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 bioactiv e entity of lipopolysaccharide of the Gram-negative bacterial cell surface, the molecular conformation of its tetraacyl biosynthetic precursor in dime thyl sulfoxide was unambiguously determined by means of NMR using both 6-C- 13-labeled and nonlabeled synthetic specimens. The conformation of the hydr ophilic moiety was determined by an NMR analysis based on the spin-coupling constants and nuclear Overhauser enhancement data around the glycosidic li nkage. The whole molecular shape of the glycolipid was then elaborated with the aid of molecular mechanics calculations.