Fluorination methods for drug discovery and development

Deoxytrifluoromethylation/aromatization of cyclohexan(en)ones to access highly substituted trifluoromethyl arenes

Trifluoromethyl arenes (Ar-CF3) are amongst the commonly encountered fluorinated substructures in pharmaceutical, agrochemical, and material sciences. However, predominant methods to access Ar-CF3 possess several limitations, including harsh conditions, lack of availability of substrates, and poor regioselectivity, which combined restrict access to desirable highly functionalized Ar-CF3-containing compounds. To expand the scope of accessible Ar-CF3-based molecules, we present an orthogonal deoxyfluoroalkylation/aromatization approach that exploits readily accessible and programable cyclohexan(en)one substrates, which undergo a reliable 1,2-addition reaction with the Ruppert-Prakash reagent (TMSCF3) followed by aromatization to deliver highly functionalized Ar-CF3 compounds in a one/two-pot sequence. This general strategy enables access to highly substituted Ar-CF3-containing molecules that are difficult, expensive, and/or impossible to access by current synthetic methods.

α-Fluorination of tropane compounds and its impact on physicochemical and ADME properties

Using an electrochemical C(sp3)-H fluorination reaction, a series of α-fluorinated tropane compounds were synthesized and their druglikeness parameters were assessed to compare with the parent compounds. Improvements were observed in membrane permeability, P-gp liability, and inhibitory effects on hERG and Nav1.5 channels, accompanied with a trend of decreased aqueous solubility and microsomal stability. It was also revealed that α-fluorination reduced the basicity of tropane nitrogen atom for about 1000-fold.

Discovery of a Highly Potent Oxysterol Receptor GPR183 Antagonist Bearing the Benzo[d]thiazole Structural Motif for the Treatment of Inflammatory Bowel Disease (IBD)

Accumulating evidence has demonstrated a critical pathological role of oxysterol receptor GPR183 in various inflammatory and autoimmune diseases, including inflammatory bowel disease (IBD). However, the currently reported GPR183 antagonists are very limited and not qualified for in vivo studies due to their inferior druglike properties. Herein, we conducted a structural elaboration focusing on improving its PK and safety profile based on a reference antagonist NIBR189. Of note, compound 33, bearing an aminobenzothiazole motif, exhibited reduced hERG inhibition, improved PK properties, and robust antagonistic activity (IC50 = 0.82 nM) with high selectivity against GPR183. Moreover, compound 33 displayed strong in vitro antimigration and anti-inflammatory activity in monocytes. Oral administration of compound 33 effectively improved the pathological symptoms of DSS-induced experimental colitis. All of these findings demonstrate that compound 33 is a novel and promising GPR183 antagonist suitable for further investigation to treat IBD.

Late-stage modification of bioactive compounds: Improving druggability through efficient molecular editing

Synthetic chemistry plays an indispensable role in drug discovery, contributing to hit compounds identification, lead compounds optimization, candidate drugs preparation, and so on. As Nobel Prize laureate James Black emphasized, "the most fruitful basis for the discovery of a new drug is to start with an old drug"1. Late-stage modification or functionalization of drugs, natural products and bioactive compounds have garnered significant interest due to its ability to introduce diverse elements into bioactive compounds promptly. Such modifications alter the chemical space and physiochemical properties of these compounds, ultimately influencing their potency and druggability. To enrich a toolbox of chemical modification methods for drug discovery, this review focuses on the incorporation of halogen, oxygen, and nitrogen-the ubiquitous elements in pharmacophore components of the marketed drugs-through late-stage modification in recent two decades, and discusses the state and challenges faced in these fields. We also emphasize that increasing cooperation between chemists and pharmacists may be conducive to the rapid discovery of new activities of the functionalized molecules. Ultimately, we hope this review would serve as a valuable resource, facilitating the application of late-stage modification in the construction of novel molecules and inspiring innovative concepts for designing and building new drugs.

