A cell permeable inhibitor that blocks the binding of BH3 peptides to Bcl-xL, inducing apoptosis; inhibits interactions of BH3 domain-containing proteins with Bcl-xL, Bcl-2, and Bcl-W, inducing apoptosis in Bcl-2 or Bcl-W expressing cells with Ki values of 43.4 and 124 μM, respectively