The present invention relates to S1P analogs that have activity as S1P receptor modulating agents and the use of such compounds to treat diseases associated with inappropriate S1P receptor activity. The compounds have the general structure (I), wherein R.sub.1 is C.sub.8 C.sub.22 alkyl, C.sub.8 C.sub.22 alkenyl or R.sub.12 is O, or R.sub.1 and R.sub.12 taken together form an optionally substituted aryl or an optionally substituted heteroaryl; R.sub.17 is H, alkyl or alkylaryl; R.sub.18 is N or CH; R.sub.2 and R.sub.3 are independently selected from the group consisting of H, NH.sub.2, and OH, with the proviso that at least one of R.sub.2 and R.sub.3 is NH.sub.2; R.sub.4 is selected from the group consisting of hydroxyl, phosphate, phosphonate methylene phosphonate, .alpha.-substituted methylene phosphonate, thiophoasphate and thiophosphonate; and R.sub.5 is C.sub.8 C.sub.22alkenyl. ##STR00001##