The hydrochloride salt of a small-molecule inhibitor of IAP (Inhibitor of Apoptosis Protein) family proteins with potential antineoplastic activity. IAP inhibitor HGS1029 selectively inhibits the biological activity of IAP proteins, which may restore apoptotic signaling pathways; this agent may work synergistically with cytotoxic drugs to overcome tumor cell resistance to apoptosis. IAPs are overexpressed by many cancer cell types, suppressing apoptosis by binding and inhibiting active caspases-3, -7 and -9 via their BIR (baculoviral lAP repeat) domains.