Monoterpenoid-based inhibitors of filoviruses targeting the glycoprotein-mediated entry process

Biostability, in vivo antiviral activity against respiratory syncytial virus, and pharmacokinetic profiles of (-)-borneol esters

Respiratory syncytial virus (RSV) is a leading cause of severe lower respiratory tract infections, particularly in vulnerable populations such as infants and the elderly. In this study, we evaluated the metabolic stability, in vivo antiviral activity, and pharmacokinetic profiles of (-)-borneol esters, which were identified as potent RSV inhibitors through screening of a compound library. Two hit compounds, ST-2 and AS-645, caused a reduction in viral titers in RSV-infected mice. Intranasal administration of ST-2 proved more effective than oral one and showed enhanced antiviral activity and improved pharmacokinetic properties. Additionally, ST-2 manifested superior metabolic stability in human blood compared to murine and rat blood, suggesting that carboxylesterase activity is a key factor in the hydrolysis resistance. Given that carboxylesterase activity is higher in mouse blood than in human blood, this difference likely contributes to the observed stability of ST-2 in human blood. Molecular modeling confirmed the role of carboxylesterase in the hydrolysis of (-)-borneol esters. These findings suggest that ST-2 has potential for further development of drugs for RSV and other viral infections.

(+)-fenchol and (-)-isopinocampheol derivatives targeting the entry process of filoviruses

The increasing frequency of filovirus outbreaks in African countries has led to a pressing need for the development of effective antifilovirus agents. In continuation of our previous research on the antifilovirus activity of monoterpenoid derivatives, we synthesized a series of (+)-fenchol and (-)-isopinocampheol derivatives by varying the type of heterocycle and linker length. Derivatives with an N-alkylpiperazine cycle proved to be the most potent antiviral compounds, with half-maximal inhibitory concentration (IC50) 1.4-20 μМ against Lenti-EboV-GP infection and 11.3-47 μМ against Lenti-MarV-GP infection. Mechanism-of-action experiments revealed that the compounds may exert their action by binding to surface glycoproteins (GPs). It was demonstrated that the binding of the synthesized compounds to the Marburg virus GP is less efficient as compared to the Ebola virus GP. Furthermore, it was shown that the compounds possess lysosomotropic properties. Thus, the antiviral activity may be due to dual effects. This study offers new antiviral agents that are worthy of further exploration.

Design, synthesis and antiviral evaluation of novel conjugates of the 1,7,7-trimethylbicyclo[2.2.1]heptane scaffold and saturated N-heterocycles via 1,2,3-triazole linker

A new series of heterocyclic derivatives with a 1,7,7-trimethylbicyclo[2.2.1]heptane fragment was designed, synthesised and biologically evaluated. Synthesis of the target compounds was performed using the Cu(I) catalysed cycloaddition reaction. The key starting substances in the click reaction were an alkyne containing a 1,7,7-trimethylbicyclo[2.2.1]heptane fragment and a series of azides with saturated nitrogen-containing heterocycles. Some of the derivatives were found to exhibit strong antiviral activity against Marburg and Ebola pseudotype viruses. Lysosomal trapping assays revealed the derivatives to possess lysosomotropic properties. The molecular modelling study demonstrated the binding affinity between the compounds investigated and the possible active site to be mainly due to hydrophobic interactions. Thus, combining a natural hydrophobic structural fragment and a lysosome-targetable heterocycle may be an effective strategy for designing antiviral agents.

Quantum biochemical analysis of the binding interactions between a potential inhibitory drug and the Ebola viral glycoprotein

Ebola virus disease (EVD) causes outbreaks and epidemics in West Africa that persist until today. The envelope glycoprotein of Ebola virus (GP) consists of two subunits, GP1 and GP2, and plays a key role in anchoring or fusing the virus to the host cell in its active form on the virion surface. Toremifene (TOR) is a ligand that mainly acts as an estrogen receptor antagonist; however, a recent study showed a strong and efficient interaction with GP. In this context, we aimed to evaluate the energetic affinity features involved in the interaction between GP and toremifene by computer simulation techniques using the Molecular Fractionation Method with Conjugate Caps (MFCC) scheme and quantum-mechanical (QM) calculations, as well as missense mutations to assess protein stability. We identified ASP522, GLU100, TYR517, THR519, LEU186, LEU515 as the most attractive residues in the EBOV glycoprotein structure that form the binding pocket. We divided toremifene into three regions and evaluated that region i was more important than region iii and region ii for the formation of the TOR-GP1/GP2 complex, which might control the molecular remodeling process of TOR. The mutations that caused more destabilization were ARG134, LEU515, TYR517 and ARG559, while those that caused stabilization were GLU523 and ASP522. TYR517 is a critical residue for the binding of TOR, and is highly conserved among EBOV species. Our results may help to elucidate the mechanism of drug action on the GP protein of the Ebola virus and subsequently develop new pharmacological approaches against EVD.Communicated by Ramaswamy H. Sarma.

