Sulfur-Fluoride Exchange (SuFEx)-Mediated Synthesis of Sterically Hindered and Electron-Deficient Secondary and Tertiary Amides via Acyl Fluoride Intermediates

Benzene-1,3-disulfonyl Fluoride Mediated Synthesis of Glycosyl Fluorides from Glycosyl Hemiacetals

We developed an efficient method for synthesizing glycosyl fluorides from glycosyl hemiacetals using benzene-1,3-disulfonyl fluoride (S2) as the fluorinating agent in combination with the base DBU (1,8-diazabicyclo[5.4.0]undec-7-ene) under mild conditions. This approach enabled the successful synthesis of 17 glycosyl fluorides with various functional groups, including disaccharides and deoxysulfates, with yields of up to 99%. The utility of these synthesized glycosyl fluorides was further demonstrated in the synthesis of important O- and C-glycosides.

Deoxyfluorinated amidation and esterification of carboxylic acid by pyridinesulfonyl fluoride

Amide bond synthesis is one of the most used reactions in medicinal chemistry. We report an amide bond formation reaction through deoxyfluorinated carboxylic acids under mild conditions using 2-pyridinesulfonyl fluoride. The reaction procedure has been used in a one-pot synthesis of amides and esters via in situ generation of acyl fluoride. This one-pot synthetic method provides easy access to amides and esters. Using this method, we have sequentially synthesized a tetrapeptide and calceolarioside-B glycoside derivative with good yields.

What is the future of click chemistry in drug discovery and development?

INTRODUCTION

The concept of click chemistry was introduced in 2001 as an effective, efficient, and sustainable approach to making functional groups harnessing the thermodynamic properties of a set of known chemical reactions that are based on nature. Some of the most common examples include reactions that produce 1,2,3-triazoles, which have been used with great success in drug discovery and development, and in chemical biology. The reactions unite two molecules quickly and irreversibly, and the reactions can be performed inside living cells, without harming the cell.

AREAS COVERED

The main focus of this perspective is the future of click chemistry in drug discovery and development, exemplified by novel click chemistry approaches and other aspects of the drug development enterprise, like SPAAC and analogous techniques, PROTACs, as well as diversity-oriented click chemistry.

EXPERT OPINION

Drug discovery and development has benefited enormously from the amazing advances that have been made in the field of click chemistry since 2001. The methods most likely to have the most future applications include metal-catalyzed azide-alkyne cycloadditions giving 1,2,3-triazoles, SPAAC for medical diagnostics and vaccine development, other congeners, Sulfur-Fluoride Exchange (SuFEx) and Diversity-Oriented Clicking (DOC), a concept with diverse molecular methodology with the potential for obtaining extensive molecular diversity.

Synthesis of acyl fluorides through deoxyfluorination of carboxylic acids

A direct deoxyfluorination of carboxylic acids by utilizing inorganic potassium fluoride (KF) as a safe and inexpensive fluoride source has been developed. Both aryl carboxylic acids and cinnamyl carboxylic acids could be efficiently transformed into valuable acyl fluorides in moderate to high yields with good functional group tolerance. A scale-up reaction could be carried out smoothly under solvent-free conditions, which further demonstrated the practicality of this reaction in organic synthesis.

Triflylpyridinium as Coupling Reagent for Rapid Amide and Ester Synthesis

An effective method has been developed to facilitate the synthesis of amides and esters at ambient temperature within 5 min, in which a stable and easily accessible triflylpyridinium reagent is used. Remarkably, this method not only has a wide range of substrate compatibility but also could realize the scalable synthesis of peptide and ester via a continuous flow process. Moreover, excellent chirality retentions are presented during activation of carboxylic acid.

