Synthesis and applications of fluorinated nucleoside analogues

Effects of polystyrene microplastics on the metabolic level of Pseudomonas aeruginosa

Given the widespread presence of Pseudomonas aeruginosa in water and its threat to human health, the metabolic changes in Pseudomonas aeruginosa when exposed to polystyrene microplastics (PS-MPs) exposure were studied, focusing on molecular level. Through non-targeted metabolomics, a total of 64 differential metabolites were screened out under positive ion mode and 44 under negative ion mode. The content of bacterial metabolites changed significantly, primarily involving lipids, nucleotides, amino acids, and organic acids. Heightened intracellular oxidative damage led to a decrease in lipid molecules and nucleotide-related metabolites. The down-regulation of amino acid metabolites, such as L-Glutamic and L-Proline, highlighted disruptions in cellular energy metabolism and the impaired ability to synthesize proteins as a defense against oxidation. The impact of PS-MPs on organic acid metabolism was evident in the inhibition of pyruvate and citrate, thereby disrupting the cells' normal participation in energy cycles. The integration of Kyoto Encyclopedia of Genes and Genomes (KEGG) analysis revealed that PS-MPs mainly caused changes in metabolic pathways, including ABC transporters, Aminoacyl-tRNA biosynthesis, Purine metabolism, Glycerophospholipid metabolism and TCA cycle in Pseudomonas aeruginosa. Most of the differential metabolites enriched in these pathways were down-regulated, demonstrating that PS-MPs hindered the expression of metabolic pathways, ultimately impairing the ability of cells to synthesize proteins, DNA, and RNA. This disruption affected cell proliferation and information transduction, thus hampering energy circulation and inhibiting cell growth. Findings of this study supplemented the toxic effects of microplastics and the defense mechanisms of microorganisms, in turn safeguarding drinking water safety and human health.

Synthesis of fluorinated and nonfluorinated sugar alkenylphosphonates via highly stereoselective Horner-Wadsworth-Emmons olefination

New fluorinated and nonfluorinated sugar alkenylphosphonates were obtained. In all cases 1,2;5,6-di-O-isopropylidene-α-d-glucofuranose was used as the starting material. The synthesis of alkenylphosphonates was based on Horner-Wadsworth-Emmons olefination. The process led to products with E-stereochemistry exclusively or predominately.

4'-Ethynyl-2'-deoxy-2'-β-fluoro-2-fluoroadenosine: A Highly Potent and Orally Available Clinical Candidate for the Treatment of HIV-1 Infection

2'-Deoxy-2'-β-fluoroadenosines bearing 4'-azido or 4'-ethynyl groups designed for the treatment of HIV-1 infection have been synthesized. All these compounds possess nanomolar anti-HIV-1 activity, with the 4'-ethynyl-2-fluoroadenosine analog 1c (CL-197) being the most potent compound with low cytotoxicity (EC50 = 0.9 nM, CC50 > 100 μM). It also shows potent inhibitory activities on drug resistant and clinical HIV-1 strains. Oral administration of 1c to Beagle dogs resulted in high levels of its bioactive form 1c-TP in peripheral blood mononuclear cells, the HIV-1 target cells, where the resulting triphosphate exhibited a long-term intracellular retention and could prevent HIV-1 infection for an extended time. 1c displayed low in vivo toxicity and favorable pharmacokinetics profiles in Sprague-Dawley rats. The preclinical data support further development of 1c as a highly potent and orally bioavailable clinical candidate to treat HIV-1 infection. Currently, CL-197 is in clinical trials in China (registration number: CXHL2200529).

Approaches to the synthesis of heterocyclic C-nucleosides

This review is focused on the synthetic strategies to heterocyclic C-nucleosides and covers the literature from 2011 to 2021. The main attention is paid to the following three approaches: the direct C-C coupling of a carbohydrate moiety with a preformed aglycon unit, the construction of a (pseudo)sugar residue on a pre-formed aglycon, and the construction of an aglycon on a pre-formed (pseudo)sugar. In each Section, the literature data are categorized in terms of the size of aglycon from simple to complex, the advantages and drawbacks of the reviewed approaches are discussed.

