TC-H 106, also known as Pimelic Diphenylamide 106, is a class I HDAC inhibitor, demonstrating no activity against class II HDACs. TC-H 106 is a slow, tight-binding inhibitor of HDACs 1, 2, and 3, although inhibition for these enzymes occurs through different mechanisms. TC-H 106 also has preference toward HDAC3 with K(i) of approximately 14 nm, 15 times lower than the K(i) for HDAC1. In comparison, the hydroxamate suberoylanilide hydroxamic acid does not discriminate between these enzymes and exhibits a fast-on/fast-off inhibitory mechanism.