CHK1-IN-12 (Compound example 1-5) is a highly selective and orally active checkpoint kinase 1 (CHK1) inhibitor, demonstrating an in vitro enzyme IC50 of ≤10 nM and a cellular IC50 of ≤50 nM. This compound suppresses the phosphorylation activity of CHK1 kinase, disrupts DNA damage response pathways, and induces tumor cell cycle arrest and apoptosis. CHK1-IN-12 shows promise for cancer research applications.