Compounds of formula (X): wherein: R2 is H or an optionally substituted C1-4 alkyl group; Y is either —(CH2)n—X—, where n is 1 or 2 and X is O, S, S(═O), S(═O)2, or NRN1, where RN1 is selected from H or optionally substituted C1-4 alkyl, or Y is —C(═O)NRN2—, where RN2 is selected from H, and optionally substituted C1-7 alkyl or C5-20 aryl; R3 is an optionally substituted C6 aryl group linked to a further optionally substituted C6 aryl group, wherein if both C6 aryl groups are benzene rings, there may be an oxygen bridge between the two rings, bound adjacent the link on both rings; A is a single bond or a C1-3 alkylene group; and R5 is either: (i) carboxy; (ii) a group of formula (II): or (iii) a group of formula (III): wherein R is optionally substituted C1-7 alkyl, C5-20 aryl or NRN3RN4, where RN3 and RN4 are independently selected from optionally substituted alkyl; (iv) tetrazol-5-yl.