pharmaceuticals as modulators of sphingosine 1 phosphate receptors application_number US 201314069967 A description it is to be understood that both the foregoing general description and the following detailed description are exemplary and explanatory only and are not restrictive of the invention claimed as used herein the use of the singular includes the plural unless specifically stated otherwise it will be readily apparent to those skilled in the art that some of the compounds of the invention may contain one or more asymmetric centers such that the compounds may exist in enantiomeric as well as in diastereomeric forms unless it is specifically noted otherwise the scope of the present invention includes all enantiomers diastereomers and racemic mixtures some of the compounds of the invention may form salts with pharmaceutically acceptable acids or bases and such pharmaceutically acceptable salts of the compounds described herein are also within the scope of the invention the present invention includes all pharmaceutically acceptable isotopically enriched compounds any compound of the invention may contain one or more isotopic atoms enriched or different than the natural ratio such as deuterium 2 h or d in place of protium 1 h or h or use of 13 c enriched material in place of 12 c and the like similar substitutions can be employed for n o and s the use of isotopes may assist in analytical as well as therapeutic aspects of the invention for example use of deuterium may increase the in vivo half life by altering the metabolism rate of the compounds of the invention these compounds can be prepared in accord with the preparations described by use of isotopically enriched reagents the following examples are for illustrative purposes only and are.