HDAC6-IN-17 (compound 5b) is a potent HDAC6 inhibitor with IC 50 values of 150 nM, 1400 nM, and 2300 nM for HDAC6 , HDAC8 , and HDAC4 , respectively. HDAC6-IN-17 has cytotoxic activity on human cancer cell lines. HDAC6-IN-17 can be used in research of cancer.