The present invention provides carboxylic acid derivatives of the general formula: ##STR1## wherein R.sub.1 and R.sub.2, which can be the same or different, are optionally substituted aryl radicals or optionally substituted heterocyclic radicals, A is a straight-chained or branched, saturated or unsaturated alkylene chain containing up to 10 carbon atoms which can contain an oxygen, sulphur or nitrogen atom and is optionally substituted by a hydroxyl group, Y is an S(O).sub.n group or an oxygen atom, n is 0, 1 or 2 and B is a valency bond or a saturated or unsaturated alkylene radical containing up to 5 carbon atoms; as well as the physiologically acceptable salts, esters and amides thereof, with the proviso that(a) R.sub.1 and R.sub.2 are not simultaneously aryl radicals and(b) when an unsaturated alkylene chain is present which contains a heteroatom, the heteroatom is not connected to an unsaturated aliphatic carbon atom.The present invention also provides processes for the preparation of these new compounds and pharmaceutical compositions containing them.