RIPK1 inhibitors: A key to unlocking the potential of necroptosis in drug development

Within the field of medical science, there is a great deal of interest in investigating cell death pathways in the hopes of discovering new drugs. Over the past two decades, pharmacological research has focused on necroptosis, a cell death process that has just been discovered. Receptor-interacting protein kinase 1 (RIPK1), an essential regulator in the cell death receptor signalling pathway, has been shown to be involved in the regulation of important events, including necrosis, inflammation, and apoptosis. Therefore, researching necroptosis inhibitors offers novel ways to treat a variety of disorders that are not well-treated by the therapeutic medications now on the market. The research and medicinal potential of RIPK1 inhibitors, a promising class of drugs, are thoroughly examined in this study. The journey from the discovery of Necrostatin-1 (Nec-1) to the recent advancements in RIPK1 inhibitors is marked by significant progress, highlighting the integration of traditional medicinal chemistry approaches with modern technologies like high-throughput screening and DNA-encoded library technology. This review presents a thorough exploration of the development and therapeutic potential of RIPK1 inhibitors, a promising class of compounds. Simultaneously, this review highlights the complex roles of RIPK1 in various pathological conditions and discusses potential inhibitors discovered through diverse pathways, emphasizing their efficacy against multiple disease models, providing significant guidance for the expansion of knowledge about RIPK1 and its inhibitors to develop more selective, potent, and safe therapeutic agents.

Semisynthesis and anti-cancer properties of novel honokiol derivatives in human nasopharyngeal carcinoma CNE-2Z cells

In this study, 21 new honokiol derivatives were synthesised, and their anti-cancer properties were investigated. Among these, compound 1g exhibited the most potent cytotoxic activity against human nasopharyngeal carcinoma CNE-2Z cells, human gastric cancer SGC7901 cells, human breast cancer MCF-7 cells, and mouse leydig testicular cancer I-10 lines with IC50 values of 6.04, 7.17, 6.83, and 5.30 μM, respectively. Compared to the parental compound, 1g displayed up to 5.18-fold enhancement of the cytotoxic effect on CNE-2Z cells. We further demonstrated that 1g inhibited cell growth, suppressed migration and invasion, and induced apoptosis of CNE-2Z cells by down-regulating HIF-1α, MMP-2, MMP-9, Bcl-2, Akt and up-regulating Bax protein levels. Transfection of CNE-2Z cells with HIF-1α siRNA reduced cell migration and invasion. In addition, in vivo experiments confirmed that 1g inhibited tumour growth in CNE-2Z cell-xenografted nude mice with low toxicity. Thus, our data suggested that 1g was a potent and safe lead compound for nasopharyngeal carcinoma therapy.

Deoxyfluorination of 1°, 2°, and 3° Alcohols by Nonbasic O-H Activation and Lewis Acid-Catalyzed Fluoride Shuttling

A method for deoxyfluorination of aliphatic primary, secondary, and tertiary alcohols is reported, employing a nontrigonal phosphorus triamide for base-free alcohol activation in conjunction with an organic soluble fluoride donor and a triarylborane fluoride shuttling catalyst. Mechanistic experiments are consistent with a reaction that proceeds by the collapse of an oxyphosphonium fluoroborate ion pair with fluoride transfer. The substrate scope complements existing deoxyfluorination methods and enables the preparation of homochiral secondary and tertiary alkylfluorides by stereoinversion of the substrate alcohol.

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.

Rapid Generation of P(V)-F Bonds Through the Use of Sulfone Iminium Fluoride Reagents

Phosphorus-fluorine bonds have become increasingly relevant in the pharmaceutical industry. To continue their exploration, more efficient synthetic methods are needed. Here, we report the application of sulfone iminium fluoride (SIF) reagents to the synthesis of P(V)-F bonds. The SIF reagents promote the deoxyfluorination of phosphinic acids in just 60 s with excellent yields and scope. The same P(V)-F products can also be synthesized from secondary phosphine oxides using an SIF reagent.

