BCPyr is a PROTAC-class BTK degrader ( DC 50 = 800 nM). BCPyr consists of a PROTAC target protein ligand (red part) BTK ligand 11 , an E3 ubiquitin ligase ligand (blue part) E3 ligase Ligand 20 , and a PROTAC linker (black part) (5-(Bromomethyl)pyrazin-2-yl)methanol. E3 ubiquitin ligase+linker can form E3 Ligase Ligand-linker Conjugate 146.