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: structure: ##STR00001## wherein R.sub.11 is C.sub.5-C.sub.18 alkyl or C.sub.5-C.sub.18 alkenyl; Q is C.sub.3-C.sub.6 optionally substituted cycloalkyl, C.sub.3-C.sub.6 optionally substituted heterocyclic, C.sub.3-C.sub.6 optionally substituted aryl C.sub.3-C.sub.6 optionally substituted heteroaryl or --NH(CO)--; R.sub.3 is H, C.sub.1-C.sub.4 alkyl, (C.sub.1-C.sub.4 alkyl)OH or (C.sub.1-C.sub.4 alkyl)NH.sub.2; R.sub.23 is H or C.sub.1-C.sub.4 alkyl, and R.sub.15 is hydroxy, phosphonate, or ##STR00002## wherein X and R.sub.12 is O or S; or a pharmaceutically acceptable salt or tautomer thereof.