Fluorination methods in drug discovery

Fluoride-Based Deep Eutectic Solvents with Amide Dual-Hydrogen-Bond Donors

Developing F--containing electrolytes is crucial for electrochemical and chemical fluorination. However, balancing the F- concentration and electrochemical stability of the electrolytes remains a challenge. In this study, fluoride-based deep eutectic solvents (F-DESs) were obtained by using amide hydrogen-bond donors (HBDs) containing dual N-H bonds. The obtained F-DES, [TMA]F·3.5[1,3-DMU], was prepared by facilely mixing solid compounds of tetramethylammonium fluoride ([TMA]F) and 1,3-dimethylurea (1,3-DMU), resulting in a high F- concentration (2.6 mol dm-3) and a wide electrochemical window (3.1 V) at room temperature. The electrochemical window was much wider than that of [TMA]F·3.5[EG] (EG, ethylene glycol) as another F-DES with an alcohol HBD (1.9 V). Moreover, [TMA]F·3.5[1,3-DMU] exhibited an ionic conductivity that was 2 orders of magnitude higher than that of [TMA]F·3.5[1,3-DMTU] (1,3-DMTU, 1,3-dimethylthiourea) around room temperature because of the bifurcated hydrogen bonds between the dual N-H bonds of 1,3-DMU and one F-. Thus, [TMA]F·3.5[1,3-DMU] was demonstrated to be applicable to electrochemical fluorination.

Design, Synthesis, and Bioactivity of Trifluoroethylthio-Substituted Phenylpyrazole Derivatives

As the first marketed phenylpyrazole insecticide, fipronil exhibited remarkable broad-spectrum insecticidal activity. However, it poses a significant threat to aquatic organisms and bees due to its high toxicity. Herein, 35 phenylpyrazole derivatives containing a trifluoroethylthio group on the 4 position of the pyrazole ring were designed and synthesized. The predicted physicochemical properties of all of the compounds were within a reasonable range. The biological assay results revealed that compound 7 showed 69.7% lethality against Aedes albopictus (A. albopictus) at the concentration of 0.125 mg/L. Compounds 7, 7g, 8d, and 10j showed superior insecticidal activity for the control of Plutella xylostella (P. xylostella). Notably, compound 7 showed similar insecticidal activity against Aphis craccivora (A. craccivora) compared with fipronil. Potential surface calculation and molecular docking suggested that different lipophilicity and binding models to the Musca domestica (M. domestica) gamma-aminobutyric acid receptors may be responsible for the decreased activity of the tested derivatives. Toxicity tests indicated that compound 8d (LC50 = 14.28 mg/L) induced obviously 14-fold lower toxicity than fipronil (LC50 = 1.05 mg/L) on embryonic-juvenile zebrafish development.

Photocatalytic C2-trifluoroethylation and perfluoroalkylation of 3-substituted indoles using fluoroalkyl halides

A photocatalytic reactivity platform for the C2-trifluoroethylation and perfluoroalkylation of 3-substituted indoles has been developed. A range of fluoroalkyl halides have been employed as radical precursors under mild, transition-metal-free conditions to access new (per)fluorinated chemical space featuring the indole substructure. This general protocol is also applicable to indole-containing peptides.

Recent developments in the enzymatic modifications of steroid scaffolds

Steroids are an important family of bioactive compounds. Steroid drugs are renowned for their multifaceted pharmacological activities and are the second-largest category in the global pharmaceutical market. Recent developments in biocatalysis and biosynthesis have led to the increased use of enzymes to enhance the selectivity, efficiency, and sustainability for diverse modifications of steroids. This review discusses the advancements achieved over the past five years in the enzymatic modifications of steroid scaffolds, focusing on enzymatic hydroxylation, reduction, dehydrogenation, cascade reactions, and other modifications for future research on the synthesis of novel steroid compounds and related drugs, and new therapeutic possibilities.

Synthesis of 18F-labeled Aryl Trifluoromethyl Sulfones, -Sulfoxides, and -Sulfides for Positron Emission Tomography

Positron emission tomography (PET) is becoming increasingly important in nuclear medicine and drug discovery. To date, the development of many potential PET tracers is hampered by the lack of suitable synthetic pathways for their preparation. This is particularly true for the highly desired radiolabeling of compounds bearing [18F]CF3-groups. For instance, S(O)nCF3-groups (n=0, 1, 2) serve as structural motif in a range of biologically active compounds, but their radiosynthesis remains largely unprecedented (for n=1, 2). Herein, we describe general methods for the radiosynthesis of 18F-labeled aryl trifluoromethyl sulfones, -sulfoxides, and -sulfides. All three methods are operationally straightforward, start from widely available precursors, i.e., sulfonyl fluorides and thiophenols, and make use of the recently established [18F]Ruppert-Prakash reagent. Further, the syntheses display good functional group tolerance as demonstrated by the 18F-labeling of more than 40 compounds. The applicability of the new method is demonstrated by the radiolabeling of three bioactive molecules, optionally to be used as PET tracers. In a broader context, this work presents a substantial expansion of the chemical space of radiofluorinated structural motifs to be used for the development of new PET tracers.

