Proton magnetic resonance studies of angiotensin II conformation: cis-trans isomerism in sarcosine7-containing analogs.

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 51 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.