SuFEx Click Chemistry Enabled Late-Stage Drug Functionalization

Synthesis and antitumor activities of transition metal complexes of a bis-Schiff base of 2-hydroxy-1-naphthalenecarboxaldehyde

The complexes of Schiff base have attracted much attention for their potential biological activities. In this research, five transition metal complexes TM₃L₂(OAc)₂ (TM = Cu, 1; Ni, 2; Co, 3; Mn, 4; Fe, 5) were prepared using a bis-Schiff base of N,N'-bis[(2-hydroxy-1-naphthalenyl)methylene]-propane-1,3-diamine (H₂L), which present similar linear trinuclear structures with their three metal ions consolidated by two bis-Schiff base ligands and two acetate ligands. Their antitumor activities in vitro were screened through seven human cancer cell lines by the 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide (MTT) assay. It revealed that complexes 1, 2 and 5 show much higher antitumor activities than the bis-Schiff base ligand and complexes 3 and 4, and even than cisplatin. Among them, complex 1 has the highest inhibitory effects on tumor cells with its IC₅₀ value (half-inhibitory concentration) being less than 0.5 μM for human bladder cancer cell line T-24, at which concentration complex 1 shows nearly no toxicity to the normal cell HL-7702 as revealed by flow cytometry. All of these demonstrate a potential anti-cancer candidate for complex 1, which induces tumor cell apoptosis by blocking T-24 tumor cells at the G2/M phase of the cell cycle, reducing mitochondrial membrane potential, increasing the concentration of reactive oxygen species and Ca²⁺ in the cell, and changing the expression of proteins.

A one-pot protocol for the fluorosulfonation and Suzuki coupling of phenols and bromophenols, streamlined access to biaryls and terphenyls

A one-pot protocol for the fluorosulfation and Suzuki coupling of phenols is described. The tandem reaction proceeds efficiently at room temperature, and various biaryls and biaryl fluorosulfates were obtained in good to excellent yields. Furthermore, biaryl fluorosulfates were utilized as versatile building blocks for the preparation of terphenyls.

Synthesis of 18F-Labeled Aryl Fluorosulfates via Nucleophilic Radiofluorination

Sulfuryl fluoride gas is a key reagent for SO₂F transfer. However, conventional SO₂F transfer reactions have limited ¹⁸F-radiochemistry translation, due to the inaccessibility of gaseous [¹⁸F]SO₂F₂. Herein, we report the first SO₂F₂-free synthesis of aryl [¹⁸F]fluorosulfates from both phenolic and isolated aryl imidazylate precursors with cyclotron-produced ¹⁸F^-. The radiochemical yields ranged from moderate to good with excellent functional group tolerance. The reliability of our approach was validated by the automated radiosynthesis of 4-acetamidophenyl [¹⁸F]fluorosulfate.

Sulfur(VI) Fluoride Exchange (SuFEx)-Enabled High-Throughput Medicinal Chemistry

Optimization of small-molecule probes or drugs is a synthetically lengthy, challenging, and resource-intensive process. Lack of automation and reliance on skilled medicinal chemists is cumbersome in both academic and industrial settings. Here, we demonstrate a high-throughput hit-to-lead process based on the biocompatible sulfur(VI) fluoride exchange (SuFEx) click chemistry. A high-throughput screening hit benzyl (cyanomethyl)carbamate (K_i = 8 μM) against a bacterial cysteine protease SpeB was modified with a SuFExable iminosulfur oxydifluoride [RN═S(O)F₂] motif, rapidly diversified into 460 analogs in overnight reactions, and the products were directly screened to yield drug-like inhibitors with 480-fold higher potency (K_i = 18 nM). We showed that the improved molecule is active in a bacteria-host coculture. Since this SuFEx linkage reaction succeeds on picomole scale for direct screening, we anticipate our methodology can accelerate the development of robust biological probes and drug candidates.

