Optimization of 4-Aminopiperidines as Inhibitors of Influenza A Viral Entry That Are Synergistic with Oseltamivir

Modular Biomimetic Strategy Enables Discovery and SAR Exploration of Oxime Macrocycles as Influenza A Virus (H1N1) Inhibitors

Although vaccination remains the prevalent prophylactic means for controlling Influenza A virus (IAV) infections, novel structural antivirus small-molecule drugs with new mechanisms of action for treating IAV are highly desirable. Herein, we describe a modular biomimetic strategy to expeditiously achieve a new class of macrocycles featuring oxime, which might target the hemagglutinin (HA)-mediated IAV entry into the host cells. SAR analysis revealed that the size and linker of the macrocycles play an important role in improving potency. Particularly, as a 14-membered macrocyclic oxime, 37 exhibited potent inhibitory activity against IAV H1N1 with an EC50 value of 23 nM and low cytotoxicity, which alleviated cytopathic effects and protected cell survival obviously after H1N1 infection. Furthermore, 37 showed significant synergistic activity with neuraminidase inhibitor oseltamivir in vitro.

Development of a virus-based affinity ultrafiltration method for screening virus-surface-protein-targeted compounds from complex matrixes: Herbal medicines as a case study

Herbal medicines (HMs) are one of the main sources for the development of lead antiviral compounds. However, due to the complex composition of HMs, the screening of active compounds within these is inefficient and requires a significant time investment. We report a novel and efficient virus-based screening method for antiviral active compounds in HMs. This method involves the centrifugal ultrafiltration of viruses, known as the virus-based affinity ultrafiltration method (VAUM). This method is suitable to identify virus specific active compounds from complex matrices such as HMs. The effectiveness of the VAUM was evaluated using influenza A virus (IAV) H1N1. Using this method, four compounds that bind to the surface protein of H1N1 were identified from dried fruits of Terminalia chebula (TC). Through competitive inhibition assays, the influenza surface protein, neuraminidase (NA), was identified as the target protein of these four TC-derived compounds. Three compounds were identified by high performance liquid chromatography (HPLC) and liquid chromatography/mass spectrometry (LC/MS), and their anti-H1N1 activities were verified by examining the cytopathic effect (CPE) and by performing a virus yield reduction assay. Further mechanistic studies demonstrated that these three compounds directly bind to NA and inhibit its activity. In summary, we describe here a VAUM that we designed, one that can be used to accurately screen antiviral active compounds in HMs and also help improve the efficiency of screening antiviral drugs found in natural products.

Efficiency of membrane fusion inhibitors on different hemagglutinin subtypes: insight from a molecular dynamics simulation perspective

The challenge in vaccine development, along with drug resistance issues, has encouraged the search for new anti-influenza drugs targeting different viral proteins. Hemagglutinin (HA) glycoprotein, crucial in the viral replication cycle, has emerged as a promising therapeutic target. CBS1117 and JNJ4796 were reported to exhibit similar potencies against infectious group 1 influenza, which included H1 and H5 HAs; however, their potencies were significantly reduced against group 2 HA. This study aims to explore the molecular binding mechanisms and group specificity of these fusion inhibitors against both group 1 (H5) and group 2 (H3) HA influenza viruses using molecular dynamics simulations. CBS1117 and JNJ4796 exhibit stronger interactions with key residues within the H5 HA binding pocket compared to H3-ligand complexes. Hydrogen bonding and hydrophobic interactions involving residues, such as H381, Q401, T3251 (H5-CBS1117), T3181 (H5-JNJ4796), W212, I452, V482, and V522 predominantly contribute to stabilizing H5-ligand systems. In contrast, these interactions are notably weakened in H3-inhibitor complexes. Predicted protein-ligand binding free energies align with experimental data, indicating CBS1117 and JNJ4796's preference for heterosubtypic group 1 HA binding. Understanding the detailed atomistic mechanisms behind the varying potencies of these inhibitors against the two HA groups can significantly contribute to the development and optimization of effective HA fusion inhibitors. To accomplish this, the knowledge of the transition of HA from its pre- to post-fusion states, the molecular size of ligands, and their potential binding regions, could be carefully considered.Communicated by Ramaswamy H. Sarma.