Diastereoselective Addition of PhSCF2SiMe3 to Chiral N-tert-Butanesulfinyl Ketimines Derived from Isatins: Synthesis of Enantioenriched gem-Difluoromethylenated Spiro-pyrrolidinyl and Spiro-piperidinyl Oxindoles

A convenient and efficient synthetic strategy to prepare enantioenriched gem-difluoromethylenated spiro-pyrrolidinyl and spiro-piperidinyl oxindoles is described. Fluoride-mediated diastereoselective nucleophilic addition of PhSCF₂SiMe₃ to chiral N-tert-butanesulfinyl ketimines derived from isatins was a key step and provided diastereomeric adducts, which were readily separable. Removal of the chiral sulfinyl group followed by structural manipulation afforded chiral gem-difluoromethylenated spiro-pyrrolidinyl and spiro-piperidinyl oxindoles.

A Unified Strategy to Fluorinated Nucleoside Analogues Via an Electrophilic Manifold

Herein, we present a strategy for the preparation of 3'-fluorinated nucleoside analogues via the aminocatalytic, electrophilic fluorination of readily accessible and bench-stable 2'-ketonucleosides. Initially developed to facilitate the manufacture of 3'-fluoroguanosine (3'-FG)─a substructure of anticancer therapeutic MK-1454─this strategy has been extended to the synthesis of a variety of 3'-fluoronucleosides. Finally, we demonstrate the utility of the 2'-ketonucleoside synthon as a platform for further diversification and suggest that this methodology should be broadly applicable to the discovery of novel nucleoside analogues.

Design and Synthesis of New α-hydroxy β-fluoro/β-trifluoromethyl and Unsaturated Phosphonates from Carbohydrate-Derived Building Blocks via Pudovik and Horner–Wadsworth–Emmons Reactions

Herein, we present the application of fluorinated carbohydrate-derived building blocks for α-hydroxy β-fluoro/β-trifluoromethyl and unsaturated phosphonates synthesis. Pudovik and Horner–Wadsworth–Emmons reactions were applied to achieve this goal. The proposed pathway of the key reactions is supported by the experimental results, as well as quantum chemical calculations. The structure of the products was established by spectroscopic (1D, 2D NMR) and spectrometric (MS) techniques. Based on our data received, we claim that the progress of the Pudovik and HWE reactions is significantly influenced by the acidic protons present in the molecules as assessed by pKa values of the reagent.

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.

A comprehensive update on the structure and synthesis of potential drug targets for combating the coronavirus pandemic caused by SARS-CoV-2

The outbreak of the coronavirus pandemic COVID-19 created by its severe acute respiratory syndrome corona virus-2 (SARS-CoV-2) variant, known for producing a very severe acute respiratory syndrome, has created an unprecedented situation by its continual assault around the world. The crisis caused by the SARS-CoV-2 variant has been a global challenge, calling to mitigate this unprecedented pandemic that has engulfed the whole world. Since the outbreak and spread of COVID-19, many researchers globally have been grappling to find new clinically trialed active drugs with anti-COVID-19 activity, from antimalarial drugs to JAK inhibitors, antiviral drugs, immune suppressants, and so forth. This article presents a brief discussion on the activity and synthesis of some active molecules such as favipiravir, hydroxychloroquine, pirfenidone, remdesivir, lopinavir, camostat, chloroquine, baricitinib, molnupiravir, and so forth, which are under trial.

Fluorinated Nucleosides: Synthesis, Modulation in Conformation and Therapeutic Application

Over the last twenty years, fluorination on nucleoside has established itself as the most promising tool to use to get biologically active compounds that could sustain the clinical trial by affecting the pharmacodynamics and pharmacokinetic properties. Due to fluorine's inherent unique properties and its judicious introduction into the molecule, makes the corresponding nucleoside metabolically very stable, lipophilic, and opens a new site of intermolecular binding. Fluorination on various nucleosides has been extensively studied as a result, a series of fluorinated nucleosides come up for different therapeutic uses which are either approved by the FDA or under the advanced stage of the clinical trial. Here in this review, we are summarizing the latest development in the chemistry of fluorination on nucleoside that led to varieties of new analogs like carbocyclic, acyclic, and conformationally biased nucleoside and their biological properties, the influence of fluorine on conformation, oligonucleotide stability, and their use in therapeutics.

