Analogs of oxytocin conformationally restricted in the N-terminal part of the molecule.

In this study we describe the synthesis and some pharmacological properties of four analogs of oxytocin. Three of these peptides contain the ethylene-bridged dipeptide D-Phe-D-Phe at positions 2 and 3; one had two N-Me-D-Phe residues. All analogs were tested for vasopressor and uterotonic activities in vitro. Although the results obtained demonstrate that the proposed modifications either suppressed or greatly reduced all the activities verified, two peptides are very selective, because they do not seem to interact with V1a receptors. Our results may open up new possibilities for the design of antagonists of oxytocin.