Synthesis and biological evaluations of pyrazolo[3,4-d]pyrimidines as cyclin-dependent kinase 2 inhibitors

A series of 1,4,6-trisubstituted pyrazolo[3,4-d]pyrimidines 15-19, 30-38 capable of selectively inhibiting CDK2 activity were synthesized by derivatization at C-4, C-6 and N-1 with various amines and lower alkyl groups. For above synthetic compounds, biological evaluation was carried out and structure-activity relationship was examined. In our series, 4-anilino compounds exhibited better CDK2 inhibitory activity and antitumor activity compared to 4-benzyl compounds. The compounds 33a,b having a 3-fluoroaniline group at C-4 showed comparable or superior CDK2 inhibitory activity to those of olomoucine and roscovitine as reference compounds. In general, the unsubstituted compounds (30a,b, 33a,b, 36a,b) at N-1 possessed higher potency than the substituted compounds (32a,b, 34a,b) for the CDK2 inhibitory activity. As for EGFR inhibitory activity, most compounds didnot have a significant activity. The compounds 32a,b exhibited potent cell growth inhibitory activity against human cancer cell lines, but their CDK2 inhibitory activities were slightly poorer than olomoucine.