MW: 560.6. Geldanamycin is a small molecule produced by fermentation. Glendanamycin (GA), a benzoquinone ansamycin antibiotic, interferes with the action of Hsp90 leading to degradation of Hsp90 client proteins. GA itself however has undesirable properties such as poor aqueous solubility and liver toxicity; therefore, numerous analogs have been synthesized, such as 17-AAG(1). 17-AAG is an HSP-90 inhibitor that displays a 100-fold higher affinity for HSP-90 derived from tumor cells compared to HSP-90 from normal cells(2). 17-AAG inhibits Akt activation and expression in tumors and synergizes with a number of antitumor agents such as taxol(3), cisplatin(4) and UCN-01 (400 nM 17-AAG, U937 cells)(5).