Diversity Oriented Clicking (DOC): Divergent Synthesis of SuFExable Pharmacophores from 2-Substituted-Alkynyl-1-Sulfonyl Fluoride (SASF) Hubs

Diversity Oriented Clicking (DOC) is a unified click-approach for the modular synthesis of lead-like structures through application of the wide family of click transformations. DOC evolved from the concept of achieving "diversity with ease", by combining classic C-C π-bond click chemistry with recent developments in connective SuFEx-technologies. We showcase 2-Substituted-Alkynyl-1-Sulfonyl Fluorides (SASFs) as a new class of connective hub in concert with a diverse selection of click-cycloaddition processes. Through the selective DOC of SASFs with a range of dipoles and cyclic dienes, we report a diverse click-library of 173 unique functional molecules in minimal synthetic steps. The SuFExable library comprises 10 discrete heterocyclic core structures derived from 1,3- and 1,5-dipoles; while reaction with cyclic dienes yields several three-dimensional bicyclic Diels-Alder adducts. Growing the library to 278 discrete compounds through late-stage modification was made possible through SuFEx click derivatization of the pendant sulfonyl fluoride group in 96 well-plates-demonstrating the versatility of the DOC approach for the rapid synthesis of diverse functional structures. Screening for function against MRSA (USA300) revealed several lead hits with improved activity over methicillin.

SO2F2-Mediated one-pot cascade process for transformation of aldehydes (RCHO) to cyanamides (RNHCN)

A simple, mild and practical cascade process for the direct conversion of aldehydes to cyanamides was developed featuring a wide substrate scope and great functional group tolerability. This method allows for transformations of readily available, inexpensive, and abundant aldehydes to highly valuable cyanamides in a pot, atom, and step-economical manner with a green nitrogen source. This protocol will serve as a robust tool for the installation of the cyanamide moiety in various complicated molecules.

Liganding Functional Tyrosine Sites on Proteins Using Sulfur-Triazole Exchange Chemistry

Tuning reactivity of sulfur electrophiles is key for advancing click chemistry and chemical probe discovery. To date, activation of the sulfur electrophile for protein modification has been ascribed principally to stabilization of a fluoride leaving group (LG) in covalent reactions of sulfonyl fluorides and arylfluorosulfates. We recently introduced sulfur-triazole exchange (SuTEx) chemistry to demonstrate the triazole as an effective LG for activating nucleophilic substitution reactions on tyrosine sites of proteins. Here, we probed tunability of SuTEx for fragment-based ligand discovery by modifying the adduct group (AG) and LG with functional groups of differing electron-donating and -withdrawing properties. We discovered the sulfur electrophile is highly sensitive to the position of modification (AG versus LG), which enabled both coarse and fine adjustments in solution and proteome activity. We applied these reactivity principles to identify a large fraction of tyrosine sites (∼30%) on proteins (∼44%) that can be liganded across >1500 probe-modified sites quantified by chemical proteomics. Our proteomic studies identified noncatalytic tyrosine and phosphotyrosine sites that can be liganded by SuTEx fragments with site specificity in lysates and live cells to disrupt protein function. Collectively, we describe SuTEx as a versatile covalent chemistry with broad applications for chemical proteomics and protein ligand discovery.

3-Oxo-β-sultam as a Sulfonylating Chemotype for Inhibition of Serine Hydrolases and Activity-Based Protein Profiling

3-Oxo-β-sultams are four-membered ring ambident electrophiles that can react with nucleophiles either at the carbonyl carbon or at the sulfonyl sulfur atoms, and that have been reported to inhibit serine hydrolases via acylation of the active-site serine residue. We have developed a panel of 3-oxo-β-sultam inhibitors and show, through crystallographic data, that they are regioselective sulfonylating electrophiles, covalently binding to the catalytic serine of human and porcine elastases through the sulfur atom. Application of 3-oxo-β-sultam-derived activity-based probes in a human proteome revealed their potential to label disease-related serine hydrolases and proteasome subunits. Activity-based protein profiling applications of 3-oxo-β-sultams should open up new opportunities to investigate these classes of enzymes in complex proteomes and expand the toolbox of available sulfur-based covalent protein modifiers in chemical biology.

