Discovery of Highly Potent Pinanamine-Based Inhibitors against Amantadine- and Oseltamivir-Resistant Influenza A Viruses

Recent Efforts in Identification of Privileged Scaffolds as Antiviral Agents

Viral infections are the most important health concern nowadays to mankind, which is unexpectedly increasing the health complications and fatality rate worldwide. The recent viral infection outbreak developed a pressing need for small molecules that can be quickly deployed for the control/treatment of re-emerging or new emerging viral infections. Numerous viruses, including the human immunodeficiency virus (HIV), hepatitis, influenza, SARS-CoV-1, SARS-CoV-2, and others, are still challenging due to emerging resistance to known drugs. Therefore, there is always a need to search for new antiviral small molecules that can combat viral infection with new modes of action. This review highlighted recent progress in developing new antiviral molecules based on natural product-inspired scaffolds. Herein, the structure-activity relationship of the FDA-approved drugs along with the molecular docking studies of selected compounds have been discussed against several target proteins. The findings of new small molecules as neuraminidase inhibitors, other than known drug scaffolds, Anti-HIV and SARS-CoV are incorporated in this review paper.

Palladium-Catalyzed Synthesis of Cyclopropylthiophenes and Their Derivatization

The cyclopropylthiophene moiety has attracted the attention of the scientific community for its potential pharmaceutical applications. However, synthesis of the compounds containing this framework remains challenging, has rarely been reported and remains unresolved. Here we provide optimized syntheses for cyclopropylthiophenes and their derivatives, containing carbonyl, acetyl, carboxylic acid, methyl carboxylate, nitrile, bromide and sulfonyl chloride moieties.

Molecular Modeling of Viral Type I Fusion Proteins: Inhibitors of Influenza Virus Hemagglutinin and the Spike Protein of Coronavirus

The fusion of viral and cell membranes is one of the basic processes in the life cycles of viruses. A number of enveloped viruses confer fusion of the viral envelope and the cell membrane using surface viral fusion proteins. Their conformational rearrangements lead to the unification of lipid bilayers of cell membranes and viral envelopes and the formation of fusion pores through which the viral genome enters the cytoplasm of the cell. A deep understanding of all the stages of conformational transitions preceding the fusion of viral and cell membranes is necessary for the development of specific inhibitors of viral reproduction. This review systematizes knowledge about the results of molecular modeling aimed at finding and explaining the mechanisms of antiviral activity of entry inhibitors. The first section of this review describes types of viral fusion proteins and is followed by a comparison of the structural features of class I fusion proteins, namely influenza virus hemagglutinin and the S-protein of the human coronavirus.

Anti-influenza properties of tiliroside isolated from Hibiscus mutabilis L

ETHNOPHARMACOLOGICAL RELEVANCE

Fu Rong Ye (FRY), the leaf of Hibiscus mutabilis L., is a Chinese medicinal herb used to treat coughs and respiratory diseases. FRY is the major herbal component of the patent medicine Fupo Ganmao Granules for treating common cold. However, its anti-influenza active components and mechanism were not identified.

AIM

Here, we aim to a) isolate the anti-influenza phytochemicals from FRY extract and b) explore its anti-flu mechanism.

MATERIAL AND METHODS

Bioassay guided isolation was performed to get anti-influenza virus components. Influenza virus infected cells and mouse model were employed for efficacy evaluation.

RESULTS

Using bioassay-guided isolation, the flavonoid tiliroside was obtained, which inhibited four IAV strains in MDCK cells with EC₅₀ ranging from 3.87 to 27.61 μM by suppressing the viral ribonucleoprotein activity. Tiliroside also significantly downregulated the expression of cytokines/chemokines in A549 cells, and protected 50% of PR8-infected BALB/c mice from death and at 800 mg/kg/day, improved lung edema conditions.

CONCLUSION

Tiliroside is effective for influenza virus infection treatment and promising for further drug development. This study is the first to demonstrate that tiliroside in FRY acts against influenza virus.

Inhibitory effects of Patchouli alcohol on the early lifecycle stages of influenza A virus

Background

The antiviral activity and underlying mechanism of Patchouli alcohol remain unclear.

