Compounds of formula (IA) or (IB), are inhibitors of aurora kinase activity: Formula (IA), (IB) wherein -L1Y1-[CH2]z- is a linker radical wherein Y1, L1 and z are as defined in the claims; R6 is C1-C4alkoxy, hydrogen or halo; W represents a bond, —CH2—, —O—, —S—, —S(═O)2—, or —NR5— where R5 is hydrogen or C1-C4 alkyl; Q is ═N—, ═CH— or ═C(X1)— wherein X1 is cyano, cyclopropyl or halo; linker radicals L2 are as defined in the claims; 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-C7 cycloalkyl, 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 D is a mono-cyclic heterocyclic ring of 5 or 6 ring atoms.