Compounds of formula (I): ##STR00001## wherein: R.sup.2 is H or an optionally substituted C.sub.1-4 alkyl group; Y is either --(CH.sub.2).sub.n--X--, where n is 1 or 2 and X is O, S, S(.dbd.O), S(.dbd.O).sub.2, or NR.sup.N1, where R.sup.N1 is selected from H or optionally substituted C.sub.1-4 alkyl, or Y is --C(.dbd.O)NR.sup.N2--, where R.sup.N2 is selected from H, and optionally substituted C.sub.1-7 alkyl or C.sub.5-20 aryl; R.sup.3 is an optionally substituted C.sub.6 aryl group linked to a further optionally substituted C.sub.6 aryl group, wherein if both C.sub.6 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 C.sub.1-3 alkylene group; and R.sup.5 is either: (i) carboxy; (ii) a group of formula (II): ##STR00002## or (iii) a group of formula (III): ##STR00003## wherein R is optionally substituted C.sub.1-7 alkyl, C.sub.5-20 aryl or NR.sup.N3R.sup.N4, where R.sup.N3 and R.sup.N4 are independently selected from optionally substituted C.sub.1-4 alkyl; (iv) tetrazol-5-yl.