Aminocoumarin antibiotics,such as novobiocin and clorobiocin,represent a weak but unique class of Hsp90 inhibitors that bind to the ATP-binding site located within the C-terminal domain of the protein.Previous studies unveiled that simplified analogues of these natural products exhibited significantly improved protein binding affinities,but not antiproliferative activities in cancer cells.We report herein that replacement of the 3-OH in the noviose moiety with an amino group would provide a useful solution to this problem.