Hit to Lead optimization of a novel class of squarate-containing polo-like kinases inhibitors.

A high throughput screening (HTS) hit, 1 (Plk1 Ki=2.2μM) was optimized and evaluated for the enzymatic inhibition of Plk-1 kinase. Molecular modeling suggested the importance of adding a hydrophobic aromatic amine side chain in order to improve the potency by a classic kinase H-donor–acceptor binding mode. Extensive SAR studies led to the discovery of 49 (Plk1 Ki=5 nM; EC50=1.05μM), which demonstrated moderate efficacy at 100mpk in a MiaPaCa tumor model, with no overt toxicity.