Novel pyrazolopyrimidines of formula (I):
are discussed. These pyrazolopyrimidines are capable of inhibiting the activity of cyclin-dependent kinases, most particularly cyclin-dependent kinase 1 (Cdk1), cyclin-dependent kinase 2 (Cdk2), and cyclin-dependent kinase 4 (Cdk4) and are thus useful, inter alia, in the treatment or control of cancer, in particular solid tumors. This invention also provides pharmaceutical compositions containing such compounds and to methods of treating or controlling cancer, most particularly the treatment or control of breast, lung, colon and prostate tumors.