A series of N-phenyl-imidazo [4, 5-b] pyridin-2-amines, 4-indazolyl-N-phenylpyrimidin-2- amines and N-phenyl-4-pyrazolo [3, 4-b] pyridin-pyrimidin-2-amines have been synthesized. Their anti-proliferative activities were tested in HCT-116 human colon carcinoma and MCF-7 breast carcinoma cell lines. Many exhibited potent anti-proliferative and CDK9 inhibitory activities. A lead compound 18b demonstrated the ability to reduce the level of Mcl-1 anti- ...