The synthesis of a series of novel analogues of lipid A, the lipophilic terminal of lipopolysaccharides (LPS), and lipidX, the reducing monosaccharide unit in lipid A, is reported. In these compounds, the native 1-O-phosphate group has been replaced by a "bioisosteric" CH2COOH substituent. The new N,O-acylated monosaccharide C-glycosides were obtained by Wittig reaction of suitably protected glucosamine
In order to study structure-activity relationships of lipid A derivatives, a series of fluorinated analogues of lipid X was synthesized. Subsequently, these were converted enzymatically into the corresponding disccaharidic lipid A analogues using lipid A synthase. This further demonstrates the low substrate specificity of this enzyme.