A series of tetrahydro-β-carboline (THβC)-based hydroxamic acids were rationally designed and synthesized as novel selective HDAC6 inhibitors (sHDAC6is) by the application of scaffold hopping strategy. Several THβC analogues were highly potent (IC(50) < 5 nM) and selective against HDAC6 enzyme and exhibited good antiproliferative activity against human multiple myeloma (MM) cell. Molecular docking interpreted the structure activity relationship (SAR). Target engagement of HDAC6 was confirmed …