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

Recent progress in therapeutic applications of fluorinated five-membered heterocycles and their benzo-fused systems

Heterocyclic derivatives grafted with fluorine atom(s) have attracted the attention of scientists due to the unique physicochemical properties of the C-F bond. The inclusion of fluorine atom(s) into organic compounds often increases their lipophilicity and metabolic stability, enhancing their bioavailability and affinity for target proteins. Therefore, it is not surprising to find that more than 20% of the medications on the market contain fluorine, and nearly 300 fluorine-containing drugs have been officially approved for use as medicines. In this review article, we are interested in classifying and describing the reports comprising varied therapeutic activities of the directly fluorinated five-membered heterocycles and their fused systems during the last two decades. These therapeutic activities included antiviral, anti-inflammatory, enzymatic inhibitory, antimalarial, anticoagulant, antipsychotic, antioxidant, antiprotozoal, histamine-H3 receptor, serotonin receptor, chemokine receptor, prostaglandin-D2 receptor, and PBR inhibition activities. In many cases, the activities of fluorinated azoles were almost equal to or exceeded the potency of reference drugs.

Synthesis of C,N-Glycosides via Brønsted Acid-Catalyzed Azidation of exo-Glycals

The reaction of exo-glycals with azidotrimethylsilane in the presence of a Brønsted acid leads to the generation of the corresponding C,N-glycosyl azides. The majority of these glycosylation reactions proceed at room temperature with short reaction times. In addition, the targeted products were obtained in high yields with exclusive diastereoselectivity to the α-anomer in pyranose-based derivatives. Carbohydrate units based on mannose, galactose, arabinose, and ribose were also shown to proceed in high yields.

A Literature Review Focusing on the Antiviral Activity of [1,2,4] and [1,2,3]-triazoles

Out of a variety of heterocycles, triazole scaffolds have been shown to play a significant part in a wide array of biological functions. Many drug compounds containing a triazole moiety with important antimicrobial, anticancer and antidepressant properties have been commercialized. In addition, the triazole scaffold exhibits remarkable antiviral activity either incorporated into nucleoside analogs or non-nucleosides. Many synthetic techniques have been produced by scientists around the world as a result of their wide-ranging biological function. In this review, we have tried to summarize new synthetic methods produced by diverse research groups as well as provide a comprehensive description of the function of [1,2,4] and [1,2,3]-triazole derivatives as antiviral agents. Antiviral triazole compounds have been shown to target a wide variety of molecular proteins. In addition, several strains of viruses, including the human immunodeficiency virus, SARS virus, hepatitis B and C viruses, influenza virus, Hantavirus, and herpes virus, were discovered to be susceptible to triazole derivatives. This review article covered the reports for antiviral activity of both 1,2,3- and 1,2,4-triazole moieties up to 2022.

Fluorinated triazoles as privileged potential candidates in drug development—focusing on their biological and pharmaceutical properties

Fluorinated heterocycles have attracted extensive attention not only in organic synthesis but also in pharmaceutical and medicinal sciences due to their enhanced biological activities than their non-fluorinated counterparts. Triazole is a simple five-membered heterocycle with three nitrogen atoms found in both natural and synthetic molecules that impart a broad spectrum of biological properties including but not limited to anticancer, antiproliferative, inhibitory, antiviral, antibacterial, antifungal, antiallergic, and antioxidant properties. In addition, incorporation of fluorine into triazole and its derivatives has been reported to enhance their pharmacological activity, making them promising drug candidates. This mini-review explores the current developments of backbone-fluorinated triazoles and functionalized fluorinated triazoles with established biological activities and pharmacological properties.

