The biological effects of PGD2 are transduced by at least two 7-transmembrane G-protein coupled receptors, designated DP1 and CRTH2/DP2. BAY-u3405 (Ramatroban) is an approved human medication for the treatment of allergic rhinitis that has documented activity as an antagonist of both the TP and CRTH2/DP2 receptors. CAY10471 is an analog of BAY-u3405 which contains modifications that increase both its potency and selectivity for the human CRTH2/DP2 receptor. CAY10471 binds to the human CRTH2/DP2, DP1, and TP receptors with Ki values of 0.6, 1200, and >10,000 nM, respectively.