Compounds of formula (I) are inhibitors of histone deacetylase activity, and are useful in the treatment of, for example, cancers: wherein Y1 is a bond, &mdash；(C&boxH；O)&mdash；, &mdash；S(O2)&mdash；, &mdash；C(&boxH；O)O&mdash；, &mdash；OC(&boxH；O)&mdash；, &mdash；(C&boxH；O)NR3&mdash；, &mdash；NR3(C&boxH；O)&mdash；, &mdash；S(O2)NR3&mdash；, &mdash；NR3S(O2)&mdash；, or &mdash；NR3(C&boxH；O)NR5&mdash；, wherein R3 and R5 are independently hydrogen or optionally substituted (C1-C6)alkyl, L1 is a divalent radical of formula -(Alk1)m(Q)n(Alk2)p wherein m, n, p, Alk1, Alk2 and Q are as defined in the claims； z is 0 or 1； A represents an optionally substituted mono-, bi&mdash； or tri-cyclic carbocyclic or heterocyclic ring system； -[Linker]- represents a divalent linker radical； R is a radical of formula (X) or (Y): wherein R1 is a carboxylic acid group (&mdash；COOH), or an ester group which is hydrolysable by one or more intracellular carboxylesterase enzymes to a carboxylic acid group； R4 is hydrogen； or optionally substituted C1-C6 alkyl, C3-C7cycloalkyl, aryl, aryl(C1-C6 alkyl)-, heteroaryl, heteroaryl(C1-C6 alkyl)-, &mdash；(C&boxH；O)R3, &mdash；(C&boxH；O)OR3, or &mdash；(C&boxH；O)NR3 wherein R3 is hydrogen or optionally substituted (C1-C6)alkyl, C3-C7 cycloalkyl, aryl, aryl(C1-C6 alkyl)-, heteroaryl, or heteroaryl(C1-C6 alkyl)-； R41 is hydrogen or optionally substituted C1-C6 alkyl； and B is a monocyclic heterocyclic ring of 5 or 6 ring atoms wherein R1 is linked to a ring carbon adjacent the ring nitrogen shown, and ring B is optionally fused to a second carbocyclic or heterocyclic ring of 5 or 6 ring atoms in which case the bond shown intersected by a wavy line may be from a ring atom in said second ring.
