– FF2039 (compound 1j) is a PROTAC degrader specifically targeting HDAC1, HDAC6, and various subtypes of class I, IIa, and IIb HDACs. It induces cell cycle arrest and apoptosis, showing significant antiproliferative activity against both hematological and solid tumor cell lines. The IC50 values for FF2039 against HDAC1, HDAC2, HDAC4, and HDAC6 are 1.03, 2.15, 12.4, and 0.053 μM, respectively. FF2039 exhibits antiproliferative effects on solid tumors such as MM.1S, MDA-MB-231, and U-87MG, with EC50 values of 2.8, 28, and 30 μM, respectively.