| Abstract: | 1H-NMR spectra for the angiotensin agonist sarcosine-(Sar)Arg-Val-Tyr-Ile-His-Sar-Phe [( Sar1,Sar7]Ang II) and the antagonist Sar-Arg-Val-Tyr-Ile-His-Sar-Ile in dimethylsulfoxide-d6 were examined at 400 MHz. Splitting of the resonances for Tyr, His, and Sar protons revealed that the His6-Sar7 peptide bond existed in both cis and trans forms, with one isomer predominating in the ratio 5:1 in both peptides. Comparison of the chemical shifts for the His6 and Phe8 ring protons in these peptides suggested a His/Phe stacking interaction in [Sar1,Sar7]Ang II which is important for agonist activity. |
