The complete synthesis of favipiravir from 2-aminopyrazine

Investigation of substituent effects on the electronic structure and antiviral activity of favipiravir derivatives for Covid-19 treatment using DFT and molecular docking

In this study, Density-functional theory/Time-dependent density-functional theory (DFT/TDDFT) and Molecular docking method was used to investigate the effect of methyl acetate, tetrahydrofuran and cyanobenzylidene substituents on the electronic structure and antiviral activity of favipiravir for treating COVID-19. The DFT and TDDFT computations were employed using the Gaussian 09 software package. The values were calculated using the 6-311++G(d, p) basis set and the hybrid B3LYP functional method. Autodock vina software was used for simulations to better predictions and to validate the modified compounds' binding affinities and poses. Results of the study indicate that compounds 1 to 6 all displayed a planar structure, where the pyrazine ring, carboxamide, hydroxyl groups, and other substituents are all situated within the same plane. In addition, the energy gaps (Egap) of these six compounds (Cpd 1, 2, 3, 4, 5, and 6) were compared. The significant dipole moment and binding affinity achieved implies a particular orientation for binding within the target protein, signaling the anticipated strength of the binding interaction. In all six compounds, the electrophilic domain is situated in the vicinity of the amine functional group within the carboxamide compound, whereas the nucleophilic domain encompasses both the carbonyl and hydroxyl groups. The most negatively charged sites are susceptible to electrophilic interactions. In conclusion, compounds 5 and 6 exhibit a high binding affinity of the target protein, while compound 6 has a high energy gap, which could enhance its antiviral activity against the COVID-19 virus.

Structural flexibility of favipiravir and its structural analogues in solutions: experimental and computational insight

Combined UV-vis and quantum chemical studies of the structural flexibility and tautomerism of 6-R-3-hydroxy-2-pyrazine carboxamides in solutions revealed that their keto-enol transformations are accompanied by the deprotonation of enol tautomers and the formation of the corresponding anionic species. Both the solvent and the 6-R substituent strongly influence the relative abundance of the above forms in solutions. Anions are not formed in 1,2-dichloroethane (DCE), but the probability of deprotonation in neutral water and N,N-dimethylformamide (DMF) increases in the order R = H < F < NO2. Only enol tautomers of all solutes are found in DCE. DMF stabilizes keto forms only moderately and assists much strongly in the deprotonation of all three compounds. Water tends to stabilize both keto tautomers and deprotonated anions: the keto form dominates in the case of R = H (antiviral drug T-1105), the anions are found exclusively for R = NO2, and the aqueous solution of another antiviral drug, favipiravir (R = F), contains both the keto tautomer and the anionic form. The results of quantum chemical free energy calculations are in agreement with the experimental observations.

Natural Products-Pyrazine Hybrids: A Review of Developments in Medicinal Chemistry

Pyrazine is a six-membered heterocyclic ring containing nitrogen, and many of its derivatives are biologically active compounds. References have been downloaded through Web of Science, PubMed, Science Direct, and SciFinder Scholar. The structure, biological activity, and mechanism of natural product derivatives containing pyrazine fragments reported from 2000 to September 2023 were reviewed. Publications reporting only the chemistry of pyrazine derivatives are beyond the scope of this review and have not been included. The results of research work show that pyrazine-modified natural product derivatives have a wide range of biological activities, including anti-inflammatory, anticancer, antibacterial, antiparasitic, and antioxidant activities. Many of these derivatives exhibit stronger pharmacodynamic activity and less toxicity than their parent compounds. This review has a certain reference value for the development of heterocyclic compounds, especially pyrazine natural product derivatives.

Optimized synthesis of anti-COVID-19 drugs aided by retrosynthesis software

Considering the millions of COVID-19 patients worldwide, a global critical challenge of low-cost and efficient anti-COVID-19 drug production has emerged. Favipiravir is one of the potential anti-COVID-19 drugs, but its original synthetic route with 7 harsh steps gives a low product yield (0.8%) and has a high cost ($68 per g). Herein, we demonstrated a low-cost and efficient synthesis route for favipiravir designed using improved retrosynthesis software, which involves only 3 steps under safe and near-ambient air conditions. A yield of 32% and cost of $1.54 per g were achieved by this synthetic route. We also used the same strategy to optimize the synthesis of sabizabulin. We anticipate that these synthetic routes will contribute to the prevention and treatment of COVID-19.

