Compounds of formula (I), pharmaceutical compositions comprising compounds
of formula (I) and methods of inhibiting Hsp90 in a cell, treating or
preventing a proliferation disorder in a mammal and treating cancer in a
mammal comprising administering a compound of formula (I) to a patient or
a cell. ##STR00001## Variable R.sub.5 is an optionally substituted
heteroaryl; an optionally substituted 6 to 14-membered aryl; a bicyclic
9-member heterocycle optionally substituted at any substitutable nitrogen
or carbon atoms; or a substituent R.sub.18, defined herein. Ring A is an
aryl or a heteroaryl optionally further substituted with one or more
substituents in addition to R.sub.3. Substituent R.sub.3 is defined
herein.