Synthesis and binding characteristics of two sulfhydryl‐reactive probes for vasopressin receptors

摘要

>The present study describes the synthesis and receptor binding affinities of the sulfhydryl-reactive vasopressin analogs deamino[Dab(N 8-N-maleoyl-β-alanin e)4]AVP (1a) and deamino[Lys(N 8-N-maleoyl-β-alanine)8VP (2a). The analogs were obtained by introducing the sulfhydryl-reactive maleoyl-β-alanyl group at the δ-amino group of Dab4 in deamino[Dab4]IAVP (1) and at the ε-amino group of Lys8 in deamino[Lys8]VP (2), which were synthesized by the solid-phase method. Furthermore, the analog modified at Dab4 was prepared as tritium labeled compound (1b) after catalytic iodine tritium exchange at Tyr2 in deamino[Dab4]AVP. The sulfhydryl-reactive vasopressin analogs retained high binding affinity for the V₂ vasopressin receptor in membranes derived from bovine kidney inner medulla. Apparent dissociation constants K _d of 45 nM (compound 1a) and 15 nM (compound 2a) were determined. Incubation of the ligand receptor complexes at pH 5.5 resulted in dissociation of the sulfhydryl-reactive vasopressin analogs from the V₂ receptor. No indications of a covalent reaction between analogs 1a, 2a and 1b and sulfhydryl groups in or close to the hormone binding site of the V₂ receptor were found.