A diversity oriented clicking strategy: the stereoselective synthesis of highly-functionalised olefins from 2-substituted-alkynyl-1-sulfonyl fluorides

A novel series of addition reactions of highly reactive 2-substituted-alkynyl-1-sulfonyl fluoride (SASF) hubs with DMSO and DMF for the synthesis of two unique sulfonyl fluoride cores is described. The stereoselective chemistry allowed the unprecedented syntheses of 12 (Z)-2-(dimethylsulfonio)-2-(fluorosulfonyl)-1-substitutedethen-1-olates and 10 (E)-1-(dimethylamino)-3-oxo-3-substitutedprop-1-ene-2-sulfonyl fluorides from DMSO and DMF, respectively. The reactions proceed expediently to give single products in excellent yield without the need for chromatographic purification. Furthermore, the utility of the DMSO derived products is demonstrated in the synthesis of synthetically valuable β-keto sulfonyl fluorides under hydrogenation conditions in excellent yields.

Ni-catalysed deamidative fluorination of amides with electrophilic fluorinating reagents

We describe here a Ni-catalysed deamidative fluorination of diverse amides with electrophilic fluorinating reagents. Different types of amides including aromatic amides and olefinic amides were well compatible, affording the corresponding acyl fluorides in good to excellent yields.

SuFEx-enabled, chemoselective synthesis of triflates, triflamides and triflimidates

Sulfur(vi) Fluoride Exchange (SuFEx) chemistry has emerged as a next-generation click reaction, designed to assemble functional molecules quickly and modularly. Here, we report the ex situ generation of trifluoromethanesulfonyl fluoride (CF3SO2F) gas in a two chamber system, and its use as a new SuFEx handle to efficiently synthesize triflates and triflamides. This broadly tolerated protocol lends itself to peptide modification or to telescoping into coupling reactions. Moreover, redesigning the SVI-F connector with a S[double bond, length as m-dash]O → S[double bond, length as m-dash]NR replacement furnished the analogous triflimidoyl fluorides as SuFEx electrophiles, which were engaged in the synthesis of rarely reported triflimidate esters. Notably, experiments showed H2O to be the key towards achieving chemoselective trifluoromethanesulfonation of phenols vs. amine groups, a phenomenon best explained-using ab initio metadynamics simulations-by a hydrogen bonded termolecular transition state for the CF3SO2F triflylation of amines.

Deoxyfluorination of Carboxylic Acids with CpFluor: Access to Acyl Fluorides and Amides

3,3-Difluoro-1,2-diphenylcyclopropene (CpFluor), a bench-stable fluorination reagent, has been developed in the deoxyfluorination of carboxylic acids to afford various acyl fluorides. This all-carbon-based fluorination reagent enabled the efficient transformation of (hetero)aryl, alkyl, alkenyl, and alkynyl carboxylic acids to the corresponding acyl fluorides under the neutral conditions. This deoxyfluorination method was featured by the synthesis of acyl fluorides with in-situ formed CpFluor, as well as the one-pot amidation reaction of carboxylic acids via in-situ formed acyl fluorides.

Recent Advances in the Synthesis of Acyl Fluorides

Acyl fluorides are valuable intermediates in organic synthesis. They are increasingly employed in peptide synthesis, in challenging esterification and amidation reactions or in transition-metal-catalyzed transformations. This review summarizes recent advances in their preparation.

1 Introduction

2 Nucleophilic Fluorination

2.1 α-Fluoroamine Reagents

2.2 Sulfur-Based Reagents

2.3 Metal Catalysts

2.4 Phosphorus-Based Reagents

2.5 N,N′-Dicyclohexylcarbodiimide/HF·Pyridine

2.6 Uranium Hexafluoride

2.7 Bromine Trifluoride

3 Radical Fluorination

4 Conclusion

Synthesis of Acyl Fluorides from Carboxylic Acids Using NaF-Assisted Deoxofluorination with XtalFluor-E

The synthesis of acyl fluorides using the deoxofluorination reaction of carboxylic acids using XtalFluor-E is described. This transformation, assisted by a catalytic amount of NaF, occurs at room temperature in EtOAc, where XtalFluor-E behaves as the activating agent and the fluoride source. A wide range of acyl fluorides were obtained in moderate to excellent yields (36-99%) after a simple filtration on a pad of silica gel. We also demonstrated that sequential deoxofluorination/amidation was possible.

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.

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.

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.

