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.

Analogues of arginine vasopressin modified in position 2 or 3 with naphthylalanine: selective antagonists of oxytocin in-vitro.

In this study we describe the synthesis and some pharmacological properties of six new analogues of arginine vasopressin (AVP). Five of the peptides were substituted in position 2 with L-1-naphthylalanine (L-1-Nal) or D-1-naphthylalanine (D-1-Nal); one had D-1-Nal in position 3. All analogues were tested in bioassays for pressor and antidiuretic activity. We also tested the uterotonic activity of the peptides in-vitro. Two of the new peptides were moderately potent V1a and oxytocin antagonists. The modifications proposed resulted in a drop or the removal of antidiuretic activity and in the removal of pressor activity, or conversion into moderate antagonists. Two peptides ([Mpa1, (L-1-Nal)2]AVP and [Mpal, (D-1-Nal)2]AVP) which appear not to interact with V1a and V2 receptors were exceptionally selective oxytocin antagonists in vitro. These compounds with selective oxytocin antagonistic activity may be promising candidates for the development of potential tocolytic agents for the prevention of pre-term labour.

Analogs of arginine vasopressin modified in position 3 with (R)-alpha-hydroxymethylphenylalanine.

This study describes the synthesis and some pharmacological properties of three new analogs of arginine vasopressin (AVP) substituted in position 3 with (R)-alpha-hydroxymethylphenylalanine ([R]-HmPhe). All new peptides were tested for vasopressor and antidiuretic as well as uterotonic activity. None of the 3 analogs showed any pressor activity and their uterotonic activity was negligible. Only analog [Mpa1,(R)-HmPhe3]AVP exhibited significant antidiuretic activity.

Biologically active analogues of arginine vasopressin containing conformationally restricted dipeptide fragments.

In this study we described the synthesis and pharmacological properties of five new analogues of arginine vasopressin (AVP). Four of these analogues contained ethylene-bridged dipeptide Phe-Phe in positions 2 and 3; one had two N-Me-Phe residues. All new peptides were tested for vasopressor and antidiuretic activities. We also estimated the uterotonic activities of these compounds in vitro. Three analogues were highly potent V1-antagonists. One of them, namely [Cpa1,(Phe-Phe)2,3,Val4]AVP, which seemed to not interact with either V2 and oxytocic receptors, was outstandingly selective. It is interesting that the high antipressor potency of our second peptide, [(N-Me-Phe)2,3]AVP, was achieved without modification of position 1. Our results open new possibilities for the design of very potent and selective V1-antagonists of AVP.