less corrosive method using triethylsilanol as reactant. Tubular membranes hydrolyzed with this new procedure were characterized and tested in an electrolyzer laboratory test setup.

Non-symmetric stapling of native peptides

Stapling has emerged as a powerful technique in peptide chemistry. It enables precise control over peptide conformation leading to enhanced properties such as improved stability and enhanced binding affinity. Although symmetric stapling methods have been extensively explored, the field of non-symmetric stapling of native peptides has received less attention, largely as a result of the formidable challenges it poses - in particular the complexities involved in achieving the high chemo-selectivity and site-selectivity required to simultaneously modify distinct proteinogenic residues. Over the past 5 years, there have been significant breakthroughs in addressing these challenges. In this Review, we describe the latest strategies for non-symmetric stapling of native peptides, elucidating the protocols, reaction mechanisms and underlying design principles. We also discuss current challenges and opportunities this field offers for future applications, such as ligand discovery and peptide-based therapeutics.

Therapeutic stapled peptides: Efficacy and molecular targets

Peptide stapling, by employing a stable, preformed alpha-helical conformation, results in the production of peptides with improved membrane permeability and enhanced proteolytic stability, compared to the original peptides, and provides an effective solution to accelerate the rapid development of peptide drugs. Various reviews present peptide stapling chemistries, anchoring residues and one- or two-component cyclization, however, therapeutic stapled peptides have not been systematically summarized, especially focusing on various disease-related targets. This review highlights the latest advances in therapeutic peptide drug development facilitated by the application of stapling technology, including different stapling techniques, synthetic accessibility, applicability to biological targets, potential for solving biological problems, as well as the current status of development. Stapled peptides as therapeutic drug candidates have been classified and analysed mainly by receptor- and ligand-based stapled peptide design against various diseases, including cancer, infectious diseases, inflammation, and diabetes. This review is expected to provide a comprehensive reference for the rational design of stapled peptides for different diseases and targets to facilitate the development of therapeutic peptides with enhanced pharmacokinetic and biological properties.

Covalent Polymer-RNA Conjugates for Potent Activation of the RIG-I Pathway

RNA ligands of retinoic acid-inducible gene I (RIG-I) are a promising class of oligonucleotide therapeutics with broad potential as antiviral agents, vaccine adjuvants, and cancer immunotherapies. However, their translation has been limited by major drug delivery barriers, including poor cellular uptake, nuclease degradation, and an inability to access the cytosol where RIG-I is localized. Here this challenge is addressed by engineering nanoparticles that harness covalent conjugation of 5'-triphospate RNA (3pRNA) to endosome-destabilizing polymers. Compared to 3pRNA loaded into analogous nanoparticles via electrostatic interactions, it is found that covalent conjugation of 3pRNA improves loading efficiency, enhances immunostimulatory activity, protects against nuclease degradation, and improves serum stability. Additionally, it is found that 3pRNA could be conjugated via either a disulfide or thioether linkage, but that the latter is only permissible if conjugated distal to the 5'-triphosphate group. Finally, administration of 3pRNA-polymer conjugates to mice significantly increases type-I interferon levels relative to analogous carriers that use electrostatic 3pRNA loading. Collectively, these studies have yielded a next-generation polymeric carrier for in vivo delivery of 3pRNA, while also elucidating new chemical design principles for covalent conjugation of 3pRNA with potential to inform the further development of therapeutics and delivery technologies for pharmacological activation of RIG-I.

Iterative SuFEx approach for sequence-regulated oligosulfates and its extension to periodic copolymers

The synthesis of sequence-regulated oligosulfates has not yet been established due to the difficulties in precise reactivity control. In this work, we report an example of a multi-directional divergent iterative method to furnish oligosulfates based on a chain homologation approach, in which the fluorosulfate unit is regenerated. The oligosulfate sequences are determined by high resolution mass spectrometry of the hydrolyzed fragments, and polysulfate periodic copolymers are synthesized by using oligomeric bisfluorosulfates in a bi-directional fashion. The synthetic utility of this iterative ligation is demonstrated by preparing crosslinked network polymers as synthetic adhesive materials.