Palladium-catalyzed alkynylation of allylic gem-difluorides

Herein, a palladium-catalyzed regioselective alkynylation, esterification, and amination of allylic gem-difluorides via C-F bond activation/transmetallation/β-C elimination or nucleophilic attack has been achieved. This innovative protocol showcases an extensive substrate range and operates efficiently under mild reaction conditions, resulting in high product yields and Z-selectivity. Particularly noteworthy is its exceptional tolerance towards a wide array of functional groups. This developed methodology provides effective and convenient routes to access a diverse array of essential fluorinated enynes, esters and amines.

Design, Synthesis, and Activity Evaluation of Fluorine-Containing Scopolamine Analogues as Potential Antidepressants

This study aimed to develop novel rapid-acting antidepressants with sustained efficacy and favorable safety profiles. We designed and synthesized a series of fluorine-containing scopolamine analogues and evaluated their antidepressant potential. In vitro cytotoxicity assays showed that most of these compounds exhibited minimal toxicity against neuronal and non-neuronal mammalian cell lines (IC50 > 100 μM). The antidepressant activities of the compounds were evaluated using the tail suspension test, and S-3a was identified as a lead compound with potent and sustained antidepressant effects. Behaviorally, S-3a alleviated depressive symptoms in mice and displayed a higher cognitive safety margin than scopolamine. Toxicological assessments confirmed S-3a's safety, while pharmacokinetics showed a rapid clearance (half-life: 16.6 min). Mechanistically, S-3a antagonized M1 receptors and elevated BDNF levels, suggesting its potential as an antidepressant for further exploration.

Synthesis of fluorinated amino acids by low-specificity, promiscuous aldolases coupled to in situ fluorodonor generation

Fluorine (F) is an important element in the synthesis of molecules broadly used in medicine, agriculture, and materials. F addition to organic structures represents a unique strategy for tuning molecular properties, yet this atom is rarely found in Nature and approaches to produce fluorometabolites (such as fluorinated amino acids, key building blocks for synthesis) are relatively scarce. This chapter discusses the use of L-threonine aldolase enzymes (LTAs), a class of enzymes that catalyze reversible aldol addition to the α-carbon of glycine. The C-C bond formation ability of LTAs, together with their known substrate promiscuity, make them ideal for in vitro F biocatalysis. Here, we describe protocols to harness the activity of the low-specificity LTAs isolated from Escherichia coli and Pseudomonas putida on 2-fluoroacetaldehyde to efficiently synthesize 4-fluoro-L-threonine in vitro. This chapter also provides a comprehensive account of experimental protocols to implement these activities in vivo. These methods are illustrative and can be adapted to produce other fluorometabolites of interest.

BF3-Promoted Ring Expansion of Iminylphosphiranes and Acylphosphiranes for Divergent Access to 1,2-Azaphospholidines and 1,2-Dihydrophosphetes

Ring expansion of strained small rings provides an efficient method for the synthesis of various high-value carbocycles and heterocycles. Here we report BF3·Et2O as both an activating reagent and fluorine source, enabling ring expansion of phosphirane and P-F bond formation. Treatment of 1-iminylphosphirane complexes with BF3·Et2O resulted in 1,2-azaphospholidines, while the reaction of 1-acylphosphirane complexes with BF3·Et2O afforded 1,2-dihydrophosphetes. The reaction path was tuned by the nucleophilicity of the N and O atoms toward the intermediate phosphenium cation.

The Role of Small Molecules Containing Fluorine Atoms in Medicine and Imaging Applications

The fluorine atom possesses many intrinsic properties that can be beneficial when incorporated into small molecules. These properties include the atom's size, electronegativity, and ability to block metabolic oxidation sites. Substituents that feature fluorine and fluorine-containing groups are currently prevalent in drugs that lower cholesterol, relieve asthma, and treat anxiety disorders, as well as improve the chemical properties of various medications and imaging agents. The dye scaffolds (fluorescein/rhodamine, coumarin, BODIPY, carbocyanine, and squaraine dyes) reported will address the incorporation of the fluorine atom in the scaffold and the contribution it provides to its application as an imaging agent. It is also important to recognize radiolabeled fluorine atoms used for PET imaging in the early detection of diseases. This review will discuss the many benefits of incorporating fluorine atoms into small molecules and give examples of fluorinated molecules used in the pharmaceutical industry and imaging techniques.

Asymmetric Construction of Carbon-Fluorine Quaternary Stereogenic Centers via Synergistic Pd/Cu Catalysis

We developed an asymmetric decarboxylative allylic alkylation of vinylethylene carbonates with α-fluoro pyridinyl acetates through a synergistic palladium/copper catalysis. This protocol provides chiral allylic alcohol with carbon-fluorine quaternary stereogenic centers in good yield with good enantioselectivities and excellent regioselectivities. The utility of this approach was further demonstrated via a gram-scale experiment and derivatizations of the product.

Electrochemical Fluorination Functionalization of gem-Difluoroalkenes with CsF as a Fluorine Source: Access to Fluoroalkyl Building Blocks

Using easily handled CsF as a fluorine source, an electrochemically metal-free protocol for chemo- and regioselective synthesis of various types of long-chain perfluoroalkyl aromatics with gem-difluoroalkene as a substrate and an alcohol or azole as an additional nucleophile was developed. The eletrochemical transformation could tolerate several functional groups, such as halogens, cyanos, benzyls, and heterocycles, and is amenable to gram-scale. The application of this electrochemical method in radiofluorination was also tested.