Methods

This study evaluated the cytotoxicity, optimal methods for drug administration, anti-influenza A activity of Patchouli alcohol. The antiviral mechanism of Patchouli alcohol was also assessed via qRT-PCR, western blot, hemagglutination inhibiting (HAI) assay, and hemolysis inhibiting assay.

Results

Patchouli alcohol was shown to have low cytotoxicity and its strongest antiviral effect was associated with premixed administration. Patchouli alcohol inhibited virus replication during the early lifecycle stages of influenza A virus infection and specifically prevented expression of the viral proteins, HA and NP. In both the HAI and hemolysis inhibiting assays, Patchouli alcohol was able to block HA2-mediated membrane fusion under low pH conditions. Patchouli alcohol had lower binding energy with HA2 than HA1.

Conclusion

These findings suggest that Patchouli alcohol could be a promising membrane fusion inhibitor for the treatment of influenza A infection.

Novel O-acylated amidoximes and substituted 1,2,4-oxadiazoles synthesised from (+)-ketopinic acid possessing potent virus-inhibiting activity against phylogenetically distinct influenza A viruses

This article describes the synthesis and antiviral activity evaluation of new substituted 1,2,4-oxadiazoles containing a bicyclic substituent at position 5 of the heterocycle and O-acylated amidoximes as precursors for their synthesis. New compounds were obtained from the (+)-camphor derivative (+)-ketopinic acid. The chemical library was tested in vitro for cytotoxicity against the MDCK cell line and for antiviral activity against influenza viruses of H1N1 and H7N9 subtypes. The synthesised compounds exhibited high virus-inhibiting activity against the H1N1 influenza virus. Some synthesised compounds were also active against the influenza virus of a different antigenic subtype: H7N9. The mechanism of the virus-inhibiting activity of these compounds is based on their interference with the fusion activity of viral hemagglutinin (HA). No interference with the receptor-binding activity of HA has been demonstrated. According to molecular docking results, the selective antiviral activity of O-acylated amidoximes and 1,2,4-oxadiazoles is associated with their structural features. O-Acylated amidoximes are likely more complementary to the binding site located at the site of the fusion peptide, and 1,2,4-oxadiazoles are more complimentary to the site located at the site of proteolysis. Significant differences in the amino acid residues of the binding sites of HA's of different types allow us to explain the selective antiviral activity of the compounds under study.

Naturally Occurring Terpenes: A Promising Class of Organic Molecules to Address Influenza Pandemics

Since the olden times, infectious diseases have largely affected human existence. The newly emerged infections are excessively caused by viruses that are largely associated with mammal reservoirs. The casualties of these emergencies are significantly influenced by the way human beings interact with the reservoirs, especially the animal ones. In our review we will consider the evolutionary and the ecological scales of such infections and their consequences on the public health, with a focus on the pathogenic influenza A virus. The nutraceutical properties of fungal and plant terpene-like molecules will be linked to their ability to lessen the symptoms of viral infections and shed light on their potential use in the development of new drugs. New challenging methods in antiviral discovery will also be discussed in this review. The authors believe that pharmacognosy is the "wave of future pharmaceuticals", as it can be continually produced and scaled up under eco-friendly requirements. Further diagnostic methods and strategies however are required to standardise those naturally occurring resources.

Small Molecule Inhibitors of Influenza Virus Entry

Hemagglutinin (HA) plays a critical role during influenza virus receptor binding and subsequent membrane fusion process, thus HA has become a promising drug target. For the past several decades, we and other researchers have discovered a series of HA inhibitors mainly targeting its fusion machinery. In this review, we summarize the advances in HA-targeted development of small molecule inhibitors. Moreover, we discuss the structural basis and mode of action of these inhibitors, and speculate upon future directions toward more potent inhibitors of membrane fusion and potential anti-influenza drugs.

