Imidazopyridazine Hepatitis C Virus Polymerase Inhibitors. Structure–Activity Relationship Studies and the Discovery of a Novel, Traceless Prodrug Mechanism

By reducing the basicity of the core heterocycle in a series of HCV NS5B inhibitors, the hERG liability was reduced. The SAR was then systematically explored in order to increase solubility and enable dose escalation while retaining potency. During this exploration, a facile decarboxylation was noted and was exploited as a novel prodrug mechanism. The synthesis and characterization of these prodrugs and their utilization in chronic toxicity studies are presented

Rational Design of Potent Non-Nucleoside Inhibitors of HIV‑1 Reverse Transcriptase

A new series of non-nucleoside reverse transcriptase inhibitors based on an imidazole-amide biarylether scaffold has been identified and shown to possess potent antiviral activity against HIV-1, including the NNRTI-resistant Y188L mutated virus. X-ray crystallography of inhibitors bound to reverse transcriptase, including a structure of the Y188L RT protein, was used extensively to help identify and optimize the key hydrogen-bonding motif. This led directly to the design of compound <b>43</b> that exhibits remarkable antiviral activity (EC₅₀ < 1 nM) against a wide range of NNRTI-resistant viruses and a favorable pharmacokinetic profile across multiple species

Discovery of Selective Small Molecule Type III Phosphatidylinositol 4‑Kinase Alpha (PI4KIIIα) Inhibitors as Anti Hepatitis C (HCV) Agents

Hepatitis C virus (HCV) assembles many host cellular proteins into unique membranous replication structures as a prerequisite for viral replication, and PI4KIIIα is an essential component of these replication organelles. RNA interference of PI4KIIIα results in a breakdown of this replication complex and cessation of HCV replication in Huh-7 cells. PI4KIIIα is a lipid kinase that interacts with the HCV nonstructural 5A protein (NS5A) and enriches the HCV replication complex with its product, phosphoinositol 4-phosphate (PI4P). Elevated levels of PI4P at the endoplasmic reticulum have been linked to HCV infection in the liver of HCV infected patients. We investigated if small molecule inhibitors of PI4KIIIα could inhibit HCV replication in vitro. The synthesis and structure–activity relationships associated with the biological inhibition of PI4KIIIα and HCV replication are described. These efforts led directly to identification of quinazolinone <b>28</b> that displays high selectivity for PI4KIIIα and potently inhibits HCV replication in vitro

Imidazo[1,2-<i>a</i>]pyridines That Directly Interact with Hepatitis C NS4B: Initial Preclinical Characterization

A series of imidazo­[1,2-<i>a</i>]­pyridines which directly bind to HCV Non-Structural Protein 4B (NS4B) is described. This series demonstrates potent <i>in vitro</i> inhibition of HCV replication (EC₅₀ < 10 nM), direct binding to purified NS4B protein (IC₅₀ < 20 nM), and an HCV resistance pattern associated with NS4B (H94N/R, V105L/M, F98L) that are unique among reported HCV clinical assets, suggestive of the potential for additive or synergistic combination with other small molecule inhibitors of HCV replication

Hepatitis C Replication Inhibitors That Target the Viral NS4B Protein

We describe the preclinical development and in vivo efficacy of a novel chemical series that inhibits hepatitis C virus replication via direct interaction with the viral nonstructural protein 4B (NS4B). Significant potency improvements were realized through isosteric modifications to our initial lead <b>1a</b>. The temptation to improve antiviral activity while compromising physicochemical properties was tempered by the judicial use of ligand efficiency indices during lead optimization. In this manner, compound <b>1a</b> was transformed into (+)-<b>28a</b> which possessed an improved antiviral profile with no increase in molecular weight and only a modest elevation in lipophilicity. Additionally, we employed a chimeric “humanized” mouse model of HCV infection to demonstrate for the first time that a small molecule with high in vitro affinity for NS4B can inhibit viral replication in vivo. This successful proof-of-concept study suggests that drugs targeting NS4B may represent a viable treatment option for curing HCV infection

Discovery of a Potent Boronic Acid Derived Inhibitor of the HCV RNA-Dependent RNA Polymerase

A boronic acid moiety was found to be a critical pharmacophore for enhanced in vitro potency against wild-type hepatitis C replicons and known clinical polymorphic and resistant HCV mutant replicons. The synthesis, optimization, and structure–activity relationships associated with inhibition of HCV replication in a subgenomic replication system for a series of non-nucleoside boron-containing HCV RNA-dependent RNA polymerase (NS5B) inhibitors are described. A summary of the discovery of <b>3</b> (GSK5852), a molecule which entered clinical trials in subjects infected with HCV in 2011, is included