Using Mechanochemistry to Activate Commodity Plastics as Initiators for Radical Chain Reactions of Small Organic Molecules

Radical initiators such as azo compounds and organic peroxides have been widely used to facilitate numerous transformations of free radicals, which enable the efficient synthesis of structurally complex molecules, natural products, polymers, and functional materials. However, these high-energy reagents are potentially explosive and thus often require special precautions or delicate operating conditions. We postulated that a more convenient and safer alternative for radical chain initiation could be developed by mechanical activation of thermodynamically stable covalent bonds. Here, we show that commodity plastics such as polyethylene and poly(vinyl acetate) are capable of acting as efficient initiators for radical chain reactions under solvent-free mechanochemical conditions. In this approach, polymeric mechanoradicals, which are generated by homolytic cleavage of the polymer chains in response to the applied mechanical energy provided by ball milling, react with tris(trimethylsilyl)silane to initiate radical chain dehalogenation of organic halides. Preliminary calculations support our proposed force-induced radical chain mechanism.

Selectfluor Mediated Direct C-H Fluorination of 3-Heteroaryl-Oxindoles

An efficient transition-metal-free fluorination synthesis of N-H-free 3-heteroaryl-oxindoles with Selectfluor was depicted. Under mild reaction conditions, a series of 3-heteroaryl-fluorooxindoles were produced in yield of 62-88% using Selectfluor as a fluorine source.

Discovery of a 4-Hydroxy-3'-Trifluoromethoxy-Substituted Resveratrol Derivative as an Anti-Aging Agent

With the intensification of population aging, aging-related diseases are attracting more and more attention, thus, the study of aging mechanisms and anti-aging drugs is becoming increasingly urgent. Resveratrol is a potential candidate as an anti-aging agent, but its low bioavailability limits its application in vivo. In this work, a 4-hydroxy-3'-trifluoromethoxy-substituted resveratrol derivative (4-6), owing to its superior cell accumulation, could inhibit NO production in an inflammatory cell model, inhibit oxidative cytotoxicity, and reduce ROS accumulation and the population of apoptotic cells in an oxidative stress cell model. In D-galactose (D-gal)-stimulated aging mice, 4-6 could reverse liver and kidney damage; protect the serum, brain, and liver against oxidative stress; and increase the body's immunity in the spleen. Further D-gal-induced brain aging studies showed that 4-6 could improve the pathological changes in the hippocampus and the dysfunction of the cholinergic system. Moreover, protein expression related to aging, oxidative stress, and apoptosis in the brain tissue homogenate measured via Western blotting also showed that 4-6 could ameliorate brain aging by protecting against oxidative stress and reducing apoptosis. This work revealed that meta-trifluoromethoxy substituted 4-6 deserved to be further investigated as an effective anti-aging candidate drug.

Recent advances on non-precious metal-catalysed fluorination, difluoromethylation, trifluoromethylation, and perfluoroalkylation of N-heteroarenes

This review highlights the recent advances, from 2015 to 2023, on the introduction of organo-fluorine derivatives at the N-heteroarene core. Notable features considering new technologies based on organofluorine compounds such as: (i) approaches based on non-precious metal catalysis (Fe, Co, Mn, Ni, etc.), (ii) the development of new strategies using non-precious metal-catalysts for the introduction of organo-fluorinine derivatives using N-heterocycles with one or more heteroatoms, (iii) newer reagents for fluorination, difluoromethylation, trifluoromethylation, or perfluoroalkylation of N-heteroarenes using different approaches, (iv) mechanistic studies on various catalytic transformations, as and when required, and (v) the synthetic applications of various bio-active organo-fluorine compounds, including post-synthetic drug derivatization, are discussed.

Potent gene delivery from fluorinated poly(β-amino ester) in adhesive and suspension difficult-to-transfect cells for apoptosis and ferroptosis

Tremendous efforts have been made to improve polymeric property in gene delivery performances, especially when obstacle of transferring gene construct into difficult-to-transfect cells occurs. Innovations in the area of fluorination and fluorinated compounds with biomedical potential in medicinal chemistry are believed to assist in the development of new therapeutics. Fluorine modified polymers have shown to navigate the gene transfection cellular barriers and promoted the transfection outcomes. Gene transfer into some liver cancer cells and human leukemia cells has always been a challenge. Here, by facile incorporation of a fluorine containing amine monomer, 1H,1H-undecafluorohexylamine, fluorinated poly(β-amino ester) (FPAE) was synthesized to significantly improve the transfection performance, achieving high transfection efficiency of 87% and 55% in two representative difficult-to-transfect cells, HepG2 and Molt-4, which were cultured in adhesive and suspension condition, respectively. However, the potency of Lipofectamine 3000 was very limited. More importantly, functional studies revealed that FPAE can dramatically outperform Lipofectamine 3000 in delivering Bcl-xL and PKCβII to either provide the protection against apoptosis or promote the ferroptosis in HepG2 cells. This work facilitates gene therapies by overcoming biological barriers for targeting difficult-to-transfect cells and disease models when medically necessary.

