In Vitro Antiviral Activity of some Novel Isatin Derivatives against HCV and SARS-CoV Viruses

Identification of sulphonamide-tethered N-((triazol-4-yl)methyl)isatin derivatives as inhibitors of SARS-CoV-2 main protease

SARS-CoV-2 pandemic in the end of 2019 led to profound consequences on global health and economy. Till producing successful vaccination strategies, the healthcare sectors suffered from the lack of effective therapeutic agents that could control the spread of infection. Thus, academia and the pharmaceutical sector prioritise SARS-CoV-2 antiviral drug discovery. Here, we exploited previous reports highlighting the anti-SARS-CoV-2 activities of isatin-based molecules to develop novel triazolo-isatins for inhibiting main protease (Mpro) of the virus, a crucial enzyme for its replication in the host cells. Particularly, sulphonamide 6b showed promising inhibitory activity with an IC50= 0.249 µM. Additionally, 6b inhibited viral cell proliferation with an IC50 of 4.33 µg/ml, and was non-toxic to VERO-E6 cells (CC50 = 564.74 µg/ml) displaying a selectivity index of 130.4. In silico analysis of 6b disclosed its ability to interact with key residues in the enzyme active site, supporting the obtained in vitro findings.

Synthesis, Characterization, and Antibacterial Activity of New Isatin Derivatives

1H-indol-2,3-dione (isatin) class of biologically active compounds have analgesic, anti-microbial, anti-inflammatory, anti-tubercular, anti-proliferative properties, and is also useful for the treatment of SARS-CoV. Schiff bases containing isatin moiety are known to have broad spectrum of biological activities like anti-viral, anti-tubercular, anti-fungal, and anti-bacterial. In this work, several Schiff base derivatives have been synthesized using two methods (synthetic and microwave) by reacting isatin with o-phenylenediamine. The synthesized compounds were structurally characterized and their in-vivo antimicrobial activity was tested against Gram-negative and Gram-positive bacteria using the inhibition zone method. Several newly synthesized isatin derivatives were found effective as antimicrobial agents and showed good potency (compounds 3c, 3d, 6a, 6b, 6d). Compound 3c displayed higher antimicrobial activity than standard drug (Amoxicillin) against Staphylococcus aureus at higher concentration (16 μg/mL) and against Escherichia coli at lower concentration (1 μg/mL).

Determination of potential inhibitors based on isatin derivatives against SARS-CoV-2 main protease (mpro): a molecular docking, molecular dynamics and structure-activity relationship studies

SARS-COV-2, the novel coronavirus and root of global pandemic COVID-19 caused a severe health threat throughout the world. Lack of specific treatments raised an effort to find potential inhibitors for the viral proteins. The recently invented crystal structure of SARS-CoV-2 main protease (Mpro) and its key role in viral replication; non-resemblance to any human protease makes it a perfect target for inhibitor research. This article reports a computer-aided drug design (CADD) approach for the screening of 118 compounds with 16 distinct heterocyclic moieties in comparison with 5 natural products and 7 repurposed drugs. Molecular docking analysis against Mpro protein were performed finding isatin linked with a oxidiazoles (A2 and A4) derivatives to have the best docking scores of -11.22 kcal/mol and -11.15 kcal/mol respectively. Structure-activity relationship studies showed a good comparison with a known active Mpro inhibitor and repurposed drug ebselen with an IC50 value of -0.67 μM. Molecular Dynamics (MD) simulations for 50 ns were performed for A2 and A4 supporting the stability of the two compounds within the binding pocket, largely at the S1, S2 and S4 domains with high binding energy suggesting their suitability as potential inhibitors of Mpro for SARS-CoV-2.

Isatin derivatives as broad-spectrum antiviral agents: the current landscape

In recent decades, several viruses have resulted in large outbreaks with serious health, economic and social consequences. The current unprecedented outbreak of the new coronavirus, SARS-COV-2, necessitates intensive efforts for delivering effective therapies to eradicate such a deadly virus. Isatin is an opulent heterocycle that has been proven to provide tremendous opportunities in the area of drug discovery. Over the last fifty years, suitably functionalized isatin has shown remarkable and broad-spectrum antiviral properties. The review herein is an attempt to compile all of the reported information about the antiviral activity of isatin derivatives with an emphasis on their structure-activity relationships (SARs) along with mechanistic and molecular modeling studies. In this regard, we are confident that the review will afford the scientific community a valuable platform to generate more potent and cost-effective antiviral therapies based on isatin templates.

