Cyclin-dependent kinase 5 (CDK5) and Casein kinase 1 (CK1) are both involved in the hyperphosphorylation of the Tau protein and in the amyloid-b production, the two major hallmarks of Alzheimer's disease. In the present paper, we describe the synthesis and biological evaluation of new series of 2,6,9-trisubstituted purines derived from DRF53, a dual specificity inhibitor of the kinase activity of CDK5 (IC50 = 80 nM) and CK1 (IC50 = 10 nM), and are able to prevent in a dose-dependent manner the CK1-dependent production of amyloid-b in a cell model. Several molecules (e.g., 6e, 6g, 7c) displayed potent kinase inhibitory activities against CDK5 and CK1 (IC50 values ranging from 20 to 50 nM) among which a selective inhibitor of CK1 has been identified (5a, IC50 = 60 nM). In addition, some compounds exhibit submicromolar activities against DYRK1A (dual specificity, tyrosine phosphorylation regulated kinase 1A), a kinase involved in Down syndrome and Alzheimer's disease (6g, IC50 = 510 nM).