A Hydrogen‐Deuterium Exchange Study of the Amide Protons of Polymyxin B by Nuclear‐Magnetic‐Resonance Spectroscopy

Publisher Website
Google Scholar
Abstract
PMR spectra at 270 MHz of polymyxin B, a cationic oligopeptide antibiotic, show the influence of the inorganic counteranion present in solution. Hydrogen-deuterium exchange rates for amide protons are of 2 types, depending on whether the anion is monovalent or polyvalent. Polyvalent anions catalyze the acid-catalyzed reaction more than monovalent anions. The structure in solution was monitored using proton signals of the amides, the phenylalanine aromatic protons and the leucine methyl and .gamma.-CH protons in several polymyxin salts. Temperature coefficients of chemical shifts of N-H protons are used to identify 2 .beta. turns in the cyclic ring of polymyxin B. Variation in chemical shift of N-H protons, aromatic protons and leucine protons are correlated with anionic size and electronegativity.