An economical and practical procedure of favipiravir synthesis for the treatment of Covid-19

Favipiravir is a wide-spectrum antiviral generic drug that has received large attention during the recent COVID-19 pandemic. While there are synthetic strategies for favipiravir synthesis, economical procedures could contribute to industrial scale synthesis and availability. Accordingly, our efforts focused on an economic and scalable procedure for favipiravir synthesis via the 3,6-dichloropyrazine-2-carbonitrile intermediate obtained from 3-aminopyrazine-2-carboxylic acid. The process afforded favipiravir with 43% yield (from 3,6-dichloropyrazine-2-carbonitrile, by fluorination, hydroxylation, and nitrile hydrolysis reactions) and greater than 99% purity without a chromatographic purification step.

Graphical abstract

Supplementary Information

The online version contains supplementary material available at 10.1007/s11696-022-02595-1.

Development of Analytical Methods for the Determination of N-Bromosuccinimide in Different Active Pharmaceutical Ingredients by High-Performance Ion Chromatography with Suppressed Conductivity Detection

Product safety is important for medicines. For drugs on the market, it must be demonstrated that the levels of toxic contaminants are below the permitted limits. These impurities are used as reagents or are generated during synthesis. N-bromosuccinimide is used as a brominating agent in the synthesis of some active pharmaceutical ingredients. The determination of N-bromosuccinimide is difficult due to its high reactivity. In this work, a high-performance ion chromatographic method was developed for the determination of N-bromosuccinimide. The ion chromatographic measurement can be performed in two ways, one involves the assay of the resulting bromide ion and the other is via the assay of the 3-carbamoyl propanoic acid ion produced from the succinimide. Both acid ions were analyzed on an anion exchange column by gradient elution with potassium hydroxide eluent and detection was performed by a suppressed conductivity detector. During the method development, the results showed that the measurement of bromide ion was more selective than the measurement of 3-carbamoyl propanoic acid ion. Two different types of active pharmaceutical ingredients (API), i.e., prasugrel and favipiravir, were chosen to test the developed method and sample preparation. For both APIs, sample preparation was performed in a vial and consists of liquid–liquid extraction with an alkaline reagent. Finally, the anion exchange ion chromatography method was validated at the limit value level, and harmonized with the guidelines. For prasugrel, the quantification limits and the accuracy at the limit level are 7.2 ppm and 96.4%, while for favipiravir these are 7.5 ppm and 114.7%, respectively.

Voltammetric Determination of Favipiravir Used as an Antiviral Drug for the Treatment of Covid-19 at Pencil Graphite Electrode

This work describes the sensitive voltammetric determination of favipiravir (FAV) based on its reduction for the first time with a low-cost and disposable pencil graphite electrode (PGE). In addition, the determination of FAV was also performed based on its oxidation. Differential pulse (DP) voltammograms recorded in 0.5 M H2SO4 for the reduction of FAV show that peak currents increase linearly in the range of 1.0 to 600.0 μM with a limit of detection of 0.35 μM. The acceptable recovery values (98.9-106.0 %) obtained from a pharmaceutical tablet, real human urine, and artificial blood serum samples spiked with FAV confirm the high accuracy of the proposed method.

Review on fluorinated nucleoside/non-nucleoside FDA-approved antiviral drugs

FDA-approved antiviral agents represent an important class that has attracted attention in recent years to combat current and future threats of viral pandemics. Fluorine ameliorates the electronic, lipophilic and steric problems of drugs. Additionally, fluorine can prolong drug activity and improve metabolic stability, thereby, modifying their pharmacodynamic and pharmacokinetic character. Herein, we summarized the fluorinated FDA-approved antiviral agents, dealing with biological aspects, mechanisms of action, and synthetic pathways.

