Selective inhibitor of casein kinase (CK) 1δ (IC50 values are 290 nM, 1.3 μM and 2.5 μM for CK1δ, ε and α); displays no inhibitory activity at CK2. Inhibits CK1δ-dependent phosphorylation and degradation of PER1 protein. Shown to lengthen the circadian period in U2OS cells, with minimal effect on amplitude. Purity 98%. MW (observed): 316.81