Prostanoids are potent oxygenated lipid molecules that contribute to a wide variety of physiological responses and pathological processes. There are currently five primary bioactive types of prostanoids: PGD2, PGE2, PGF2R, PGI2, and thromboxane A2 (TXA2).

All prostanoid receptors belong to the G-protein coupled receptor superfamily. Unlike other receptors of this family the Prostaglandin D2 receptor (also known as CRTH2, GPR44) is structurally distinct and belongs to the family of leukocyte chemoattractant receptors.

The DP2 receptor is expressed in Th2 cells, basophils, and eosinophils, and it mediates the chemotaxis of these cells in response to PGD2. The ability of PGD2 to promote eosinophil accumulation in the airways is mimicked by selective DP2 agonists but not DP1 agonists.

Much effort has been directed toward developing DP2 agonists and antagonists. Indomethacin and ramatroban, which act, respectively, as an agonist and an antagonist, were the first nonprostanoid compounds to be identified as DP2 ligands. These two compounds have frequently used as leads for identifying new selective compounds¹.