H-NMR Spectra of Angiotensin II Analogues

Abstract

Seven analogues of angiotensin II, in which the N-terminal residue is commonly sarcosine were chemically synthesized in the liquid phase. The activity of those analogues as antagonist against increasing of blood pressure by angiotensin IL was measured for rats. Their 'H-NMR spectra in D20 solutions were measured at 200 MHz to know the relation between the activity and conformation or mobility of the molecules. The assignment of the observed peaks was made with spin decoupling measurements. The half-band widths of His6 e-CH were found to spread from 5 to 29 Hz, among which the two inactive analogues as antagonist were found to have the smallest band widths below 10 Hz. These results show that the imidazole ring of His is immobilized in some state in the conformation of active analogues.