The invention provides compounds represented by the formula I, each of which compounds may have sphingosine-1-phosphate receptor agonist and or antagonist biological activity: ##STR00001## and wherein the variables Y, R.sup.4, n, A, X, Z, R.sup.1, o, R.sup.3, R.sup.2 and p are as defined in the specification. These compounds are useful for treating a disease or condition selected from the group consisting of glaucoma, dry eye, angiogenesis, cardiovascular conditions and diseases, and wound healing.