Novel piperazine based compounds as potential inhibitors for SARS-CoV-2 Protease Enzyme: Synthesis and molecular docking study

Structurally diverse piperazine-based compounds hybrid with thiadiazole, isatin or with sulfur/nitrogen, functionalities were synthesized. The structures of the new compounds were established based on their spectral data and elemental analysis. The physicochemical, bioactivity scores and pharmacokinetic behavior of all the prepared ligands were evaluated using in silico computational tools. The new piperazine ligands have been screened for their inhibition activity against SARS-CoV-2 protease enzyme using molecular docking analysis. The docking studies showed that all the ligands have been docked with negative dock energy onto the target protease protein. Moreover, Molecular interaction studies revealed that SARS-CoV-2 protease enzyme had strong hydrogen bonding interactions with piperazine ligands. The present in silico study thus, provided some guidance to facilitate drug design targeting the SARS-CoV-2 main protease.

Synthesis of 2-Aminoethanesulfonamides of Betulinic and Betulonic Acids

New potentially biologically active sulfonamide derivatives of pentacyclic lupane-type triterpenoids, the sulfonamide group of which was bonded to C-17 of the triterpene skeleton through an amidoethane spacer, were synthesized via conjugation of 2-aminoethanesulfonamides to betulinic and betulonic acids in the presence of Mukaiyama reagent (2-bromo-1-methylpyridinium iodide).

Isatin-based virtual high throughput screening, molecular docking, DFT, QM/MM, MD and MM-PBSA study of novel inhibitors of SARS-CoV-2 main protease

Coronavirus disease 2019 (COVID-19), caused by severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2), is a rapidly growing health care emergency across the world. One of the viral proteases called main protease or Mpro, plays a crucial role in the replication of SARS-CoV-2. As the structure of Mpro of SARS-CoV-2 is similar to the Mpro of SARS-CoV-1 (responsible for SARS outbreak between 2002 and 2004), we hypothesize that the inhibitors of SARS-CoV-1 Mpro can also inhibit the Mpro of SARS-CoV-2. To test this hypothesis, a total of 79 isatin derivatives, which inhibited Mpro activity under in vitro conditions, were selected from the literature, and then screened through AutoDock Vina. The chemical features of the top 5 isatin derivatives with low binding energies (-8.5 to -8.2 kcal/mol) were used to screen similar types of compounds from several small-molecule libraries containing 15856508 compounds. A total of 1,609 compounds with similarity score ≥ 6 were screened and then subjected to docking as well as ADME analysis. Among the compounds screened, 4 ligands form Zinc drug-like library (ZINC000008848565, ZINC000009513563, ZINC000036759789 and ZINC000046053855) showed good ADMET properties, low binding energy (-8.4 to -8.6 kcal/mol), low interaction energy (-72.62 to -50.01 kcal/mol) and high structural stability with Mpro. Hence, the selected ligands might serve as the lead candidates for further wet laboratory validation, optimization and development.Communicated by Ramaswamy H. Sarma.

The development of Coronavirus 3C-Like protease (3CLpro) inhibitors from 2010 to 2020

This review fully describes the coronavirus 3CL^pro peptidomimetic inhibitors and nonpeptidic small molecule inhibitors developed from 2010 to 2020. Specifically, the structural characteristics, binding modes and SARs of these 3CL^pro inhibitors are expounded in detail by division into two categories: peptidomimetic inhibitors mainly utilize electrophilic warhead groups to covalently bind the 3CL^pro Cys145 residue and thereby achieve irreversible inhibition effects, whereas nonpeptidic small molecule inhibitors mainly interact with residues in the S1', S1, S2 and S4 pockets via hydrogen bonds, hydrophobic bonds and van der Waals forces. Based on the emerging PROTAC technology and the existing 3CL^pro inhibitors, 3CL^pro PROTAC degraders are hypothesised to be next-generation anti-coronavirus drugs.

