MRL-SYKi is a chemical probe with high selectivity and potent activity against spleen tyrosine kinase (SYK) . MRL-SYKi potently binds to SYK gain-of-function (GoF) variants (SYK (S550Y), SYK (S550F), and SYK (P342T) ) in intact live cells, with IC50 values of 2.1 nM, 14 nM, and 4.6 nM respectively in digitonin-permeabilized cell assays. MRL-SYKi effectively reduces catalytic activity (IC50 = 63 nM for SYK (S550F) and 95 nM for SYK (P342T) in PhosphoSens SOX peptide assays) . MRL-SYKi can decrease the phosphorylation level of SYK (S550Y) at Y525/526 in SW480 cells. MRL-SYKi can be used for the study of inflammation[1].