The present invention relates to oxopiperazines that mimic helix αB of the C-terminal transactivation domain of HIF1α. Also disclosed are pharmaceutical compositions containing these oxopiperazines and methods of using these oxopiperazines (e.g., to reduce gene transcription, treat or prevent disorders mediated by interaction of HIF1a with CREB-binding protein and/or p300, reduce or prevent angiogenesis in a tissue, induce apoptosis, and decrease cell survival and/or proliferation).