Selective fluorescent nonpeptidic antagonists for vasopressin V₂ GPCR: application to ligand screening and oligomerization assays.

A series of fluorescent benzazepine ligands for the arginine-vasopressin V₂ receptor (AVP V₂R) was synthesized using "Click" chemistry. Their in vitro pharmacological profile at AVP V₂R, V(1a)R, V(1b)R, and oxytocin receptor was measured by binding assay and functional studies. Compound 9p, labeled with Lissamine Rhodamine B using novel solid-phase organic tagging (SPOrT) resin, exhibited a high affinity for V₂R (4.0 nM), an excellent selectivity toward V₂R and antagonist properties. By changing the nature of the dye, DY647 and Lumi4-Tb probes 44 and 47 still display a high affinity for V₂R (5.6 and 5.8 nM, respectively). These antagonists constitute the first high-affinity selective nonpeptidic fluorescent ligands for V₂R. They enabled the development of V₂R time-resolved FRET-based assay readily amenable to high-throughput screening. Taking advantage of their selectivity, these compounds were also successfully involved in the study of V(1a)R-V₂R dimerization on cell surface.