Abstract: The present invention relates to compounds of formula (I), or pharmaceutically acceptable salts, solvates or prodrugs thereof, that bind to Inhibitor of Apoptosis Proteins (IAPs). The compounds of the invention may be used as diagnostic and therapeutic agents in the treatment of proliferative diseases, such as cancer, for promoting apoptosis in proliferating cells, and for sensitizing cells to inducers of apoptosis. The present invention furthermore provides a polymeric compound of formulas (VI) or (VII), comprising either at least two monomeric units of compounds of formula (I), or at least one monomeric unit of a compound of formula (I) and an entity E. The present invention further relates to pharmaceutical compositions comprising said compounds of formulas (I), (VI), and (VII) and the use of said compounds in medicine.