A cell-permeable thiazolyliminopyrogallol that selectively neutralizes Mcl-1, but not Bcl-XL, antiapoptotic activity, by directly targeting Mcl-1 BH3-binding site, effectively competing against Bid BH3 sequence for Mcl-1 binding (IC50 = 4.8 µM) without affecting Bcl-XL interaction with Bad or Bid BH3 sequence (IC50 >50 µM). Shown to induce caspase 3/7 activation and cell death in Mcl-1-, but not Bcl-XL-, dependent B-ALL cultures (6% vs. 82% survival, respectively, [MIM1] = 10 µM). In comparison, ABT-737 (Cat. No. 197333) affects only Bcl-XL-, but not Mcl-1-, dependent B-ALL cultures (0% vs. 98% survival, respectively, [ABT-737] = 10 µM). Neither MIM1 nor ABT-737 significantly affects the survival of wild-type (81% and 79% survival in the presence of 10 µM respective inhibitor) or Bax-/-Bak-/- MEF (93% and 84% survival in the presence of 10 µM respective inhibitor).