Biocatalytic approach to chiral fluoroaromatic scaffolds

Ten different fluorinated aromatic epoxides have been tested as potential substrates for halohydrin dehalogenase (HHDH) HheC. The majority of investigated epoxides are useful building blocks in synthetic chemistry applications, with a number of them being polysubstituted. Moderate to high enantioselectivities (E_R = 15 → 200) were observed in azidolysis, allowing the synthesis of enantioenriched (R)-azido alcohols containing fluorine in the molecule. In the case where a reaction runs over 50% conversion, enantiopure (S)-epoxides are also available. While o-F-styrene oxide was easily converted into a product, a sterically challenging o-CF₃-derivative was not accepted by HheC. In silico probing of the binding site indicates that, in order to accommodate an o-CF₃-derivative in the HheC active site, it is necessary to eliminate steric hindrance. Hence, we extended our research by probing several available HheC variants containing relevant modifications in the active site. The active mutant P84V/F86P/T134A/N176A (named HheC-M4) was identified, showing not only high activity towards o-CF₃-styrene oxide, but also inverted enantioselectivity (E_S = 27). Since (S)-enantioselective HHDHs are rare and therefore valuable for their synthetic application, this enzyme was screened on the initial panel of substrates. The observed (S)-enantioselectivity (E_S = 1-111) is ascribed to the formation of the additional space by introduced mutations in HheC-M4, which is also confirmed by classical MD simulations. Successive molecular docking demonstrated that this newly formed tunnel located close to the protein surface is a critical feature of HheC-M4, representing a novel binding site.

Impact of β-perfluoroalkyl substitution of proline on the proteolytic stability of its peptide derivatives

A series of all stereoisomers of β-CF₃ or β-C₂F₅ substituted prolines and their dipeptide derivatives were synthesized. Mouse plasma stability assay was carried out to study the impact of fluoroalkyl substituents on the proteolytic stability of proline-derived peptides. The effect of the (R)-/(S)-configuration at the C-2 atom in combination with electronic and steric effects imposed by fluoroalkyl groups was addressed to rationalize the difference in the half-life stability of diastereomeric β-CF₃-Pro-Gly and β-C₂F₅-Pro-Gly derivatives and compared to those of parent (S)-Pro-Gly and (R)-Pro-Gly dipeptides. The steric effect was predominant when the β-CF₃ or β-C₂F₅ group was placed properly to create a spatial interference within the pockets of proteases, thereby protecting the substances from degradation (e.g., for cis-isomeric derivatives). Otherwise, a smaller electronic effect accelerating proteolysis was in charge (i.e., for the (2S,3S) isomers).

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.

Photoredox-catalyzed fluorodifluoroacetylation of alkenes with FSO2CF2CO2Me and Et3N·3HF

Photoredox-catalyzed three-component fluorodifluoroacetylation of aromatic alkenes is reported, which features a wide substrate scope and functional group tolerance. An advantage of the reaction is the use of a nucleophilic fluoride source and a general difluoroacetylation reagent for the fluorodifluoroacetylation of alkenes.

Small, but powerful and attractive: 19F in biomolecular NMR

Nuclear magnetic resonance (NMR) spectroscopy is a versatile tool for probing structure, dynamics, folding, and interactions at atomic resolution. While naturally occurring magnetically active isotopes, such as ¹H, ¹³C, or ¹⁵N, are most commonly used in biomolecular NMR, with ¹⁵N and ¹³C isotopic labeling routinely employed at the present time, ¹⁹F is a very attractive and sensitive alternative nucleus, which offers rich information on biomolecules in solution and in the solid state. This perspective summarizes the unique benefits of solution and solid-state ¹⁹F NMR spectroscopy for the study of biological systems. Particular focus is on the most recent studies and on future unique and important potential applications of fluorine NMR methodology.

Recent Advances in Transition-Metal Mediated Trifluoromethylation Reactions

Fluorine compounds are known for their abundance in more than 20% of pharmaceutical and agrochemical products mainly due to the enhanced lipophilicity, metabolic stability and pharmacokinetic properties of organofluorides. Consequently,...