An orally active entry inhibitor of influenza A viruses protects mice and synergizes with oseltamivir and baloxavir marboxil

Seasonal or pandemic illness caused by influenza A viruses (IAVs) is a major public health concern due to the high morbidity and notable mortality. Although there are several approved drugs targeting different mechanisms, the emergence of drug resistance calls for new drug candidates that can be used alone or in combinations. Small-molecule IAV entry inhibitor, ING-1466, binds to hemagglutinin (HA) and blocks HA-mediated viral infection. Here, we show that this inhibitor demonstrates preventive and therapeutic effects in a mouse model of IAV with substantial improvement in the survival rate. When administered orally it elicits a therapeutic effect in mice, even after the well-established infection. Moreover, the combination of ING-1466 with oseltamivir phosphate or baloxavir marboxil enhances the therapeutic effect in a synergistic manner. Overall, ING-1466 has excellent oral bioavailability and in vitro absorption, distribution, metabolism, excretion, and toxicity profile, suggesting that it can be developed for monotherapy or combination therapy for the treatment of IAV infections.

Development of chalcone-like derivatives and their biological and mechanistic investigations as novel influenza nuclear export inhibitors

Concerning the emergence of resistance to current anti-influenza drugs, our previous phenotypic-based screening study identified the compound A9 as a promising lead compound. This chalcone analog, containing a 2,6-dimethoxyphenyl moiety, exhibited significant inhibitory activity against oseltamivir-resistant strains (H1N1 pdm09), with an EC50 value of 1.34 μM. However, it also displayed notable cytotoxicity, with a CC50 value of 41.46 μM. Therefore, compound A9 was selected as a prototype structure for further structural optimization in this study. Initially, it was confirmed that the substituting the α,β-unsaturated ketone with pent-1,4-diene-3-one as a linker group significantly reduced the cytotoxicity of the final compounds. Subsequently, the penta-1,4-dien-3-one group was utilized as a privileged fragment for further structural optimization. Following two subsequent rounds of optimizations, we identified compound IIB-2, which contains a 2,6-dimethoxyphenyl- and 1,4-pentadiene-3-one moieties. This compound exhibited inhibitory effects on oseltamivir-resistant strains comparable to its precursor (compound A9), while demonstrating reduced toxicity (CC50 > 100 μM). Furthermore, we investigated its mechanism of action against anti-influenza virus through immunofluorescence, Western blot, and surface plasmon resonance (SPR) experiments. The results revealed that compound IIB-2 can impede virus proliferation by blocking the export of influenza virus nucleoprotein. Thusly, our findings further emphasize influenza nuclear export as a viable target for designing novel chalcone-like derivatives with potential inhibitory properties that could be explored in future lead optimization studies.

Allopregnanolone targets nucleoprotein as a novel influenza virus inhibitor

Influenza A virus (IAV) poses a global public health concern and remains an imminent threat to human health. Emerging antiviral resistance to the currently approved influenza drugs emphasizes the urgent need for new therapeutic entities against IAV. Allopregnanolone (ALLO) is a natural product that has been approved as an antidepressant drug. In the present study, we repurposed ALLO as a novel inhibitor against IAVs. Mechanistic studies demonstrated that ALLO inhibited virus replication by interfering with the nucleus translocation of viral nucleoprotein (NP). In addition, ALLO showed significant synergistic activity with compound 16, a hemagglutinin inhibitor of IAVs. In summary, we have identified ALLO as a novel influenza virus inhibitor targeting NP, providing a promising candidate that deserves further investigation as a useful anti-influenza strategy in the future.

