Selectively inhibits heat shock protein 90 (Hsp90). Binds to the ATP site of Hsp90 (Kd = 1.2 μM) and inhibits its chaperone activity. Consequently inhibits activities of oncogenic kinases (e.g. src, Raf), p53 and steroid receptors. Demonstrates antiproliferative effect on breast cancer stem-like cells. Purity 98%. MW (observed): 560.64