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, —(C═O)—, —S(O2)—, —C(═O)O—, —OC(═O)—, —(C═O)NR3—, —NR3(C═O)—, —S(O2)NR3—, —NR3S(O2)—, or —NR3(C═O)NR5—, 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— 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 (—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)-, —(C═O)R3, —(C═O)OR3, or —(C═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.