Potent Antagonists of the Antidiuretic Responses to Arginine-vasopressin Based on Modifications of arginine-vasopressin at Position 4

Article abstract of DOI:10.1021/jm00365a011

As part of a program in wich we are attempting (a) to delineate the structural features at positions 1-9 in our previously reported antidiuretic antagonists required for antidiuretic antagonism and (b) to obtain analogues with enhanced antiantidiuretic potency and/or selectiviy, we have synthesized 14 new analogues of the antidiuretic antagonist <1-(β-mercapto-β,β-cyclopentamethylenepropionic acid),2-D-phenylalanine,4-valine>arginine-vasopressin 2VAVP), in which the valine residue at position 4 was replaced by the following L-amino acids and glycine: Ile, Abu, Thr, Ala, Gln, Lys, Cha, Nle, Nva, Phe, Leu, Gly, Tyr, and Pro.These analogues are 1, d(CH2)5-D-Phe²,Ile⁴AVP; 2, d(CH2)5-D-Phe²,Abu⁴AVP; 3, d(CH2)5-D-Phe²,Thr⁴AVP; 4, d(CH2)5-D-Phe²,Ala⁴AVP; 5, d(CH2)5-D-Phe²AVP; 6, d(CH2)5-D-Phe²,Lys⁴AVP; 7, d(CH2)5-D-Phe²,Cha⁴AVP; 8, d(CH2)5-D-Phe²,Nle⁴AVP; 9, d(CH2)5-D-Phe²,Nva⁴AVP; 10, d(CH2)5-D-Phe²Phe⁴AVP; 11, d(CH2)5-D-Phe²,Leu⁴AVP; 12, d(CH2)5-D-Phe²,Gly⁴AVP; 13, d(CH2)5-D-Phe²,Tyr⁴AVP; 14, d(CH2)5-D-Phe²,Pro⁴AVP.The protected intermediates required for the synthesis of all of these peptides were prepared by the solid-phase method and cleaved from the resin by ammonolysis.Following deblocking with Na in NH3 and oxidizing with K3, each peptide was purified on Sephadex G-15 in a two-step procedure using 50percent HOAc and 0.2 M HOAc as eluants.Analogues 1-14 were tested for agonistic and antagonistic activities by antidiuretic, vasopressor, and oxytoxic assays in rats.Analogues 1, 2, and 4-6 exhibit no detectable antidiuretic agonistic activity.All analogues, with the exception of the Pro⁴-containing analogue, are antidiuretic antagonists.Their antiantidiuretic pA₂ values are as follows: 1, 8.24 +/- 0.08; 2, 7.96 +/- 0.07; 3, 7.62 +/- 0.09; 4, 7.52 +/- 0.03; 5, 7.21 +/- 0.07; 6, 7.22 +/- 0.12; 7, 7.19 +/- 0.08; 8, 7.12 +/- 0.09; 9, 6.99 +/- 0.06; 10, 6.07 +/- 0.11; 11, 6.07 +/- 0.11; 12, 5.85 +/- 0.05; 13, ca. 5.57; 14, a week agonist (0.004 U/mg).Analogues 1-14 also antagonize the vascular responses to arginine-vasopressin (AVP) and the in vitro oxytocic responses to oxytocin.Analogues 1, 2, 3, and 5 have also been shown to antagonize the in vivo oxytocic responses to oxytocin.Five of these analogues (1, 2, 3, 6, and 7) exhibit enhanced antiantidiuretic/antivasopressor selectivity. d(CH2)5-D-Phe²,Lys⁴AVP and other position-4 analogues with side-chain functional groups may be useful covalent ligands with which to probe the structural characteristics of AVP renal and vascular receptors.With an antiantidiuretic "effective dose" of 0.46 +/- 0.07 nmol/kg and a pA₂ value of 8.24 +/- 0.08, d(CH2)5-D-Phe²,Ile⁴AVP (1) appears to be the most potent antidiuretic antagonist reported to date.This and some of the other analogues reported here should prove to be useful pharmacological tools for studies on the role(s)...