ITF5924 (compound 1) is a potent and highly selective HDAC6 inhibitor with an IC₅₀ of 7.7 nM. ITF5924 shows greater than 104-fold selectivity for HDAC6 over all other HDAC subtypes. ITF5924 containing a difluoromethyl-1,3,4-oxadiazole (DFMO) moiety is slow-binding substrate analog of HDAC6 that undergo an enzyme-catalyzed ring opening reaction, forming a tight and long-lived enzyme-inhibitor complex^[1].