Silicon-Free SuFEx Reactions of Sulfonimidoyl Fluorides: Scope, Enantioselectivity, and Mechanism

SuFEx reactions, in which an S−F moiety reacts with a silyl‐protected phenol, have been developed as powerful click reactions. In the current paper we open up the potential of SuFEx reactions as enantioselective reactions, analyze the role of Si and outline the mechanism of this reaction. As a result, fast, high‐yielding, “Si‐free” and enantiospecific SuFEx reactions of sulfonimidoyl fluorides have been developed, and their mechanism shown, by both experimental and theoretical methods, to yield chiral products.

Discovery of Lysine-Targeted eIF4E Inhibitors through Covalent Docking

Eukaryotic translation initiation factor 4E (eIF4E) binds the m7GTP cap structure at the 5'-end of mRNAs, stimulating the translation of proteins implicated in cancer cell growth and metastasis. eIF4E is a notoriously challenging target, and most of the reported inhibitors are negatively charged guanine analogues with negligible cell permeability. To overcome these challenges, we envisioned a covalent targeting strategy. As there are no cysteines near the eIF4E cap binding site, we developed a covalent docking approach focused on lysine. Taking advantage of a "make-on-demand" virtual library, we used covalent docking to identify arylsulfonyl fluorides that target a noncatalytic lysine (Lys162) in eIF4E. Guided by cocrystal structures, we elaborated arylsulfonyl fluoride 2 to 12, which to our knowledge is the first covalent eIF4E inhibitor with cellular activity. In addition to providing a new tool for acutely inactivating eIF4E in cells, our computational approach may offer a general strategy for developing selective lysine-targeted covalent ligands.

Arenesulfonyl Fluoride Synthesis via Copper-Catalyzed Fluorosulfonylation of Arenediazonium Salts

We report herein a general and practical copper-catalyzed fluorosulfonylation reaction of a wide range of abundant arenediazonium salts to smoothly prepare various arenesulfonyl fluorides using the 1,4-diazabicyclo[2.2.2]octane-bis(sulfur dioxide) adduct as a convenient sulfonyl source in combination with KHF₂ as an ideal fluorine source and without the need for additional oxidants. Interestingly, the electronic character of the arene ring in the starting arenediazonium salts has a significant impact on the reaction mechanistic pathway.

Clickable coupling of carboxylic acids and amines at room temperature mediated by SO2F2: a significant breakthrough for the construction of amides and peptide linkages

The construction of amide bonds and peptide linkages is one of the most fundamental transformations in all life processes and organic synthesis. The synthesis of structurally ubiquitous amide motifs is essential in the assembly of numerous important molecules such as peptides, proteins, alkaloids, pharmaceutical agents, polymers, ligands and agrochemicals. A method of SO2F2-mediated direct clickable coupling of carboxylic acids with amines was developed for the synthesis of a broad scope of amides in a simple, mild, highly efficient, robust and practical manner (>110 examples, >90% yields in most cases). The direct click reactions of acids and amines on a gram scale are also demonstrated using an extremely easy work-up and purification process of washing with 1 M aqueous HCl to provide the desired amides in greater than 99% purity and excellent yields.

Highly Stable Copper(I)-Thiacalix[4]arene-Based Frameworks for Highly Efficient Catalysis of Click Reactions in Water

Environmentally friendly metal-organic frameworks (MOFs) have gained considerable attention for their potential use as heterogeneous catalysts. Herein, two Cu^I -based MOFs, namely, [Cu₄ Cl₄ L]⋅CH₃ OH⋅1.5 H₂ O (1-Cl) and [Cu₄ Br₄ L]⋅DMF⋅0.5 H₂ O (1-Br), were assembled with new functionalized thiacalix[4]arenes (L) and halogen anions X^- (X=Cl and Br) under solvothermal conditions. Remarkably, catalysts 1-Cl and 1-Br exhibit great stability in aqueous solutions over a wide pH range. Significantly, MOFs 1-Cl and 1-Br, as recycled heterogeneous catalysts, are capable of highly efficient catalysis for click reactions in water. The MOF structures, especially the exposed active Cu^I sites and 1D channels, play a key role in the improved catalytic activities. In particular, their catalytic activities in water are greatly superior to those in organic solvents or even in mixed solvents. This work proposes an attractive route for the design and self-assembly of environmentally friendly MOFs with high catalytic activity and reusability in water.