Probing fluconazole deposition inside mesoporous silica using solid-state NMR spectroscopy: Crystallization of a confined metastable form and phase transformations under storage conditions

Encapsulation of molecules into mesoporous silica carriers continues to attract considerable interest in the area of drug delivery and crystal engineering. Here, MCM-41, SBA-15 and MCF silica matrices were used to encapsulate fluconazole (FLU), a pharmaceutically relevant molecule with known conformational flexibility, using the melting method. The composites have been characterized using 1H, 13C and 19F NMR spectroscopy, nitrogen adsorption, PXRD and thermal analysis (DSC, TGA). Drug loading up to 50 wt% allowed us to probe the crystallization process and to detect different local environments of confined FLU molecules. 19F NMR spectroscopy enabled us to detect the gradual pore filling of silica with FLU and differentiate the amorphous domains and surface species. The use of the complementary structural and thermal techniques enabled us to monitor crystallization of the metastable FLU form II in MCF. Using 1H and 19F NMR spectroscopy we observed pore-size dependent reversible dehydration/hydration behaviour in the MCM and SBA composites. As water content has considerable importance in understanding of physicochemical stability and shelf-life of pharmaceutical formulations, experimental evidence of the effect of API-water-carrier interactions on the API adsorption mechanism on silica surface is highlighted.

Synthesis of Fluoro 3(2H)-Furanones via a TFA-Catalyzed Dehydrofluorinative Cyclization of 2,2-Difluoro-3-hydroxy-1,4-diketones

A TFA-catalyzed dehydrofluorinative cyclization of 2,2-difluoro-3-hydroxy-1,4-diketones has been developed in the presence of amines under mild conditions in which the difluorinated substrates are readily prepared according to our reported literature. This protocol provides a rapid construction of fluoro 3(2H)-furanones in good to excellent yields with good functional group tolerance. Easy scale-up synthesis also shows a practical advantage.

Fluorination effects probed in 4-fluoroacetophenone and its monohydrate

Rotational spectra of the 4-fluoroacetophenone monomer and its monohydrate were investigated by Fourier transform microwave spectroscopy complemented with quantum chemical calculations. One conformer of 4-fluoroacetophenone and two isomers of 4-fluoroacetophenone-H2O have been observed in the pulsed jets. The observation of all mono-substituted 13C isotopologues in natural abundance allows an accurate structural determination of the 4-fluoroacetophenone monomer. Both detected isomers of 4-fluoroacetophenone-H2O are stabilized by a dominant O-H⋯O and a secondary C-H⋯O hydrogen bond. The fluorination effects on the geometries, intermolecular non-covalent interactions and V3 barrier of the methyl internal rotation were analysed. The relative population ratio of the two observed isomers for 4-fluoroacetophenone-H2O was also estimated to be NI/NII ≈ 7/1.

Hypervalent Fluoro-iodane-Triggered Semipinacol Rearrangements: Synthesis of α-Fluoro Ketones

Hypervalent fluoro-λ3-iodanes have emerged as versatile reagents that provide unusual fluorination selectivities under mild reaction conditions. Here, we report on adding a semipinacol rearrangement, fluorination, and aryl migration cascade reaction of styrene derivatives. Thus, various cyclopentanones became accessible in up to 96% yield, all bearing tertiary C,F-carbon centers adjacent to the ketone group. Such fluorinated structural motifs are difficult to build with previously established methods. Preliminary experiments on enantioselective processes validated that asymmetric transformations are likewise feasible.

Ring-Opening Fluorination of Carbo/Heterocycles and Aromatics: Construction of Complex and Diverse Fluorine-Containing Molecules

Fluorine-containing molecules have attracted much attention in medicinal, agrochemical, and materials sciences because they offer unique physical and biological properties. Therefore, many efficient fluorination reactions have been developed over the years. Recent advancements in fluorination chemistry have expanded the range of substrates, and regioselectivity/stereoselectivity control has also been achieved. Ring-opening fluorination is an efficient method to construct complex fluorine-containing molecules with diversity, starting from simple cyclic compounds. This review aims to summarize developments in ring-opening fluorination, particularly with larger-sized cyclic compounds. Fluorine introduction and bond cleavage of cyclic compounds such as carbocycles, heterocycles, and aromatics provide efficient access to fluorine-containing compounds that are difficult to be synthesized by conventional methods.

Cross-Coupling Reactions Enabled by Well-Defined Ag(III) Compounds: Main Focus on Aromatic Fluorination and Trifluoromethylation

AgIII compounds are considered strong oxidizers of difficult handling. Accordingly, the involvement of Ag catalysts in cross-coupling via 2e- redox sequences is frequently discarded. Nevertheless, organosilver(III) compounds have been authenticated using tetradentate macrocycles or perfluorinated groups as supporting ligands, and since 2014, first examples of cross-coupling enabled by AgI /AgIII redox cycles saw light. This review collects the most relevant contributions to this field, with main focus on aromatic fluorination/perfluoroalkylation and the identification of AgIII key intermediates. Pertinent comparison between the activity of AgIII RF compounds in aryl-F and aryl-CF3 couplings vs. the one shown by its CuIII RF and AuIII RF congeners is herein disclosed, thus providing a more profound picture on the scope of these transformations and the pathways commonly associated to C-RF bond formations enabled by coinage metals.

