Poseltinib is an orally active, selective, and irreversible Bruton's tyrosine kinase (BTK) inhibitor, exhibiting a half-maximal inhibitory concentration (IC 50) of 1.95 nM. It demonstrates 0.3, 2.3, and 2.4-fold greater selectivity for BTK over BMX, TEC, and TXK, respectively. This compound covalently binds to BTK's active site at the cysteine 481 residue, effectively inhibiting signaling pathways mediated by the B cell receptor (BCR), Fc receptor (FcR), and Toll-like receptor (TLR).