Pyrimidothiophene compounds

Compounds of formula (1) are inhibitors of HSP90 activity , and of use in the treatment of , cancer: wherein R is a group of formula -(Ar)-(Alk)-(Z)-(Alk2)-Q wherein Ar is an optionally substituted aryl or heteroaryl radical, Alk' and Alk 2 are optionally substituted divalent C-C alkylene or C-C alkenylene radicals, m, p, r and s are independently 0 or 1, Z is -0-, -S-, -(C=O)-, -(C=S)-, -S0-, -C(=O)O-, -C(=O) NR - , -C(=S)NR -, -S0NR -, -NR C(=O)_, -NR S0- or-NR -wherein R is hydrogen or C-C alkyl, and Q is hydrogen or an optionally substituted carbocyclic or heterocyclic radical; R is hydrogen, an optional substituent, or an optionally substituted (C-C)alkyl, aryl or heteroaryl radical; and R is a carboxylic ester, carboxamide or sulfonamide group.