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 R1 is C8-C22 alkyl, C8-C22 alkenyl or R12 is O, or R1 and R12 taken together form an optionally substituted aryl or an optionally substituted heteroaryl; R17 is H, alkyl or alkylaryl; R18 is N or CH; R2 and R3 are independently selected from the group consisting of H, NH2, and OH, with the proviso that at least one of R2 and R3 is NH2; R4 is selected from the group consisting of hydroxyl, phosphate, phosphonate methylene phosphonate, α-substituted methylene phosphonate, thiophoasphate and thiophosphonate; and R5 is C8-C22alkenyl.