Novel analogues of arginine vasopressin containing alpha-2-indanylglycine enantiomers in position 2.

Continuing our efforts to obtain potent and selective analogues of AVP we synthesized and pharmacologically evaluated ten new compounds modified at position 2 with alpha-2-indanylglycine or its D-enantiomer (Igl or D-Igl, respectively). All the peptides were tested for pressor, antidiuretic, and in vitro uterotonic activities. We also determined the binding affinity of these compounds to human OT receptor. The Igl(2) substitution resulted in a significant change of the pharmacological profile of the peptides. The new analogues were moderate or potent OT antagonists (pA(2) values ranging from 7.19 to 7.98) and practically did not interact with V(1a) and V(2) receptors. It is worth emphasizing that these new peptides were exceptionally selective. On the other hand, the D-Igl(2) substituted counterparts turned out to be weak antagonists of the pressor response to AVP and displayed no antidiuretic activity. Some of the results were unexpected, e.g. dual activity in the rat uterotonic test in vitro: the D-Igl peptides showed a strong antioxytocic potency (pA(2) values ranging from 7.70 to 8.20) at low concentrations and full agonism at high concentrations. The results provided useful information about the SAR of AVP analogues.