The Revival of Enantioselective Perfluoroalkylation - Update of New Synthetic Approaches from 2015-2022

Over the last years, methods devoted to the synthesis of asymmetric molecules bearing a perfluoroalkylated chain have been limited in number. Among them, only a few can be used on a large variety of scaffolds. This microreview aims at summarizing these recent advances in enantioselective perfluoroalkylation (-CF3 , -CF2 H, -Cn F2n+1 ) and highlights the need for new enantioselective methods to easily synthesize chiral fluorinated molecules which would be useful for the pharmaceutical and agrochemical industries. Some perspectives are also mentioned.

Pentafluorocyclopropanation of (Hetero)arenes Using Sulfonium Salts: Applications in Late-Stage Functionalization

The evaluation of the pentafluorocyclopropyl group as a chemotype in crop protection and medicinal chemistry has been hampered in the past by the lack of suitable methodologies that enable the practical incorporation of this moiety into advanced synthetic intermediates. Herein, we report the gram-scale synthesis of an unprecedented sulfonium salt, 5-(pentafluorocyclopropyl)dibenzothiophenium triflate, and its use as a versatile reagent for the photoinduced C-H pentafluorocyclopropylation of a broad series of non-previously functionalized (hetero)arenes through a radical mediated mechanism. The scope and potential benefits of the protocol developed are further demonstrated by the late-stage introduction of the pentafluorocyclopropyl unit into biologically relevant molecules and widely used pharmaceuticals.

Metal-Free Photoredox Four-Component Strategy to 1,3-Functionalized BCP Derivatives

Trifluoromethyl bicyclo[1.1.1]pentanes (BCPs) have attracted significant attention from the scientific community and pharmaceutical industries due to their advantageous physicochemical properties as arene bioisosteres. Initial photoredox perfluoroalkylation of [1.1.1]propellane triggers the tandem reaction to the perfluoroalkyl BCP radical followed by Giese addition to an in situ generated electron-deficient alkene by Knoevenagel condensation in a four-component fashion to form 1,3-functionalized BCPs. This strategy provides easy access to various 1,3-functionalized perfluoroalkyl BCP derivatives with the added advantage of nitrile group as a functional handle to diversified transformations. This methodology offers scalability and late-stage derivatization of drug molecules with high chemoselectivity.

From cyclic (alkyl)(amino)carbene (CAAC) precursors to fluorinating reagents. Experimental and theoretical study

Addition of anhydrous HF to the hydrochloride [^MeCAACH][Cl(HCl)_0.5] resulted in the formation of salts with high HF content. By stepwise removal of HF in vacuo, we selectively prepared [^MeCAACH][F(HF)₂] (3) and [^MeCAACH][F(HF)₃] (4). We also characterised a salt with [F(HF)₄]^- anions within the structure of [^MeCAACH][F(HF)_3.5] (5). Compounds with a lower content of HF were not accessible under vacuum conditions. ^MeCAAC(H)F (1) was selectively prepared by abstraction of HF from 3 with CsF or KF, while [^MeCAACH][F(HF)] (2) was prepared by mixing 3 and 1 in a 1 : 1 ratio. Compound 2 proved to be quite unstable as it tends to disproportionate into 1 and 3. This observation triggered our computational study, in which the structural relationships between CAAC-based fluoropyrrolidines and dihydropyrrolium fluorides were investigated using different DFT methods. The study showed that the results were very sensitive to the computational method used. For a correct description, the quality of the triple-ζ basis set was crucial. Surprisingly, the isodesmic reaction of [^MeCAACH][F] + [^MeCAACH][F(HF)₂] → [^MeCAACH][F(HF)] + [^MeCAACH][F(HF)] did not confirm the low thermodynamic stability of 2. Furthermore, the use of 3 as a nucleophilic fluorinating reagent was tested on a range of organic substrates, as it is the most stable compound in this series. It was found to have the potential to fluorinate benzyl bromides, 1- and 2-alkyl bromides, silanes and sulfonyls with good to excellent yields of the target fluorides.

Design, synthesis and biological evaluation of 4-(4-aminophenoxy)picolinamide derivatives as potential antitumor agents

Cancer is a leading cause of death in humans. Molecular targeted therapy for cancer has become a research hotspot as it is associated with low toxicity and high efficiency. In this study, a total of 36 derivatives of 4-(4-aminophenoxy)pyridinamide were designed and synthesized, based on the analysis of the binding patterns of cabozantinib and BMS-777607 to MET protein. Most target compounds exhibited moderate to excellent antiproliferative activity against three different cell lines (A549, HeLa and MCF-7). A total of 7 compounds had stronger inhibitory activities than cabozantinib, and the IC₅₀ value of the most promising compound 46 was 0.26 μM against the A549 cells, which was 2.4 times more active than that of cabozantinib. The structure-activity relationship of the target compounds was analyzed and summarized, and the action mechanism was discussed. The acridine orange (AO) staining assay and cell cycle apoptosis revealed that compound 46 dose-dependently induced apoptosis of A549 cells, and blocked the cells mainly in G0/G1 phase. The IC₅₀ value of compound 46 on c-Met kinase was 46.5 nM. Further docking studies and molecular dynamics simulations signaled that compound 46 formed four key hydrogen bonds to c-Met kinase, and these key amino acids played a major role in binding free energy. In addition, compound 46 also showed good pharmacokinetic characteristics in rats. In conclusion, compound 46 is a promising antitumor agent.

