A compound of formula (2) ##STR11## wherein R3 is a hydrogen atom or an alkyl, aryl or aralkyl group;R4 is a C6-12 aryl or C3-8 heteroaryl group; Y is a group --OR1 where R1 is an optionally substituted straight or branched C1-3 alkyl group; n is zero or an integer of value 1, 2 or 3; or the salts, solvates or hydrates thereof. 9.