Influenza virus cell entry and targeted antiviral development

Influenza virus infection is currently one of the most prevalent and transmissible diseases in the world causing local outbreaks every year. It has the potential to cause devastating global pandemics as well. The development of anti-influenza drugs possessing novel mechanisms of action is urgently needed to control the spread of influenza infections; thus, drugs that inhibit influenza virus entry into target cells are emerging as a hot research topic. In addition to discussing the biological significance of hemagglutinin in viral replication, this article provides recent updates on the natural products, small molecules, proteins, peptides, and neutralizing antibody-like proteins that have anti-influenza potency.

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.

Therapeutic potential of salicylamide derivatives for combating viral infections

Since time immemorial human beings have constantly been fighting against viral infections. The ongoing and devastating coronavirus disease 2019 pandemic represents one of the most severe and most significant public health emergencies in human history, highlighting an urgent need to develop broad-spectrum antiviral agents. Salicylamide (2-hydroxybenzamide) derivatives, represented by niclosamide and nitazoxanide, inhibit the replication of a broad range of RNA and DNA viruses such as flavivirus, influenza A virus, and coronavirus. Moreover, nitazoxanide was effective in clinical trials against different viral infections including diarrhea caused by rotavirus and norovirus, uncomplicated influenza A and B, hepatitis B, and hepatitis C. In this review, we summarize the broad antiviral activities of salicylamide derivatives, the clinical progress, and the potential targets or mechanisms against different viral infections and highlight their therapeutic potential in combating the circulating and emerging viral infections in the future.

Nine-valent oleanolic acid conjugates as potent inhibitors blocking the entry of influenza A virus

The influenza pandemic remains a major public health challenge that endangers the lives of many vulnerable and immune-compromised individuals worldwide. The high infectivity and genetic variability of influenza virus make it particularly challenging to design effective drugs to inhibit the virus. In previous studies, we determined that oleanolic acid (OA) and its derivatives block interactions between influenza and host cells, thus endowing OA with anti-viral efficacy. Inspired by the role of cluster glycosides in the interactions between hemagglutinins (HA) and sialic acid receptors (SA), we designed and synthesized a series of OA nonamers via the CuAAC reaction, and evaluated their anti-viral activities in vitro. We determined that among these nonamers, compound 15 displayed the highest potency (IC₅₀ = 5.23 μM), equivalent to the antiviral drug oseltamivir which is routinely prescribed for influenza A virus strain A/WSN/33 (H1N1). In addition, these compounds also displayed antiviral activity against influenza B. Mechanistic experiments indicated that OA nonamers can effectively target the influenza HA protein. This study collectively demonstrates that multivalent structure-activity binding strategy is an effective method for designing influenza virus inhibitors.

Synthesis, Optimization, and Structure-Activity Relationships of Imidazo[1,2-a]pyrimidines as Inhibitors of Group 2 Influenza A Viruses

The influenza A virus (IAV) is a highly contagious virus that causes pandemics and seasonal epidemics, which are major public health issues. Current anti-influenza therapeutics are limited partly due to the continuous emergence of drug-resistant IAV strains; thus, there is an unmet need to develop novel anti-influenza therapies. Here, we present a novel imidazo[1,2-a]pyrimidine scaffold that targets group 2 IAV entry. We have explored three different regions of the lead compound, and we have developed a series of small molecules that have nanomolar activity against oseltamivir-sensitive and -resistant forms of group 2 IAVs. These small molecules target hemagglutinin (HA), which mediates the viral entry process. Mapping a known small-molecule-binding cavity of the HA structure with resistant mutants suggests that these molecules bind to that cavity and block HA-mediated membrane fusion.

