Convergent Synthesis of the NS5B Inhibitor GSK8175 Enabled by Transition Metal Catalysis

J Org Chem. 2019 Apr 19;84(8):4680-4694. doi: 10.1021/acs.joc.8b02269. Epub 2018 Oct 29.

Abstract

A convergent eight-stage synthesis of the boron-containing NS5B inhibitor GSK8175 is described. The previous route involves 13 steps in a completely linear sequence, with an overall 10% yield. Key issues include a multiday SNAr arylation of a secondary sulfonamide using HMPA as solvent, multiple functional group interconversions after all of the carbon atoms are installed (including a Sandmeyer halogenation), use of carcinogenic chloromethyl methyl ether to install a protecting group late in the synthesis, and an unreliable Pd-catalyzed Miyaura borylation as the penultimate step. We have devised an orthogonal approach using a Chan-Lam coupling between a halogenated aryl pinacol boronate ester and an aryl methanesulfonamide. This reaction is performed using a cationic Cu(I) precatalyst, which can be easily generated in situ using KPF6 as a halide abstractor. High-throughput screening revealed a new Pd catalyst system to effect the penultimate borylation chemistry using simple monodentate phosphine ligands, with PCyPh2 identified as optimal. Reaction progress analysis of this borylation indicated likely mass-transfer rate limitations under standard conditions using KOAc as the base. We have devised a K2CO3/pivalic acid system as an alternative, which dramatically outperforms the standard conditions. This new synthesis proceeds in eight stages with a 20% overall yield.

MeSH terms

  • Antiviral Agents / chemical synthesis
  • Antiviral Agents / chemistry
  • Antiviral Agents / pharmacology*
  • Borates / chemical synthesis
  • Borates / chemistry
  • Borates / pharmacology*
  • Boronic Acids / chemical synthesis
  • Boronic Acids / chemistry
  • Boronic Acids / pharmacology*
  • Catalysis
  • Molecular Structure
  • Palladium / chemistry*
  • Viral Nonstructural Proteins / antagonists & inhibitors*
  • Viral Nonstructural Proteins / metabolism

Substances

  • Antiviral Agents
  • Borates
  • Boronic Acids
  • GSK8175
  • Viral Nonstructural Proteins
  • Palladium
  • NS-5 protein, hepatitis C virus