Selective, Hsp90 competitive inhibitor (Ki = 1.7 nM). Displays no significant activity at a range of ATP-binding kinases or Na+K+ ATPase. Induces degradation of HER-2 in vitro (EC50 = 38 nM in MCF-7 cells). Inhibits growth and promotes cell death in a variety of human tumor cells. Orally bioavailable. Purity 98%. MW (observed): 318.76