Conformational Study of a Tetraacyl Biosynthetic Precursor of Lipid A by NMR

During the course of a conformational study of lipid A, which is a bioactive entity of lipopolysaccharide of the Gram-negative bacterial cell surface, the molecular conformation of its tetraacyl biosynthetic precursor in dimethyl sulfoxide was unambiguously determined by means of NMR using both 6-13C-labeled and nonlabeled synthetic specimens. The conformation of the hydrophilic moiety was determined by an NMR analysis based on the spin-coupling constants and nuclear Overhauser enhancement data around the glycosidic linkage. The whole molecular shape of the glycolipid was then elaborated with the aid of molecular mechanics calculations.