Geminal Diheteroatomic Motifs: Some Applications of Acetals, Ketals, and Their Sulfur and Nitrogen Homologues in Medicinal Chemistry and Drug Design

Acetals and ketals and their nitrogen and sulfur homologues are often considered to be unconventional and potentially problematic scaffolding elements or pharmacophores for the design of orally bioavailable drugs. This opinion is largely a function of the perception that such motifs might be chemically unstable under the acidic conditions of the stomach and upper gastrointestinal tract. However, even simple acetals and ketals, including acyclic molecules, can be sufficiently robust under acidic conditions to be fashioned into orally bioavailable drugs, and these structural elements are embedded in many effective therapeutic agents. The chemical stability of molecules incorporating geminal diheteroatomic motifs can be modulated by physicochemical design principles that include the judicious deployment of proximal electron-withdrawing substituents and conformational restriction. In this Perspective, we exemplify geminal diheteroatomic motifs that have been utilized in the discovery of orally bioavailable drugs or drug candidates against the backdrop of understanding their potential for chemical lability.

Synthesis and evaluation of 3'-fluorinated 7-deazapurine nucleosides as antikinetoplastid agents

Kinetoplastid parasites are the causative agents of neglected tropical diseases with an unmet medical need. These parasites are unable to synthesize the purine ring de novo, and therefore rely on purine salvage to meet their purine demand. Evaluating purine nucleoside analogs is therefore an attractive strategy to identify antikinetoplastid agents. Several anti-Trypanosoma cruzi and anti-Trypanosoma brucei 7-deazapurine nucleosides were previously discovered, with the removal of the 3'-hydroxyl group resulting in a significant boost in activity. In this work we therefore decided to assess the effect of the introduction of a 3'-fluoro substituent in 7-deazapurine nucleosides on the anti-kinetoplastid activities. Hence, we synthesized two series of 3'-deoxy-3'-fluororibofuranosyl and 3'-deoxy-3'-fluoroxylofuranosyl nucleosides comprising 7-deazaadenine and -hypoxanthine bases and assayed these for antiparasitic activity. Several analogs with potent activity against T. cruzi and T. brucei were discovered, indicating that a fluorine atom in the 3'-position is a promising modification for the discovery of antiparasitic nucleosides.

Broad-Spectrum Antiviral Activity of 3'-Deoxy-3'-Fluoroadenosine against Emerging Flaviviruses

Emerging flaviviruses are causative agents of severe and life-threatening diseases, against which no approved therapies are available. Among the nucleoside analogues, which represent a promising group of potentially therapeutic compounds, fluorine-substituted nucleosides are characterized by unique structural and functional properties. Despite having first been synthesized almost 5 decades ago, they still offer new therapeutic opportunities as inhibitors of essential viral or cellular enzymes active in nucleic acid replication/transcription or nucleoside/nucleotide metabolism. Here, we report evaluation of the antiflaviviral activity of 28 nucleoside analogues, each modified with a fluoro substituent at different positions of the ribose ring and/or heterocyclic nucleobase. Our antiviral screening revealed that 3'-deoxy-3'-fluoroadenosine exerted a low-micromolar antiviral effect against tick-borne encephalitis virus (TBEV), Zika virus, and West Nile virus (WNV) (EC₅₀ values from 1.1 ± 0.1 μM to 4.7 ± 1.5 μM), which was manifested in host cell lines of neural and extraneural origin. The compound did not display any measurable cytotoxicity up to concentrations of 25 μM but had an observable cytostatic effect, resulting in suppression of cell proliferation at concentrations of >12.5 μM. Novel approaches based on quantitative phase imaging using holographic microscopy were developed for advanced characterization of antiviral and cytotoxic profiles of 3'-deoxy-3'-fluoroadenosine in vitro In addition to its antiviral activity in cell cultures, 3'-deoxy-3'-fluoroadenosine was active in vivo in mouse models of TBEV and WNV infection. Our results demonstrate that fluoro-modified nucleosides represent a group of bioactive molecules with excellent potential to serve as prospective broad-spectrum antivirals in antiviral research and drug development.

