Synthesis and in vitro evaluation of a selective antagonist and the corresponding radioligand for the prostaglandin D2 receptor CRTH2

Synthesis and preliminary in vitro biological evaluation of a selective high-affinity CRTH2 antagonist is described. The stability of an N-benzyl group facilitated synthesis of the corresponding radioligand by tritiation of a brominated precursor. The compound [3H]TRQ11238 represents the first selective CRTH2 antagonist radioligand and exhibited a specific radioactivity of 52 Ci/mmol and a pKd of 9.0.