Prostaglandins

A compound of formula

• wherein ##STR74## is one of the divalent cyclic groups ##STR75## the letters a and b indicating in each case the points of attachment of the substituents R.sup.1 and C(R.sup.2)HOH respectively;
• R.sup.1 is a group of the formula R'--COQ where R' is selected from the group consisting of --(CH.sub.2).sub.j -- where j is an integer from 4 to 8;
• --CH.dbd.CH--(CH.sub.2).sub.k --, where k is 2 or 3;
• --CH.sub.2 --CH.dbd.CH--(CH.sub.2).sub.m --, where m is an integer from 1 to 5;
• --CH.sub.2 --CH.sub.2 --CH.dbd.CH--(CH.sub.2).sub.n --, where n is 0 or an integer from 1 to 4;
• --X--(CH.sub.2).sub.p, where p is an integer from 3 to 7;
• --CH.sub.2 --X--(CH.sub.2).sub.q --, where q is an integer from 2 to 6;
• and --CH.sub.2 --CH.sub.2 --X--(CH.sub.2).sub.m --, where X is O or S;
• and COQ is carboxy, a physiologically acceptable carboxylate salt, a C.sub.1 -C.sub.5 alkyl ester or CONHSO.sub.2 CH.sub.3 ;
• and
• R.sup.2 is selected from the group consisting of C.sub.1-10 aliphatic hydrocarbon groups and C.sub.1-10 aliphatic hydrocarbon groups substituted by Ar, OAr or SAr, where Ar represents a phenyl, naphthyl, fluorenyl, dibenzocyclohexyl, dibenzocycloheptyl, pyridyl, benzthiazolyl, dihydrobenzthiazolyl, N-methyldihydrobenzthiazolyl, benzoxazolyl, dihydrobenzoxazolyl or N-methyldihydrobenzoxazolyl group or such a group substituted by one or more substituents selected from C.sub.1-10 alkoxy, halogen, C.sub.1-10 halogen-substituted alkyl, sulphamoyl, amino, hydroxyl, nitro and C.sub.1-10 alkyl groups.