Global targeting of functional tyrosines using sulfur-triazole exchange chemistry

Covalent probes serve as valuable tools for global investigation of protein function and ligand binding capacity. Despite efforts to expand coverage of residues available for chemical proteomics (e.g. cysteine and lysine), a large fraction of the proteome remains inaccessible with current activity-based probes. Here, we introduce sulfur-triazole exchange (SuTEx) chemistry as a tunable platform for developing covalent probes with broad applications for chemical proteomics. We show modifications to the triazole leaving group can furnish sulfonyl probes with ~5-fold enhanced chemoselectivity for tyrosines over other nucleophilic amino acids to investigate, for the first time, more than 10,000 tyrosine sites in lysates and live cells. We discover that tyrosines with enhanced nucleophilicity are enriched in enzymatic, protein-protein interaction, and nucleotide recognition domains. We apply SuTEx as a chemical phosphoproteomics strategy to monitor activation of phosphotyrosine sites. Collectively, we describe SuTEx as a biocompatible chemistry for chemical biology investigations of the human proteome.

Rh-Catalyzed Highly Enantioselective Synthesis of Aliphatic Sulfonyl Fluorides

Rh-catalyzed, highly enantioselective (up to 99.8% ee) synthesis of aliphatic sulfonyl fluorides was accomplished. This protocol provides a portal to a class of novel 2-aryl substituted chiral sulfonyl fluorides, which are otherwise extremely difficult to access. This asymmetric synthesis has the feature of mild conditions, excellent functional group compatibility, and wide substrate scope (51 examples) generating a wide array of structurally unique chiral β-arylated sulfonyl fluorides for sulfur(VI) fluoride exchange (SuFEx) click reaction and drug discovery.

A cascade process for directly converting nitriles (RCN) to cyanamides (RNHCN) via SO2F2-activated Tiemann rearrangement

A simple, mild and practical process for the direct conversion of nitriles to cyanamides was newly discovered and exhibited a wide substrate scope as well as great functional group-tolerability (36 examples). In this efficient strategy, the in situ generated amidoximes obtained from the reaction of nitriles with hydroxylamine subsequently underwent Tiemann rearrangement, producing the corresponding cyanamides with great isolated yields under SO2F2. Additionally, the control experiments reportedly shed light on the tentative mechanism involved in the formation and elimination of the key intermediate: a sulfonyl ester.

SuFEx-enabled, agnostic discovery of covalent inhibitors of human neutrophil elastase

Sulfur fluoride exchange (SuFEx) has emerged as the new generation of click chemistry. We report here a SuFEx-enabled, agnostic approach for the discovery and optimization of covalent inhibitors of human neutrophil elastase (hNE). Evaluation of our ever-growing collection of SuFExable compounds toward various biological assays unexpectedly revealed a selective and covalent hNE inhibitor: benzene-1,2-disulfonyl fluoride. Synthetic derivatization of the initial hit led to a more potent agent, 2-(fluorosulfonyl)phenyl fluorosulfate with IC₅₀ 0.24 μM and greater than 833-fold selectivity over the homologous neutrophil serine protease, cathepsin G. The optimized, yet simple benzenoid probe only modified active hNE and not its denatured form.

Installation of -SO2F groups onto primary amides

A protocol of SO₂F₂-mediated installation of sulfonyl fluoride onto primary amides has been developed providing a new portal to sulfur(VI) fluoride exchange (SuFEx) click chemistry. The generated molecules contain pharmaceutically important amide and -SO₂F moieties for application in the discovery of new therapeutics.

