Histone deacetylase inhibitors

A compound having a structure of formula (I), or a pharmaceutically acceptable salt thereof

• wherein
• ring A is a 4-7 membered saturated heterocycle containing one nitrogen ring atom or a 7-9 membered saturated bicyclic heterocycle containing one nitrogen ring atom;
• Z is O, NR3, S, SO, or SO2;
• R1 is H, C1-6alkyl, C1-6hydroxyalkyl, C(O)C1-6alkyl, C0-3alkylene-C3-10cycloalkyl, or saturated C0-3alkylene-C2-5heterocycle having 1 or 2 heteroatoms selected from O, S, N, and N(C1-4alkyl);
• R2 is H, F, Cl, or CH3;
• R3 is H, C1-6alkyl, C1-6haloalkyl, C0-3alkylene-C3-7cycloalkyl, C(O)C1-6-alkyl, or C(O)C0-3alkylene-C3-7cycloalkyl;
• and
• R4 is H or C1-3alkyl.