Quest for a Cure: Potential Small-Molecule Treatments for COVID-19, Part 2

A path from synthesis to emergency use authorization of molnupiravir as a COVID-19 therapy

Coronaviruses are a group of enveloped viruses with non-segmented, single-stranded, and positive-sense RNA genomes. It belongs to the 'Coronaviridae family', responsible for various diseases, including the common cold, SARS, and MERS. The COVID-19 pandemic, which began in March 2020, has affected 209 countries, infected over a million people, and claimed over 50,000 lives. Significant efforts have been made by repurposing several approved drugs including antiviral, to combat the COVID-19 pandemic. Molnupiravir is found to be the first orally acting efficacious drug to treat COVID-19 cases. It was approved for medical use in the UK in November 2021 and other countries, including USFDA, which granted approval an emergency use authorization (EUA) for treating adults with mild to moderate COVID-19 patients. Considering the importance of molnupiravir, the present review deals with its various synthetic strategies, pharmacokinetics, bio-efficacy, toxicity, and safety profiles. The comprehensive information along with critical analysis will be very handy for a wide range of audience including medicinal chemists in the arena of antiviral drug discovery especially anti-viral drugs against any variant of COVID-19.

Drug repositioning in the COVID-19 pandemic: fundamentals, synthetic routes, and overview of clinical studies

INTRODUCTION

Drug repositioning is a strategy to identify a new therapeutic indication for molecules that have been approved for other conditions, aiming to speed up the traditional drug development process and reduce its costs. The high prevalence and incidence of coronavirus disease 2019 (COVID-19) underline the importance of searching for a safe and effective treatment for the disease, and drug repositioning is the most rational strategy to achieve this goal in a short period of time. Another advantage of repositioning is the fact that these compounds already have established synthetic routes, which facilitates their production at the industrial level. However, the hope for treatment cannot allow the indiscriminate use of medicines without a scientific basis.

RESULTS

The main small molecules in clinical trials being studied to be potentially repositioned to treat COVID-19 are chloroquine, hydroxychloroquine, ivermectin, favipiravir, colchicine, remdesivir, dexamethasone, nitazoxanide, azithromycin, camostat, methylprednisolone, and baricitinib. In the context of clinical tests, in general, they were carried out under the supervision of large consortiums with a methodology based on and recognized in the scientific community, factors that ensure the reliability of the data collected. From the synthetic perspective, compounds with less structural complexity have more simplified synthetic routes. Stereochemical complexity still represents the major challenge in the preparation of dexamethasone, ivermectin, and azithromycin, for instance.

CONCLUSION

Remdesivir and baricitinib were approved for the treatment of hospitalized patients with severe COVID-19. Dexamethasone and methylprednisolone should be used with caution. Hydroxychloroquine, chloroquine, ivermectin, and azithromycin are ineffective for the treatment of the disease, and the other compounds presented uncertain results. Preclinical and clinical studies should not be analyzed alone, and their methodology's accuracy should also be considered. Regulatory agencies are responsible for analyzing the efficacy and safety of a treatment and must be respected as the competent authorities for this decision, avoiding the indiscriminate use of medicines.

Potential Anti-SARS-CoV-2 Prodrugs Activated by Phosphorylation and Their Role in the Aged Population

The COVID-19 pandemic has flared across every part of the globe and affected populations from different age groups differently. People aged from 40 to 80 years or older are at an increased risk of morbidity and mortality due to COVID-19. Therefore, there is an urgent requirement to develop therapeutics to decrease the risk of the disease in the aged population. Over the last few years, several prodrugs have demonstrated significant anti-SARS-CoV-2 effects in in vitro assays, animal models, and medical practice. Prodrugs are used to enhance drug delivery by improving pharmacokinetic parameters, decreasing toxicity, and attaining site specificity. This article discusses recently explored prodrugs such as remdesivir, molnupiravir, favipiravir, and 2-deoxy-D-glucose (2-DG) and their implications in the aged population, as well as investigating recent clinical trials.

Identification and semisynthesis of (-)-anisomelic acid as oral agent against SARS-CoV-2 in mice

(-)-Anisomelic acid, isolated from Anisomeles indica (L.) Kuntze (Labiatae) leaves, is a macrocyclic cembranolide with a trans-fused α-methylene-γ-lactone motif. Anisomelic acid effectively inhibits SARS-CoV-2 replication and viral-induced cytopathic effects with an EC50 of 1.1 and 4.3 μM, respectively. Challenge studies of SARS-CoV-2-infected K18-hACE2 mice showed that oral administration of anisomelic acid and subcutaneous dosing of remdesivir can both reduce the viral titers in the lung tissue at the same level. To facilitate drug discovery, we used a semisynthetic approach to shorten the project timelines. The enantioselective semisynthesis of anisomelic acid from the naturally enriched and commercially available starting material (+)-costunolide was achieved in five steps with a 27% overall yield. The developed chemistry provides opportunities for developing anisomelic-acid-based novel ligands for selectively targeting proteins involved in viral infections.

