Compounds of formula (I): wherein: Q represents an optionally substituted 5- or 6-membered aryl or heteroaryl ring; X represents O, S, NR5 or CR6 R7; Y represents CHOH, CHSH, NOR8, CNR8 or CNOR8; Z represents a bond, CR10R11, O, S, SO, SO2, NR10, OCR10R11, CR10R11 O or Z, R4 and Q together form an optionally substituted fused tricyclic group; R1, R1′, R3 and R3′ each independently represents H, C1-6 alkyl or C1-4 alkylaryl; R2 represents CO2R8, CONR5OR9 or NR5COR9; R4 represents optionally substituted 5- or 6-membered aryl or heteroaryl; R5 represents H or C1-3 alkyl; R6 and R7 each independently represents H, C1-3 alkyl or halo; R8 represents H or C1-2 alkyl; R9 represents H or C1-3 alkyl; R10 and R11 each independently represents H, C1-6 alkyl or C1-4 alkylaryl; and physiologically functional derivatives thereof, processes for their preparation, pharmaceutical formulations containing them and their use as inhibitors of matrix metalloproteinase enzymes (MMPs) are described.