Synthesis and purification by HPLC of des-O-acyl partial structures of Escherichia coli Re lipopolysaccharide

Abstract

Four compounds corresponding to partial structures of Re-type lipopolysaccharide (LPS) were synthesized for precise investigation of immunological properties of the 3-deoxy-D- manno-2-octulosonic acid (Kdo)-containing inner core and lipid A regions of LPS. The synthetic compounds lack all the ester-bound acyl groups which are present in natural LPS but known to be not essential for the antigenicity. The simplest compound is N,N'-diacylated glucosamine β1-6 disaccharide 4'-monophosphate 2 which corresponds to the des- O-acyl derivative of 1-dephospho lipid A. The other three contain one or two Kdo moieties linked to 2. The most complex one is a tetrasaccharide equivalent to the des- O-acylated 1-dephosphorylated derivative of LPS from Escherichia coli Re-mutant. Syntheses were performed by stepwise condensation of appropriately protected sugar moieties and final hydrogenolytic deprotection. The synthetic des- O-acyl LPS analogs were effectively purified by means of reversed phase HPLC to give homogeneous preparations.