Purity >98%. CI-994 is an inhibitor of class I HDACs displaying IC50 values of 0.9, 0.9, 1.2, and >20 μM when screened in vitro against recombinant human HDAC 1, 2, 3, and 8, respectively. CI-994 has a wide spectrum of antitumor activity, particularly in tumors normally refractory to conventional anticancer agents, in preclinical models both in vitro and in vivo and has advanced through phase I and II clinical trials in combination therapy treatments.