Synthesis and Antiviral Activity of Camphene Derivatives against Different Types of Viruses

To date, the 'one bug-one drug' approach to antiviral drug development cannot effectively respond to the constant threat posed by an increasing diversity of viruses causing outbreaks of viral infections that turn out to be pathogenic for humans. Evidently, there is an urgent need for new strategies to develop efficient antiviral agents with broad-spectrum activities. In this paper, we identified camphene derivatives that showed broad antiviral activities in vitro against a panel of enveloped pathogenic viruses, including influenza virus A/PR/8/34 (H1N1), Ebola virus (EBOV), and the Hantaan virus. The lead-compound 2a, with pyrrolidine cycle in its structure, displayed antiviral activity against influenza virus (IC50 = 45.3 µM), Ebola pseudotype viruses (IC50 = 0.12 µM), and authentic EBOV (IC50 = 18.3 µM), as well as against pseudoviruses with Hantaan virus Gn-Gc glycoprotein (IC50 = 9.1 µM). The results of antiviral activity studies using pseudotype viruses and molecular modeling suggest that surface proteins of the viruses required for the fusion process between viral and cellular membranes are the likely target of compound 2a. The key structural fragments responsible for efficient binding are the bicyclic natural framework and the nitrogen atom. These data encourage us to conduct further investigations using bicyclic monoterpenoids as a scaffold for the rational design of membrane-fusion targeting inhibitors.

Emerging and state of the art hemagglutinin-targeted influenza virus inhibitors

Introduction: Seasonal influenza vaccination, together with FDA-approved neuraminidase (NA) and polymerase acidic (PA) inhibitors, is the most effective way for prophylaxis and treatment of influenza infections. However, the low efficacy of prevailing vaccines to newly emerging influenza strains and increasing resistance to available drugs drives intense research to explore more effective inhibitors. Hemagglutinin (HA), one of the major surface proteins of influenza strains, represents an attractive therapeutic target to develop such new inhibitors.Areas covered: This review summarizes the current progress of HA-based influenza virus inhibitors and their mechanisms of action, which may facilitate further research in developing novel antiviral inhibitors for controlling influenza infections.Expert opinion: HA-mediated entry of influenza virus is an essential step for successful infection of the host, which makes HA a promising target for the development of antiviral drugs. Recent progress in delineating the crystal structures of HA, especially HA-inhibitors complexes, has revealed a number of key residues and conserved binding pockets within HA. This has opened up important insights for developing HA-based antiviral inhibitors that have a high resistance barrier and broad-spectrum activities.

Structure-aided optimization of 3-O-β-chacotriosyl epiursolic acid derivatives as novel H5N1 virus entry inhibitors

It is urgent to develop new antiviral agents due to the continuous emergence of drug-resistant strains of influenza virus. Our earlier studies have identified that certain pentacyclic triterpene saponins with 3-O-β-chacotriosyl residue are novel H5N1 virus entry inhibitors. In the present study, a series of C-28 modified 3-O-β-chacotriosyl epiursolic acid derivatives via conjugation with different kinds of sides were synthesized, of which anti-H5N1 activities in A549 cells were evaluated in vitro. Among them, 10 exhibited strongest anti-H5N1 potency at the low-micromole level without cytotoxicity, surpassing the potency of ribavirin. Further mechanism studies of the lead compound 10 based on HI, SPR and molecular modeling revealed that these new 3-epiursolic acid saponins could bind tightly to the viral envelope HA protein, thus blocking the invasion of H5N1 viruses into host cells.

Design and synthesis of pinane oxime derivatives as novel anti-influenza agents

Parasitic characteristics, mutations and resistance of influenza A virus make it difficult for current influenza antiviral drugs to maintain long-term effectiveness. Currently, to design non-adamantane compounds targeting the S31N mutant of M2 proton channel is a promising direction for the development of novel anti-influenza drugs. In our previous research, a pinanamine-based antiviral M090 was discovered to target hemagglutinin instead of M2, with its structure being highly similar to reported M2-S31N inhibitors. Herein, a series of pinane oxime derivatives were designed from scratch and evaluated for anti-influenza activity and their cytotoxicity in vitro. Utilizing a combination of structure-activity relationship analysis, electrophysiological assay and molecular docking, the most potent compound 11h, as a M2-S31N blocker, exhibited excellent activity with EC₅₀ value at the low micromolar level against both H3N2 and H1N1. No significant toxicity of 11h was observed. In addition, compound 11h was located tightly in the pore of the drug-binding site with the thiophene moiety facing down toward the C-terminus, and did not adopt a similar position and orientation as the reference inhibitor.