Selective electrophilic di- and mono-fluorinations for the synthesis of 4-difluoromethyl and 4-fluoromethyl quinazolin(thi)ones by Selectfluor-triggered multi-component reaction

A simple and efficient domino protocol for the selective synthesis of 4-difluoromethyl and 4-fluoromethyl quinazolin(thi)ones was established from readily available 2-aminoacetophenones and iso(thio)cyanates mediated by Selectfluor. The reaction outcomes are...

Rapid Access to Fluorinated Anilides via DAST-Mediated Deoxyfluorination of Arylhydroxylamines

A new strategy for the synthesis of fluorinated anilides in the absence of metals and oxidants has been developed. This deoxyfluorination of N-arylhydroxylamines with diethylaminosulfur trifluoride (DAST) proceeded smoothly under mild conditions, and the ortho- or para-fluorinated aromatic amine products were prepared in moderate to good yields. Structurally diverse fluorinated anilides, including heterocyclic and pharmaceutically relevant molecules, can be efficiently constructed by this protocol.

Green chemistry meets medicinal chemistry: a perspective on modern metal-free late-stage functionalization reactions

The progress of drug discovery and development is paced by milestones reached in organic synthesis. In the last decade, the advent of late-stage functionalization (LSF) reactions has represented a valuable breakthrough. Recent literature has defined these reactions as the chemoselective modification of complex molecules by means of C-H functionalization or the manipulation of endogenous functional groups. Traditionally, these diversifications have been accomplished by organometallic means. However, the presence of metals carries disadvantages related to their cost, environmental hazard and health risks. Fundamentally, green chemistry directives can help minimize such hazards through the development of metal-free LSF methodologies. In this review, we expand the current discussion on metal-free LSF reactions by providing an overview of C(sp2)-H, and C(sp3)-H functionalizations, as well as the utilization of heteroatom-containing functional groups as chemical handles. Selected topics such as metal-free cross-dehydrogenative coupling (CDC) reactions, organocatalysis, electrochemistry and photochemistry are also discussed. By writing the first review on metal-free LSF methodologies, we aim to highlight current advances in the field with examples that reveal specific challenges and solutions, as well as future research opportunities.

Applications of fluorine to the construction of bioisosteric elements for the purposes of novel drug discovery

Introduction There continues to be an exponential rise in the number of small molecule drugs that contain either a fluorine atom or a fluorinated fragment. While the unique properties of fluorine enable the precise modulation of a molecule's physicochemical properties, strategic bioisosteric replacement of fragments with fluorinated moieties represents an area of significant growth.Areas covered This review discusses the strategic employment of fluorine substitution in the design and development of bioisosteres in medicinal chemistry. In addition, the classic exploitation of trifluoroethylamine group as an amide bioisostere is discussed. In each of the case studies presented, emphasis is placed on the context-dependent influence of the fluorinated fragment on the overall properties/binding of the compound of interest.Expert opinion Whereas utilization of bioisosteric replacements to modify molecular structures is commonplace within drug discovery, the overarching lesson to be learned is that the chances of success with this strategy significantly increase as the knowledge of the structure/environment of the biological target grows. Coupled to this, breakthroughs and learnings achieved using bioisosteres within a specific program are context-based, and though may be helpful in guiding future intuition, will not necessarily be directly translated to future programs. Another important point is to bear in mind what implications a structural change based on a bioisosteric replacement will have on the candidate molecule. Finally, the development of new methods and reagents for the controlled regioselective introduction of fluorine and fluorinated moieties into biologically relevant compounds particularly in drug discovery remains a contemporary challenge in organic chemistry.

