A semi-synthetic derivative of Geldanamycin (Cat. No. 1564-1,5) that displays greater stability and lower in vivo toxicity compared to Geldanamycin. Binds to Heat shock protein 90 (Hsp90) (EC₅₀ = 7.2 µM) in a manner similar to geldanamycin. Exhibits 100-fold higher affinity for tumor-derived Hsp90 over normal cells. Also inhibits Akt activation and HER2 expression in tumor cells.