Multi-dimensional NMR structural analyses of purified Lipid X and Lipid A (endotoxin)

The NMR structural analyses of unmodified, intact Lipid X and Lipid A (endotoxin) purified from wild-type Escherichia coli K-12 are described. Selective inverse decoupling difference spectroscopy (SIDDS) is introduced as a simple and practical method for establishing phosphate linkage sites in Lipid A and related compounds. Homo- and heteronuclear multi-dimensional correlation NMR methods (COSY, TOCSY, HMQC, HMBC) were used in tandem to determine acyl and phosphate attachment sites and to derive detailed 1H, 13C and 31P NMR assignments. The NOESY results confirm the β-glycosidic linkage and chair conformations of the glucosamine rings in E. coli Lipid A.