4-Fluoro-Threonine: From Diastereoselective Synthesis to pH-Dependent Conformational Equilibrium in Aqueous Solution

4-Fluoro-threonine, the only fluoro amino acid of natural origin discovered so far, is an interesting target for both synthetic and theoretical investigations. In this work, we lay the foundation for spectroscopic characterization of 4-fluoro-threonine. First, we report a diastereoselective synthetic route, which is suitable to produce synthetic material for experimental characterization. The addition of the commercially available ethyl isocyanoacetate to benzyloxyacetaldehyde led to the corresponding benzyloxy-oxazoline, which was hydrolyzed and transformed into ethyl (4S*,5S*)-5-hydroxymethyl-2-oxo-4-oxazolidinecarboxylate in a few steps. Fluorination with diethylamino sulfur trifluoride (DAST) afforded ethyl (4S*,5S*)-5-fluoromethyl-2-oxo-4-oxazolidinecarboxylate, which was deprotected to give the desired diastereomerically pure 4-fluoro-threonine, in 8-10% overall yield. With the synthetic material in our hands, acid-base titrations have been carried out to determine acid dissociation constants and the isoelectric point, which is the testing ground for the theoretical analysis. We have used machine learning coupled with quantum chemistry at the state-of-the-art to analyze the conformational space of 4-fluoro-threonine, with the aim of gaining insights from the comparison of computational and experimental results. Indeed, we have demonstrated that our approach, which couples a last-generation double-hybrid density functional including empirical dispersion contributions with a model combining explicit first-shell molecules and a polarizable continuum for describing solvent effects, provides results and trends in remarkable agreement with experiments. Finally, the conformational analysis applied to fluoro amino acids represents an interesting study for the effect of fluorine on the stability and population of conformers.

Pd-Catalysed direct C(sp2)-H fluorination of aromatic ketones: concise access to anacetrapib

The Pd-cataylsed direct ortho-C(sp2)-H fluorination of aromatic ketones has been developed for the first time. The reaction features good regioselectivity and simple operations, constituting an alternative shortcut to access fluorinated ketones. A concise synthesis of anacetrapib has also been achieved by using late-stage C-H fluorination as a key step.

Hydrofluorination of Alkenes: A Review

In this minireview, we explore the different approaches used to perform the hydrofluorination reaction of alkenes. Contrary to other hydrohalogenation reactions, the hydrofluorination requires specific conditions due to the lower reactivity of HF. Over the years, many different approaches have been explored among which the use of HF complexes has particularly proved to be useful as these reagents are easier to handle. The enantioselective hydrofluorination has been demonstrated using electrophilic sources of fluorine, while radical fluorination proved compatible with a vast range of functional groups that are generally problematic with strong acids and some fluoride sources. This review will cover the different conditions developed through the years, starting with the first reported addition using gaseous HF, up to the most recent method described in October 2020.

Fluoroarene Separations in Metal-Organic Frameworks with Two Proximal Mg2+ Coordination Sites

Fluoroarenes are widely used in medicinal, agricultural, and materials chemistry, and yet their production remains a critical challenge in organic synthesis. Indeed, the nearly identical physical properties of these vital building blocks hinders their purification by traditional methods, such as flash chromatography or distillation. As a result, the Balz-Schiemann reaction is currently employed to prepare fluoroarenes instead of more atom-economical C-H fluorination reactions, which produce inseparable mixtures of regioisomers. Herein, we propose an alternative solution to this problem: the purification of mixtures of fluoroarenes using metal-organic frameworks (MOFs). Specifically, we demonstrate that controlling the interaction of fluoroarenes with adjacent coordinatively unsaturated Mg²⁺ centers within a MOF enables the separation of fluoroarene mixtures with unparalleled selectivities. Liquid-phase multicomponent equilibrium adsorption data and breakthrough measurements coupled with van der Waals-corrected density functional theory calculations reveal that the materials Mg₂(dobdc) (dobdc^4- = 2,5-dioxidobenzene-1,4-dicarboxylate) and Mg₂(m-dobdc) (m-dobdc^4- = 2,4-dioxidobenzene-1,5-dicarboxylate) are capable of separating the difluorobenzene isomers from one another. Additionally, these frameworks facilitate the separations of fluoroanisoles, fluorotoluenes, and fluorochlorobenzenes. In addition to enabling currently unfeasible separations for the production of fluoroarenes, our results suggest that carefully controlling the interaction of isomers with not one but two strong binding sites within a MOF provides a general strategy for achieving challenging liquid-phase separations.