A Neuroprotective Dose of Isatin Causes Multilevel Changes Involving the Brain Proteome: Prospects for Further Research

Isatin (indole-2,3-dione) is an endogenous regulator, exhibiting a wide range of biological and pharmacological activities. At doses of 100 mg/kg and above, isatin is neuroprotective in different experimental models of neurodegeneration. Good evidence exists that its effects are realized via interaction with numerous isatin-binding proteins identified in the brain and peripheral tissues studied. In this study, we investigated the effect of a single dose administration of isatin to mice (100 mg/kg, 24 h) on differentially expressed proteins and a profile of the isatin-binding proteins in brain hemispheres. Isatin administration to mice caused downregulation of 31 proteins. However, these changes cannot be attributed to altered expression of corresponding genes. Although at this time point isatin influenced the expression of more than 850 genes in brain hemispheres (including 433 upregulated and 418 downregulated genes), none of them could account for the changes in the differentially expressed proteins. Comparative proteomic analysis of brain isatin-binding proteins of control and isatin-treated mice revealed representative groups of proteins sensitive to isatin administration. Control-specific proteins (n = 55) represent specific targets that interact directly with isatin. Appearance of brain isatin-binding proteins specific to isatin-treated mice (n = 94) may be attributed to the formation of new clusters of protein–protein interactions and/or novel binding sites induced by a high concentration of this regulator (ligand-induced binding sites). Thus, isatin administration produces multiple effects in the brain, which include changes in gene expression and also profiles of isatin-binding proteins and their interactomes. Further studies are needed for deeper insight into the mechanisms of the multilevel changes in the brain proteome induced by isatin. In the context of the neuroprotective action, these changes may be aimed at interruption of pathological links that begin to form after initiation of pathological processes.

Toward development of generic inhibitors against the 3C proteases of picornaviruses

Development of novel antivirals, which requires knowledge of the viral life cycle in molecular detail, is a daunting task, involving extensive investments, and frequently resulting in failure. As there exist significant commonalities among virus families in the manner of host interaction, identifying and targeting common rather than specific features may lead to the development of broadly useful antivirals. Here, we have targeted the 3C protease of Hepatitis A Virus (HAV), a feco-orally transmitted virus of the family Picornaviridae, for identification of potential antivirals. The 3C protease is a viable drug target as it is required by HAV, as well as by other picornaviruses, for post-translational proteolysis of viral polyproteins and for inhibiting host innate immune pathways. Computational screening, followed by chemical synthesis and experimental validation resulted in identification of a few compounds which, at low micromolar concentrations, could inhibit HAV 3C activity. These compounds were further tested experimentally against the 3C protease of Human Rhinovirus, another member of the Picornaviridae family, with comparable results. Computational studies on 3C proteases from other members of the picornavirus family have indicated that the compounds identified could potentially be generic inhibitors for picornavirus 3C proteases.

3-Hydroxy-3-(2-oxo-2,3-dihydro-1H-indol-3-yl)-2,3-dihydro-1H-indol-2-one

The conformation of the title molecule, C16H12N2O3, is partly determined by an intramolecular C=O...π interaction between one carbonyl group and the five-membered ring of the other indolinone moiety. The crystal packing consists of layers parallel to (001) formed by a combination of N—H...O and O—H...O hydrogen bonds and π–π stacking interactions. Both the N—H...O and O—H...O hydrogen bonds generate inversion dimers.

Synthesis and Evaluation of Antitumour Activities of Novel Fused Tri- and Tetracyclic Uracil Derivatives

Simple one-pot syntheses of indenopyrrolopyrimidines and indolopyrrolopyrimidines were achieved via the cyclocondensation of 6-aminouracils and, respectively, ninhydrin and isatin in the presence of catalytic amounts of glacial acetic acid. Similarly, 5,6-diaminouracil derivatives were used as starting materials for the synthesis of indenopteridines and indolopteridines via their reaction with ninhydrin and isatin, respectively. The synthesised compounds were evaluated for antitumour activity against a human hepatocellular carcinoma cell line (HepG2), some showing antitumour activity comparable with 5-fluorouracil and imatinib.

Medicinal plants against hepatitis C virus

Hepatitis C virus (HCV) is a global health concern which is responsible for most of the liver diseases. Currently, there is no vaccine available for prevention of HCV infection due to the high degree of strain variation. The current standard of care is a combination of pegylated interferon α with ribavirin and boceprevir/telaprevir. This treatment was partially effective and had significant side effects. Hence, there is a need to develop new antiviral agents that interfere with different stages of the HCV life cycle. Recent advances in the understanding of both the cellular and molecular mechanisms of HCV replication have provided the basis for novel therapeutic strategies. Several hundred plant species and their phyto-constituents have been isolated for screening against HCV, and some have been shown to have great medicinal value in preventing and/or ameliorating viral diseases in pre-clinical and clinical trials. This review summarizes medicinal plants and their phytochemicals which inhibit different stages of HCV life cycle and discuss their potential use in HCV therapy.