PF-05251749 (CK1-IN-2, Compound Nr.4) is a potent, selective, brain-penetrant inhibitor of Casein Kinase 1 (CK1) in a concentration-dependent manner, with IC50 values of 33.1 nM for CK1d and 51.6 nM for CK1e. It also functions as an inducer of CYP3A, with the potential to treat circadian rhythm disruptions in Alzheimer’s and Parkinson’s diseases.