Compounds according to formula (I) wherein the radicals R.sup.1, R.sup.2 and R.sup.3 are as herein defined, and wherein Ar represents an aryl group or heteroaryl group, preferably phenyl, n is 1 or 2, and the radical X represents a group selected from --C(R.sup.a)(R.sup.b)--, --C(R.sup.a)(R.sup.b)--C(R.sup.a)(R.sup.b)--, --C(R.sup.a).dbd.C(R.sup.a)--, OC(R.sup.a)(R.sup.b)-- or SC(R.sup.a)(R.sup.b)--. These compounds and their pharmaceutical acceptable salts are used in pharmaceutical compositions as prostaglandine D2 receptor antagonists useful in the treatment of CRTH2-mediated diseases such as respiratory, inflammatory or allergic conditions among others. ##STR00001##