Purvalanol B is a cyclin-dependent kinase inhibitor with IC50 values of 6, 6, 9, > 10,000, and 6 nM for cdc2/cyclin B, cdk2/cyclin A, cdk2/cyclin E, cdk4/cyclin D1 and cdk5-p35 respectively.

In vitro inhibitory activity against Cyclin-dependent kinase 1-cyclin B complex from starfish oocytes is 6 nM (IC50). In addition to CDK1, p42/p44 MAPK were found to be two major purvalanol-interacting proteins in five different mammalian cell lines (CCL39, PC12, HBL100, MCF-7 and Jurkat cells), suggesting the generality of the purvalanol/p42/p44 MAPK interaction. When cells were treated with purvalanol, p42/p44 MAPK and CDK1 activities were inhibited in a dose-dependent manner. Furthermore, purvalanol inhibited the nuclear accumulation of p42/p44 MAPK, an event dependent on the catalytic activity of these kinases.