Synthesis and Structure-Activity Relationship of Tetra-Substituted Cyclohexyl Diol Inhibitors of Proviral Insertion of Moloney Virus (PIM) Kinases

Overexpression of PIM 1, 2, and 3 kinases is frequently observed in many malignancies. Previously, we discovered a potent and selective pan-PIM kinase inhibitor, compound 2, currently in phase I clinical trials. In this work, we were interested in replacing the amino group on the cyclohexane ring in compound 2 with a hydroxyl group. Structure-based drug design led to cellularly potent but metabolically unstable tetra-substituted cyclohexyl diols. Efforts on the reduction of Log D by introducing polar heterocycles improved metabolic stability. Incorporating fluorine to the tetra-substituted cyclohexyl diol moiety further reduced Log D, resulting in compound 14, a cellularly potent tetra-substituted cyclohexyl diol inhibitor with moderate metabolic stability and good permeability. We also describe the development of efficient and scalable synthetic routes toward synthetically challenging tetra-substituted cyclohexyl diol compounds. In particular, intermediate 36 was identified as a versatile intermediate, enabling a large-scale synthesis of highly substituted cyclohexane derivatives.

On the hydrolysis of diethyl 2-(perfluorophenyl)malonate

Diethyl 2-(perfluorophenyl)malonate was synthesized in 47% isolated yield by the reaction of sodium diethyl malonate and hexafluorobenzene. The resulting compound was considered as a starting material for synthesizing 2-(perfluorophenyl)malonic acid by hydrolysis. It was found that the desired 2-(perfluorophenyl)malonic acid could not be obtained from this ester by hydrolysis, neither under basic nor under acidic conditions. Nevertheless, hydrolysis of the ester with a mixture of HBr and AcOH gave 2-(perfluorophenyl)acetic acid in a good preparative yield of 63%. A significant advantage of this new approach to 2-(perfluorophenyl)acetic acid is that handling toxic substances such as cyanides and perfluorinated benzyl halides is avoided.

Intersecting Xenobiology and Neometabolism To Bring Novel Chemistries to Life

The diversity of life relies on a handful of chemical elements (carbon, oxygen, hydrogen, nitrogen, sulfur and phosphorus) as part of essential building blocks; some other atoms are needed to a lesser extent, but most of the remaining elements are excluded from biology. This circumstance limits the scope of biochemical reactions in extant metabolism - yet it offers a phenomenal playground for synthetic biology. Xenobiology aims to bring novel bricks to life that could be exploited for (xeno)metabolite synthesis. In particular, the assembly of novel pathways engineered to handle nonbiological elements (neometabolism) will broaden chemical space beyond the reach of natural evolution. In this review, xeno-elements that could be blended into nature's biosynthetic portfolio are discussed together with their physicochemical properties and tools and strategies to incorporate them into biochemistry. We argue that current bioproduction methods can be revolutionized by bridging xenobiology and neometabolism for the synthesis of new-to-nature molecules, such as organohalides.

Fluorinated scaffolds for antimalarial drug discovery

INTRODUCTION

The unique physicochemical properties and chemical diversity of organofluorine compounds have remarkably contributed for their wide utility in the area of pharmaceuticals, materials and agrochemicals. The noteworthy characteristics of fluorine include high electron affinity, lipophilicity and bioavailability, extending the half-life of the drugs. The incorporation of fluorine substituents, particularly trifluoromethyl groups, into organic molecules has led to their high potency against various diseases, including malaria. Hence, organofluorinated molecules offer valuable avenues for the design of new drug candidates against malaria.

AREAS COVERED

In this review, the authors discuss the importance of fluorine substituents present in the chemical compounds, and their potential applications for antimalarial drug discovery.

