Heteroaromatic 5-hydroxytryptamine receptor agonists

A compound of formula I, or a pharmaceutically acceptable salt or prodrug thereof:

• ##STR20## wherein the broken circle represents two non-adjacent double bonds in any position in the five-membered ring;
• W, X, Y and Z independently represent oxygen, sulphur, nitrogen or carbon, provided that one of W, X, Y and Z represents oxygen or sulphur and at least one of W, X, Y and Z represents carbon;
• A represents hydrogen, hydrocarbon, a heterocyclic group, halogen, cyano, trifluoromethyl, --OR.sup.x, --SR.sup.x, --NR.sup.x R.sup.y, --NR.sup.x CO.sub.2 R.sup.y, --NR.sup.x CO2R.sup.y, --NR.sup.x SO.sub.2 R.sup.y, or --NR.sup.z CTNR.sup.x R.sup.y ;
• E represents a bond or a straight or branched alkylene chain containing from i to 4 carbon atoms;
• F represents a group of formula ##STR21## U represents nitrogen or C--R.sup.2 ;
• B represents oxygen, sulphur or N--R.sup.3 ;
• R.sup.1 represents --CH.sub.2 .multidot.CHR.sup.4 .multidot.NR.sup.6 R.sup.7 or a group of formula ##STR22## in which the broken line represents an optional chemical bond;
• R.sup.2, R.sup.3, R.sup.4, R.sup.5, R.sup.6 and R.sup.7 independently represent hydrogen or C.sub.1-6 alkyl;
• R.sup.x and R.sup.y independently represent hydrogen, hydrocarbon or a heterocyclic group, or R.sup.x and R.sup.y together represent a C.sub.2-6 alkylene group;
• R.sup.z represents hydrogen, hydrocarbon or a heterocyclic group;
• T represents oxygen, sulphur or a group of formula .dbd.N.G;
• and
• G represents hydrocarbon, a heterocyclic group or an electron-withdrawing group.