Discovery of pentacyclic compounds as potent inhibitors of hepatitis C virus NS5B RNA polymerase

Tandem (4 + 3)-Annulation of Aziridines: Stereoselective Access to Fused Azepinoindoles

A stereoselective tandem (4 + 3)-coupling of aziridines with 4-alkylidene indole malonates has been disclosed under Cu-catalysis involving a base-promoted annulation. The methodology serves as a potential approach toward the facile construction of fused azepinoindoles with good yields and diastereoselectivities. Late-stage natural product and drug modification as well as preliminary investigations for the enantioselective (4 + 3)-annulation are important practical features.

Research progress of indole-fused derivatives as allosteric modulators: Opportunities for drug development

Allosteric modulation is a direct and effective method for regulating the function of biological macromolecules, which play vital roles in various cellular activities. Unlike orthosteric modulators, allosteric modulators bind to sites distant from the protein's orthosteric/active site and can have specific effects on the protein's function or activity without competing with endogenous ligands. Compared to traditional orthosteric modulators, allosteric modulators offer several advantages, including reduced side effects, greater specificity, and lower toxicity, making them a promising strategy for developing novel drugs. Indole-fused architectures are widely distributed in natural products and bioactive drug leads, displaying diverse biological activities that attract the interest of both chemists and biologists in drug discovery. Currently, an increasing number of indole-fused compounds have exhibited potent activities in allosteric modulation. In this review, we provide a brief summary of examples of allosteric modulators based on the indole-fused complex architecture, highlighting the strategies for drug design/discovery and the structure-activity relationships of allosteric modulators from the perspective of medicinal chemistry.

Copper-Catalyzed Cycloisomerization of Unactivated Allene-Tethered O-Propargyl Oximes: A Domino Reaction Sequence toward the Synthesis of Hexahydropyrrolo[3,4-b]azepin-5(4H)-ones

A novel copper-catalyzed cycloisomerization of unactivated allene-tethered O-propargyl oximes has been developed for the synthesis of hexahydropyrrolo[3,4-b]azepin-5(4H)-ones. This one-pot domino reaction proceeds via a [2,3]-sigmatropic rearrangement, a [3 + 2] cycloaddition, and another [3,3]-sigmatropic rearrangement. The methodology offers a practical and straightforward route for the rapid assembly of both ring components of the fused bicyclic motifs from acyclic precursors by simultaneously forming four new bonds (a C═O, a C═N, and two C-C bonds) in a single step.

Benzoazepine-Fused Isoindolines via Intramolecular (3 + 2)-Cycloadditions of Azomethine Ylides with Dinitroarenes

Aminobenzaldehydes bearing a pendant 3,5-dinitrophenyl group react thermally with N-substituted α-amino acids to form unprecedented benzoazepine-fused isoindolines. The reaction proceeds via a dearomatization/rearomatization sequence involving an intramolecular (3 + 2)-cycloaddition between the in situ formed azomethine ylide and the dinitroarene. Various glycine derivatives are tolerated as well as branched substrates based on cyclic, α-mono-, and α,α-disubstituted amino acids, giving single diastereomers in many cases. The method is scalable and gives products with a nitro group ready for further manipulation.

Discovery of hit molecules targeting allosteric site of hepatitis C virus NS5B polymerase

Nonstructural protein 5B (NS5B), the RNA-dependent RNA polymerase of Hepatitis C Virus (HCV), plays a key role in viral amplification and is an attractive and most explored target for discovery of new therapeutic agents for Hepatitis C. Though safe and effective, NS5B inhibitors were launched in 2013 (Sovaldi) and 2014 (Harvoni, Viekira Pak), the high price tags of these medications limit their use among poor people in developing countries. Hence, still there exists a need for cost-effective and short duration anti-HCV agents especially those targeting niche patient population who were non-respondent to earlier therapies or with comorbid conditions. The present study describes the discovery of novel non-nucleoside (NNI) inhibitors of NS5B using a series of rational drug design techniques such as virtual screening, scaffold matching and molecular docking. 2D and 3D structure based virtual screening technique identified 300 hit compounds. Top 20 hits were screened out from identified hits using molecular docking technique. Four molecules, that are representative of 20 hits were evaluated for binding affinity under in vitro conditions using surface plasmon resonance-based assay and the results emphasized that compound with CoCoCo ID: 412075 could exhibit good binding response toward NS5B and could be a potential candidate as NS5B inhibitor.Communicated by Ramaswamy H. Sarma.