4'-Modified Nucleosides for Antiviral Drug Discovery: Achievements and Perspectives

Modified nucleosides show therapeutic promise for antiviral therapies. However, issues including the emergence of drug resistance, toxicity, and coinfections have posed new challenges for nucleoside-based antiviral drug discovery, particularly in the era of the coronavirus disease 2019 (COVID-19) pandemic. Chemical manipulation could impact the antiviral potency, safety, and drug resistance of nucleosides. Generally, modified nucleosides are difficult to recognize by intracellular important enzymes as substrates and thus exhibit low toxicity. 4'-Modified nucleosides represent an important subclass of modified nucleosides for antiviral therapies. To prevent the occurrence of drug resistance, 4'-modified nucleosides should have 3'-OH, which should also be chemically unreactive for proviral DNA biosynthesis. The absence of 3'-OH may explain the occurrence of drug resistance for censavudine. The introduction of 4'-substituents improves enzymatic and acidic stability and makes the nucleosides more lipophilic, thus improving cell permeability and bioavailability. Steric hindrance between the 4'-substituent and 3'-OH changes the furanose conformation to the 3'-endo type, in which the oxygen lone pair on the furanose ring could not form an oxocarbonium ion for glycolysis. Currently, seven 4'-modified nucleoside drug candidates such as azvudine (also known as FNC), islatravir, censavudine, balapiravir, lumicitabine, AL-335, and 4-azidothymidine have progressed into clinical stages for treating viral infections. Of note, FNC was officially approved by NMPA in July 2021 for use in adult patients with high HIV-1 virus loads (nos. H20210035 and H20210036), providing an alternative therapeutic for patients with HIV-1. The long-term cellular retention of FNC suggests its potential as a long-lasting pre-exposure prophylaxis (PrEP) agent for preventing HIV-1 infection. Mechanistically, FNC not only inhibited HIV-1 reverse transcription and replication but also restored A3G expression in peripheral blood CD4⁺ T cells in HIV-1 patients receiving FNC. The 4'-azido group in azvudine stabilizes the 3'-C-endo (north) conformation by steric effects and the formation of an intramolecular hydrogen bond with the 3'-OH group, thus decreasing the nucleophilicity of 3'-OH. The north conformation may also enhance the phosphorylation efficiency of FNC by cellular kinases. Encouragingly, FNC, islatravir, and balapiravir show promise for the treatment of coronaviruses, of which FNC has advanced to phase 3 clinical trials in different countries to treat patients with COVID-19 (clinical trial numbers: NCT04668235 and NCT04425772). FNC cured the COVID-19 disease in almost all patients and showed better therapeutic efficacy than remdesivir. In this Account, we provide an overview of 4'-modified nucleoside analogs in clinical stages for antiviral therapies, highlighting the drug discovery strategies, structure-activity relationship studies, and preclinical/clinical studies and also give our perspectives on nucleoside-based antiviral drug discovery.

Green synthesis of triazolo-nucleoside conjugates via azide–alkyne C–N bond formation

Modified nucleosides are the core precursors for the synthesis of artificial nucleic acids, and are important in the field of synthetic and medicinal chemistry. In order to synthesize various triazolo-compounds, copper and ruthenium catalysed azide–alkyne 1,3-dipolar cycloaddition reactions also known as click reaction have emerged as a facile and efficient tool due to its simplicity and convenient conditions. Introduction of a triazole ring in nucleosides enhances their therapeutic value and various photophysical properties. This review primarily focuses on the plethora of synthetic methodologies being employed to synthesize sugar modified triazolyl nucleosides, their therapeutic importance and various other applications.

Modified Nucleosides, Nucleotides and Nucleic Acids via Click Azide-Alkyne Cycloaddition for Pharmacological Applications

The click azide = alkyne 1,3-dipolar cycloaddition (click chemistry) has become the approach of choice for bioconjugations in medicinal chemistry, providing facile reaction conditions amenable to both small and biological molecules. Many nucleoside analogs are known for their marked impact in cancer therapy and for the treatment of virus diseases and new targeted oligonucleotides have been developed for different purposes. The click chemistry allowing the tolerated union between units with a wide diversity of functional groups represents a robust means of designing new hybrid compounds with an extraordinary diversity of applications. This review provides an overview of the most recent works related to the use of click chemistry methodology in the field of nucleosides, nucleotides and nucleic acids for pharmacological applications.