Mechanistic Insight into Antiretroviral Potency of 2'-Deoxy-2'-β-fluoro-4'-azidocytidine (FNC) with a Long-Lasting Effect on HIV-1 Prevention

In preclinical and phase I and II clinical studies, 2'-deoxy-2'-β-fluoro-4'-azidocytidine (FNC) displays a potent and long-lasting inhibition of HIV-1 infection. To investigate its mechanism of action, we compared it with the well-documented lamivudine (3TC). Pharmacokinetic studies revealed that the intracellular retention of FNC triphosphate in peripheral blood mononuclear cells was markedly longer than that of the 3TC triphosphate. FNC selectively enters and is retained in HIV target cells, where it exerts long-lasting prevention of HIV-1 infection. In addition to inhibition of HIV-1 reverse transcription, FNC also restores A3G expression in CD4⁺ T cells in FNC-treated HIV-1 patients. FNC binds to the Vif-E3 ubiquitin ligase complex, enabling A3G to avoid Vif-induced ubiquitination and degradation. These data reveal the mechanisms underlying the superior anti-HIV potency and long-lasting action of FNC. Our results also suggest a potential clinical application of FNC as a long-lasting pre-exposure prophylactic agent capable of preventing HIV infection.

Synthesis of 4-amino-5-fluoropyrimidines and 5-amino-4-fluoropyrazoles from a β-fluoroenolate salt

A synthesis of fluorinated pyrimidines under mild conditions from amidine hydrochlorides and the recently described potassium 2-cyano-2-fluoroethenolate was developed. A broad substrate scope was tested and mostly excellent yields were obtained. The synthesis of fluorinated aminopyrazoles from the same fluorinated precursor could be demonstrated but proceeded with lower efficiency.

Theoretical analyses and experimental validation of the effects caused by the fluorinated substituent modification of DNA

Halogen-modified nucleic acid molecules, such as trifluorothymidine (FTD) and 5-fluorouracil, are widely used in medical science and clinical site. These compounds have a very similar nucleobase structure. It is reported that both of these compounds could be incorporated into DNA. The incorporation of FTD produces highly anti-tumor effect. However, it is not known whether to occur a significant effect by the incorporation of 5-fluorouracil. Nobody knows why such a difference will occur. To understand the reason why there is large differences between trifluorothymidine and 5-fluorouracil, we have performed the molecular dynamics simulations and molecular orbital calculations. Although the active interaction energy between Halogen-modified nucleic acids or and complementary adenine was increased, in only FTD incorporated DNA, more strongly dispersion force interactions with an adjacent base were detected in many thermodynamic DNA conformations. As the results, the conformational changes occur even if it is in internal body temperature. Then the break of hydrogen bonding between FTD and complementary adenine base occur more frequently. The double helix structural destabilization of DNA with FTD is resulted from autoagglutination caused by the bonding via halogen orbitals such as halogen bonding and the general van der Waals interactions such as CH–\documentclass[12pt]{minimal} \usepackage{amsmath} \usepackage{wasysym} \usepackage{amsfonts} \usepackage{amssymb} \usepackage{amsbsy} \usepackage{mathrsfs} \usepackage{upgreek} \setlength{\oddsidemargin}{-69pt} \begin{document}$${\rm{\pi }}$$\end{document}π, lone pair (LP)–\documentclass[12pt]{minimal} \usepackage{amsmath} \usepackage{wasysym} \usepackage{amsfonts} \usepackage{amssymb} \usepackage{amsbsy} \usepackage{mathrsfs} \usepackage{upgreek} \setlength{\oddsidemargin}{-69pt} \begin{document}$${\rm{\pi }}$$\end{document}π, and \documentclass[12pt]{minimal} \usepackage{amsmath} \usepackage{wasysym} \usepackage{amsfonts} \usepackage{amssymb} \usepackage{amsbsy} \usepackage{mathrsfs} \usepackage{upgreek} \setlength{\oddsidemargin}{-69pt} \begin{document}$${\rm{\pi }}$$\end{document}π–\documentclass[12pt]{minimal} \usepackage{amsmath} \usepackage{wasysym} \usepackage{amsfonts} \usepackage{amssymb} \usepackage{amsbsy} \usepackage{mathrsfs} \usepackage{upgreek} \setlength{\oddsidemargin}{-69pt} \begin{document}$${\rm{\pi }}$$\end{document}π interactions. Therefore, it is strongly speculated that such structural changes caused by trifluoromethyl group is important for the anti-tumor effect of FTD alone.

