Novel inhibitor of heat shock protein 90 (Hsp90) ATPase activity (IC50 = 5.7 μM) that displays selectivity over human Hsp72 and topoisomerase II. Inhibits proliferation of HCT116 human colon tumor cells and produces upregulation of Hsp70 and downregulation of c-Raf and cdk4. More soluble than 17-AAG (Cat. No. 1515) and is independent of NQO1/DT-diaphorase and P-glycoprotein expression.