Salmochelins represent novel carbohydrate containing catecholate siderophores, which are excreted by Salmonella enterica and uropathogenic Escherichia coli strains under low-iron stress. While previous analytical data showed salmochelins to contain 2,3-dihydroxybenzoyl-L-serine and glucose, the molecular structure remained elusive. Structure elucidation with electrospray ionization-Fourier transform ion cyclotron resonance-mass spectrometry (ESI-FTICR-MS), GC-MS and 2D-NMR now revealed that salmochelins are enterobactin-related compounds, which are beta-C-glucosylated at the 5-position of a 2,3-dihydroxybenzoyl residue. The key compound salmochelin S4 is a twofold beta-C-glucosylated enterobactin analogue. Comparison of partial structures of salmochelin with a C-glycosylated compound previously characterized by another group strongly suggest that salmochelins represent the long sought compounds termed Salmonella resistance factors (SRF) or pacifarins. Transformation of iro-genes into enterobactin-producing E. coli K12 confers the ability to produce salmochelins. A detailed analysis proved iroB to be the sole gene with glycosyltransferase activity necessary for salmochelin production. Salmochelins compared to enterobactin are the better siderophores in the presence of serum albumin. This may indicate for salmochelins a considerably more important role for pathogenic processes in certain Escherichia coli and Salmonella infections than formerly assigned to enterobactin. This conclusion is supported by the location of the iro genes on pathogenicity islands of uropathogenic E. coli strains.

Escherichia coli, Salmonella enterica, salmochelins, siderophores

13C NMR data:
Linkage	Residue	C1	C2	C3	C4	C5	C6	C7
3,3,2,5	bD1dGlcp	81.2	74.0	78.1	70.3	81.0	61.2
3,3,2	Subst	168.8	115.4	148.1	145.4	118.8	130.3	117.9
3,3	xLSer	169.4	50.9	63.0
3,2,5	bD1dGlcp	81.2	74.0	78.1	70.3	81.0	61.2
3,2	Subst	168.8	115.4	148.1	145.4	118.8	130.3	117.9
3	xLSer	169.4	50.9	63.0
2	Subst	168.8	115.3	149.8	146.1	118.8	118.2	117.9
	xLSer	169.3	50.9	63.0


1H NMR data:
Linkage	Residue	H1	H2	H3	H4	H5	H6	H7
3,3,2,5	bD1dGlcp	3.87	3.21	3.25	3.16	3.20	3.43-3.69
3,3,2	Subst	-	-	-	-	6.93	-	7.35
3,3	xLSer	-	4.89	4.36-4.67
3,2,5	bD1dGlcp	3.87	3.21	3.25	3.16	3.20	3.43-3.69
3,2	Subst	-	-	-	-	6.93	-	7.35
3	xLSer	-	4.89	4.36-4.67
2	Subst	-	-	-	-	6.95	6.74	7.35
	xLSer	-	4.91	4.38-4.63


1H/13C HSQC data:
Linkage	Residue	C1/H1	C2/H2	C3/H3	C4/H4	C5/H5	C6/H6	C7/H7
3,3,2,5	bD1dGlcp	81.2/3.87	74.0/3.21	78.1/3.25	70.3/3.16	81.0/3.20	61.2/3.43-3.69
3,3,2	Subst					118.8/6.93		117.9/7.35
3,3	xLSer		50.9/4.89	63.0/4.36-4.67
3,2,5	bD1dGlcp	81.2/3.87	74.0/3.21	78.1/3.25	70.3/3.16	81.0/3.20	61.2/3.43-3.69
3,2	Subst					118.8/6.93		117.9/7.35
3	xLSer		50.9/4.89	63.0/4.36-4.67
2	Subst					118.8/6.95	118.2/6.74	117.9/7.35
	xLSer		50.9/4.91	63.0/4.38-4.63

There is only one chemically distinct structure:

SVGMWSMILES3D molIonize

 

*OC[C@H](NC(=O)c1cc([C@@H]2O[C@H](CO)[C@@H](O)[C@H](O)[C@H]2O)cc(O)c1O)C(=O)OC[C@H](NC(=O)c1cc([C@@H]2O[C@H](CO)[C@@H](O)[C@H](O)[C@H]2O)cc(O)c1O)C(=O)OC[C@H](NC(=O)c1cccc(O)c1O)C(*)=O

993.834 g/mol (C₄₂H₄₇R₂N₃O₂₅, R = next and previous repeats, not counted in mol weight)