1The 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 of Formula (I) wherein R.sub.11 is C.sub.5-C.sub.18 alkyl or C.sub.5-C.sub.18 alkenyl; Q is selected from the group consisting of 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 and --NH(CO)--; R.sub.2 is selected from the group consisting of H, C.sub.1-C.sub.4 alkyl, (C.sub.1-C.sub.4 alkyl)OH and (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 selected from the group consisting of hydroxy, phosphonate, and of Formula (II) wherein X and R.sub.15 is selected from the group consisting of O and S; or a pharmaceutically acceptable salt or tautomer thereof.