Thalidomide -4-NH-PEG1-COO(t-Bu) is a t-Bu modified Thalidomide , which acts as a Cereblon ligand to recruit CRBN protein. The t-Bu protecting group at the end of Thalidomide -4-NH-PEG1-COO(t-Bu) can be removed under acidic conditions to participate in the synthesis of PROTAC molecules. Thalidomide -4-NH-PEG1-COO(t-Bu) is a key intermediate in the synthesis of CRBN-based PROTAC molecules.