Cyclin-dependent kinases (cdk) have recently raised considerable interest in view of their essential role in the regulation of the cell division cycle. The structure-activity relationships of cdk inhibition showed that the 1, 3, and 7 positions of the purine ring must remain free, probably for a direct interaction, in which it behaves as a hydrogen bond acceptor. Olomoucine (6-(benzylamino)-2-[(2-hydroxyethyl) amino]-9-methylpurine, OC), roscovitine ...