A rapid access to aliphatic sulfonyl fluorides

The past few years have witnessed a fast-growing research interest on the study of sulfonyl fluorides as reactive probes in chemical biology and molecular pharmacology, which raises an urgent need for the development of effective synthetic methods to expand the toolkit. Herein, we present the invention of a facile and general approach for the synthesis of aliphatic sulfonyl fluorides via visible-light-mediated decarboxylative fluorosulfonylethylation. The method is based on abundant carboxylic acid feed stock, applicable to various alkyl carboxylic acids including primary, secondary, and tertiary acids, and is also suitable for the modification of natural products like amino acids, peptides, as well as drugs, forging a rapid, metal-free approach to build sulfonyl fluoride compound libraries of considerable structural diversity. Further diversification of the SO₂F-containing products is also demonstrated, which allows for access to a range of pharmaceutically important motifs such as sultam, sulfonate, and sulfonamide.

Sulfonyl fluorides are important probes in chemical biology and molecular pharmacology. Here, the authors report a mild visible light-mediated decarboxylative fluorosulfonylethylation for the synthesis of aliphatic sulfonyl fluorides from a wide range of carboxylic acids, including natural products and drug derivatives.

Overview of Recent Strategic Advances in Medicinal Chemistry

Introducing novel strategies, concepts, and technologies that speed up drug discovery and the drug development cycle is of great importance both in the highly competitive pharmaceutical industry as well as in academia. This Perspective aims to present a "big-picture" overview of recent strategic innovations in medicinal chemistry and drug discovery.

Recent applications of click chemistry in drug discovery

Introduction: Click chemistry has been exploited widely in the past to expedite lead discovery and optimization. Indeed, Copper-catalyzed azide-alkyne cycloaddition (CuAAC) click chemistry is a bioorthogonal reaction of widespread utility throughout medicinal chemistry and chemical biology. Areas covered: The authors review recent applications of CuAAC click chemistry to drug discovery based on the literature published since 2013. Furthermore, the authors provide the reader with their expert perspectives on the area including their outlook on future developments. Expert opinion: Click chemistry reactions are an important part of the medicinal chemistry toolbox and offer substantial advantages to medicinal chemists in terms of overcoming the limitations of useful chemical synthesis, increasing throughput, and improving the quality of compound libraries. To explore new chemical spaces for drug-like molecules containing a high degree of structural diversity, it may be useful to merge the diversity-oriented synthesis and 'privileged' substructure-based strategy with bioorthogonal reactions using sophisticated automation and flow systems to improve productivity. Large compound libraries obtained in this way should be of great value for the discovery of bioactive compounds and therapeutic agents.

Cascade Process for Direct Transformation of Aldehydes (RCHO) to Nitriles (RCN) Using Inorganic Reagents NH2OH/Na2CO3/SO2F2 in DMSO

A simple, mild, and practical process for direct conversion of aldehydes to nitriles was developed feathering a wide substrate scope and great functional group tolerability (52 examples, over 90% yield in most cases) using inorganic reagents (NH₂OH/Na₂CO₃/SO₂F₂) in DMSO. This method allows for transformations of readily available, inexpensive, and abundant aldehydes to highly valuable nitriles in a pot, atom, and step-economical manner without transition metals. This protocol will serve as a robust tool for the installation of cyano-moieties to complicated molecules.

Transition-metal-free regioselective construction of 1,5-diaryl-1,2,3-triazoles through dehydrative cycloaddition of alcohols with aryl azides mediated by SO2F2

A novel, simple and practical method for mild, efficient, cost-effective and regioselective synthesis of highly valuable 1,5-diaryl-1,2,3-triazoles was achieved through dehydrative annulation of readily available alcohols with aryl azides. The reaction proceeded at room temperature, without any metal catalysts, exhibiting excellent compatibility to a large variety of functional groups (>50 examples), resulting in up to quantitative yields.