Identifying the Hot Spot Residues of the SARS-CoV-2 Main Protease Using MM-PBSA and Multiple Force Fields

In this study, we investigated the binding affinities between the main protease of SARS-CoV-2 virus (Mpro) and its various ligands to identify the hot spot residues of the protease. To benchmark the influence of various force fields on hot spot residue identification and binding free energy calculation, we performed MD simulations followed by MM-PBSA analysis with three different force fields: CHARMM36, AMBER99SB, and GROMOS54a7. We performed MD simulations with 100 ns for 11 protein-ligand complexes. From the series of MD simulations and MM-PBSA calculations, it is identified that the MM-PBSA estimations using different force fields are weakly correlated to each other. From a comparison between the force fields, AMBER99SB and GROMOS54a7 results are fairly correlated while CHARMM36 results show weak or almost no correlations with the others. Our results suggest that MM-PBSA analysis results strongly depend on force fields and should be interpreted carefully. Additionally, we identified the hot spot residues of Mpro, which play critical roles in ligand binding through energy decomposition analysis. It is identified that the residues of the S4 subsite of the binding site, N142, M165, and R188, contribute strongly to ligand binding. In addition, the terminal residues, D295, R298, and Q299 are identified to have attractive interactions with ligands via electrostatic and solvation energy. We believe that our findings will help facilitate developing the novel inhibitors of SARS-CoV-2.

Preparing anti-SARS-CoV-2 agent EIDD-2801 by a practical and scalable approach, and quick evaluation via machine learning

EIDD-2801 is an orally bioavailable prodrug, which will be applied for emergency use authorization from the U.S. Food and Drug Administration for the treatment of COVID-19. To investigate the optimal parameters, EIDD-2801 was optimized via a four-step synthesis with high purity of 99.9%. The hydroxylamination procedure was telescoped in a one-pot and the final step was precisely controlled on reagents, temperature and reaction time. Compared to the original route, the yield of the new route was enhanced from 17% to 58% without column chromatography. The optimized synthesis has been successfully determinated on a decagram scale: the first step at 200 g and the final step at 20 g. Besides, the relationship between yield and temperature, time, and reagents in the deprotection step was investigated via Shapley value explanation and machine learning approach-decision tree method. The results revealed that reagents have the greatest impact on yield estimation, followed by the temperature.

Discovery, Development, and Patent Trends on Molnupiravir: A Prospective Oral Treatment for COVID-19

The COVID-19 pandemic needs no introduction at present. Only a few treatments are available for this disease, including remdesivir and favipiravir. Accordingly, the pharmaceutical industry is striving to develop new treatments for COVID-19. Molnupiravir, an orally active RdRp inhibitor, is in a phase 3 clinical trial against COVID-19. The objective of this review article is to enlighten the researchers working on COVID-19 about the discovery, recent developments, and patents related to molnupiravir. Molnupiravir was originally developed for the treatment of influenza at Emory University, USA. However, this drug has also demonstrated activity against a variety of viruses, including SARS-CoV-2. Now it is being jointly developed by Emory University, Ridgeback Biotherapeutics, and Merck to treat COVID-19. The published clinical data indicate a good safety profile, tolerability, and oral bioavailability of molnupiravir in humans. The patient-compliant oral dosage form of molnupiravir may hit the market in the first or second quarter of 2022. The patent data of molnupiravir revealed its granted compound patent and process-related patent applications. We also anticipate patent filing related to oral dosage forms, inhalers, and a combination of molnupiravir with marketed drugs like remdesivir, favipiravir, and baricitinib. The current pandemic demands a patient compliant, safe, tolerable, and orally effective COVID-19 treatment. The authors believe that molnupiravir meets these requirements and is a breakthrough COVID-19 treatment.

Evolution of the Synthesis of Remdesivir. Classical Approaches and Most Recent Advances

The broad-spectrum antiviral Remdesivir, a monophosphate nucleoside analogue prodrug (ProTide), was repurposed. In May 2020, it received emergency approval by the FDA, being the first drug approved to fight the new coronavirus (COVID-19) disease which targets the virus directly. The main synthetic strategies toward Remdesivir, and their relevant modifications, are presented and discussed, to provide a panoramic view of the state-of-the-art and the more important advances in this field. Recent progress, proposed improvements, and uses of novel technologies for the synthetic sequence are also detailed.

Photosensitizing Antivirals

Antiviral action of various photosensitizers is already summarized in several comprehensive reviews, and various mechanisms have been proposed for it. However, a critical consideration of the matter of the area is complicated, since the exact mechanisms are very difficult to explore and clarify, and most publications are of an empirical and "phenomenological" nature, reporting a dependence of the antiviral action on illumination, or a correlation of activity with the photophysical properties of the substances. Of particular interest is substance-assisted photogeneration of highly reactive singlet oxygen (1O2). The damaging action of 1O2 on the lipids of the viral envelope can probably lead to a loss of the ability of the lipid bilayer of enveloped viruses to fuse with the lipid membrane of the host cell. Thus, lipid bilayer-affine 1O2 photosensitizers have prospects as broad-spectrum antivirals against enveloped viruses. In this short review, we want to point out the main types of antiviral photosensitizers with potential affinity to the lipid bilayer and summarize the data on new compounds over the past three years. Further understanding of the data in the field will spur a targeted search for substances with antiviral activity against enveloped viruses among photosensitizers able to bind to the lipid membranes.