Advance of structural modification of nucleosides scaffold

With Remdesivir being approved by FDA as a drug for the treatment of Corona Virus Disease 2019 (COVID-19), nucleoside drugs have once again received widespread attention in the medical community. Herein, we summarized modification of traditional nucleoside framework (sugar + base), traizole nucleosides, nucleoside analogues assembled by other drugs, macromolecule-modified nucleosides, and their bioactivity rules. 2'-"Ara"-substituted by -F or -CN group, and 3'-"ara" substituted by acetylenyl group can greatly influence their anti-tumor activities. Dideoxy dehydrogenation of 2',3'-sites can enhance antiviral efficiencies. Acyclic nucleosides and L-type nucleosides mainly represented antiviral capabilities. 5-F Substituted uracil analogues exihibit anti-tumor effects, and the substrates substituted by -I, -CF3, bromovinyl group usually show antiviral activities. The sugar coupled with 1-N of triazolid usually displays anti-tumor efficiencies, while the sugar coupled with 2-N of triazolid mainly represents antiviral activities. The nucleoside analogues assembled by cholesterol, polyethylene glycol, fatty acid and phospholipid would improve their bioavailabilities and bioactivities, or reduce their toxicities.

Advances in Nucleoside and Nucleotide Analogues in Tackling Human Immunodeficiency Virus and Hepatitis Virus Infections

Nucleoside and nucleotide analogues are structurally similar antimetabolites and are promising small-molecule chemotherapeutic agents against various infectious DNA and RNA viruses. To date, these analogues have not been documented in-depth as anti-human immunodeficiency virus (HIV) and anti-hepatitis virus agents, these are at various stages of testing ranging from pre-clinical, to those withdrawn from trials, or those that are approved as drugs. Hence, in this review, the importance of these analogues in tackling HIV and hepatitis virus infections is discussed with a focus on the viral genome and the mechanism of action of these analogues, both in a mutually exclusive manner and their role in HIV/hepatitis coinfection. This review encompasses nucleoside and nucleotide analogues from 1987 onwards, starting with the first nucleoside analogue, zidovudine, and going on to those in current clinical trials and even the drugs that have been withdrawn. This review also sheds light on the prospects of these nucleoside analogues in clinical trials as a treatment option for the COVID-19 pandemic.

Design, Synthesis and Bioactive Evaluation of Oxime Derivatives of Dehydrocholic Acid as Anti-Hepatitis B Virus Agents

Oxime derivatives of dehydrocholic acid and its esters were designed for anti-hepatitis B virus (HBV) drugs according to principles of assembling active chemical fragments. Twelve compounds were synthesized from dehydrocholic acid by esterification and oxime formation, and their anti-hepatitis B virus (HBV) activities were evaluated with HepG 2.2.15 cells. Results showed that 5 compounds exhibited more effective inhibition of HBeAg than positive control, among them 2b-3 and 2b-1 showed significant anti-HBV activities on inhibiting secretion of HBeAg (IC_{50 (2b-3)} = 49.39 ± 12.78 μM, SI _(2b-3) = 11.03; IC_{50 (2b-1)} = 96.64 ± 28.99 μM, SI _(2b-1) = 10.35) compared to the Entecavir (IC₅₀ = 161.24 μM, SI = 3.72). Molecular docking studies showed that most of these compounds interacted with protein residues of heparan sulfate proteoglycan (HSPG) in host hepatocyte and bile acid receptor.

