(S)-Sabutoclax ((S)-BI-97C1), an optically pure apogossypol derivative, is pan-active inhibitor of antiapoptotic B-cell lymphoma/leukemia-2 ( Bcl-2 ) family proteins. (S)-Sabutoclax (Compound II) inhibits the binding of BH3 peptides to Bcl-XL , Bcl-2 , Mcl-1 , and Bfl-1 with IC 50 values of 0.31, 0.32, 0.20, and 0.62 μM, respectively. (S)-Sabutoclax also potently inhibits cell growth of human prostate cancer , lung cancer , and lymphoma cell lines with EC 50 values of 0.13, 0.56, and 0.049 μM, respectively. (S)-Sabutoclax can be used for the research of apoptosis-based therapies against cancer.