Structures and Relative Glycosidic Bond Stabilities of Protonated 2'-Fluoro-Substituted Purine Nucleosides

The 2'-substituent is the primary distinguishing feature between DNA and RNA nucleosides. Modifications to this critical position, both naturally occurring and synthetic, can produce biologically valuable nucleoside analogues. The unique properties of fluorine make it particularly interesting and medically useful as a synthetic nucleoside modification. In this work, the effects of 2'-fluoro modification on the protonated gas-phase purine nucleosides are examined using complementary tandem mass spectrometry and computational methods. Direct comparisons are made with previous studies on related nucleosides. Infrared multiple photon dissociation action spectroscopy performed in both the fingerprint and hydrogen-stretching regions allows for the determination of the experimentally populated conformations. The populated conformers of protonated 2'-fluoro-2'-deoxyadenosine, [Adofl+H]⁺, and 2'-fluoro-2'-deoxyguanosine, [Guofl+H]⁺, are highly parallel to their respective canonical DNA and RNA counterparts. Both N3 and N1 protonation sites are accessed by [Adofl+H]⁺, stabilizing syn and anti nucleobase orientations, respectively. N7 protonation and anti nucleobase orientation dominates in [Guofl+H]⁺. Spectroscopically observable intramolecular hydrogen-bonding interactions with fluorine allow more definitive sugar puckering determinations than possible for the canonical systems. [Adofl+H]⁺ adopts C2'-endo sugar puckering, whereas [Guofl+H]⁺ adopts both C2'-endo and C3'-endo sugar puckering. Energy-resolved collision-induced dissociation experiments with survival yield analyses provide relative glycosidic bond stabilities. The N-glycosidic bond stabilities of the protonated 2'-fluoro-substituted purine nucleosides are found to exceed those of their canonical analogues. Further, the N-glycosidic bond stability is found to increase with increasing electronegativity of the 2'-substituent, i.e., H < OH < F. The N-glycosidic bond stability is also greater for the adenine nucleoside analogues than the guanine nucleoside analogues.

The evolution of antiviral nucleoside analogues: A review for chemists and non-chemists. Part II: Complex modifications to the nucleoside scaffold

This is the second of two invited articles reviewing the development of nucleoside analogue antiviral drugs, written for a target audience of virologists and other non-chemists, as well as chemists who may not be familiar with the field. As with the first paper, rather than providing a chronological account, we have chosen to examine particular examples of structural modifications made to nucleoside analogues that have proven fruitful as various antiviral, anticancer, and other therapeutics. The first review covered the more common, and in most cases, single modifications to the sugar and base moieties of the nucleoside scaffold. This paper focuses on more recent developments, especially nucleoside analogues that contain more than one modification to the nucleoside scaffold. We hope that these two articles will provide an informative historical perspective of some of the successfully designed analogues, as well as many candidate compounds that encountered obstacles.

Synthesis and biological assay of new 2'-deoxyuridine dimers containing a 1,2,3-triazole linker. Part I

We describe a simple method for the synthesis of modified dinucleosides containing pyrimidine nucleoside analogues (2'-deoxyuridine, thymidine and 5-fluoro-2'-deoxyuridine). Six different dimers with a 1,2,3-triazole linkage were obtained by azide-alkyne 1,3-dipolar cycloaddition (click reaction), starting from propargylated 2'-deoxyuridine and 5'-azido-nucleoside derivatives. Their cytotoxic activity was tested in five human cancer cell lines: cervical (HeLa), high grade gliomas (U-118 MG, U-87 MG, T98G), liver (HepG2), and normal human fibroblast cell line (MRC-5) using the sulforhodamine B (SRB) assay. The experiment showed that the obtained dimers with a 1,2,3-triazole moiety were very stable compounds, also in the physiological-like media, and had no anticancer activity.

The evolution of nucleoside analogue antivirals: A review for chemists and non-chemists. Part 1: Early structural modifications to the nucleoside scaffold

This is the first of two invited articles reviewing the development of nucleoside-analogue antiviral drugs, written for a target audience of virologists and other non-chemists, as well as chemists who may not be familiar with the field. Rather than providing a simple chronological account, we have examined and attempted to explain the thought processes, advances in synthetic chemistry and lessons learned from antiviral testing that led to a few molecules being moved forward to eventual approval for human therapies, while others were discarded. The present paper focuses on early, relatively simplistic changes made to the nucleoside scaffold, beginning with modifications of the nucleoside sugars of Ara-C and other arabinose-derived nucleoside analogues in the 1960's. A future paper will review more recent developments, focusing especially on more complex modifications, particularly those involving multiple changes to the nucleoside scaffold. We hope that these articles will help virologists and others outside the field of medicinal chemistry to understand why certain drugs were successfully developed, while the majority of candidate compounds encountered barriers due to low-yielding synthetic routes, toxicity or other problems that led to their abandonment.

