Alkyl substituted aminal derivatives of HCV NS5A inhibitor MK-8742

Synthesis of Indole-Fused Six-, Seven-, or Eight-Membered N,O-Heterocycles via Rhodium-Catalyzed NH-Indole-Directed C-H Acetoxylation/Hydrolysis/Annulation

We report herein the facile synthesis of indole-fused six-, seven-, or eight-membered N,O-heterocycles through rhodium-catalyzed C-H acetoxylation/hydrolysis/annulation. The notable features of this method include C-H acetoxylation using NH-indole as the intrinsic directing group, high functional group compatibility, and construction of indole-fused medium-sized rings.

Indole - a promising pharmacophore in recent antiviral drug discovery

The bicyclic molecule indole has been in the limelight because of its numerous pharmacological potencies. It is used as an excellent scaffold in drug discovery of medicinal drugs such as antimicrobials, anticancer agents, antihypertensives, anti-proliferative agents and anti-inflammatory agents. In spite of its diverse therapeutic activity, it is used as a key pharmacophore in synthesizing the most potent biological agents. Besides, viral infections are ubiquitous and their prevention and cure have become a great challenge. In this regard, the design of indole-containing antiviral drugs is accomplished to combat viral infections. A lot of research is being carried out towards antiviral drug discovery by many researchers round the clock. Herein, the antiviral activity of recently discovered indole scaffolds is compiled and critically evaluated to give a meaningful summary. In addition, the structure-activity relationship of remarkable antiviral agents is discussed. Also, the structural motifs attributed to noteworthy antiviral properties are highlighted to guide future antiviral research.

QSAR studies on hepatitis C virus NS5A protein tetracyclic inhibitors in wild type and mutants by CoMFA and CoMSIA

Several 3D-QSAR models were built based on 196 hepatitis C virus (HCV) NS5A protein inhibitors. The bioactivity values EC₉₀ for three types of inhibitors, the wild type (GT1a) and two mutants (GT1a Y93H and GT1a L31V), were collected to build three datasets. The programs OMEGA and ROCS were used for generating conformations and aligning molecules of the dataset, respectively. Each dataset was randomly divided into a training set and a test set three times to reduce the contingency of only one random selection. QSAR models were computed by comparative molecular field analysis (CoMFA) and comparative molecular similarity indices analysis (CoMSIA). For the datasets GT1a, GT1a Y93H, and GT1a L31V, the best models CoMFA-INDX, CoMSIA-SEHA, and CoMSIA-SEHA showed an r² value of 0.682 ± 0.033, 0.779 ± 0.036, and 0.782 ± 0.022 on the test sets, respectively. From the contour maps of the three best models, we summarized the favourable and unfavourable substituents on the tetracyclic core, the Z group, the proline group, and the valine group of inhibitors. We guessed the mutants could change the electrostatic surfaces of the wild type active pocket. In addition, we used ECFP analyses to find important substructures and could intuitively understand the results from QSAR models.

In Vitro Antiviral Profile of Ruzasvir, a Potent and Pangenotype Inhibitor of Hepatitis C Virus NS5A

Inhibition of NS5A has emerged as an attractive strategy to intervene in hepatitis C virus (HCV) replication. Ruzasvir (formerly MK-8408) was developed as a novel NS5A inhibitor to improve upon the potency and barrier to resistance of early compounds. Ruzasvir inhibited HCV RNA replication with 50% effective concentrations (EC50s) of 1 to 4 pM in Huh7 or Huh7.5 cells bearing replicons for HCV genotype 1 (GT1) to GT7. The antiviral activity was modestly (10-fold) reduced in the presence of 40% normal human serum. The picomolar potency in replicon cells extended to sequences of clinical isolates available in public databases that were synthesized and tested as replicons. In GT1a, ruzasvir inhibited common NS5A resistance-associated substitutions (RASs), with the exception of M28G. De novo resistance selection studies identified pathways with certain amino acid substitutions at residues 28, 30, 31, and 93 across genotypes. Substitutions at position 93 were more common in GT1 to -4, while changes at position 31 emerged frequently in GT5 and -6. With the exception of GT4, the reintroduction of selected RASs conferred a ≥100-fold potency reduction in the antiviral activity of ruzasvir. Common RASs from other classes of direct-acting antiviral agents (DAAs) did not confer cross-resistance to ruzasvir. The interaction of ruzasvir with an NS3/4A protease inhibitor (grazoprevir) and an NS5B polymerase prodrug (uprifosbuvir) was additive to synergistic, with no evidence of antagonism or cytotoxicity. The antiviral profile of ruzasvir supported its further evaluation in human trials in combination with grazoprevir and uprifosbuvir.

