Isolation and structural characterization of a (Kdo-isosteric) d-glycero-α-d-talo-oct-2-ulopyranosidonic acid (Ko) interlinking lipid A and core oligosaccharide in the lipopolysaccharide of Acinetobacter calcoaceticus NCTC 10305

• We analyzed the stereochemistry of d-glycero-α-d-talo-oct-2-ulopyranosidonic acid.
• Structural relation between Kdo and DgDt-Ko could be determined for the first time.
• Determination of natural DgDt-Ko structure was based on synthetic reference compounds.

In Acinetobacter calcoaceticus NCTC 10305 and A. haemolyticus NCTC 10305 lipopolysaccharide (LPS) a Kdo (3-deoxy-d-manno-oct-2-ulosonic acid)-related octulosonic acid (Ko) interlinks the lipid A with the core-oligosaccharide. This Ko replaces the first Kdo (KdoI) attached to the lipid A backbone in the LPS. The only structural difference between Kdo and Ko is the 3-hydroxylation. After the discovery of the final step in Ko-biosynthesis it is now generally accepted that Ko is structurally related to Kdo, although a final proof so far is lacking. In the present paper we describe the stereochemical determination of the natural Ko isolated from the LPS of A. calcoaceticus NCTC 10305 by chemical, mass spectrometry (MS), and 1H and 13C NMR spectroscopy. Our results show that in A. calcoaceticusd-glycero-α-d-talo-oct-2-ulopyranosonic acid (DgαDt-Kop) represents the Kdo-related sugar interlinking the core-oligosaccharide and the lipid A backbone.

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