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 3 (GSK5852), a molecule which entered clinical trials in subjects infected with HCV in 2011, is included.

Rapid clinical progress of hepatitis C virus (HCV) replication inhibitors, including these selecting for resistance in the NS5A region (NS5A inhibitors), promises to revolutionize HCV treatment. Herein, we describe our explorations of diverse spiropyrrolidine motifs in novel NS5A inhibitors and a proposed interaction model. We discovered that the 1,4-dioxa-7-azaspiro[4.4]nonane motif in inhibitor 41H (GSK2236805) supported high potency against genotypes 1a and 1b as well as in genotype 1b L31V and Y93H mutants. Consistent with this, 41H potently suppressed HCV RNA in the 20-day RNA reduction assay. Pharmacokinetic and safety data supported further progression of 41H to the clinic.

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 28 that displays high selectivity for PI4KIIIα and potently inhibits HCV replication in vitro.