EXPERT OPINION

Fluorinated molecules represent a reliable strategy to develop new antimalarial drugs. Fluorine or fluorinated groups have been identified as a promising precursor, and their presence in approximately twenty-five percent of approved drugs is notable. Selective fluorination of chemical entities has the potential to be applied not only to improve the activity profile against the malaria parasite, but could be extrapolated for favorable pharmacological applications. Hazardous reagents such as HF, F₂ and SF₄ used for fluorination, are not considered as safe, and therefore, this process remains challenging, particularly for the pharmaceutical industry.

5-Fluoro-2'-deoxycytidine as a Probe for the Study of B/Z-DNA Transition by 19F NMR Spectroscopy

5-Fluoro-2'-deoxycytidine was synthesized by treating 5-fluoro-2'-deoxyuridine with 2,4,6-trimethylphenol in the presence of 1-methylpyrrolidine and trifluoroacetic anhydride, followed by aminolysis. Among N-acetyl, pivaloyl, and benzoyl, N-acetyl was found to be suitable for the protection of the exocyclic amine of 5-fluoro-2'-deoxycytidine because of the stability of the N ⁴-protected nucleoside under acidic conditions and its ease of removal after solid-phase synthesis. This modified nucleoside was incorporated into d(CG)₆ sequences through the phosphoramidite chemistry-based solid-phase synthesis. Circular dichroism experiments suggest that replacement of 2'-deoxycytidine with 5-fluoro-2'-deoxycytidine does not lead to detectable conformational changes, either in the B- or Z-form. ¹⁹F NMR spectroscopy of d(CG)₆ containing 5-fluoro-2'-deoxycytidine revealed that B/Z-DNA transition induced by sodium chloride is likely initiated at terminal ends, leading to unwinding at the middle of duplexes, and eventual switch of handedness when sodium chloride concentration reaches a threshold value.

Photoredox-catalyzed deoxyfluorination of activated alcohols with Selectfluor®

Herein we disclose a deoxyfluorination of alcohols with an electrophilic fluorine source via visible-light photoredox catalysis. This radical-mediated C-F coupling is capable of fluorinating secondary and tertiary alcohols efficiently, complementing previously reported nucleophilic deoxyfluorination protocols.

Identification of the Raf kinase inhibitor TAK-632 and its analogues as potent inhibitors of necroptosis by targeting RIPK1 and RIPK3

BACKGROUND AND PURPOSE

Necroptosis is a form of programmed, caspase-independent, cell death, mediated by receptor-interacting protein kinases, RIPK1 and RIPK3, and the mixed lineage kinase domain-like (MLKL). Necroptosis contributes to the pathophysiology of various inflammatory, infectious, and degenerative diseases. Thus, identification of low MW inhibitors for necroptosis has broad therapeutic relevance. Here, we identified that the pan-Raf inhibitor TAK-632 was also an inhibitor of necroptosis. We have further generated a more selective, highly potent analogue of TAK-632 by targeting RIPK1 and RIPK3.

EXPERIMENTAL APPROACH

Cell viability was measured by MTT, propidium staining, or CellTiter-Glo luminescent assays. Effects of TAK-632 on necroptosis signalling pathways were investigated by western blotting, immunoprecipitation, and in vitro kinase assays. Downstream targets of TAK-632 were identified by a drug affinity responsive target stability assay and a pull-down assay with biotinylated TAK-632. A mouse model of TNF-α-induced systemic inflammatory response syndrome (SIRS) was further used to explore the role of TAK-632 in protecting against necroptosis-associated inflammation in vivo.

KEY RESULTS

TAK-632 protected against necroptosis in human and mouse cells but did not protect cells from apoptosis. TAK-632 directly bound with RIPK1 and RIPK3 to inhibit kinase activities of both enzymes. In vivo, TAK-632 alleviated TNF-induced SIRS. Furthermore, we performed a structure-activity relationship analysis of TAK-632 analogues and generated SZM594, a highly potent inhibitor of RIPK1/3.

CONCLUSIONS AND IMPLICATIONS

TAK-632 is an inhibitor of necroptosis and represents a new lead compound in the development of highly potent inhibitors of RIPK1 and RIPK3.