Synthesis of conjugates of (aR,7S)-colchicine with monoterpenoids and investigation of their biological activity

Conjugates of the natural alkaloid (aR,7S)-colchicine with bicyclic monoterpenoids and their derivatives were synthesized for the first time. Molecular docking of the synthesized agents in the active site of the main viral protease of the SARS-CoV-2 virus was carried out. The cytotoxic properties of the agents against different cell lines and the ability to inhibit the main viral protease 3CLPro were studied.

Synthesis of N-heterocyclic amides based on (+)-camphoric acid and study of their antiviral activity and pharmacokinetics

Efficient conditions for the synthesis of nitrogen-containing heterocyclic derivatives of (1R,3S)(+)-camphoric acid were selected. A series of heterocyclic compounds based on (+)-camphoric acid bearing pharmacophoric fragments was synthesized using the developed methodology. The compounds were tested for their antiviral activity against SARS-CoV-2 and H1N1 influenza viruses, and efficient inhibitors were identified that are of significant interest for further studies. The stability of the compounds and pharmaco-kinetics of the leader compound were studied when administered intragastrically and intramuscularly to mice at a dose of 200 mg kg^-1 using the HPLC-MS/MS method.

(+)-Usnic Acid and Its Derivatives as Inhibitors of a Wide Spectrum of SARS-CoV-2 Viruses

In order to test the antiviral activity, a series of usnic acid derivatives were synthesized, including new, previously undescribed compounds. The activity of the derivatives against three strains of SARS-CoV-2 virus was studied. To understand the mechanism of antiviral action, the inhibitory activity of the main protease of SARS-CoV-2 virus was studied using the developed model as well as the antiviral activity against the pseudoviral system with glycoprotein S of SARS-CoV-2 virus on its surface. It was shown that usnic acid exhibits activity against three strains of SARS-CoV-2 virus: Wuhan, Delta, and Omicron. Compounds 10 and 13 also showed high activity against the three strains. The performed biological studies and molecular modeling allowed us to assume that the derivatives of usnic acid bind in the N-terminal domain of the surface glycoprotein S at the binding site of the hemoglobin decay metabolite.

Synthesis and Antiviral Properties of Camphor-Derived Iminothiazolidine-4-Ones and 2,3-Dihydrothiazoles

A set of heterocyclic products was synthesized from natural (+)-camphor and semi-synthetic (−)-camphor. Then, 2-Imino-4-thiazolidinones and 2,3-dihydrothiazoles were obtained using a three-step procedure. For the synthesized compounds, their antiviral activity against the vaccinia virus and Marburg virus was studied. New promising agents active against both viruses were found among the tested compounds.

Discovery of potent ebola entry inhibitors with (3S,4aS,8aS)-2-(3-amino-2-hydroxypropyl) decahydroisoquinoline-3-carboxamide scaffold

Ebola virus (EBOV), one member of the family Filoviridae, can causes hemorrhagic fever and other severe diseases in humans with a high mortality rate (25-90%). Until recently, there were no approved drugs and very limited treatment method for Ebola virus disease. In this study, we discovered a series of potent Ebola entry inhibitors with the (3S,4aS,8aS)-2-(3-amino-2-hydroxypropyl)decahydroisoquinoline-3-carboxamide scaffold from high-throughput screening in reported pseudotyped virus system. Further optimization resulted a most potent compound 28 (IC₅₀= 0.05 μM, SI = 98), which displayed 3-fold potency compared to the known inhibitor Toremifene (IC₅₀= 0.17 μM, SI = 55). Moreover, compound 28 exhibited the remarkable selectivity between EBOV-GP and VSV-G (Spec. Index = 58), thus could exclude nonspecific effects. Structure-activity relationship and molecular docking analysis of the new chemical scaffold provided more information on the binding modes and the spare volume at the binding cavity, thus can guide the design of the further potent compounds.

Borneol Ester Derivatives as Entry Inhibitors of a Wide Spectrum of SARS-CoV-2 Viruses

In the present work we studied the antiviral activity of the home library of monoterpenoid derivatives using the pseudoviral systems of our development, which have glycoproteins of the SARS-CoV-2 virus strains Wuhan and Delta on their surface. We found that borneol derivatives with a tertiary nitrogen atom can exhibit activity at the early stages of viral replication. In order to search for potential binding sites of ligands with glycoprotein, we carried out additional biological tests to study the inhibition of the re-receptor-binding domain of protein S. For the compounds that showed activity on the pseudoviral system, a study using three strains of the infectious SARS-CoV-2 virus was carried out. As a result, two leader compounds were found that showed activity on the Wuhan, Delta, and Omicron strains. Based on the biological results, we searched for the potential binding site of the leader compounds using molecular dynamics and molecular docking methods. We suggested that the compounds can bind in conserved regions of the central helices and/or heptad repeats of glycoprotein S of SARS-CoV-2 viruses.

