The structure of the O-antigen polysaccharide (PS) from Escherichia coli O74 has been determined. Component analysis, together with (1)H and (13)C NMR spectroscopy as well as (1)H,(15)N-HSQC experiments were employed to elucidate the structure. Inter-residue correlations were determined by (1)H,(1)H-NOESY and (1)H,(13)C-heteronuclear multiple-bond correlation experiments. The PS is composed of tetrasaccharide repeating units with the following structure: Cross-peaks of low intensity from an α-linked N-acetylglucosamine residue were present in the NMR spectra, and spectral analysis indicates that they originate from the penultimate residue in the polysaccharide. Consequently, the biological repeating unit has a 3-substituted N-acetyl-d-glucosamine residue at its reducing end. The (1)H, (13)C and (15)N NMR chemical shifts of the α- and β-anomeric forms of d-Fucp3NAc are also reported. The repeating unit of the E. coli O74 O-antigen is identical to that of the capsular polysaccharide from E. coli K45.

Lipopolysaccharide, NMR, Escherichia coli, capsular polysaccharide, biological repeating unit

13C NMR data:
Linkage	Residue	C1	C2	C3	C4	C5	C6
3	Ac	175.22	22.90
	aDFucp3N	92.67	66.99	51.81	71.29	67.12	16.25


1H NMR data:
Linkage	Residue	H1	H2	H3	H4	H5	H6
3	Ac	-	2.06
	aDFucp3N	5.21	3.82	4.16	3.75	4.25	1.18


1H/13C HSQC data:
Linkage	Residue	C1/H1	C2/H2	C3/H3	C4/H4	C5/H5	C6/H6
3	Ac		22.90/2.06
	aDFucp3N	92.67/5.21	66.99/3.82	51.81/4.16	71.29/3.75	67.12/4.25	16.25/1.18

There is only one chemically distinct structure:

SVGMWSMILES3D molIonize

 

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

205.21 g/mol (C₈H₁₅NO₅)