Propargyl-PEG1-acid is a PEG-based PROTAC linker can be used in the synthesis of BTK-CRBN PROTACs Ibrutinib(HY-10997)-based PROTAC 4 and PROTAC 5. PROTAC 5 causes the degradation of BTK and induces the degradation of CSK, LYN, and LAT2 at 10 μM. Propargyl-PEG1-acid is a click chemistry reagent, it contains an Alkyne group and can undergo copper-catalyzed azide-alkyne cycloaddition (CuAAc) with molecules containing Azide groups.