The invention provides novel compounds that are inhibitors of IAPs having the general formula: wherein X1, X2, X3, Y, A, R1, R2, R3, R4, R4′, R5, R5′, R6 and R6′ are as described herein. The compouds of the invention may be used to induce apoptosis in cells (or sensitise cells to apoptosis) in which IAPs are overexpressed or otherwise implicated in resistance to normal apoptotic processes. Accordingly, the compounds may be provided in pharmaceutically acceptable compositions and used for the treatment cancers.