N-Fluorosulfonyl Guanidine: An Entry to N-Guanyl Sulfamides and Sulfamates

Here, we present the straightforward synthesis of N-fluorosulfonyl guanidine (1) from two industrial feedstocks, guanidine hydrochloride and sulfuryl fluoride (SO2F2), using SuFEx chemistry. Compound 1 exhibits excellent stability under ambient conditions and displays unique SuFEx reactivity toward amines and phenols to generate N-guanyl sulfamides and sulfamates that have rarely been accessed. Notably, water serves as an effective solvent in this process. Our protocol provides a reliable pathway for the synthesis and investigation of these novel guanidine-containing molecules.

Virtual Screening of a Chemically Diverse "Superscaffold" Library Enables Ligand Discovery for a Key GPCR Target

The advent of ultra-large libraries of drug-like compounds has significantly broadened the possibilities in structure-based virtual screening, accelerating the discovery and optimization of high-quality lead chemotypes for diverse clinical targets. Compared to traditional high-throughput screening, which is constrained to libraries of approximately one million compounds, the ultra-large virtual screening approach offers substantial advantages in both cost and time efficiency. By expanding the chemical space with compounds synthesized from easily accessible and reproducible reactions and utilizing a large, diverse set of building blocks, we can enhance both the diversity and quality of the discovered lead chemotypes. In this study, we explore new chemical spaces using reactions of sulfur(VI) fluorides to create a combinatorial library consisting of several hundred million compounds. We screened this virtual library for cannabinoid type II receptor (CB2) antagonists using the high-resolution structure in conjunction with a rationally designed antagonist, AM10257. The top-predicted compounds were then synthesized and tested in vitro for CB2 binding and functional antagonism, achieving an experimentally validated hit rate of 55%. Our findings demonstrate the effectiveness of reliable reactions, such as sulfur fluoride exchange, in diversifying ultra-large chemical spaces and facilitate the discovery of new lead compounds for important biological targets.

Stereoselective Fluorosulfonylation of Vinylboronic Acids for (E)-Vinyl Sulfonyl Fluorides with Copper Participation

A practical synthetic method for the synthesis of vinyl sulfonyl fluorides through copper-promoted direct fluorosulfonylation has been developed. The reaction of the vinylboronic acids with DABSO and then NFSI is performed under mild reaction conditions. This transformation efficiently affords aryl or alkyl vinyl sulfonyl fluorides with good reaction yields, exclusive E-configuration, broad substrate scope, excellent compatibility, and operational simplicity.

Identification of clickable HIV-1 capsid-targeting probes for viral replication inhibition

Of the targets for HIV-1 therapeutics, the capsid core is a relatively unexploited but alluring drug target due to its indispensable roles throughout virus replication. Because of this, we aimed to identify "clickable" covalent modifiers of the HIV-1 capsid protein (CA) for future functionalization. We screened a library of fluorosulfate compounds that can undergo sulfur(VI) fluoride exchange (SuFEx) reactions, and five compounds were identified as hits. These molecules were further characterized for antiviral effects. Several compounds impacted in vitro capsid assembly. One compound, BBS-103, covalently bound CA via a SuFEx reaction to Tyr145 and had antiviral activity in cell-based assays by perturbing virus production, but not uncoating. The covalent binding of compounds that target the HIV-1 capsid could aid in the future design of antiretroviral drugs or chemical probes that will help study aspects of HIV-1 replication.

Protocol for producing phosphoramidate using phosphorus fluoride exchange click chemistry

Phosphorus fluoride exchange (PFEx) is a catalytic click reaction that involves exchanging high oxidation state P-F bonds with alcohol and amine nucleophiles, reliably yielding P-O- and P-N-linked compounds. Here, we describe steps for preparing a phosphoramidic difluoride and performing two sequential PFEx reactions to yield a phosphoramidate through careful catalyst selection. We then detail procedures for handling and quenching potentially toxic P-F-containing compounds to ensure user safety when conducting PFEx reactions. For complete details on the use and execution of this protocol, please refer to Sun et al.1.

Desmethyl SuFEx-IT: SO2F2-Free Synthesis and Evaluation as a Fluorosulfurylating Agent

Access to SuFExable compounds was remarkably simplified by introduction of the solid FO2S-donor SuFEx-IT. However, the published process for preparation of this reagent relies on the use of sulfuryl fluoride (SO2F2), which is difficult to obtain and highly toxic. Herein, we disclose a simple protocol for SO2F2-free, hectogram-scale preparation of the analogous desmethyl SuFEx-IT from inexpensive starting materials. The reagent was prepared in a high (85%) total yield and without chromatographic purification steps. In addition, we demonstrate the utility of desmethyl SuFEx-IT by successful preparation of a series of fluorosulfates and sulfamoyl fluorides in high to excellent yields. As such, our work recognizes desmethyl SuFEx-IT as a valuable alternative to common FO2S-donors and enables cost-efficient access to substrates for SuFEx click chemistry.

