The present invention relates to oligooxopiperazines for reactivating p53. The oligooxopiperazines comprise two or three oxopiperazine rings and substantially mimic helix αB of the C-terminal transactivation domain of Hypoxia-Inducible Factor 1α. Methods of using the oligooxopiperazines are also disclosed. Exemplary oligooxopiperazines include those of Formula I below (wherein A, R1, R2, R3, R4, and B are as defined herein).