Purinylpyridinylamino-based DFG-in/αC-helix-out B-Raf inhibitors: Applying mutant versus wild-type B-Raf selectivity indices for compound profiling

Bioorg Med Chem. 2016 May 15;24(10):2215-34. doi: 10.1016/j.bmc.2016.03.055. Epub 2016 Apr 13.


One of the challenges for targeting B-Raf(V600E) with small molecule inhibitors had been achieving adequate selectivity over the wild-type protein B-Raf(WT), as inhibition of the latter has been associated with hyperplasia in normal tissues. Recent studies suggest that B-Raf inhibitors inducing the 'DFG-in/αC-helix-out' conformation (Type IIB) likely will exhibit improved selectivity for B-Raf(V600E). To explore this hypothesis, we transformed Type IIA inhibitor (1) into a series of Type IIB inhibitors (sulfonamides and sulfamides 4-6) and examined the SAR. Three selectivity indices were introduced to facilitate the analyses: the B-Raf(V600E)/B-Raf(WT) biochemical ((b)S), cellular ((c)S) selectivity, and the phospho-ERK activation ((p)A). Our data indicates that α-branched sulfonamides and sulfamides show higher selectivities than the linear derivatives. We rationalized this finding based on analysis of structural information from the literature and provided evidence for a monomeric B-Raf-inhibitor complex previously hypothesized to be responsible for the desired B-Raf(V600E) selectivity.

Keywords: B-Raf; C-helix; DFG; Inhibitor; Selectivity; Sulfonamide; Wild-type; v600e.

MeSH terms

  • Amination
  • Crystallography, X-Ray
  • Drug Design
  • Humans
  • Models, Molecular
  • Point Mutation
  • Protein Conformation, alpha-Helical / drug effects
  • Protein Kinase Inhibitors / chemistry*
  • Protein Kinase Inhibitors / pharmacology*
  • Proto-Oncogene Proteins B-raf / antagonists & inhibitors*
  • Proto-Oncogene Proteins B-raf / chemistry
  • Proto-Oncogene Proteins B-raf / genetics
  • Proto-Oncogene Proteins B-raf / metabolism
  • Purines / chemistry*
  • Purines / pharmacology*
  • Pyridines / chemistry*
  • Pyridines / pharmacology*
  • Structure-Activity Relationship


  • Protein Kinase Inhibitors
  • Purines
  • Pyridines
  • Proto-Oncogene Proteins B-raf