A structurally diverse capsular polysaccharide that surrounds the bacterial cell plays an important role in virulence of Acinetobacter baumannii, a cause of nosocomial infections worldwide. Various isomers of 5,7-diacylamido-3,5,7,9-tetradeoxynon-2-ulosonic acid have been identified as components of bacterial polysaccharides. In this work, we report on the identification of a new isomer having the d-glycero-l-manno configuration (8-epipseudaminic acid) in the capsular polysaccharide of A. baumannii Res546. The higher sugar was isolated by Smith degradation of the polysaccharide followed by mild acid hydrolysis and identified by a comparison with all isomers using NMR spectroscopy and optical rotation.

Acinetobacter baumannii, capsular polysaccharide, 5, 7, 9-tetradeoxynon-2-ulosonic acid, 7-diacetamido-3, higher monosaccharide

13C NMR data:
Linkage	Residue	C1	C2	C3	C4	C5	C6	C7	C8	C9
5	Ac
7	Ac
	?X8ePsep	?	?	36.2	66.8	50.3	70.4	54.8	66.0	20.2


1H NMR data:
Linkage	Residue	H1	H2	H3	H4	H5	H6	H7	H8	H9
5	Ac
7	Ac
	?X8ePsep	-	-	1.81-1.93	4.20	4.25	4.21	3.79	4.14	1.08


1H/13C HSQC data:
Linkage	Residue	C1/H1	C2/H2	C3/H3	C4/H4	C5/H5	C6/H6	C7/H7	C8/H8	C9/H9
5	Ac
7	Ac
	?X8ePsep			36.2/1.81-1.93	66.8/4.20	50.3/4.25	70.4/4.21	54.8/3.79	66.0/4.14	20.2/1.08

The spectrum also has 2 signals at unknown positions (not plotted).

There is only one chemically distinct structure:

SVGMWSMILES3D molIonize

 

CC(=O)N[C@H]1[C@@H](O)CC(O)(C(=O)O)O[C@H]1[C@@H](NC(C)=O)[C@@H](C)O

334.325 g/mol (C₁₃H₂₂N₂O₈)