Analytical Performance and Greenness Evaluation of Five Multi-Level Design Models Utilized for Impurity Profiling of Favipiravir, a Promising COVID-19 Antiviral Drug

In 2018, the discovery of carcinogenic nitrosamine process related impurities (PRIs) in a group of widely used drugs led to the recall and complete withdrawal of several medications that were consumed for a long time, unaware of the presence of these genotoxic PRIs. Since then, PRIs that arise during the manufacturing process of the active pharmaceutical ingredients (APIs), together with their degradation impurities, have gained the attention of analytical chemistry researchers. In 2020, favipiravir (FVR) was found to have an effective antiviral activity against the SARS-COVID-19 virus. Therefore, it was included in the COVID-19 treatment protocols and was consequently globally manufactured at large-scales during the pandemic. There is information indigence about FVR impurity profiling, and until now, no method has been reported for the simultaneous determination of FVR together with its PRIs. In this study, five advanced multi-level design models were developed and validated for the simultaneous determination of FVR and two PRIs, namely; (6-chloro-3-hydroxypyrazine-2-carboxamide) and (3,6-dichloro-pyrazine-2-carbonitrile). The five developed models were classical least square (CLS), principal component regression (PCR), partial least squares (PLS), genetic algorithm-partial least squares (GA-PLS), and artificial neural networks (ANN). Five concentration levels of each compound, chosen according to the linearity range of the target analytes, were used to construct a five-level, three-factor chemometric design, giving rise to twenty-five mixtures. The models resolved the strong spectral overlap in the UV-spectra of the FVR and its PRIs. The PCR and PLS models exhibited the best performances, while PLS proved the highest sensitivity relative to the other models.

A comprehensive update on the structure and synthesis of potential drug targets for combating the coronavirus pandemic caused by SARS-CoV-2

The outbreak of the coronavirus pandemic COVID-19 created by its severe acute respiratory syndrome corona virus-2 (SARS-CoV-2) variant, known for producing a very severe acute respiratory syndrome, has created an unprecedented situation by its continual assault around the world. The crisis caused by the SARS-CoV-2 variant has been a global challenge, calling to mitigate this unprecedented pandemic that has engulfed the whole world. Since the outbreak and spread of COVID-19, many researchers globally have been grappling to find new clinically trialed active drugs with anti-COVID-19 activity, from antimalarial drugs to JAK inhibitors, antiviral drugs, immune suppressants, and so forth. This article presents a brief discussion on the activity and synthesis of some active molecules such as favipiravir, hydroxychloroquine, pirfenidone, remdesivir, lopinavir, camostat, chloroquine, baricitinib, molnupiravir, and so forth, which are under trial.

Favipiravir and Its Structural Analogs: Antiviral Activity and Synthesis Methods

1,4-Pyrazine-3-carboxamide-based antiviral compounds have been under intensive study for the last 20 years. One of these compounds, favipiravir (6-fluoro-3-hydroxypyrazine-2-carboxamide, T-705), is approved for use against the influenza infection in a number of countries. Now, favipiravir is being actively used against COVID-19. This review describes the in vivo metabolism of favipiravir, the mechanism of its antiviral activity, clinical findings, toxic properties, and the chemical synthesis routes for its production. We provide data on the synthesis and antiviral activity of structural analogs of favipiravir, including nucleosides and nucleotides based on them.

Therapeutic dilemmas in addressing SARS-CoV-2 infection: Favipiravir versus Remdesivir

Coronavirus disease 2019 (COVID-19) represents an unmet clinical need, due to a high mortality rate, rapid mutation rate in the virus, increased chances of reinfection, lack of effectiveness of repurposed drugs and economic damage. COVID-19 pandemic has created an urgent need for effective molecules. Clinically proven efficacy and safety profiles have made favipiravir (FVP) and remdesivir (RDV) promising therapeutic options for use against severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) infection. Even though both are prodrug molecules with an antiviral role based on a similar mechanism of action, differences in pharmacological, pharmacokinetic and pharmacotoxicological mechanisms have been identified. The present study aims to provide a comprehensive comparative assessment of FVP and RDV against SARS-CoV-2 infections, by centralizing medical data provided by significant literature and authorized clinical trials, focusing on the importance of a better understanding of the interactions between drug molecules and infectious agents in order to improve the global management of COVID-19 patients and to reduce the risk of antiviral resistance.

