The chemical constitution of lipid A from Serratia marcescens

Abstract

The lipopolysaccharide of Serratia marcescens, under mild hydrolysis conditions (0.25 N H2SO4 for 2.5 h at 100°), yielded a lipid A containing D-glucosamine, fatty acids, acetyl and phosphate groups (approximate molar ratio 3:9:4:2), a small amount of ethanolamine, and a trace of galactosamine. Lipid A on methylation and subsequent hydrolysis yielded 3,4-di-O-methyl-D-glucosamine and 3,4,6-tri-O-methyl-D-glucosamine identified by gas–liquid chromatography as their glucitol acetates. These sugars were further identified by ninhydrin degradation to yield 2,3-di-O-methyl-L-arabinose and 2,3,5-tri-O-methyl-L-arabinose. From these findings, it was concluded that the D-glucosamine units in the lipid A were linked 1 → 6. A negative optical rotation of the lipid A suggested a β linkage. On the basis of the glycosidic linkage evidence and additional compositional data, a possible structure for the lipid A of S. marcescens is proposed and discussed in detail.