Ibrutinib is a potent and highly selective Brutons tyrosine kinase (Btk) inhibitor with IC50 of 0.5 nM in cell-free assays, modestly potent to Bmx, CSK, FGR, BRK, HCK, less potent to EGFR, Yes, ErbB2, JAK3, etc. Ibrutinib is applicable as a Btk ligand in the synthesis of a series of PROTACs including P13I.