Cell-permeable. An oxindole derivative that acts as a potent, reversible, and ATP-competitive Spleen tyrosine kinase (Syk) inhibitor (IC₅₀ = 14 nM). Has been shown to effectively inhibit FcεRI-mediated degranulation in the rat basophilic leukemia cell line, RBL-2H3 (EC₅₀ = 313 nM).