5-Substituted 3-isopropyl-7-[4-(2-pyridyl)benzyl]amino-1(2)H-pyrazolo[4,3-d]pyrimidines with anti-proliferative activity as potent and selective inhibitors of cyclin-dependent kinases

Eur J Med Chem. 2016 Mar 3;110:291-301. doi: 10.1016/j.ejmech.2016.01.011. Epub 2016 Jan 18.


A series of 5-substituted 3-isopropyl-7-[4-(2-pyridyl)benzyl]amino-1(2)H-pyrazolo[4,3-d]pyrimidine derivatives was synthesized and evaluated for their cyclin-dependent kinase (CDK) inhibition activity. The most potent compounds contained various hydroxyalkylamines at the 5 position and possessed low nanomolar IC50 values for CDK2 and CDK5. Preliminary profiling of one of the most active compounds on a panel of 50 protein kinases revealed its high selectivity for CDKs. The compounds arrested cells in S and G2/M phases, and induced apoptosis in various cancer cell lines. Significant dephosphorylation of the C-terminus of RNA polymerase II and focal adhesion kinase (FAK), well-established substrates of CDKs, has been found in treated cells. Cleavage of PARP-1, down-regulation of Mcl-1 and activation of caspases correlated well with CDK inhibition and confirmed apoptosis as the primary type of cell death induced in cancer cells treated with the compounds in vitro. A comparison of known purine-based CDK inhibitor CR8 with its pyrazolo[4,3-d]pyrimidine bioisosteres confirmed that the novel compounds are more potent in cellular assays than purines. Therefore, pyrazolo[4,3-d]pyrimidine may emerge as a novel scaffold in medicinal chemistry and as a source of potent CDK inhibitors.

Keywords: Bioisostere; Cyclin-dependent kinase; Inhibitor; Selectivity.

Publication types

  • Research Support, Non-U.S. Gov't

MeSH terms

  • Antineoplastic Agents / chemistry*
  • Antineoplastic Agents / pharmacology*
  • Apoptosis / drug effects
  • Cell Cycle / drug effects
  • Cell Line, Tumor
  • Cell Proliferation / drug effects
  • Cyclin-Dependent Kinases / antagonists & inhibitors*
  • Cyclin-Dependent Kinases / metabolism
  • G2 Phase / drug effects
  • Humans
  • Neoplasms / drug therapy
  • Neoplasms / enzymology
  • Protein Kinase Inhibitors / chemistry*
  • Protein Kinase Inhibitors / pharmacology*
  • Pyrazoles / chemistry
  • Pyrazoles / pharmacology
  • Pyrimidines / chemistry*
  • Pyrimidines / pharmacology*


  • Antineoplastic Agents
  • Protein Kinase Inhibitors
  • Pyrazoles
  • Pyrimidines
  • Cyclin-Dependent Kinases