New Pyrazolobenzothiazine Derivatives as Hepatitis C Virus NS5B Polymerase Palm Site I Inhibitors

J Med Chem. 2014 Apr 24;57(8):3247-62. doi: 10.1021/jm401688h. Epub 2014 Apr 2.


We have previously identified the pyrazolobenzothiazine scaffold as a promising chemotype against hepatitis C virus (HCV) NS5B polymerase, a validated and promising anti-HCV target. Herein we describe the design, synthesis, enzymatic, and cellular characterization of new pyrazolobenzothiazines as anti-HCV inhibitors. The binding site for a representative derivative was mapped to NS5B palm site I employing a mutant counterscreen assay, thus validating our previous in silico predictions. Derivative 2b proved to be the best selective anti-HCV derivative within the new series, exhibiting a IC50 of 7.9 μM against NS5B polymerase and antiviral effect (EC50 = 8.1 μM; EC90 = 23.3 μM) coupled with the absence of any antimetabolic effect (CC50 > 224 μM; SI > 28) in a cell based HCV replicon system assay. Significantly, microscopic analysis showed that, unlike the parent compounds, derivative 2b did not show any significant cell morphological alterations. Furthermore, since most of the pyrazolobenzothiazines tested altered cell morphology, this undesired aspect was further investigated by exploring possible perturbation of lipid metabolism during compound treatment.

Publication types

  • Research Support, N.I.H., Extramural
  • Research Support, Non-U.S. Gov't

MeSH terms

  • Antiviral Agents / chemical synthesis*
  • Antiviral Agents / pharmacology
  • Binding Sites
  • Drug Design
  • Hepacivirus / drug effects
  • Humans
  • Pyrazoles / chemical synthesis*
  • Pyrazoles / pharmacology
  • Structure-Activity Relationship
  • Viral Nonstructural Proteins / antagonists & inhibitors*


  • Antiviral Agents
  • NS-5 protein, hepatitis C virus
  • Pyrazoles
  • Viral Nonstructural Proteins