Pyrazine and Phenazine Heterocycles: Platforms for Total Synthesis and Drug Discovery

There are numerous pyrazine and phenazine compounds that demonstrate biological activities relevant to the treatment of disease. In this review, we discuss pyrazine and phenazine agents that have shown potential therapeutic value, including several clinically used agents. In addition, we cover some basic science related to pyrazine and phenazine heterocycles, which possess interesting reactivity profiles that have been on display in numerous cases of innovative total synthesis approaches, synthetic methodologies, drug discovery efforts, and medicinal chemistry programs. The majority of this review is focused on presenting instructive total synthesis and medicinal chemistry efforts of select pyrazine and phenazine compounds, and we believe these incredible heterocycles offer promise in medicine.

Thermodynamic properties of active pharmaceutical ingredients that are of interest in COVID-19

The pure component properties are estimated for active pharmaceutical ingredients that are related or proposed for the treatment of severe acute respiratory syndrome-CoronaVirus-2. These include Baricitinib, Camostat, Chloroquine, Dexamethasone, Hydroxychloroquine, Fingolimod, Favipiravir, Thalidomide, and Umifenovir. The estimations are based on group contribution⁺ (GC) models that contain combined group contribution and atom connectivity index with uncertainties in the estimated property values. The thermodynamic properties that are reported include boiling point, critical temperature, critical pressure, critical volume, melting point, standard Gibb's energy of formation, standard enthalpy of formation, enthalpy of fusion, enthalpy of vaporization at 298 K, enthalpy of vaporization at boiling point, entropy of vaporization at boiling point, flash point, Hildebrand solubility parameter, octanol/water partition coefficient, acentric factor, and liquid molar volume at 298 K. The reported properties are not available in the literature and thereby is an incremental development for reliable process engineering.

Scalable synthesis of favipiravir via conventional and continuous flow chemistry

Decagram scale synthesis of favipiravir was performed in 9 steps using diethyl malonate as cheap starting material. Hydrogenation and bromination steps were achieved by employing a continuous flow reactor. The synthetic process provided a total of 16% yield and it is suitable for larger-scale synthesis and production.

Drugs that Might Be Possibly Used for Treatment of COVID-19 Patients

The drug development process for Coronavirus disease (COVID-19) is the research process to create a preventive vaccine or therapeutic prescription drug to relieve the severity of 2019-2020 (COVID-19). In different stages of preclinical or clinical research, several hundred special scientific research centers, research organizations, and health agencies have developed and tried enormous numbers of vaccine candidates and new drugs for COVID-19 disease. In order to identify new therapies against COVID-19, several clinical trials have been in progress worldwide.

Recent trends in the chemistry of Sandmeyer reaction: a review

Metal-catalyzed reactions play a vital part to construct a variety of pharmaceutically important scaffolds from past few decades. To carry out these reactions under mild conditions with low-cost easily available precursors, various new methodologies have been reported day by day. Sandmeyer reaction is one of these, first discovered by Sandmeyer in 1884. It is a well-known reaction mainly used for the conversion of an aryl amine to an aryl halide in the presence of Cu(I) halide via formation of diazonium salt intermediate. This reaction can be processed with or without copper catalysts for the formation of C-X (X = Cl, Br, I, etc.), C-CF₃/CF₂, C-CN, C-S, etc., linkages. As a result, corresponding aryl halides, trifluoromethylated compounds, aryl nitriles and aryl thioethers can be obtained which are effectively used for the construction of biologically active compounds. This review article discloses various literature reports about Sandmeyer-related transformations developed during 2000-2021 which give different ideas to synthetic chemists about further development of new and efficient protocols for Sandmeyer reaction. An updated compilation of new approaches for Sandmeyer reaction is described in this review to construct a variety of carbon-halogen, carbon-phosphorous, carbon-sulfur, carbon-boron etc. linkages.

