Minor structural modifications convert the dual TP/CRTH2 antagonist ramatroban into a highly selective and potent CRTH2 antagonist

Ramatroban, a thromboxane A(2) receptor (TP) antagonist with clinical efficacy in asthma and allergic rhinitis, was recently shown to also antagonize the prostaglandin D(2) receptor CRTH2. Here we report that minor structural changes to ramatroban result in a compound (13) with complete lack of activity on TP but sub-nanomolar potency toward CRTH2. This is the first selective CRTH2 antagonist described to date, and should prove highly valuable in further elucidating the biological significance of CRTH2.