N-Acetyl-[2-(O-methyl)tyrosine]arginine-vasopressin, an interesting antagonist of the vasopressor response to vasopressin

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Abstract
The synthesis of N-acetyl-[2-(O-methyl)tyrosine]arginine-vasopressin [Ac-Tyr(Me)AVP] was undertaken utilizing a combination of the stepwise active ester and fragment condensation methods. Ac-Tyr(Me)AVP is an antagonist of the vasopressor response to vasopressin (pA2 = 7.18 +/- 0.08), devoid of vasopressor agonist activity, and has an antidiuretic potency of 0.026 +/- 0.002 unit/mg, a 15 000-fold decrease over the antidiuretic activity of [2-(O-methyl)tyrosine]arginine-vasopressin. The analogue is also an antagonist of the in vitro uterotonic activity of oxytocin with pA2 values of 7.29 +/- 0.08 in the absence of Mg2+ and 6.73 +/- 0.14 in 0.5 mM Mg2+. This result of Nalpha-acetylation of Tyr(Me)AVP parallels similar results in the oxytocin series and suggests that this substitution should be considered in the design of potential antagonists of the antidiuretic response to vasopressin.

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