Synthetic Attempts Towards Eminent Anti-Viral Candidates of SARS-CoV

Severe Acute Respiratory Syndrome (SARS) aka SARS-CoV spread over southern China for the first time in 2002-2003 and history repeated again since last year and take away more than two million people so far. On March 11, 2020 COVID-19 outbreak was officially declared as pandemic by World Health Organization (WHO). Entire world united to fight back against this ultimate destruction. Around 90 vaccines are featured against SARS-CoV-2 and more than 300 active clinical trials are underway by several groups and individuals. So far, no drugs are currently approved that completely eliminates the deadly corona virus. The promising SARS-CoV-2 anti-viral drugs are favipiravir, remdesivir, lopinavir, ribavirin and avifavir. In this review, we have discussed the synthetic approaches elaborately made so far by different groups and chemical companies all around the world towards top three convincing anti-viral drugs against SARS-CoV-2 which are favipiravir, remdesivir and lopinavir.

Plain 1 H nuclear magnetic resonance analysis streamlines the quality control of antiviral favipiravir and congeneric World Health Organization essential medicines

Favipiravir is an established antiviral that is currently being assessed as an investigational drug for the treatment of COVID-19. Favipiravir is strikingly similar to two molecules that the World Health Organization (WHO) lists as essential medicines, which also consist of a six-membered aromatic N-heterocycle bearing a carboxamide function: the anti-tuberculosis agent, pyrazinamide, and nicotinamide, also known as vitamin B₃ . We demonstrate the utility of ¹ H nuclear magnetic resonance (NMR) profiling, an emerging pharmacopoeial tool, for the highly specific identification, selective differentiation of congeners, and subsequent detection of drug falsification or adulteration of these medicines. The straightforward comparison of basic 1-D ¹ H NMR spectra, obtained with benchtop or advanced NMR instruments alike, offers a rapid identity assay and works independently of physical reference materials. This approach accelerates and advances pharmaceutical quality control measures under situations of increased drug demand and altered economy, such as during a pandemic.

A Mini Review on Emerging Targets and Approaches for the Synthesis of Anti-viral Compounds: In Perspective to COVID-19

The novel Coronavirus disease (COVID-19) is an epidemic disease that appeared at the end of the year 2019 with a sudden increase in number and came to be considered as a pandemic disease caused by a viral infection which has threatened most countries for an emergency search for new anti-SARS-COV drugs /vaccines. At present, the number of clinical trials is ongoing worldwide on different drugs i.e. Hydroxychloroquine, Remedisvir, Favipiravir that utilize various mechanisms of action. A few countries are currently processing clinical trials, which may result in a positive outcome. Favipiravir (FPV) represents one of the feasible treatment options for COVID-19, if the result of the trials turns out positive. Favipiravir will be one of the developed possibly authoritative drugs to warrant benefits to mankind with large-scale production to meet the demands of the current pandemic Covid-19 outbreak and future epidemic outbreaks. In this review, the authors tried to explore key molecules, which will be supportive for devising COVID-19 research.

Repurposed Antiviral Drugs for the Treatment of COVID-19: Syntheses, Mechanism of Infection and Clinical Trials

COVID-19 is a public health emergency of international concern. Although considerable knowledge has been acquired with time about the viral mechanism of infection and mode of replication, yet no specific drugs or vaccines have been discovered against SARS-CoV-2 to date. There are few small molecule antiviral drugs like Remdesivir and Favipiravir, which have shown promising results in different advanced stages of clinical trials. Chloroquinine, Hydroxychloroquine, and Lopinavir- Ritonavir combination, although initially were hypothesized to be effective against SARSCoV- 2, are now discontinued from the solidarity clinical trials. This review provides a brief description of their chemical syntheses along with their mode of action, and clinical trial results available on Google and in different peer-reviewed journals till 24th October 2020.

Potential Drugs for the Treatment of COVID-19: Synthesis, Brief History and Application

Coronaviruses (CoVs) belonging to the Betacoronavirus group, an unusually large RNA genome, are characterized by club-like spikes that project from their surface. An outbreak of a novel coronavirus 2019 (nCOVID-19) showing a unique replication strategy and infection has posed a significant threat to international health and the economy around the globe. Scientists around the world are investigating few previously used clinical drugs for the treatment of COVID-19. This review provides synthesis and mode of action of recently investigated drugs like Chloroquine, Hydroxychloroquine, Ivermectin, Selamectin, Remdesivir, Baricitinib, Darunavir, Favipiravir, Lopinavir/ritonavir and Mefloquine hydrochloride that constitute an option for COVID-19 treatment.