Modular synthesis of functional libraries by accelerated SuFEx click chemistry

Accelerated SuFEx Click Chemistry (ASCC) is a powerful method for coupling aryl and alkyl alcohols with SuFEx-compatible functional groups. With its hallmark favorable kinetics and exceptional product yields, ASCC streamlines the synthetic workflow, simplifies the purification process, and is ideally suited for discovering functional molecules. We showcase the versatility and practicality of the ASCC reaction as a tool for the late-stage derivatization of bioactive molecules and in the array synthesis of sulfonate-linked, high-potency, microtubule targeting agents (MTAs) that exhibit nanomolar anticancer activity against multidrug-resistant cancer cell lines. These findings underscore ASCC's promise as a robust platform for drug discovery.

One-Pot Three-Component Synthesis of Indolyl-4H-chromene-3-sulfonyl Fluoride: A Class of Important Pharmacophore

A one-pot, sequential three-component reaction between salicylaldehyde, indole, and 2-bromoprop-2-ene-1-sulfonyl fluoride (BPESF) has been demonstrated for the synthesis of sulfonyl fluoride substituted 4H-chromene derivatives in moderate to excellent yields (45%-94%). This one-pot sequential method features easily available starting materials, wide substrate scope, mild conditions, and great efficiency.

Enantioselective sulfur(VI) fluoride exchange reaction of iminosulfur oxydifluorides

Linkage chemistry and functional molecules derived from the stereogenic sulfur(VI) centre have important applications in organic synthesis, bioconjugation, drug discovery, agrochemicals and polymeric materials. However, existing approaches for the preparation of optically active S(VI)-centred compounds heavily rely on synthetic chiral S(IV) pools, and the reported linkers of S(VI) lack stereocontrol. A modular assembly method, involving sequential ligand exchange at the S(VI) centre with precise control of enantioselectivity, is appealing but remains elusive. Here we report an asymmetric three-dimensional sulfur(VI) fluoride exchange (3D-SuFEx) reaction based on thionyl tetrafluoride gas (SOF4). A key step involves the chiral ligand-induced enantioselective defluorinative substitution of iminosulfur oxydifluorides using organolithium reagents. The resulting optically active sulfonimidoyl fluorides allow for further stereospecific fluoride-exchange by various nucleophiles, thereby establishing a modular platform for the asymmetric SuFEx ligation and the divergent synthesis of optically active S(VI) functional molecules.

Piperazine-Fused Cyclic Disulfides Unlock High-Performance Bioreductive Probes of Thioredoxins and Bifunctional Reagents for Thiol Redox Biology

We report piperazine-fused six-membered-cyclic disulfides as redox substrates that unlock best-in-class bioreduction probes for live cell biology, since their self-immolation after reduction is unprecedentedly rapid. We develop scalable, diastereomerically pure, six-step syntheses that access four key cis- and trans-piperazine-fused cyclic dichalcogenides without chromatography. Fluorogenic redox probes using the disulfide piperazines are activated >100-fold faster than the prior art monoamines, allowing us to deconvolute reduction and cyclization rates during activation. The cis- and trans-fused diastereomers have remarkably different reductant specificities, which we trace back to piperazine boat/chair conformation effects: the cis-fused disulfide C-DiThia is activated only by strong vicinal dithiol reductants, but the trans-disulfide T-DiThia is activated even by moderate concentrations of monothiols such as GSH. Thus, in cellular applications, cis-disulfide probes selectively report on the reductive activity of the powerful thioredoxin proteins, while trans-disulfides are rapidly but promiscuously reactive. Finally, we showcase late-stage diversifications of the piperazine-disulfides, promising their broad applicability as redox-cleavable cores for probes and prodrugs that interface powerfully with cellular thiol/disulfide redox biology, for solid phase synthesis and purification, and for stimulus-responsive linkers in bifunctional reagents and antibody-drug conjugates - in addition to their dithiols' potential as high-performance reducing agents.