Recent advances on the synthesis of hepatitis C virus NS5B RNA-dependent RNA-polymerase inhibitors

Hepatitis C is a viral liver infection considered as the major cause of cirrhosis and hepatocellular carcinoma (HCC). The HCV NS5B polymerase, an RNA-dependent RNA polymerase, is essential for HCV replication, which is able to catalyze the synthesis of positive (genomic) and negative (template) strand HCV RNA, but has no functional equivalent in mammalian cells. Therefore, the NS5B polymerase has emerged as an attractive target for the development of specifically targeted antiviral therapy for HCV (DAA, for direct-acting antivirals). Recently, a growing number of compounds have been reported as the NS5B polymerase inhibitors, some of which especially have been licensed in clinical trials. This review describes recent advances on the synthesis of the NS5B polymerase inhibitors, focusing on the merits and demerits of their synthetic methods. In particular, inspiration from the synthesis and the future direction of the NS5B polymerase inhibitors are highlighted.

Expedient synthesis of fused azepine derivatives using a sequential rhodium(II)-catalyzed cyclopropanation/1-aza-Cope rearrangement of dienyltriazoles

A general method for the formation of fused dihydroazepine derivatives from 1-sulfonyl-1,2,3-triazoles bearing a tethered diene is reported. The process involves an intramolecular cyclopropanation of an α-imino rhodium(II) carbenoid, leading to a transient 1-imino-2-vinylcyclopropane intermediate which rapidly undergoes a 1-aza-Cope rearrangement to generate fused dihydroazepine derivatives in moderate to excellent yields. The reaction proceeds with similar efficiency on gram scale. The use of catalyst-free conditions leads to the formation of a novel [4.4.0] bicyclic heterocycle.

Conformation-based restrictions and scaffold replacements in the design of hepatitis C virus polymerase inhibitors: discovery of deleobuvir (BI 207127)

Conformational restrictions of flexible torsion angles were used to guide the identification of new chemotypes of HCV NS5B inhibitors. Sites for rigidification were based on an acquired conformational understanding of compound binding requirements and the roles of substituents in the free and bound states. Chemical bioisosteres of amide bonds were explored to improve cell-based potency. Examples are shown, including the design concept that led to the discovery of the phase III clinical candidate deleobuvir (BI 207127). The structure-based strategies employed have general utility in drug design.

Design and Development of NS5B Polymerase Non‐nucleoside Inhibitors for the Treatment of Hepatitis C Virus Infection

The hepatitis C virus (HCV) infects an estimated 130–170 million people worldwide and is associated with life‐threatening liver diseases. The recent introduction of the first two HCV direct‐acting antivirals (DAAs) as a complement to the interferon/ribavirin standard of care has provided patients with improved outcomes. Still, 25–30% of subjects infected with genotype 1 HCV do not respond adequately to treatment owing to the emergence of resistant virus and many suffer from severe side effects. A paradigm shift towards the development of interferon‐free combinations of DAAs with complementary modes of action is currently taking place. Virally encoded proteins and enzymes have become the target of HCV drug discovery efforts and several promising new agents are currently being evaluated in the clinic for treatment of chronic HCV infection. The NS5B RNA‐dependent RNA polymerase is responsible for replication of viral RNA and plays a pivotal role in the virus life cycle. NS5B is undoubtedly the most druggable HCV target and is susceptible to several classes of allosteric inhibitors that bind to four distinct sites on the enzyme. This chapter describes successful strategies that have led to the discovery of HCV NS5B antivirals. It is divided according to allosteric sites and describes how each of the known families of inhibitors was discovered, characterized and optimized to provide clinical candidates. When available, the strategies adopted by medicinal chemists to optimize initial leads and address challenges and liabilities encountered on the path to candidate selection are described, along with reported clinical outcomes.