Strategies for Nucleophilic C(sp3)-(Radio)Fluorination

This Perspective surveys the progress and current limitations of nucleophilic fluorination methodologies. Despite the long and rich history of C(sp³)-F bond construction in chemical research, the inherent challenges associated with this transformation have largely constrained nucleophilic fluorination to a privileged reaction platform. In recent years, the Doyle group─along with many others─has pursued the study and development of this transformation with the intent of generating deeper mechanistic understanding, developing user-friendly fluorination reagents, and contributing to the invention of synthetic methods capable of enabling radiofluorination. Studies from our laboratory are discussed along with recent developments from others in this field. Fluoride reagent development and the mechanistic implications of reagent identity are highlighted. We also outline the chemical space inaccessible by current synthetic technologies and a series of future directions in the field that can potentially fill the existing dark spaces.

Cobalt-catalysed nucleophilic fluorination in organic carbonates

The novel P-N ligand 1-((diphenylphosphaneyl)methyl)-1H-benzo-1,2,3-triazole (1), based on a benzotriazole scaffold, has been prepared. The reaction of 1 with [CoCp*(CH₃CN)₃][BF₄]₂ and [CoCp*(I)₂]₂ (Cp* = pentamethylcyclopentadienyl) affords the chelate complexes [CoCp*(CH₃CN)(P-N)][BF₄]₂ (2) and [CoCp*(I)(P-N)]I (3), respectively. Complexes 2 and 3 were studied as catalysts in the fluorination of aromatic and aliphatic acyl chlorides in CH₂Cl₂, with 3 showing notably higher activities than 2. Subsequently, organic carbonates (dimethyl carbonate and propylene carbonate) were also employed as solvents, which led to shorter reaction times and to the broadening of the substrate scope to a variety of aliphatic halides. Comparative studies between 3 and the analogous complex [CoCp*(I)₂(PMePh₂)], which features a monodentate phosphane ligand, showed that higher yields were obtained in the case of the former. DFT calculations and experimental studies were performed in order to shed light on the reaction mechanism, which entails the formation of a cobalt fluoride species that reacts via nucleophilic attack with the substrate to afford the corresponding fluorinated compounds.

Merging Copper(I) Photoredox Catalysis and Iodine(III) Chemistry for the Oxy-monofluoromethylation of Alkenes

A simple process for the oxy-monofluoromethylation of alkenes is described. In combination with visible-light copper(I) photoredox catalysis, an easily accessible iodine(III) reagent containing monofluoroacetoxy ligands serves as a powerful source of a monofluoromethyl (CH₂ F) radical, enabling the step economical synthesis of γ-fluoro-acetates from a broad range of olefinic substrates under mild conditions. Applications to late-stage diversification of alkenes derived from complex molecules, amino acids and the synthesis of fluoromethylated heterocycles are also demonstrated.

Enantioselective Synthesis of cis- and trans-Cycloheptyl β-Fluoro Amines by Sequential aza-Henry Addition/Ring-Closing Metathesis

The synthesis of 7-membered carbocyclic β-fluoroamines is accomplished by a combination of the enantioselective aza-Henry reaction of aliphatic N-Boc imines and ring-closing metathesis. Use of reductive denitration gives both diastereomers of the β-fluoro amine carbocycle, each with high enantiomeric excess.

Detection, discrimination and quantification of amphetamine, cathinone and nor-ephedrine regioisomers using benchtop 1 H and 19 F nuclear magnetic resonance spectroscopy

Amphetamine and cathinone derivatives are abused recreationally due to the sense of euphoria they provide to the user. Methodologies for the rapid detection of the drug derivative present in a seized sample, or an indication of the drug class, are beneficial to law enforcement and healthcare providers. Identifying the drug class is prudent because derivatisation of these drugs, to produce regioisomers, for example, occurs frequently to circumvent global and local drug laws. Thus, newly encountered derivatives might not be present in a spectral library. Employment of benchtop nuclear magnetic resonance (NMR) could be used to provide rapid analysis of seized samples as well as identifying the class of drug present. Discrimination of individual amphetamine-, methcathinone-, N-ethylcathinone and nor-ephedrine-derived fluorinated and methylated regioisomers is achieved herein using qualitative automated ¹ H NMR analysis and compared to gas chromatography-mass spectrometry (GC-MS) data. Two seized drug samples, SS1 and SS2, were identified to contain 4-fluoroamphetamine by ¹ H NMR (match score median = 0.9933) and GC-MS (RR_t  = 5.42-5.43 min). The amount of 4-fluoroamphetamine present was 42.8%-43.4% w/w and 48.7%-49.2% w/w for SS1 and SS2, respectively, from quantitative ¹⁹ F NMR analysis, which is in agreement with the amount determined by GC-MS (39.9%-41.4% w/w and 49.0%-49.3% w/w). The total time for the qualitative ¹ H NMR and quantitative ¹⁹ F NMR analysis is ~10 min. This contrasts to ~40 min for the GC-MS method. The NMR method also benefits from minimal sample preparation. Thus, benchtop NMR affords rapid, and discriminatory, analysis of the drug present in a seized sample.

