Compounds of formula (IA) or (IB) or a salt, N-
oxide,
hydrate or solvate thereof are inhibitors of HSP90, and are of value in the treatment of diseases responsive to HSP90 inhibition such as cancers. In the formulae, Ar is an
aryl,
aryl(C1-C6
alkyl),
aryl(C1-C6
alkyl), heteroaryl, heteroarylaryl(C1-C6
alkyl), or heteroarylaryl(C1-C6 alkyl) group, any of which being optionally substituted in the aryl or heteroaryl part thereof; R1, is
hydrogen or optionally substituted C1-C6 alkyl; R2 is
hydrogen, optionally substituted cycloalkyl, cycloalkenyl, C1-C6 alkyl, C1-C6 alkenyl, or C1-C6 alkynyl; or a carboxyl,
carboxamide or carboxyl ester group; and ring A is a non aromatic carbocyclic or heterocyclic ring wherein (i) a ring carbon is optionally substituted, and / or (ii) a ring
nitrogen is optionally substituted by a group of formula -(Alk1)p (Cyc)n-(Alk3)m-(Z)r (Alk2)s Q where Alk1, Alk2 and Alk3 are optionally substituted C1-C3 alkyl, Cyc is an optionally substituted carbocyclic or heterocyclic radical; m, n, p, r and s are independently 0 or 1, Z is -0-, —S—, —(C═O)—, —S02-, —C(═O)O—, —OC(═O)—, —NW—, —C(═O)NRA-, —NRAC(═O)—, —SO2NRA—, or —NRASO2— wherein RA is
hydrogen or C1-C6 alkyl, and Q is hydrogen or an optionally substituted carbocyclic or heterocyclic radical.