Applications of Isosteres of Piperazine in the Design of Biologically Active Compounds: Part 2

Applications of piperazine and homopiperazine in drug design are well-established, and these heterocycles have found use as both scaffolding and terminal elements and also as a means of introducing a water-solubilizing element into a molecule. In the accompanying review (10.1021/acs.jafc.2c00726), we summarized applications of piperazine and homopiperazine and their fused ring homologues in bioactive compound design along with illustrations of the use of 4-substituted piperidines and a sulfoximine-based mimetic. In this review, we discuss applications of pyrrolidine- and fused-pyrrolidine-based mimetics of piperazine and homopiperazine and illustrate derivatives of azetidine that include stretched and spirocyclic motifs, along with applications of a series of diaminocycloalkanes.

Aryl Sulfonamide Inhibits Entry and Replication of Diverse Influenza Viruses via the Hemagglutinin Protein

Influenza viruses cause approximately half a million deaths every year worldwide. Vaccines are available but partially effective, and the number of antiviral medications is limited. Thus, it is crucial to develop therapeutic strategies to counteract this major pathogen. Influenza viruses enter the host cell via their hemagglutinin (HA) proteins. The HA subtypes of influenza A virus are phylogenetically classified into groups 1 and 2. Here, we identified an inhibitor of the HA protein, a tertiary aryl sulfonamide, that prevents influenza virus entry and replication. This compound shows potent antiviral activity against diverse H1N1, H5N1, and H3N2 influenza viruses encoding HA proteins from both groups 1 and 2. Synthesis of derivatives of this aryl sulfonamide identified moieties important for antiviral activity. This compound may be considered as a lead for drug development with the intent to be used alone or in combination with other influenza A virus antivirals to enhance pan-subtype efficacy.

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.

Rapid Enantioselective and Diastereoconvergent Hybrid Organic/Biocatalytic Entry into the Oseltamivir Core

A formal synthesis of the antiviral drug (-)-oseltamivir (Tamiflu) has been accomplished starting from m-anisic acid via a dissolving metal or electrochemical Birch reduction. The correct absolute stereochemistry is efficiently set through enzyme-catalyzed carbonyl reduction on the resultant racemic α,β-unsaturated ketone. A screen of a broad ketoreductase (KRED) library identified several that deliver the desired allylic alcohol with nearly perfect facial selectivity at the new center for each antipodal substrate, indicating that the enzyme also is able to completely override inherent diastereomeric bias in the substrate. Conversion is complete, with d-glucose serving as the terminal hydride donor (glucose dehydrogenase). For each resulting diastereomeric secondary alcohol, O/N-interconversion is then efficiently effected either by synfacial [3,3]-sigmatropic allylic imidate rearrangement or by direct, stereoinverting N-Mitsunobu chemistry. Both stereochemical outcomes have been confirmed crystallographically. The α,β-unsaturation is then introduced via an α-phenylselenylation/oxidation/pyrolysis sequence to yield the targeted (S)-N-acyl-protected 5-amino-1,3-cyclohexadiene carboxylates, key advanced intermediates for oseltamivir pioneered by Corey (N-Boc) and Trost (N-phthalamido), respectively.

Identification of a novel inhibitor targeting influenza A virus group 2 hemagglutinins

Influenza A virus (IAV) causes seasonal epidemics and occasional but devastating pandemics, which are major public health concerns. The putative antiviral therapeutics are useful for the treatment of influenza, however, the emerging resistant strains necessitate a constant search for new drug candidates. Here we report the discovery of a novel antiviral agent, compound CBS1194, which was identified by a parallel high-throughput screening (HTS) campaign using two retroviral pseudotypes bearing H7 or H5 hemagglutinins (HAs). Subsequent analyses demonstrated that CBS1194 is specific to IAVs of group 2, while it has no effect against those of group 1. In a time-of-addition assay, CBS1194 showed a significant inhibitory effect during the early phase of viral infection. In addition, HA-mediated hemolysis can be inhibited by CBS1194 treatment, indicating that this compound may target the HA stalk region, which is responsible for membrane fusion. Escape mutant analyses and in silico docking further revealed that CBS1194 fits into a pocket near the fusion peptide, causing steric hindrance that blocks the low-pH induced rearrangement of HA. In summary, our study identifies a novel fusion inhibitor of group 2 IAVs, which has the potential as lead compound for further development.