Discovery of MK-6169, a Potent Pan-Genotype Hepatitis C Virus NS5A Inhibitor with Optimized Activity against Common Resistance-Associated Substitutions

We describe the discovery of MK-6169, a potent and pan-genotype hepatitis C virus NS5A inhibitor with optimized activity against common resistance-associated substitutions. SAR studies around the combination of changes to both the valine and aminal carbon region of elbasvir led to the discovery of a series of compounds with substantially improved potency against common resistance-associated substitutions in the major genotypes, as well as good pharmacokinetics in both rat and dog. Through further optimization of key leads from this effort, MK-6169 (21) was discovered as a preclinical candidate for further development.

Discovery of Ruzasvir (MK-8408): A Potent, Pan-Genotype HCV NS5A Inhibitor with Optimized Activity against Common Resistance-Associated Polymorphisms

We describe the research that led to the discovery of compound 40 (ruzasvir, MK-8408), a pan-genotypic HCV nonstructural protein 5A (NS5A) inhibitor with a "flat" GT1 mutant profile. This NS5A inhibitor contains a unique tetracyclic indole core while maintaining the imidazole-proline-valine Moc motifs of our previous NS5A inhibitors. Compound 40 is currently in early clinical trials and is under evaluation as part of an all-oral DAA regimen for the treatment of chronic HCV infection.

Discovery of Chromane Containing Hepatitis C Virus (HCV) NS5A Inhibitors with Improved Potency against Resistance-Associated Variants

The discovery of potent and pan-genotypic HCV NS5A inhibitors faces many challenges including the significant diversity among genotypes, substantial potency shift conferred on some key resistance-associated variants, inconsistent SARs between different genotypes and mutants, and the lacking of models of inhibitor/protein complexes for rational inhibitor design. As part of ongoing efforts on HCV NS5A inhibition at Merck, we now describe the discovery of a novel series of chromane containing NS5A inhibitors. SAR studies around the "Z" group of the tetracyclic indole scaffold explored fused bicyclic rings as alternates to the phenyl group of elbasvir (1, MK-8742) and identified novel chromane and 2,3-dihydrobenzofuran derivatives as "Z" group replacements offered good potency across all genotypes. This effort, incorporating the C-1 fluoro substitution at the tetracyclic indole core, led to the discovery of a new series of NS5A inhibitors, such as compounds 14 and 25-28, with significantly improved potency against resistance-associated variants, such as GT2b, GT1a Y93H, and GT1a L31V. Compound 14 also showed reasonable PK exposures in preclinical species (rat and dog).

Structure-activity relationships of proline modifications around the tetracyclic-indole class of NS5A inhibitors

We describe the impact of proline modifications, in our tetracyclic-indole based series of nonstructural protein 5A (NS5A) inhibitors, to their replicon profiles. This work identified NS5A inhibitors with an improved and flattened resistance profiles.

Substituted tetracyclic indole core derivatives of HCV NS5A inhibitor MK-8742

As part of an ongoing effort in NS5A inhibition at Merck we now describe our efforts for introducing substitution around the tetracyclic indole core of MK-8742. Fluoro substitution on the core combined with the fluoro substitutions on the proline ring improved the potency against GT1a Y93H significantly. However, no improvement on GT2b potency was achieved. Limiting the fluoro substitution to C-1 of the tetracyclic indole core had a positive impact on the potency against the resistance associated variants, such as GT1a Y93H and GT2b, and the PK profile as well. Compounds, such as 62, with reduced potency shifts between wild type GT1a to GT2b, GT1a Y93H, and GT1a L31V were identified.

Alternative core development around the tetracyclic indole class of HCV NS5A inhibitors

Herein, we describe our research efforts to develop unique cores in molecules which function as HCV nonstructural protein 5A (NS5A) inhibitors. In particular, various fused tetracyclic cores were identified which showed genotype and mutant activities comparable to the indole-based tetracyclic core.

Aryl or heteroaryl substituted aminal derivatives of HCV NS5A inhibitor MK-8742

Herein we describe our research efforts around the aryl and heteroaryl substitutions at the aminal carbon of the tetracyclic indole-based HCV NS5A inhibitor MK-8742. A series of potent NS5A inhibitors are described, such as compounds 45-47, 54, 56, and 65, which showed improved potency against clinically relevant and resistance associated HCV variants. The improved potency profiles of these compounds demonstrated an SAR that can improve the potency against GT2b, GT1a Y93H, and GT1a L31V altogether, which was unprecedented in our previous efforts in NS5A inhibition.