Cyanorona-20: The first potent anti-SARS-CoV-2 agent

Explicit hindrance and blockade of the viral RNA-dependent RNA polymerase (RdRp) of SARS-CoV-2 is considered one of the most promising and efficient approaches for developing highly potent remedies for COVID-19. However, almost all of the reported viral RdRp inhibitors (either repurposed or new antiviral drugs) lack specific selectivity against the novel coronaviral RdRp and still at a beginning phase of advancement. Herein, I discovered and introduce a new pyrazine derivative, (E)-N-(4-cyanobenzylidene)-6-fluoro-3-hydroxypyrazine-2-carboxamide (cyanorona-20), as the first potent SARS-CoV-2 RdRp inhibitor with very high selectivity (209- and 45-fold more potent than favipiravir and remdesivir, respectively). This promising selective specific anti-COVID-19 compound is also deemed to be the first distinctive derivative of favipiravir. Cyanorona-20, the unprecedented nucleoside/nucleotide analog, was designed, synthesized, characterized, computationally studied, and biologically evaluated for its anti-COVID-19 actions (through a precise in vitro anti-COVID-19 assay). The results of the biological assay displayed that cyanorona-20 surprisingly exhibited very high and largely significant anti-COVID-19 activities (anti-SARS-CoV-2 EC₅₀ = 0.45 μM), and, in addition, it could be also a very promising guide and lead compound for the design and synthesis of new anti-SARS-CoV-2 and anti-COVID-19 agents through structural modifications and further computational studies. Further appraisal for the improvement of cyanorona-20 medication is a prerequisite requirement in the coming days. In a word, the ascent of the second member (cyanorona-20 “Corona Antidote”) of the novel and promising class of anti-COVID-19 pyrazine derivatives would drastically make a medical uprising in the pharmacotherapeutic treatment regimens and protocols of the recently-emerged SARS-CoV-2 infection and its accompanying COVID-19.

Discovery of (E)-N-(4-cyanobenzylidene)- 6-fluoro- 3-hydroxypyrazine-2 -carboxamide (cyanorona-20): the first potent and specific anti-COVID-19 drug

Abstract

Specific inhibition of the viral RNA-dependent RNA polymerase (RdRp) of the newly-emerged severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) is a very promising strategy for developing highly potent medicines for coronavirus disease 2019 (COVID-19). However, almost all of the reported viral RdRp inhibitors (either repurposed drugs or new antiviral agents) lack selectivity against the SARS-CoV-2 RdRp. Herein, I discovered a new favipiravir derivative, (E)-N-(4-cyanobenzylidene)-6-fluoro-3-hydroxypyrazine-2-carboxamide (cyanorona-20), as the first potent SARS-CoV-2 inhibitor with very high selectivity (209- and 45-fold more potent than favipiravir and remdesivir, respectively). Based on the significant reduction in the in vitro SARS-CoV-2 replication/copies, strong computational cyanorona-20 ligand-RdRp protein interactions, and anti-RdRp activity of the parent favipiravir drug, SARS-CoV-2 inhibition is thought to be mediated through the coronaviral-2 RdRp inhibition. This promising selective anti-COVID-19 compound is also, to the best of our knowledge, the first bioactive derivative of favipiravir, the known antiinfluenza and antiviral drug. This new nucleoside analog was designed, synthesized, characterized, computationally studied (through pharmacokinetic calculations along with computational molecular modeling and prediction), and biologically evaluated for its anti-COVID-19 activities (through a validated in vitro anti-COVID-19 assay). The results of the biological assay showed that cyanorona-20 surprisingly exhibited very significant anti-COVID-19 activity (anti-SARS-CoV-2 EC₅₀ = 0.45 μM), and, in addition, it could be also a very promising lead compound for the design of new anti-COVID-19 agents. Cyanorona-20 is a new favipiravir derivative with promise for the treatment of SARS-CoV-2 infection.

Graphic abstract

Supplementary Information

The online version contains supplementary material available at 10.1007/s11696-021-01640-9.