Anti-Influenza Drug Discovery and Development: Targeting the Virus and Its Host by All Possible Means

Infections by influenza virus constitute a major and recurrent threat for human health. Together with vaccines, antiviral drugs play a key role in the prevention and treatment of influenza virus infection and disease. Today, the number of antiviral molecules approved for the treatment of influenza is relatively limited, and their use is threatened by the emergence of viral strains with resistance mutations. There is therefore a real need to expand the prophylactic and therapeutic arsenal. This chapter summarizes the state of the art in drug discovery and development for the treatment of influenza virus infections, with a focus on both virus-targeting and host cell-targeting strategies. Novel antiviral strategies targeting other viral proteins or targeting the host cell, some of which are based on drug repurposing, may be used in combination to strengthen our therapeutic arsenal against this major pathogen.

Anno 2021: Which antivirals for the coming decade?

Despite considerable progress in the development of antiviral drugs, among which anti-immunodeficiency virus (HIV) and anti-hepatitis C virus (HCV) medications can be considered real success stories, many viral infections remain without an effective treatment. This not only applies to infectious outbreaks caused by zoonotic viruses that have recently spilled over into humans such as severe acute respiratory syndrome coronavirus type 2 (SARS-CoV-2), but also ancient viral diseases that have been brought under control by vaccination such as variola (smallpox), poliomyelitis, measles, and rabies. A largely unsolved problem are endemic respiratory infections due to influenza, respiratory syncytial virus (RSV), and rhinoviruses, whose associated morbidity will likely worsen with increasing air pollution. Furthermore, climate changes will expose industrialized countries to a dangerous resurgence of viral hemorrhagic fevers, which might also become global infections. Herein, we summarize the recent progress that has been made in the search for new antivirals against these different threats that the world population will need to confront with increasing frequency in the next decade.

Advances in the development of entry inhibitors for sialic-acid-targeting viruses

Over the past decades, several antiviral drugs have been developed to treat a range of infections. Yet the number of treatable viral infections is still limited, and resistance to current drug regimens is an ever-growing problem. Therefore, additional strategies are needed to provide a rapid cure for infected individuals. An interesting target for antiviral drugs is the process of viral attachment and entry into the cell. Although most viruses use distinct host receptors for attachment to the target cell, some viruses share receptors, of which sialic acids are a common example. This review aims to give an update on entry inhibitors for a range of sialic-acid-targeting viruses and provides insight into the prospects for those with broad-spectrum potential.

Structure of avian influenza hemagglutinin in complex with a small molecule entry inhibitor

The binding properties of fusion inhibitor CBS1117 to hemagglutinin by x-ray crystallography, NMR, and mutagenesis give insights into mechanism and guidance for chemical optimization.

HA plays a critical role in influenza infection and, thus HA is a potential target for antivirals. Recently, our laboratories have described a novel fusion inhibitor, termed CBS1117, with EC₅₀ ∼3 μM against group 1 HA. In this work, we characterize the binding properties of CBS1117 to avian H5 HA by x-ray crystallography, NMR, and mutagenesis. The x-ray structure of the complex shows that the compound binds near the HA fusion peptide, a region that plays a critical role in HA-mediated fusion. NMR studies demonstrate binding of CBS1117 to H5 HA in solution and show extensive hydrophobic contacts between the compound and HA surface. Mutagenesis studies further support the location of the compound binding site proximal to the HA fusion peptide and identify additional amino acids that are important to compound binding. Together, this work gives new insights into the CBS1117 mechanism of action and can be exploited to further optimize this compound and better understand the group specific activity of small-molecule inhibitors of HA-mediated entry.