Anticancer agent 128 (compound 1) is an IAP inhibitor that covalently targets the BIR3 domains of XIAP , cIAP1 , and cIAP2. Anticancer agent 128 targets the BIR3 domains of XIAP , cIAP1 , and cIAP2 with IC 50 s of 24.9 nM, 19.3 nM, and 10.3 nM, respectively.