Design, synthesis, and biological evaluation of new 1,2,3-triazolo-2'-deoxy-2'-fluoro- 4'-azido nucleoside derivatives as potent anti-HBV agents

Novel drugs are urgently needed to combat hepatitis B virus (HBV) infection due to drug-resistant virus. In this paper, a series of novel 4-monosubstituted 2'-deoxy-2'-β-fluoro-4'-azido-β-d-arabinofuranosyl 1,2,3-triazole nucleoside analogues (1a-g) were designed, synthesized and screened for in vitro anti-HBV activity. At 5.0 μM in the cellular model, all the synthetic compounds display activities comparable to that of the positive control, lamivudine at 20 μM. Of the compounds tested, the amide-substituted analogue (1a) shows the most promising anti-HBV activity and low cytotoxicity in the cell model. In particular, it retains excellent activity against lamivudine-resistant HBV mutants. In duck HBV (DHBV)-infected duck models, both the serum and liver DHBV DNA levels (67.4% and 53.3%, respectively) were reduced markedly by the treatment with 1a. Analysis of the structure of HBV polymer/1a-triphosphate (1a-TP) complex shows that 1a-TP is stabilized by specific van der Waals interactions with the enzyme residues arising from 4-amino-1,2,3-triazole and the 4'-azido group.

Fluorination of some highly functionalized cycloalkanes: chemoselectivity and substrate dependence

A study exploring the chemical behavior of some dihydroxylated β-amino ester stereo- and regioisomers, derived from unsaturated cyclic β-amino acids is described. The nucleophilic fluorinations involving hydroxy-fluorine exchange of some highly functionalized alicyclic diol derivatives have been carried out in view of selective fluorination, investigating substrate dependence, neighboring group assistance and chemodifferentiation.

Synthesis and antiviral evaluation of 2',2',3',3'-tetrafluoro nucleoside analogs

Herein, we report the synthesis of novel 2',2',3',3'-tetrafluorinated nucleoside analogs along with their phosphoramidate prodrugs. A tetrafluoro ribose moiety was coupled with different Boc/benzoyl-protected nucleobases under Mitsunobu conditions. After deprotection, tetrafluorinated nucleosides 13b, 14b, 20b-22b were reacted with phenyl-(isopropoxy-L-alaninyl)-phosphorochloridate to afford corresponding monophosphate prodrugs 24b-28b. All synthesized compounds were evaluated against several DNA and RNA viruses including HIV, HBV, HCV, Ebola and Zika viruses.

Fluorination methods in drug discovery

Fluorination reactions of medicinal and biologically-active compounds will be discussed. Late stage fluorination strategies of medicinal targets have recently attracted considerable attention on account of the influence that a fluorine atom can impart to targets of medicinal importance, such as modulation of lipophilicity, electronegativity, basicity and bioavailability, the latter as a consequence of membrane permeability. Therefore, the recourse to late-stage fluorine substitution on compounds with already known and relevant biological activity can provide the pharmaceutical industry with new leads with improved medicinal properties. The fluorination strategies will take into account different fluorinating reagents, either of nucleophilic or electrophilic, and of radical nature. Diverse families of organic compounds such as (hetero)aromatic rings, and aliphatic substrates (sp(3), sp(2), and sp carbon atoms) will be studied in late-stage fluorination reaction strategies.

Synthesis and Potent Anti-HCMV Activity of 2',5',5'-trifluoro-3'-hydroxy-apiosyl Nucleoside Phosphonic Acid Analogues

As antiviral nucleosides containing a fluorine atom at 2'-position are endowed with increased stabilization of glycosyl bond, it was of interest to investigate the influence of three fluorine atoms at 2'- and 5'-positions of apiosyl nucleoside phosphonate analogues. Various pyrimidine and purine 2',5',5'-trifluoro-3'-hydroxy-apiose nucleoside phosphonic acid analogues were synthesized from 1,3-dihydroxyacetone. Electrophilic fluorination of lactone was performed using N-fluorodibenzenesulfonimide. Difluorophosphonation was performed by direct displacement of triflate intermediate with diethyl(lithiodifluoromethyl) phosphonate to give the corresponding (α,α-difluoroalkyl) phosphonate. Condensation successfully proceeded from a glycosyl donor with persilylated bases to yield nucleoside phosphonate analogues. Deprotection of diethyl phosphonates provided the final phosphonic acid sodium salts. The synthesized nucleoside analogues were subjected to antiviral screening against various viruses.

