An inhibitor of SETD8 (IC50 = 0.5 µM) that suppresses monomethylation of H4K20 in vitro; less potently inhibits Cdk4 (IC50 = 6 µM for Cdk4/cyclin D1); suppresses the expression of Cdc7, resulting in an ATM-dependent checkpoint response and arrest of cell cycling in S phase.