The Action of 2‐o‐methyltyrosine‐oxytocin on the Rat and Rabbit Uterus: Effect of Some Experimental Conditions on Change From Agonism to Antagonism

The Design of Effectivein VivoAntagonists of Rat Uterus and Milk Ejection Responses to Oxytocin*

“…Reprecipitation from DMF with 2% aqueous AcOH and drying in vacuo gave the pure acylopeptide amide, S-benzyl-^mercapto-/?,/?-dimethylpropionyl-Phe-Ile-Gln-AsnCys(Bzl)-Pro-Leu-Gly-NH 2 A portion (4.0 g; 2.4 mmol peptide) of the Boc pentapeptide resin used for the synthesis of dP^OT was converted in three further cycles of solid phase peptide synthesis to Boc-Phe-IleThr(Bzl)-Asn-Cys(Bzl)-Pro-Leu-Gly-resin (5.0 g; 92% yield). This material was ammonolized, and the product was isolated and purified, as described in A, to give the protected octapeptide Boc-Phe-Ile-Thr(Bzl)-Asn-Cys(Bzl)-Pro-Leu-Gly-NH 2 Boc-Gly resin (12.8 g; 6 mmol Gly) was converted in stepwise fashion to Boc-Asn-Cys(Bzl)-Pro-Orn(Tos)-Gly-resin (16.71 g; 84.25% yield). An aliquot (5.4 g; 1.8 mmol) was coupled in the usual manner with Boc Gin /?-nitrophenyl ester to give BocGln-Asn-Cys(Bzl)-Pro-Orn(Tos)-Gly-resin (5.6 g; 97%).…”

“…Antagonism is usually most marked if the uterus is studied at low temperatures and in a medium deficient in Ca ++ and Mg ++ (1)(2)(3). Antagonism may become weaker or revert to partial agonism under more physiological conditions, either in more nearly complete physiological solutions or in vivo.…”

“…The protected peptide was precipitated by the addition of H 2 O (700 ml) and dried (wt, 867 mg). Reprecipitation from DMF with MeOH and washing with hot MeOH (3 X 20 ml) gave pure Boc-Phe-Ile-Gln-Asn-Cys(Bzl)-Pro-Leu-Gly-NH 2 (6) and iV-hydroxybenzotriazole monohydrate (91.8 mg; 0.6 mmol) in DMF (0.7 ml) was cooled in ice, and DCCI (82.4 mg; 0.4 mmol) was added. This mixture was stirred for 0.5 h in ice and for 2.5 h at room temperature.…”

“…An aliquot (2.8 g) of this material was extended stepwise to give BocPhe-Ile-Gln-Asn-Cys(Bzl)-Pro-Orn(Tos)-Gly-resin (3.0 g). This material (3.0 g; 0.84 mmol) was ammonolized, and the product was isolated, as described in .A, to give the protected octapeptide Boc-Phe-Ile-Gln-Asn-Cys(Bzl)-Pro-Orn(Tos)-Gly-NH 2 An aliquot (5.4 g; 1.8 mmol) of the Boc-pentapeptide resin used for the synthesis in C was coupled, after deprotection and neutralization, with Boc-Asn p-nitrophenylester to give BocAsn-Cys(Bzl)-Pro-Orn(Tos)-Gly-resin (5.53 g; 96%). An aliquot (2.76 g) of this material was extended stepwise to give Boc-PheIle-Asn-Asn-Cys(Bzl)-Pro-Orn(Tos)-Gly-resin (3.1 g).…”

“…An aliquot (2.76 g) of this material was extended stepwise to give Boc-PheIle-Asn-Asn-Cys(Bzl)-Pro-Orn(Tos)-Gly-resin (3.1 g). This material (3.1 g; 0.85 mmol) was ammonolized, and the product was isolated and purified, as described under A, to give the protected octapeptide, Boc-Phe-Ile-Asn-Asn-Cys(Bzl)-Pro-Orn(Tos)-Gly-NH 2 …”