An investigation of position 3 in arginine vasopressin with aliphatic, aromatic, conformationally-restricted, polar and charged amino acids

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; approximately 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 pr...

Position 4 analogues of [deamino-Cys1] arginine vasopressin exhibit striking species differences for human and rat V2/V1b receptor selectivity

“…These findings show that the design of selective peptide V 2 receptor agonists, devoid of V 1b receptor agonism in rats and in humans is now a formidable challenge. These findings also raise another highly daunting and intriguing challenge: how to retrospectively pharmacologically characterize the V 1b receptor agonistic or antagonistic properties of the hundreds of published AVP and OT V 2 , V 1a and OT agonists and antagonists [31][32][33][34][35][62][63][64][65][66][67][68]. This will require the development of a cell line that stably expresses the rat V 1b receptor known to be tightly coupled to phospholipase C [69], to provide a routine bioassay for measuring V 1b receptor activity.…”

Influence of 1‐aminocyclohexane‐1‐carboxylic acid in position 2 or 3 of AVP and its analogues on their pharmacological properties

“…In subsequent studies of other authors, Arg 3 /Phe 3 interchange in the nonselective antagonist mentioned above, [Cpa 1 , d ‐Tyr(Et) 2 , Val 4 ]AVP, resulted in a series of novel, selective hypotensive vasopressin analogues (15). Furthermore, another investigation of position 3 in AVP substituted with aliphatic, aromatic, conformationally restricted, polar and charged amino acids suggests that only thienylalanine (Thi) and aliphatic amino acids are well tolerated to give analogues with appreciable retention of activity (16).…”

Design and synthesis of potent, highly selective vasopressin hypotensive agonists

“…NH 3 cleavage procedure. We have previously shown that the naphthylalanine ring is partially reduced (the addition of 2H) by this procedure [48,49]. The deprotection of the Eda peptide XVII ( Table 1) was performed by the standard TFMSA procedure [35,36], as recently described [18,] as follows: The protected peptide XVII (150 mg) was placed in a round bottomed flask with a stirring bar, 0.5 ml of thioanisole and 0.25 ml of 1,2-ethanedithiol was added, the mixture was chilled with an ice bath, and 5 ml of TFA was added.…”