Nickel-Catalyzed Alkyl-Alkyl Cross-Couplings of Fluorinated Secondary Electrophiles: A General Approach to the Synthesis of Compounds having a Perfluoroalkyl Substituent

Fluorinated organic molecules are of interest in fields ranging from medicinal chemistry to polymer science. Described herein is a mild, convenient, and versatile method for the synthesis of compounds bearing a perfluoroalkyl group attached to a tertiary carbon atom by using an alkyl-alkyl cross-coupling. A nickel catalyst derived from NiCl2 ⋅glyme and a pybox ligand achieves the coupling of a wide range of fluorinated alkyl halides with alkylzinc reagents at room temperature. A broad array of functional groups is compatible with the reaction conditions, and highly selective couplings can be achieved on the basis of differing levels of fluorination. A mechanistic investigation has established that the presence of 2,2,6,6-tetramethyl-1-piperidinyloxy (TEMPO) inhibits cross-coupling under these conditions and that a TEMPO-electrophile adduct can be isolated.

Synthesis and biological evaluation of 4-substituted fluoronucleoside analogs for the treatment of hepatitis B virus infection

A series of 4-substituted fluoronucleosides have been synthesized in order to address the toxicity issue of the parent compound 7, and after in vitro evaluation, the cyclopropylamino analog 1f was selected for in vivo study. In mice, this compound exhibited a significantly improved toxicity profile. Administered orally, compound 1f was well-tolerated at a dose up to 3 g/kg and showed insignificant toxicity on white blood cells and a low mutagenic effect at dosages up to 80 mg/kg (single) or 20 mg/kg/day (5 days). In duck HBV (DHBV)-infected duck models, both the serum and liver DHBV DNA levels (74.2 and 82.1%, respectively) were markedly reduced by the treatment of 1f at a dose of 1 mg/kg/day for 10 days. In addition, both the viral DNA levels had a lower degree of recovery after withdrawal of the test compound for 3 days.

A linear synthesis of gemcitabine

Gemcitabine, 2'-deoxy-2',2'-difluorocytidine, is currently prescribed against a number of cancers. Here we report a linear synthesis of gemcitabine with a high-yielding direct conversion of 3,5-di-O-benzoyl-2-deoxy-2,2-difluororibose into the corresponding glycosyl urea as the key step, followed by conventional conversion to the cytosine base via the uracil derivative. The process proceeded with modest anomeric selectivity.

Fluorine in medicinal chemistry

Since its first use in the steroid field in the late 1950s, the use of fluorine in medicinal chemistry has become commonplace, with the small electronegative fluorine atom being a key part of the medicinal chemist's repertoire of substitutions used to modulate all aspects of molecular properties including potency, physical chemistry and pharmacokinetics. This review will highlight the special nature of fluorine, drawing from a survey of marketed fluorinated pharmaceuticals and the medicinal chemistry literature, to illustrate key concepts exploited by medicinal chemists in their attempts to optimize drug molecules. Some of the potential pitfalls in the use of fluorine will also be highlighted.

Regio- and stereoselective synthesis of 2′-β-substituted-fluoroneplanocin A analogues as potential anticancer agents

Regio- and stereoselective synthesis of a series of 2′-β-substituted-6′-fluoro-cyclopentenyl-pyrimidines and -purines 8 and 9 as potential anticancer agents is described.

The synthesis of gemcitabine

Gemcitabine is a fluorinated nucleoside currently administered against a number of cancers. It consists of a cytosine base and a 2-deoxy-2,2-difluororibose sugar. The synthetic challenges associated with the introduction of the fluorine atoms, as well as with nucleobase introduction of 2,2-difluorinated sugars, combined with the requirement to have an efficient process suitable for large scale synthesis, have spurred significant activity towards the synthesis of gemcitabine exploring a wide variety of synthetic approaches. In addition, many methods have been developed for selective crystallisation of diastereomeric (including anomeric) mixtures. In that regard, the 2-deoxy-2,2-difluororibose sugar is one of the most investigated fluorinated carbohydrates in terms of its synthesis. The versatility of synthetic methods employed is illustrative of the current state of the art of fluorination methodology for the synthesis of CF2-containing carbohydrates, and involves the use of fluorinated building blocks, as well as nucleophilic and electrophilic fluorination of sugar precursors.