1,2,3-Triazole-containing hybrids as leads in medicinal chemistry: A recent overview

The 1,2,3-triazole ring is a major pharmacophore system among nitrogen-containing heterocycles. These five-membered heterocyclic motifs with three nitrogen heteroatoms can be prepared easily using 'click' chemistry with copper- or ruthenium-catalysed azide-alkyne cycloaddition reactions. Recently, the 'linker' property of 1,2,3-triazoles was demonstrated, and a novel class of 1,2,3-triazole-containing hybrids and conjugates was synthesised and evaluated as lead compounds for diverse biological targets. These lead compounds have been demonstrated as anticancer, antimicrobial, anti-tubercular, antiviral, antidiabetic, antimalarial, anti-leishmanial, and neuroprotective agents. The present review summarises advances in lead compounds of 1,2,3-triazole-containing hybrids, conjugates, and their related heterocycles in medicinal chemistry published in 2018. This review will be useful to scientists in research fields of organic synthesis, medicinal chemistry, phytochemistry, and pharmacology.

Synthesis, activity evaluation, and pro-apoptotic properties of novel 1,2,4-triazol-3-amine derivatives as potent anti-lung cancer agents

In this study, a series of 4,5-bis(substituted phenyl)-4H-1,2,4-triazol-3-amine compounds was designed, synthesised, and evaluated to determine their potential as anti-lung cancer agents. According to the results of screening of lung cancer cell lines A549, NCI-H460, and NCI-H23 in vitro, most of the synthesised compounds have potent cytotoxic activities with IC₅₀ values ranging from 1.02 to 48.01 µM. Particularly, compound 4,5-bis(4-chlorophenyl)-4H-1,2,4-triazol-3-amine (BCTA) was the most potent anti-cancer agent, with IC₅₀ values of 1.09, 2.01, and 3.28 µM against A549, NCI-H460, and NCI-H23 cells, respectively, meaning many-fold stronger anti-lung cancer activity than that of the chemotherapeutic agent 5-fluorouracil. We also explored the effects of BCTA on apoptosis in lung cancer cells by flow cytometry and western blotting. Our results indicated that BCTA induced apoptosis by upregulating proteins BAX, caspase 3, and PARP. Thus, the potential application of compound BCTA as a drug should be further examined.

Design, synthesis, and biological evaluation of novel 2'-deoxy-2'-fluoro-2'-C-methyl 8-azanebularine derivatives as potent anti-HBV agents

Hepatitis B virus (HBV) is a global health problem requiring more efficient and better tolerated anti-HBV agent. In this paper, a series of novel 2'-deoxy-2'-fluoro-2'-C-methyl-β-d-arabinofuranosyl 8-azanebularine analogues (1 and 2a) and N⁴-substituted 8-azaadenosine derivatives (2b-g) were designed, synthesized and screened for in vitro anti-HBV activity. Two concise and practical synthetic routes were developed toward the structural motif construction of 2'-deoxy-2'-fluoro-2'-C-methyl-β-d-arabinofuranosyl 8-azainosine from the ribonolactone 3 under mild conditions. The in vitro anti-HBV screening results showed that these 8-azanebularine analogues had a significant inhibitory effect on the expression of HBV antigens and HBV DNA at a concentration of 20 μM. Among them, halogen-substituted 8-azaadenosine derivative 2g displayed activities comparable to that of 3TC. In particular, 2g retained excellent activity against lamivudine-resistant HBV mutants.

Cycloaddition reactions for antiviral compounds

Prominent in the current stage of drug development, antiviral compounds can be efficiently prepared through cycloaddition reactions. The chapter reports the use of classical Diels–Alder and their hetero version for the design and synthesis of compounds that were tested for their antiviral activities against a variety of viruses. Furthermore, 1,3-dipolar cycloaddition reactions of selected 1,3-dipoles, such as azides, nitrones, and nitrile oxides, are reviewed in the light of their application in the preparation of key intermediates for antiviral synthesis. A few examples of [2+2] cycloaddition reactions are also presented. The products obtained from these pericyclic reaction approaches were all tested for their activities in terms of blocking the virus replication, and the relevant biological data are highlighted.