HL389-NHC2-PEG3-C2NH inhibits proliferation of cancer cells MDA-MB-231 and MCF-7, with IC 50 of 11.39 μM and 9.66 μM. HL389-NHC2-PEG3-C2NH can be utilized as a conjugate of an E3 ligase ligand and a linker, for the synthesis of PROTAC degrader HL435.