Organometallic Bridge Diversification of Bicyclo[1.1.1]pentanes

Bicyclo[1.1.1]pentane (BCP) derivatives have attracted significant recent interest in drug discovery as alkyne, tert-butyl and arene bioisosteres, where their incorporation is frequently associated with increased compound solubility and metabolic stability. While strategies for functionalisation of the bridgehead (1,3) positions are extensively developed, platforms allowing divergent substitution at the bridge (2,4,5) positions remain limited. Recent reports have introduced 1-electron strategies for arylation and incorporation of a small range of other substituents, but are limited in terms of scope, yields or practical complexity. Herein, we show the synthesis of diverse 1,2,3-trifunctionalised BCPs through lithium-halogen exchange of a readily accessible BCP bromide. When coupled with medicinally relevant product derivatisations, our developed 2-electron "late stage" approach provides rapid and straightforward access to unprecedented BCP structural diversity (>20 hitherto-unknown motifs reported). Additionally, we describe a method for the synthesis of enantioenriched "chiral-at-BCP" bicyclo[1.1.1]pentanes through a novel stereoselective bridgehead desymmetrisation.

Radical Hydro-Fluorosulfonylation of Propargylic Alcohols via Electron Donor-Acceptor Photoactivation

A radical hydro-fluorosulfonylation of propargyl alcohols with FSO2Cl is presented based on the photoactivation of the electron donor-acceptor (EDA) complex. The reaction avoids the requirement for photocatalysts, bases, hydrogen donor reagents, any other additives, and harsh conditions, enabling the facile synthesis of various functionalized γ-hydroxy (E)-alkenylsulfonyl fluorides. These multifunctional sulfonyl fluorides can be further diversified, providing access to various privileged molecules of biological relevance.

Discovery of Arylfluorosulfates as Novel Fungicidal Agents against Plant Pathogens

A series of arylfluorosulfates were synthesized as fungicide candidates through a highly efficient sulfur fluoride exchange (SuFEx) reaction. A total of 32 arylfluorosulfate derivatives with simple structures have been synthesized, and most of them exhibited fungal activities in vitro against five agricultural pathogens (Rhizoctonia solani, Botrytis cinerea, Fusarium oxysporum, Pyricularia oryzae, and Phytophthora infestans). Among the target compounds, compound 31 exhibited great antifungal activity against Rhizoctonia solani (EC50 = 1.51 μg/mL), which was comparable to commercial fungicides carbendazim and thiabendazole (EC50 = 0.53 and 0.70 μg/mL, respectively); compounds 17 and 30 exhibited antifungal activities against Pyricularia oryzae (EC50 = 1.64 and 1.73 μg/mL, respectively) comparable to carbendazim (EC50 = 1.02 μg/mL). The in vitro antifungal effect of compound 31 was also evaluated on rice plants against Rhizoctonia solani. Significant preventive and curative efficacies were observed (89.2% and 91.8%, respectively, at 200 μg/mL), exceeding that of thiabendazole. Primary study on the mechanism of action indicated that compound 31 could suppress the sclerotia formation of Rhizoctonia solani even at a very low concentration (1.00 μg/mL), destroy the cell membrane and mitochondria, trigger the release of cellular contents, produce excessive reactive oxygen species (ROS), and suppress the activity of several related enzymes. This work could bring new insights into the development of arylfluorosulfates as novel fungicides.

Chemoselective Reactions of Functionalized Sulfonyl Halides

Chemoselective transformations of functionalized sulfonyl fluorides and chlorides are surveyed comprehensively. It is shown that sulfonyl fluorides provide an excellent selectivity control in their reactions. Thus, numerous conditions are tolerated by the SO2 F group - from amide and ester formation to directed ortho-lithiation and transition-metal-catalyzed cross-couplings. Meanwhile, sulfur (VI) fluoride exchange (SuFEx) is also compatible with numerous functional groups, thus confirming its title of "another click reaction". On the contrary, with a few exceptions, most transformations of functionalized sulfonyl chlorides typically occur at the SO2 Cl moiety.

Click Chemistry in Lithium-Metal Batteries

Lithium-metal batteries (LMBs) are considered the "holy grail" of the next-generation energy storage systems, and solid-state electrolytes (SSEs) are a kind of critical component assembled in LMBs. However, as one of the most important branches of SSEs, polymer-based electrolytes (PEs) possess several native drawbacks including insufficient ionic conductivity and so on. Click chemistry is a simple, efficient, regioselective, and stereoselective synthesis method, which can be used not only for preparing PEs with outstanding physical and chemical performances, but also for optimizing the stability of solid electrolyte interphase (SEI) layer and elevate the cycling properties of LMBs effectively. Here it is primarily focused on evaluating the merits of click chemistry, summarizing its existing challenges and outlining its increasing role for the designing and fabrication of advanced PEs. The fundamental requirements for reconstructing artificial SEI layer through click chemistry are also summarized, with the aim to offer a thorough comprehension and provide a strategic guidance for exploring the potentials of click chemistry in the field of LMBs.

