Fragment-Based Design, Synthesis, and Biological Evaluation of 1-Substituted-indole-2-carboxylic Acids as Selective Mcl-1 Inhibitors.

Based on a known selective Mcl-1 inhibitor, 6-chloro-3-(3-(4-chloro-3,5-dimethylphenoxy)propyl)-1H-indole-2-carboxylic acid, we applied a fragment-based approach to obtain new molecules that extended into the p1 pocket of the BH3 groove and then exhibited binding selectivity for the Mcl-1 over the Bcl-2 protein. After we deconstructed the 1H-indole-2-carboxylic acid from the parental molecule, a benzenesulfonyl was substituted at the 1-position to adopt a geometry preferred for accessing the p1 pocket according to the binding mode of the parental molecule identified by X-ray crystallography. A linear relationship between the free energy of ligand binding (ΔG) and the count of non-hydrogen heavy atoms (HAC) was maintained during the molecular growing to occupy the p1 pocket. Finally, we not only obtained compound 12 with a 7.5-fold selectivity to Mcl-1 (Ki  = 0.48 µM by fluorescence polarization) over Bcl-2 (Ki  = 3.6 µM), but also provided evidence that additional occupation of the p1 pocket is more favorable for Mcl-1 than for Bcl-2 binding, and contributes more to Mcl-1 inhibition than occupation of the p2 pocket. Compound 12 exhibited a selective killing ability on Mcl-1-dependent cancer cells.