Development of Triazinone-Based Condensing Reagents for Amide Formation

Novel triazinone-based condensing reagents have been developed. The palladium-catalyzed O-N allylic rearrangement of 2-(allyloxy)-4,6-dichloro-1,3,5-triazine and subsequent regioselective substitution using alcohols and an amine afforded chlorotriazinones, which can be readily converted using N-methylmorpholine into the corresponding condensing reagents. The condensation of carboxylic acids and amines using these reagents proceeded to afford the desired amides in good yields. In comparison with 4-(4,6-dimethoxy-1,3,5-triazin-2-yl)-4-methylmorpholinium chloride, the newly synthesized triazinone-based condensing reagents exhibited higher reactivity.

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.

Direct Access to Acyl Fluorides from Carboxylic Acids Using a Phosphine/Fluoride Deoxyfluorination Reagent System

A fast and simple method for deoxyfluorination of carboxylic acids is presented. The protocol employs commodity chemicals (PPh₃, NBS, fluoride), affording products in excellent yields under mild conditions. Acyloxyphosphonium ion, the key reaction intermediate, was identified by NMR spectroscopic methods. Brønsted acidic conditions are essential for efficient C-F bond formation. The protocol displays scalability, high functional group tolerance, chemoselectivity, and easy purification of products. Deoxyfluorination of active pharmaceutical ingredients was established.

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.

A rapid one-step surface functionalization of polyvinyl chloride by combining click sulfur(vi)-fluoride exchange with benzophenone photochemistry

We demonstrated a rapid one-step strategy for polyvinyl chloride surface functionalization by combining click “sulfur(vi)-fluoride exchange” (SuFEx) reaction with benzophenone photochemistry.

Modification of Carbon Fibre Surfaces by Sulfur-Fluoride Exchange Click Chemistry

Technologies that enable surface modification are in high demand and are critical for the implementation of new functional materials and devices. Here, we describe the first modification of a carbon surface (in this case carbon fiber) using the sulfur-fluoride exchange (SuFEx) reaction. The parent sulfur (VI) fluoride moiety can be installed directly to the surface via electrochemical deposition of the fluorosulfate phenyldiazonium tetrafluoroborate salt, or by 'SuFExing' a phenol on the carbon surface followed by treatment of the material with SO2 F2 ; similar to a 'graft to' or 'graft from' functionalization approach. We demonstrate that these SuFEx-able surfaces readily undergo exchange with aryl silyl ethers, and that the subsequent sulfate linkages are themselves stable under electrochemical redox conditions. Finally, we showcase the utility of the SuFEx chemistry by installing a pendant amino group to the fiber surface resulting in interfacial shear strength improvements of up to 130 % in epoxy resin.

Quantitative and Orthogonal Formation and Reactivity of SuFEx Platforms

The constraints of minute reactant amounts and the impossibility to remove any undesired surface‐bound products during monolayer functionalization of a surface necessitate the selection of efficient, modular and orthogonal reactions that lead to quantitative conversions. Herein, we explore the character of sulfur–fluoride exchange (SuFEx) reactions on a surface, and explore the applicability for quantitative and orthogonal surface functionalization. To this end, we demonstrate the use of ethenesulfonyl fluoride (ESF) as an efficient SuFEx linker for creating “SuFEx‐able” monolayer surfaces, enabling three distinct approaches to utilize SuFEx chemistry on a surface. The first approach relies on a di‐SuFEx loading allowing dual functionalization with a nucleophile, while the two latter approaches focus on dual (CuAAC–SuFEx/SPOCQ–SuFEx) click platforms. The resultant strategies allow facile attachment of two different substrates sequentially on the same platform. Along the way we also demonstrate the Michael addition of ethenesulfonyl fluoride to be a quantitative surface‐bound reaction, indicating significant promise in materials science for this reaction.

Highly efficient polymerization via sulfur(vi)-fluoride exchange (SuFEx): novel polysulfates bearing a pyrazoline–naphthylamide conjugated moiety and their electrical memory performance

Two polysulfates (PolyTPP-NI and CPTPP-NI) were synthesized by a SuFEx click reaction, and their memory devices show Flash behaviors.