Arylazo sulfones: multifaceted photochemical reagents and beyond

The photochemical action of arylazo sulfones under visible light irradiation has recently gained considerable attention for the construction of carbon-carbon and carbon-heteroatom bonds in organic synthesis. The inherent dyedauxiliary group (-N2SO2R) embedded in the reagent is responsible for the absorption of visible light even in the absence of a photocatalyst, additive or oxidant, leading to the generation of three different radicals, viz. aryl (carbon-centred), sulfonyl (sulphur-centred) and diazenyl (nitrogen-centred) radicals, under different reaction conditions. Encountering a reagent with such a versatile behaviour is quite rare, which makes arylazo sulfones a highly interesting class of compounds. The mild reaction conditions under which these reagents can operate are an added advantage. Recently, they are also being used as non-ionic photoacid generators (PAGs), electron acceptors, and hydrogen atom transfer (HAT) and imination reagents in a number of synthetic transformations. They have displayed substantial damaging effect on the structure of DNA in the presence of light which can lead to their use as phototoxic pharmaceuticals for cancer treatment. Moreover, their photochemistry is also being exploited in polymerization reactions (as photoinitiators) and in materials chemistry (surface modification).

C-SuFEx linkage of sulfonimidoyl fluorides and organotrifluoroborates

Sulfur(VI) fluoride exchange, a new type of linkage reaction, has excellent potential for application in functional molecule linkage to prepare pharmaceuticals, biomolecules, and polymers. Herein, a C-SuFEx reaction is established to achieve fast (in minutes) linkage between sulfonimidoyl fluorides and aryl/alkyl organotrifluoroborates. Potassium organotrifluoroborates are instantaneously activated via a substoichiometric amount of trimethylsilyl triflate to afford organodifluoroboranes, releasing BF3 as an activating reagent in situ. This sulfur(VI) fluoride exchange technique is capable of forming S(VI)-C(alkyl), S(VI)-C(alkenyl) and S(VI)-C(aryl) bonds, demonstrating its broad scope. Natural products and pharmaceuticals with sensitive functional groups, such as valdecoxib, celecoxib and diacetonefructose, are compatible with this protocol, allowing the formation of diverse sulfoximines.

The Minimum Protein Staple? - Towards 'bio'-Baldwin's rules via inter-phosphosite linking in the MEK1 activation loop

In small molecule organic chemistry, the heuristic insight into ring-forming processes that was enabled by Baldwin's rules some 50 years ago proved a step-change in the role of mechanistically guided synthesis. It created a lens upon and marker of fundamental stereoelectronic and conformation-guided chemical processes. However, despite the widespread role of stereoelectronics and conformational control in Biology, no equivalent coherent exploitation of trapped, ring-forming processes yet exists in biomolecules. In the development of a minimal ring-closing process in intact proteins that might prove suitable in a coherent rule-set, we have tested endo-trig ring-closing conjugate thioether lanthionine (Lan) -CH2-S-CH2- formation as a limiting cyclization. Spontaneous Lan formation in proteins is rare if not non-existent and when found in natural product cyclic peptides it requires the mediation of corresponding biosynthetic enzymes as well as productive reactive conformations to guide it. Here, we show that within a conformationally flexible and functionally important protein loop - the MAPK kinase phosphorylation-targeted activation loop - Lan ring-closing is possible. Ring-closing proves to be critically dependent on the location of a trig electrophilic site in just one of two regioisomeric potential precursors to allow phosphosite-to-phosphosite 'stapling'. This first example of spontaneous protein thioether ring-closing/'stapling' and its accessibility from just one precursor (despite the potential for both to form an identical 'staple') now reveals the potential for Lan formation not only as an accessible form of minimal stapling in proteins but also as an exquisitely sensitive probe of associated protein geometries. We suggest that the use of this (as well as the development of other such, intramolecular protein traps that are dependent on inherent protein-controlled reactivity rather than forced crosslinking) may allow the broader trapping and mapping of relevant, even minor, protein states. In this way, protein ring formation may enable a form of extended 'bio-Baldwin's rules' that help to delineate relevant protein conformational space.