Novel Approaches to Access Arylfluorosulfates and Sulfamoyl Fluorides Based on Sulfur (VI) Fluoride Exchange

Sulfur (VI) fluoride exchange (SuFEx) is a new family of click chemistry reactions that relies on readily available sulfuryl fluoride (SO₂ F₂ ) and ethenesulfonyl fluoride to build diverse chemical structures bearing the S^VI -F motif, such as fluorosulfate (-OSO₂ F) and sulfonyl fluoride (-SO₂ F). These motifs could be useful functional groups and connective linkers in organic synthesis. This unit describes two protocols for performing SuFEx. The first protocol describes an in situ method for rapid generation of arylfluorosulfates in 96-well plates for high-throughput screening. The second protocol outlines use of a shelf-stable fluorosulfuryl imidazolium salt for generating arylfluorosulfates and sulfamoyl fluorides. © 2019 by John Wiley & Sons, Inc.

Applications of sulfuryl fluoride (SO2F2) in chemical transformations

A number of novel methodologies concerning the chemical, biological and medicinal applications of sulfuryl fluoride (SO₂F₂) gas have dramatically improved year by year.

Intermolecular oxidative radical fluoroalkylfluorosulfonylation of unactivated alkenes with (fluoroalkyl)trimethylsilane, silver fluoride, sulfur dioxide and N-fluorobenzenesulfonimide

Reaction of unactivated alkenes affords various fluoroalkyl-containing alkyl sulfonyl fluorides with good functional group tolerance under mild conditions.

The growing applications of SuFEx click chemistry

SuFEx (Sulfur Fluoride Exchange) is a modular, next generation family of click reactions, geared towards the rapid and reliable assembly of functional molecules.

Regioselective installation of fluorosulfate (–OSO2F) functionality into aromatic C(sp2)–H bonds for the construction of para-amino-arylfluorosulfates

The synthesis of novel para-amino-arylfluorosulfates was achieved through installing fluorosulfate functionality into aromatic C(sp²)–H bonds mediated by sulfuryl fluoride.

SO2F2 mediated transformation of pyrazolones into pyrazolyl fluorosulfates

The construction of a class of novel N-heterocyclic molecules containing both pyrazole and fluorosulfate functionalities was achieved through the reactions of pyrazolones with SO₂F₂ in good to excellent yields.

Arylfluorosulfate-Based Electrophiles for Covalent Protein Labeling: A New Addition to the Arsenal

Selective covalent modification of a targeted protein is a powerful tool in chemical biology and drug discovery, with applications ranging from identification and characterization of proteins and their functions to the development of targeted covalent inhibitors. Most covalent ligands contain an affinity motif and an electrophilic warhead that reacts with a nucleophilic residue of the targeted protein. Because the electrophilic warhead is prone to react and modify off‐target nucleophiles, its reactivity should be balanced carefully to maximize target selectivity. Arylfluorosulfates have recently emerged as latent electrophiles for selective labeling of context‐specific tyrosine and lysine residues in protein pockets. Here, we review the recent but intense introduction of arylfluorosulfates into the arsenal of available warheads for selective covalent modification of proteins. We highlight the untapped potential of this functional group for use in chemical biology and drug discovery.

SuFEx in Metal-Organic Frameworks: Versatile Postsynthetic Modification Tool

A new type of click reaction, sulfur(VI) fluoride exchange (SuFEx), has been utilized to prepare five postsynthetically modified UiO-67 series metal-organic frameworks (MOFs). The postsynthetic modification (PSM) via SuFEx can be achieved selectively for the sulfonyl fluoride (R-SO₂F) without degrading the MOF structure as confirmed by X-ray crystallographic analysis. The present SuFEx method provides a straightforward tool for introducing new functionality inside MOFs. Introduction of an imidazolium group into the MOF afforded a heterogeneous catalyst for the benzoin condensation reaction.