Discovery of New Ginsenol-Like Compounds with High Antiviral Activity

A number of framework amides with a ginsenol backbone have been synthesized using the Ritter reaction. We named the acetamide as Ginsamide. A method was developed for the synthesis of the corresponding amine and thioacetamide. The new compounds revealed a high activity against H1N1 influenza, which was confirmed using an animal model. Biological experiments were performed to determine the mechanism of action of the new agents, a ginsamide-resistant strain of influenza virus was obtained, and the pathogenicity of the resistant strain and the control strain was studied. It was shown that the emergence of resistance to Ginsamide was accompanied by a reduction in the pathogenicity of the influenza virus.

New class of hantaan virus inhibitors based on conjugation of the isoindole fragment to (+)-camphor or (-)-fenchone hydrazonesv

This work presents the design and synthesis of camphor, fenchone, and norcamphor N-acylhydrazone derivatives as a new class of inhibitors of the Hantaan virus, which causes haemorrhagic fever with renal syndrome (HFRS). A cytopathic model was developed for testing chemotherapeutics against the Hantaan virus, strain 76-118. In addition, a study of the antiviral activity was carried out using a pseudoviral system. It was found that the hit compound possesses significant activity (IC₅₀ = 7.6 ± 2 µM) along with low toxicity (CC₅₀ > 1000 µM). Using molecular docking procedures, the binding with Hantavirus nucleoprotein was evaluated and the correlation between the structure of the synthesised compounds and the antiviral activity was established.

Quaternary ammonium salts based on (-)-borneol as effective inhibitors of influenza virus

A series of compounds containing a 1,7,7-trimethylbicyclo[2.2.1]heptane fragment were evaluated for their antiviral activity against influenza A virus strain A/Puerto Rico/8/34 (H1N1) in vitro. The most potent antiviral compound proved to be a quaternary ammonium salt based on (-)-borneol, 10a. In in vitro experiments, compound 10a inhibited influenza A viruses (H1, H1pdm09, and H3 subtypes), with an IC₅₀ value of 2.4-16.8 µM (depending on the virus), and demonstrated low toxicity (CC₅₀ = 1311 µM). Mechanism-of-action studies for compound 10a revealed it to be most effective when added at the early stages of the viral life cycle. In direct haemolysis inhibition tests, compound 10a was shown to decrease the membrane-disrupting activity of influenza A virus strain A/Puerto Rico/8/34. According to molecular modelling results, the lead compound 10a can bind to different sites in the stem region of the viral hemagglutinin.

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.

Biostability study, quantitation method and preliminary pharmacokinetics of a new antifilovirus agent based on borneol and 3-(piperidin-1-yl)propanoic acid

The stability of the new antifiloviral agent AS-358, which is a derivative of borneol and 3-(piperidin-1-yl)propanoic acid, was studied in the blood and blood plasma of rats in vitro. It was found that both in the blood and in the plasma stabilized by EDTA or heparin, the compound is rapidly hydrolyzed at the ester bond. When sodium fluoride was added to the whole blood, the decomposition of the compound was significantly slowed down, which made it possible to develop and validate a method for the quantitative determination of the agent in this matrix. The method was validated in terms of selectivity, calibration dependence, LLOQ, accuracy and precision, stability in an autosampler, recovery, and carry-over. A 8:2 v/v mixture of methanol containing 2-adamantylamine hydrochloride (internal standard, IS) with 0.2 M aqueous zinc sulfate was used for blood sample treatment and protein precipitation. Analysis was performed by HPLC-MS/MS using reversed phase chromatography. MS/MS detection was performed on a triple quadrupole mass spectrometer 6500 QTRAP (SCIEX) in multiple reaction monitoring (MRM) mode. The transitions 294.5→158.2/98.1 and 152.2→107.2/93.1 were monitored for AS-358 and the IS, respectively. The calibration curve was built in the concentration range of 1-500 ng/mL, the intra-day and inter-day accuracy and precision, carry-over and recovery were within the acceptable limits. The developed method was used for a preliminary study of the pharmacokinetics of the agent AS-358 after its oral administration to rats. It was shown that when the substance was administered at a dose of 200 mg/kg, its concentration in the blood of animals reached 550 ng/mL after 1 h, despite its instability in blood.

(+)-Camphor and (-)-borneol derivatives as potential anti-orthopoxvirus agents

Although the World Health Organisation had announced that smallpox was eradicated over 40 years ago, the disease and other related pathogenic poxviruses such as monkeypox remain potential bioterrorist weapons and could also re-emerge as natural infections. We have previously reported (+)-camphor and (-)-borneol derivatives with an antiviral activity against the vaccinia virus. This virus is similar to the variola virus (VARV), the causative agent of smallpox, but can be studied at BSL-2 facilities. In the present study, we evaluated the antiviral activity of the most potent compounds against VARV, cowpox virus, and ectromelia virus (ECTV). Among the compounds tested, 4-bromo-N'-((1R,4R)-1,7,7-trimethylbicyclo[2.2.1]heptan-2-ylidene)benzohydrazide 18 is the most effective compound against various orthopoxviruses, including VARV, with an EC₅₀ value of 13.9 μM and a selectivity index of 206. Also, (+)-camphor thiosemicarbazone 9 was found to be active against VARV and ECTV.