Contrasting reactivity of fluorinated 2,6-heptanediones towards amines and ammonia, leading to cyclohexanediones or 2-oxa-6-azabicyclo[2.2.2]octanes and evaluation of their cytotoxicity

Synthesis and cytotoxic studies of cyclohexanediones and 2-oxa-6-azabicyclo[2.2.2]octanes obtained in reaction of fluorinated 2,6-hetanediones with amines and ammonia respectively.

The QM/MM-QTAIM approach reveals the nature of the different reactivity of cephalosporins in the active site of L1 metallo-β-lactamase

We combine the QM/MM and the QTAIM approaches to predict the reactivity of cephalosporins in the active site of L1 metallo-β-lactamase.

2′-Fluoro-c-di-GMP as an oral vaccine adjuvant

Bis-(3′–5′)-cyclic dimeric 2′-deoxy-2′-fluoroguanosine monophosphate (2′-F-c-di-GMP) was synthesized through the modified H-phosphonate chemistry. Oral immunization of C57BL/6 mice with Helicobacter pylori cell-free sonicate extract adjuvanted with 2′-F-c-di-GMP led to the production of antigen-specific antibodies in feces and sera, and lowered bacterial counts in the stomach upon post-vaccination infections in immunized mice. Similarly, oral vaccination of BALB/c mice with flagillin proteins from Clostridium difficile and Listeria monocytogenes adjuvanted with 2′-F-c-di-GMP led to production of antigen-specific antibodies both systemically and mucosally. The adjuvanticity of 2′-F-c-di-GMP is associated with the enhanced induction of interferon γ. These results demonstrated the excellent oral adjuvanticity of 2′-F-c-di-GMP.

2′-F-c-di-GMP was synthesized through the modified H-phosphonate chemistry. 2′-F-c-di-GMP was found to be an effective mucosal vaccine adjuvant, both intranasally and orally.

ω-Phthalimidoalkyl Aryl Ureas as Potent and Selective Inhibitors of Cholesterol Esterase

Cholesterol esterase (CEase), a serine hydrolase thought to be involved in atherogenesis and thus coronary heart disease, is considered as a target for inhibitor development. We investigated recombinant human and murine CEases with a new fluorometric assay in a structure-activity relationship study of a small library of ω-phthalimidoalkyl aryl ureas. The urea motif with an attached 3,5-bis(trifluoromethyl)phenyl group and the aromatic character of the ω-phthalimide residue were most important for inhibitory activity. In addition, an alkyl chain composed of three or four methylene groups, connecting the urea and phthalimide moieties, was found to be an optimal spacer for inhibitors. The so-optimized compounds 2 [1-(3,5-bis(trifluoromethyl)phenyl)-3-(3-(1,3-dioxoisoindolin-2-yl)propyl)urea] and 21 [1-(3,5-bis(trifluoromethyl)phenyl)-3-(4-(1,3-dioxoisoindolin-2-yl)butyl)urea] exhibited dissociation constants (K_i ) of 1-19 μm on the two CEases and showed either a competitive (2 on the human enzyme and 21 on the murine enzyme) or a noncompetitive mode of inhibition. Two related serine hydrolases-monoacylglycerol lipase and fatty acid amide hydrolase-were inhibited by ω-phthalimidoalkyl aryl ureas to a lesser extent.

Trifluoromethylation of Electron-Rich Alkenyl Iodides with Fluoroform-Derived "Ligandless" CuCF3

We herein present a flexible approach for the incorporation of CF₃ units into a predefined site of electron-rich alkenes that exploits the regiocontrolled introduction of an iodine handle and subsequent trifluoromethylation of the C(sp²)-I bond using fluoroform-derived "ligandless" CuCF₃. The broad substrate scope and functional group tolerance together with the scalability and purity of the resulting products enabled the controlled, late-stage synthesis of single regioisomers of complex CF₃-scaffolds, such as sugars, nucleosides (antivirals), and heterocycles (indoles and chromones), with potential for academic and industrial applications.