CHIR99021 (CT99021) is a glycogen synthase kinase 3β (GSK3β) inhibitor with IC50 less than 10 nM. Compared to other GSK-3 inhibitors, CHIR-99201 does not exhibit cross-reactivity against cyclin-dependent kinases (CDKs) with 350-fold selectivity toward GSK-3β compared to CDKs . Ref: Tighe A et al. BMC Cell Biol. 2007 Aug 14;8:3 Purity: Greater than 99% as determined by LC/MS analysis. LC/MS and/or NMR data available upon request. Biological Activity: In a cell-based assay measuring the activation of the TCF reporter gene, this compound gives EC50 of 50 nM.