Ansamycin antibiotic compound that inhibits Hsp90 activity (IC50 = 2 μM) by binding to the ATP-binding site. Exhibits antitumor and cytocidal activities (IC50 ~ 0.4 μM) by causing degradation of key oncogenic client proteins such as ErbB2 and cRaf1. Displays higher affinity and potency than geldanamycin (Cat. No. 1368). MW (observed): 558.67.