An investigation of position 3 in arginine vasopressin with aliphatic, aromatic, conformationally-restricted, polar and charged amino acidsSymbols and abbreviations are in accordance with the recommendations of the IUPAC-IUB Commission on Biochemical Nomenclature (Eur. J. Biochem. 180, A9-A11, 1989).

Abstract

We report the solid-phase synthesis and some pharmacological properties of 23 new analogs of arginine vasopressin (AVP) which have the Phe3 residue replaced by a broad variety of amino acids. Peptides 1–9 have at position 3: (1) the mixed aromatic/aliphatic amino acid thienylalanine (Thi) and the aliphatic amino acids; (2) cyclohexylalanine (Cha); (3) norleucine (Nle); (4) Leu; (5) norvaline (Nva); (6) Val; (7) alpha-aminobutyric acid (Abu); (8) Ala; (9) Gly. Peptides 10–23 have at position 3: the aromatic amino acids, (10) homophenylalanine (Hphe); (11) Tyr; (12) Trp; (13) 2-naphthylalanine (2-Nal); the conformationally-restricted amino acids (14) Pro; (15) 2-aminotetraline-2-carboxylic acid (Atc); the polar amino acids (16) Ser; (17) Thr; (18) Gln; and the charged amino acids (19) Asp; (20) Glu; (21) Arg; (22) Lys; (23) Orn. All 23 new peptides were evaluated for agonistic and, where appropriate, antagonistic activities in in vivo antidiuretic (V2-receptor) and vasopressor (V1a-receptor) assays and in in vitro (no Mg2+) oxytocic assays. The corresponding potencies (units/mg) in these assays for AVP are: 323±16; 369±6 and 13.9±0.5. Peptides 1–9 exhibit the following potencies (units/mg) in these three assays: (1) 379±14; 360±9; 36.2±1.9; (2) 294±21; 73.4±2.7; 0.33±0.02; (3) 249±28; 84.6±4.3; 4.72±0.16; (4) 229±19; 21.4±0.6; 2.1±0.2; (5) 134±5; 31.2±0.9; 28.4±0.2; (6) 114±9; 45.3±2.3; 11.3±1.6; (7) 86.7±2.5; 4.29±0.13; 0.45±0.03; (8) 15.5±1.5; 0.16±0.01; ∼0.02; (9) 3.76±0.03; <0.02; in vitro oxytocic agonism was not detected. These data show that the aliphatic amino acids Cha, Nle, Leu, Nva and Val are well-tolerated at position 3 in AVP with retention of surprisingly high levels of antidiuretic activity. Peptides 2–9 exhibit significant gains in both antidiuretic/vasopressor (A/P) and antidiuretic/oxytocic (A/O) selectivities relative to AVP. [Thi3]AVP appears to be a more potent antidiuretic and oxytocic agonist than AVP and is equipotent with AVP as a vasopressor agonist. The antidiuretic potencies of peptides 10–23 exhibit drastic losses relative to AVP. They range from a low of 0.018±0.001 units/mg for the Lys3 analog (peptide 22) to a high of 24.6±4.6 units/mg for the Hphe3 analog (peptide 10). Their vasopressor potencies are also drastically reduced. These range from a low of <0.002 units/mg for peptide 22 to a high of 8.99±0.44 units/mg for the Atc3 analog (peptide 15). Peptides 10–23 exhibit negligible or undetectable in vitro oxytocic agonism. The findings on peptides 10–23 show that position 3 in AVP is highly intolerant of changes with aromatic, conformationally-restricted, polar and charged amino acids. Furthermore, these findings are in striking contrast to our recent discovery that position 3 in the potent V2/V1a/OT antagonist d(CH2)5d-Tyr(Et)2VAVP tolerates a broad latitude of structural change at position 3 with many of the same amino acids, to give excellent retention of antagonistic potencies. The data on peptides 1–4 offer promising clues to the design of more potent and selective AVP V2 agonists. Copyright © 1999 European Peptide Society and John Wiley & Sons, Ltd.