Structure-based strategy was employed to design flavonoid compounds to mimic the Bim BH3 peptide as a new class of inhibitors of the anti-apoptotic Bcl-2 proteins. The most potent compound, 4 (BI-33), binds to Bcl-2 and Mcl-1 with Ki values of 17 and 18 nM, respectively. Compound 4 inhibits cell growth in the MDA-MB-231 breast cancer cell line with an IC50 value of 110 nM and effectively induces apoptosis.