An analog of angiotensin II, [Sar(1), Ile(8)]-angiotensin II, has a potent and long-lasting competitive antagonistic effect against angiotensin II when tested for its myotropic action on the isolated rabbit aorta and for its effect on blood pressure in anesthetized cats and dogs. Compared to [Ile(8)]-angiotensin II, the new analog has equal antagonistic potency on the isolated system but a much greater potency in vivo. It is assumed that sarcosine in position 1 protects the peptide against enzymatic degradation and enhances its half-life. This study demonstrates that the modification in both positions 1 and 8 are important for the in vivo antagonistic potencies of angiotensin analogs.
Tyr, 0.85. Anal. (C56H77N17013• 3CHjC00H-4H,0) C, , N. pGlu-His-Trp-Ser(Bzl)-Phe(4-N02)-Gly-Leu-Aig(Tos)-Pro-Gly-3 (II). The protected peptide was synthesized beginning with Boc-glycine resin (2.94 g, 1.0 mmol of Gly) in an analogous fashion to peptide I. However, tosyl group protection was used for His and Boc groups were removed by treatments (5 and 25 min) with 25% TFA in CHjClj. Acetic acid washes before and after deprotection were replaced by washes with CHjClj.The dried peptide-resin weighed 4.55 g (118% incorporation) and 2.0 g of this material were ammonolyzed and extracted as described. The crude powder (700 mg) was reprecipitated from refluxing MeOH-EtOAc (3:1) to yield 285 mg (40%) of protected peptide II: single spot to Ehrlich and Pauly reagents and I, vapor; Af1 (silica), 0.41. Amino acid analysis gave Phe(4-N02), 0.93;Trp, 0.87;
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