Discovery of naturally occurring aurones that are potent allosteric inhibitors of hepatitis C virus RNA-dependent RNA polymerase

We have identified naturally occurring 2-benzylidenebenzofuran-3-ones (aurones) as new templates for non-nucleoside hepatitis C virus (HCV) RNA-dependent RNA polymerase (RdRp) inhibitors. The aurone target site, identified by site-directed mutagenesis, is located in thumb pocket I of HCV RdRp. The RdRp inhibitory activity of 42 aurones was rationally explored in an enzyme assay. Molecular docking studies were used to determine how aurones bind to HCV RdRp and to predict their range of inhibitory activity. Seven aurone derivatives were found to have potent inhibitory effects on HCV RdRp, with IC(50) below 5 μM and excellent selectivity index (inhibition activity versus cellular cytotoxicity). The most active aurone analogue was (Z)-2-((1-butyl-1H-indol-3-yl)methylene)-4,6-dihydroxybenzofuran-3(2H)-one (compound 51), with an IC(50) of 2.2 μM. Their potent RdRp inhibitory activity and their low toxicity make these molecules attractive candidates as direct-acting anti-HCV agents.

Recent advances in drug discovery of benzothiadiazine and related analogs as HCV NS5B polymerase inhibitors

Hepatitis C virus (HCV) is a major health burden, with an estimated 170 million chronically infected individuals worldwide, and a leading cause of liver transplantation. Patients are at increased risk of developing liver cirrhosis, hepatocellular carcinoma and even liver failure. In the past two decades, several approaches have been adopted to inhibit non-structural viral proteins. The RNA-dependent RNA polymerase (NS5B) of HCV is one of the attractive validated targets for development of new drugs to block HCV infection. In this review, we report the recent progress made towards identifying and developing benzothiadiazines as HCV NS5B polymerase inhibitors. The substituted benzothiadiazine class was identified by HTS in 2002 as an NS5B inhibitor. Further optimization and modification of the core has improved the potency and pharmacokinetic properties of substituted benzothiadiazines. Research on palm site-binding benzothiadiazine analogs and related derivatives and analogs is discussed in this article.

Discovery of (7R)-14-cyclohexyl-7-{[2-(dimethylamino)ethyl](methyl) amino}-7,8-dihydro-6H-indolo[1,2-e][1,5]benzoxazocine-11-carboxylic acid (MK-3281), a potent and orally bioavailable finger-loop inhibitor of the hepatitis C virus NS5B polymerase

Infections caused by hepatitis C virus (HCV) are a significant world health problem for which novel therapies are in urgent demand. The polymerase of HCV is responsible for the replication of viral genome and has been a prime target for drug discovery efforts. Here, we report on the further development of tetracyclic indole inhibitors, binding to an allosteric site on the thumb domain. Structure-activity relationship (SAR) studies around an indolo-benzoxazocine scaffold led to the identification of compound 33 (MK-3281), an inhibitor with good potency in the HCV subgenomic replication assay and attractive molecular properties suitable for a clinical candidate. The compound caused a consistent decrease in viremia in vivo using the chimeric mouse model of HCV infection.

Non-nucleoside inhibitors of hepatitis C virus polymerase: current progress and future challenges

The current standard of care for hepatitis C virus (HCV) infection is a combination of PEGylated interferon and ribavirin, which offer limited efficacy and significant side effects. Novel HCV-specific inhibitors, including those directed at the viral polymerase, have become the focus of HCV drug-discovery efforts in the past decade. In addition to the active site targeted by traditional nucleoside inhibitors, at least four different allosteric-binding sites have been reported for the HCV polymerase, which offer ample opportunities for small-molecule inhibitors. In this review, we summarize the recent progress in the discovery of non-nucleoside HCV polymerase inhibitors with a focus on novel chemical matters, their clinical efficacy, safety and potential for combination therapy.

Pyrazolo[1,5-a]pyrimidine-based inhibitors of HCV polymerase

The present paper describes a novel series of HCV RNA polymerase inhibitors based on a pyrazolo[1,5-a]pyrimidine scaffold bearing hydrophobic groups and an acidic functionality. Several compounds were optimized to low nanomolar potencies in a biochemical RdRp assay. SAR trends clearly reveal a stringent preference for a cyclohexyl group as one of the hydrophobes, and improved activities for carboxylic acid derivatives.