Deuterium NMR investigation of an amphotericin B derivative in mechanically aligned lipid bilayers

Abstract

The methyl-d 3 amide derivative of the polyene antibiotic amphotericin B was synthesized, assayed for biological activity, incorporated into mechanically aligned bilayers of dipalmitoylphosphatidylcholine (DPPC), and examined by deuterium and phosphorus NMR. The amide derivative has a lesser, but qualitatively similar, biological activity relative to amphotericin B. Incorporation of the amide derivative and ergosterol into aligned DPPC bilayers resulted in a single, stable bilayer phase, as shown by phosphorus NMR of the DPPC headgroups. Deuterium NMR spectra revealed one major 2H quadrupolar splitting and one major 2H– 1H dipolar splitting in the liquid-crystalline phase, consistent with a high degree of alignment and a single, averaged physical state for amphotericin B methyl-d 3 amide in the bilayer. Variations of the quadrupolar and dipolar splittings as a function of macroscopic sample orientation and temperature indicated that the amide derivative undergoes fast rotation about a motional axis that is parallel to the bilayer normal.