Drug Re-purposing Approach and Potential Therapeutic Strategies to Treat COVID-19

The current pandemic of COVID-19 caused by SARS-Cov-2 has posed a severe threat to the whole world with its highly infectious, progressive nature with up to 10% mortality rates. The severity of the situation faced by the whole world and the lack of efficient therapeutics to treat this viral disease have led the WHO to depend on the drug-repurposing approach to tackle this major global health problem. This review aims at highlighting the various synthetic approaches employed for the synthesis of these FDA approved drugs that have been presently used for COVID-19 treatment. Additionally, a brief overview of several therapeutic strategies is also presented. This review will encourage the scientific community across the globe to come up with better and efficient synthetic protocols and also novel chemical entities along with this core with more potent activity.

Tackling COVID-19 Using Remdesivir and Favipiravir as Therapeutic Options

The human world is currently influenced largely by the outbreak of pandemic COVID-19. At this moment, most researchers focus on developing treatment strategies and measures to work against COVID-19. Treatment strategies specific for COVID-19 are lacking. This article provides an overview of the life cycle and routes of transmission of SARS-CoV-2. The therapeutic effects of two drugs [i. e., remdesivir (RDV) and favipiravir (FPV)] which can potentially tackle COVID-19 are discussed based on current published data. This review can serve as a reference for future studies.

The situation of small molecules targeting key proteins to combat SARS-CoV-2: Synthesis, metabolic pathway, mechanism of action, and potential therapeutic applications

Due to the global epidemic and high mortality of 2019 coronavirus disease (COVID-19), there is an immediate need to discover drugs that can help before a vaccine becomes available. Given that the process of producing new drugs is so long, the strategy of repurposing existing drugs is one of the promising options for the urgent treatment of severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2), the virus that causes COVID-19 disease. Although FDA has approved Remdesivir for the use in hospitalized adults and pediatric patients suffering from COVID-19, no fully effective and reliable drug has been yet identified worldwide to treat COVID-19 specifically. Thus, scientists are still trying to find antivirals specific to COVID-19. This work reviews the chemical structure, metabolic pathway, mechanism of action of existing drugs with potential therapeutic applications for COVID-19. Further, we summarized the molecular docking stimulation of the medications related to key protein targets. These already drugs could be developed for further clinical trials to supply suitable therapeutic options for patients suffering from COVID-19.

Efficacy and Safety of New and Emerging Drugs for COVID-19: Favipiravir and Dexamethasone

Purpose of Review

The widespread respiratory disease of virus known as severe acute respiratory syndrome-coronavirus 2019 (SAR-CoV-2) had infected more than 200 countries and caused pandemic and havoc in the world.

Recent Findings

The genome of the virus was sequenced rapidly to study its mechanism, epidemiology, drugs, and vaccines. Many drugs and vaccines are being studied by researchers to treat and prevent the SARS-CoV-2. Favipiravir and dexamethasone are repurposed drugs which showed therapeutic potential and pharmaceutical efficacy against SARS-CoV-2.

Summary

The review describes the path of favipiravir and dexamethasone from chemistry to mechanisms of action to combat SARS-CoV-2. In addition, the potential side effects are also summarized to study their potential to control corona virus 2019.

Drug repurposing for the treatment of COVID-19: Pharmacological aspects and synthetic approaches

In December 2019, a new variant of SARS-CoV emerged, the so-called acute severe respiratory syndrome coronavirus 2 (SARS-CoV-2). This virus causes the new coronavirus disease (COVID-19) and has been plaguing the world owing to its unprecedented spread efficiency, which has resulted in a huge death toll. In this sense, the repositioning of approved drugs is the fastest way to an effective response to a pandemic outbreak of this scale. Considering these facts, in this review we provide a comprehensive and critical discussion on the chemical aspects surrounding the drugs currently being studied as candidates for COVID-19 therapy. We intend to provide the general chemical community with an overview on the synthetic/biosynthetic pathways related to such molecules, as well as their mechanisms of action against the evaluated viruses and some insights on the pharmacological interactions involved in each case. Overall, the review aims to present the chemical aspects of the main bioactive molecules being considered to be repositioned for effective treatment of COVID-19 in all phases, from the mildest to the most severe.

