Synthesis and some pharmacological properties of [I-β-mercaptopropionic acid, 2-(3,5-dibromo- -tyrosine)]-8-lysine-vasopressin

The title compound, 1-β-mercaptopropionic acid, 2-(3,5-dibromo- -tyrosine)]-8-lysine-vasopressin (X), was synthesized by condensation of Pro-Lys(Boc)-Gly-NH₂ with the cyclic peptide 1-β-mercaptopropionic acid, 2-(3,5-dibromo- -tyrosine)]-pressinoic acid. X has no oxytocic, avian vasodepressor, pressor, or antipressor activities, but is a weak inhibitor of the responses to oxytocin in the oxytocic and avian vasodepressor assays. Its pharmacological properties are qualitatively identical to those of the corresponding analog of oxytocin, although it is a less potent antagonist than the latter compound.