Synthesis of Alkyl Fluorides and Fluorinated Unnatural Amino Acids via Photochemical Decarboxylation of α-Fluorinated Carboxylic Acids

Leveraging α-fluoroalkyl or fluorobenzyl radicals to introduce fluorinated motifs allows for the rapid preparation of fluorine-containing building blocks. Herein, we report the generation of α-fluoroalkyl or fluorobenzyl radicals from readily available α-fluorocarboxylic acids under mild reaction conditions and their utilization in the Giese-type addition on Michael acceptors and dehydroamino acids, resulting in the preparation of mono- and difluorinated Michael addition adducts and unnatural fluorinated amino acids.

Metal-Free C-H Difluoromethylation of Imidazoles with the Ruppert-Prakash Reagent

The reaction of trimethyl(trifluoromethyl)silane-tetrabutylammonium difluorotriphenylsilicate (CF₃SiMe₃-TBAT) with a series of imidazoles gives products of the formal difluorocarbene insertion into the C-H bond at the C-2 position (i.e., C-difluoromethylation). According to NMR spectra, the corresponding 2-(trimethylsilyl)difluoromethyl-substituted derivatives are likely formed as the intermediates in the reaction, and then, they slowly convert to 2-difluoromethyl-substituted imidazoles. Quantum chemical calculations of two plausible reaction mechanisms indicate that it proceeds through the intermediate imidazolide anion stabilized through the interaction with solvent molecules and counterions. In the first proposed mechanism, the anion reacts with difluorocarbene without an activation barrier, and then, the CF₂ moiety of the adduct attacks the CF₃SiMe₃ molecule. After the elimination of the CF₃ anion, 2-(trimethylsilyl)difluromethyl-substituted imidazole is formed. Another possible reaction pathway includes silylation of imidazolide anion at the N-3 atom, followed by the barrierless addition of difluorocarbene at the C-2 atom and then by 1,3-shift of the SiMe₃ group from N-3 to the carbon atom of the CF₂ moiety. Both proposed mechanisms do not include steps with high activation barriers.

5-(Trifluorovinyl)dibenzothiophenium Triflate: Introducing the 1,1,2-Trifluoroethylene Tether in Drug-Like Structures

This manuscript reports the synthesis and structure of an unprecedented sulfonium salt, 5-(trifluorovinyl)dibenzothiophenium triflate, and its use as a versatile reagent for the introduction of the bioisosteric 1,1,2-trifluoroethylene linker in drug-like structures. The protocol developed consists of the reaction of this compound with alcohols and phenols to deliver a complete set of 1,2,2-trifluoro-2-(alkoxy-/aryloxy)ethyl sulfonium salts, which have been purified by column chromatography and fully characterized. Subsequent single electron reduction under mild photochemical conditions efficiently affords the corresponding fluoroalkyl radicals that are trapped either intra- or intermolecularly through their reaction with (hetero)arenes. Theoretical calculations are used to evaluate the conformational consequences derived from the presence of the CF₂ -CHF tether.

The Application of Sulfonyl Hydrazides in Electrosynthesis: A Review of Recent Studies

Sulfonyl hydrazides are viewed as alternatives to sulfinic acids and their salts or sulfonyl halides, which are broadly used in organic synthesis or work as active pharmaceutical substances. Generally, sulfonyl hydrazides are considered good building blocks and show powerful value in a diverse range of reactions to construct C-S bonds or C-C bonds, and even C-N bonds as sulfur, carbon, or nitrogen sources, respectively. As a profound synthetic tool, the electrosynthesis method was recently used to achieve efficient and green applications of sulfonyl hydrazides. Interestingly, many unique and novel electrochemical syntheses using sulfonyl hydrazides as radical precursors have been developed, including cascade reactions, functionalization of heterocycles, as well as a continuous flow method combining with electrochemical synthesis since 2017. Accordingly, it is necessary to specifically summarize the recent developments of electrosynthesis with only sulfonyl hydrazides as radical precursors to more deeply understand and better design novel electrochemical synthesis reactions. Herein, electrosynthesis research using sulfonyl hydrazides as radical precursors since 2017 is reviewed in detail based on the chemical structures of products and reaction mechanisms.

Transition-metal-catalyzed ortho C-H functionalization of 2-arylquinoxalines

Recently, direct C-H bond activation and functionalization has become a prodigious and hot topic among synthetic organic chemists due to its step-economic nature and substantial synthetic versatility. On the other hand, quinoxaline, a fused bicycle of benzene and pyrazine, has omnipresent applications in medicinal-, industrial- and materials chemistry. The presence of the N-1 atom in 2-arylquinoxaline enables chelation formation with a metal catalyst leading to the formation of ortho-substituted products. In this review, all articles related to the ortho C-H bond functionalization of 2-arylquinoxalines published up to May 2022 are highlighted.

Visible light-enabled regioselective chlorination of coumarins using CuCl2via LMCT excitation

An efficient, regioselective chlorination of coumarins using Earth-abundant and cost-effective CuCl₂ under visible light irradiation is reported. A key feature of this protocol is the photocatalytic dissociation of the copper(II) complex in acetonitrile through ligand-to-metal charge transfer (LMCT) to give the chlorine atom which then selectively chlorinates the coumarin. This method can chlorinate a broad scope of coumarins with either electron-withdrawing or electron-donating substituents to regioselectively afford 3-chlorocoumarins in good to excellent yields and can be further extended to other electron-deficient heterocycles and olefins such as flavones, 8-methoxypsoralen and naphthoquinones.