Methods of Synthesis of Remdesivir, Favipiravir, Hydroxychloroquine, and Chloroquine: Four Small Molecules Repurposed for Clinical Trials during the Covid-19 Pandemic

The novel coronavirus (COVID-19) disease has rapidly evolved into a sweeping pandemic despite public health measures. Screening and development of new vaccines and antivirals are expensive and time consuming. However, the repositioning of available drugs is an essential and universal strategy in the development of new drugs and therefore should receive priority attention as well as international government and agency support. Significant drugs such as chloroquine, hydroxychloroquine, favipiravir and remdesivir, are currently undergoing clinical studies to test their efficacy and safety. Some promising results have been achieved thus far in the treatment of COVID-19. In this article we summarize and discuss the most common synthetic strategies to apply in the preparation of these drug molecules. It is hoped that this compendium will provide an accessible useful guide and reference source for scientists, researchers and academia in their battle against COVD-19.

1 Introduction

2 Synthesis of Chloroquine (CQ) and Hydroxychloroquine (HCQ)

2.1 Synthesis of 4,7-Dichloroquinoline 1

2.2 Synthesis of 2-Amino-5-(diethylamino)pentane (Novoldiamine) 2

2.3 Synthesis of 5-(N-Ethyl-N-2-hydroxyethylamino)-2-pentylamine 4

2.4 Developed Methods for Synthesis of Chloroquine and Hydroxychloroquine

2.5 Synthesis of (R)-Chloroquine, (S)-Chloroquine, (R)-Hydroxychloroquine and (S)-Hydroxychloroquine

3 Synthesis of Favipiravir (Avigan)

4 Synthesis of Remdesivir

5 Conclusion

Favipiravir - a Modern Antiviral Drug: Synthesis and Modifications

The routes of synthesis are considered, as well as the modifications of the promising modern antiviral drug favipiravir. Literature data from the last 10 years are reported.

Quest for a COVID-19 Cure by Repurposing Small-Molecule Drugs: Mechanism of Action, Clinical Development, Synthesis at Scale, and Outlook for Supply

The outbreak of the COVID-19 pandemic has spurred an intense global effort to repurpose existing approved drugs for its treatment. In this review, we highlight the development of seven small-molecule drugs that are currently being assessed in clinical trials for the treatment of COVID-19. Three sections are presented for each drug: (1) history, mechanism of action, and status of clinical trials; (2) scalable synthetic routes and final forms; and (3) outlook for supply should clinical trials show treatment efficacy. A brief overview of diagnostic testing and vaccine development is also presented.

Minimum costs to manufacture new treatments for COVID-19

Introduction

‘Repurposing’ existing drugs to treat COVID-19 is vital to reducing mortality and controlling the pandemic. Several promising drugs have been identified and are in various stages of clinical trials globally. If efficacy of these drugs is demonstrated, rapid, mass availability at an affordable cost would be essential to ensuring equity and access especially amongst low- and middle-income economies.

Methods

Minimum costs of production were estimated from the costs of active pharmaceutical ingredients using established methodology, which had good predictive accuracy for medicines for hepatitis C and HIV amongst others. Data were extracted from global export shipment records or analysis of the route of chemical synthesis. The estimated costs were compared with list prices from a range of countries where pricing data were available.

Results

Minimum estimated costs of production were US $0.93/day for remdesivir, $1.45/day for favipiravir, $0.08/day for hydroxychloroquine, $0.02/day for chloroquine, $0.10/day for azithromycin, $0.28/day for lopinavir/ritonavir, $0.39/day for sofosbuvir/daclatasvir and $1.09/day for pirfenidone. Costs of production ranged between $0.30 and $31 per treatment course (10–28 days). Current prices of these drugs were far higher than the costs of production, particularly in the US.

Conclusions

Should repurposed drugs demonstrate efficacy against COVID-19, they could be manufactured profitably at very low costs, for much less than current list prices. Estimations for the minimum production costs can strengthen price negotiations and help ensure affordable access to vital treatment for COVID-19 at low prices globally.