Further development of this series using
combinatorial chemistry techniques led to roscovitine
(Selicicib) (88; Scheme 17), and finally to purvalanol A (89;
Scheme 17) and purvalanol B (90; Scheme 17). Like
flavopiridol, olomucine and roscovitine are very potent
inhibitors of CDK-7 and -9. The purvalanols demonstrated
improved potency, with IC50 values in the 4-40 nM range,
compared to 450 nM for roscovitine