An orally bioavailable diaminopyrimidine cyclin-dependent kinase inhibitor (CDKI) with potential antineoplastic activity. CDKI R547 selectively binds to and inhibits CDKs, especially CDK1/cyclin B, CDK2/cyclin E, and CDK4/cyclin D1. The inhibition of CDKs results in cell cycle arrest, inhibition of tumor cell proliferation, and induction of apoptosis. Through CDK inhibition, this agent also reduces phosphorylation of the retinoblastoma (Rb) protein, thus preventing activation of transcription factor E2F and so further suppressing tumor cell proliferation. CDKs are ATP-dependent serine/threonine kinases that are important regulators of cell cycle progression and are frequently overexpressed in tumor cells.