Selective histone deacetylase inhibitors for the treatment of human disease

A method of treating cancer by inhibiting histone deacetylase (HDAC) protein in a patient in need thereof, wherein the treatment comprises administering a therapeutically effective amount of an HDAC inhibitor of formula (Ia) or formula (Ib), or a pharmaceutically acceptable salt, solvate, hydrate, cocrystal, or prodrug thereof:

• wherein in formula (Ia) and formula (Ib):
• R1 is a substituent selected from H and optionally substituted alkyl and aryl;
• R2 is a substituent selected from H and optionally substituted alkyl and aryl;
• R3 is a substituent selected from H and optionally substituted alkyl and aryl;
• and
• X is a substituent selected from —N(R4)C(O)—, —C(O)N(R4)—, —S(O)2N(R4)—, —N(R4)S(O)2—,
• where R4 is a substituent selected from H and optionally substituted alkyl and aryl, and
• n is an integer from 5 to 7.