Nitrogen heterocycles

A compound of formula (II) ##STR6## wherein J is alkyl of 1 to 6 carbon atoms, J.sup.3 is hydrogen or benzyloxycarbonyl, Z is hydrogen or alkyl, one of Z.sup.1 and Z.sup.2 is represented by the group --CH.sub.2 --X--X.sup.1 --X.sup.2 wherein X is --CH.sub.2 --CQ.sub.2 -- in which each Q is independently selected from hydrogen and alkyl or the two Q'S together form alkylene having from four to six carbon atoms;

• X.sup.1 is a covalent bond or a straight or branched alkylene chain having 1 to 6 carbon atoms;
• X.sup.2 is selected from carboxyl or alkoxycarbonyl;
• the other of Z.sup.1 and Z.sup.2 is represented by the group --Y--Y.sup.1 --Y.sup.2 --Y.sup.3, wherein Y is --CR.sub.2 --CH.sub.2 -- in which each R is independently selected from hydrogen and methyl;
• Y.sup.1 is methylene, methylene substituted by hydroxyl or methylene substituted by hydroxyl and alkyl;
• Y.sup.2 is a covalent bond or straight or branched alkylene having 1 to 7 carbon atoms optionally substituted on the carbon adjacent Y.sup.1 by one or two groups each of which is alkyl;
• Y.sup.3 is hydrogen
• or a salt thereof wherein the term alkyl as it appears above has one to six carbon atoms.