Electrophilic Reagents for the Direct Incorporation of Uncommon SCF2CF2H and SCF2CF3 Motifs

The introduction of fluoroalkylthioether groups has attracted the attention of the drug-discovery community given the special physicochemical and pharmacokinetic features they confer to bioactive compounds, yet these are often limited to standard SCF₃ and SCF₂H moieties. Herein, two saccharin-based electrophilic reagents have been disclosed for the incorporation of uncommon SCF₂CF₂H and SCF₂CF₃ motifs. Their reactivity performance, multigram-scale preparation, and divergent derivatization have been thoroughly investigated with a variety of nucleophiles, including natural products and pharmaceuticals.

Para-Fluorination of Anilides Using Electrochemically Generated Hypervalent Iodoarenes

The para-selective fluorination reaction of anilides using electrochemically generated hypervalent ArIF2 is reported, with Et3 N ⋅ 5HF serving as fluoride source and as supporting electrolyte. This electrochemical reaction is characterized by a simple set-up, easy scalability and affords a broad variety of fluorinated anilides from easily accessible anilides in good yields up to 86 %.

From Styrenes to Fluorinated Benzyl Bromides: A Photoinduced Difunctionalization via Atom Transfer Radical Addition

An operationally simple and practical method is disclosed to achieve the difunctionalization of styrenes, generating fluorinated benzyl bromides via a photoinduced atom transfer radical addition process. The developed method is mild, atom-economical, cost-effective, employs very low photocatalyst loading (1000 ppm), and is highly compatible with a broad range of functional groups on styrene. The versatility of the fluorinated benzyl bromides is demonstrated through their derivatization to a variety of valuable compounds.

A Transfer Learning Approach for Reaction Discovery in Small Data Situations Using Generative Model

Sustainable practices in chemical sciences can be better realized by adopting interdisciplinary approaches that combine the advantages of machine learning (ML) on the initially acquired small data in reaction discovery. Developing new reactions generally remains heuristic and even time and resource intensive. For instance, synthesis of fluorine-containing compounds, which constitute ∼20% of the marketed drugs, relies on deoxyfluorination of abundantly available alcohols. Herein, we demonstrate the use of a recurrent neural network-based deep generative model built on a library of just 37 alcohols for effective learning and exploration of the chemical space. The proof-of-concept ML model is able to generate good quality, synthetically accessible, higher-yielding novel alcohol molecules. This protocol would have superior utility for deployment into a practical reaction discovery pipeline.

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Dual pronged transfer learning, both to generate and predict yields of new molecules

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Demonstrated the utility for an important family of deoxyfluorination of alcohols

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Applicable for practically more likely situations with relatively smaller data

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Extendable to other reaction manifolds to facilitate expedited reaction discovery

Strategies for the Synthesis of Fluorinated Nucleosides, Nucleotides and Oligonucleotides

Fluorinated nucleosides and oligonucleotides are of specific interest as probes for studying nucleic acids interaction, structures, biological transformations, and its biomedical applications. Among various modifications of oligonucleotides, fluorination of preformed nucleoside and/or nucleotides have recently gained attention owing to the unique properties of fluorine atoms imparting medicinal properties with respect to the small size, electronegativity, lipophilicity, and ability for stereochemical control. This review deals with synthetic protocols for selective fluorination either at sugar or base moiety in a preformed nucleosides, nucleotides and nucleic acids using specific fluorinating reagents.

Application of Aromatic Substituted 2,2,2-Trifluoro Diazoethanes in Organic Reactions

Abstract:

This review provides an overview of metal-, nonmetal-, light-, or catalyst free-promoting reactions of aromatic substituted 2,2,2-trifluoro diazoethanes with organic molecules for the synthesis of trifluoromethyl-substituted compounds. Several approaches will be reviewed and divided into (i) copper-, iron-, Trop(BF4)-, B(C6F5)3-, light-, or rhodium-promoted reactions of aromatic substituted 2,2,2-trifluoro diazoethanes with silanes, amines, mercaptans, phosphonates, p-cyanophenol, benzoic acid, diphenylphosphinic acid, boranes and nBu3SnH, (ii) rhodium-catalyzed reactions of aromatic substituted 2,2,2-trifluoro diazoethanes with amides and phenylhydroxylamine, (iii) copper-, rhodium-, silver-, and light-catalyzed reactions of aromatic substituted 2,2,2-trifluoro diazoethanes with alkynes, (iv) palladium-, copper-, rhodium- and iron-catalyzed reactions of aromatic substituted 2,2,2-trifluoro diazoethanes with alkenes, (v) BF3·OEt2-, copper-, tin- or TBAB-catalyzed reactions of aromatic substituted 2,2,2-trifluoro diazoethanes with HF·Py, (difluoroiodo)toluene (p-TolIF2), TMSCF3, AgSCF3, TMSCF2Br or 1,3-dicarbonyl compounds, (vi) palladium-, copper-, gold/silver- or rhodium-catalyzed reactions of aromatic substituted 2,2,2-trifluoro diazoethanes with indoles, benzene compounds or pyridines, and (vii) palladium-catalyzed reaction of aromatic substituted 2,2,2-trifluoro diazoethanes with benzyl or allyl bromides.