The design, synthesis and evaluation of novel thieno [2, 3-d] pyrimidin-4-yl hydrazone analogues as cyclin-dependent kinase 4 (CDK4) inhibitor are described. Focusing on the optimization of the heteroaryl moiety at the hydrazone with substituted phenyl groups, 4- [(methylamino) methyl] benzaldehyde (22) and 5-isoindolinecarbaldehyde (24)(6-tert- butylthieno [2, 3-d] pyrimidin-4-yl) hydrazone derivatives have been identified. In this ...