Potent and selective monopolar spindle 1 (Mps1) kinase inhibitor (IC50 = 35 nM). Displays selectivity over 46 other kinases including Cdk1 and aurora kinase B. Interferes with chromosome alignment and overrides spindle assembly checkpoint. Inhibits the recruitment of Mad1, Mad2 and centromere protein E (CENP-E) to kinetochores. Purity 99%. MW (observed): 452.55