Strukturuntersuchungen an Mannanderivaten

The assignment of carbonyl resonances in 13C-n.m.r. spectra of peracetylated mono- and oligo-saccharides containing D-glucose and D-mannose: an alternative method for structural determination of complex carbohydrates

In the present study, proton homonuclear (COSY) and 13C-1H heteronuclear shift-correlation, n.m.r. spectroscopies have been used to assign the carbonyl carbon resonances of peracetylated D-gluco- and D-mannopyranose monosaccharides and oligosaccharides containing residues of parent D-glucopyranose monomers. Chemical shifts of these assigned resonances, particularly those arising from acetyl groups near to aglycon substitution sites, were found to be sensitive to the position and configuration of glycosidic linkages present. In addition, evidence is presented that indicates that the shifts of these carbonyl carbon resonances depend on long-range interactions with other peracetylated pyranose monomers resulting from folding of the oligosaccharide chain. These results suggest that carbonyl carbon resonances of peracetylated carbohydrates may be useful probes of oligosaccharide structure.

Proton-nuclear magnetic resonance study of peracetylated derivatives of ten oligosaccharides isolated from human milk

Proton-nuclear magnetic resonance (NMR) spectra of peracetylated derivatives of ten structurally related oligosaccharides isolated from human milk were measured for solutions in CDCl3 at 360 MHz. The following oligosaccharides were investigated: Gal beta 1 leads to 4Glc-ol (1), GlcNAc beta 1 leads to 3Gal beta 1 leads to 4Glc-ol (2), Gal beta 1 leads to 4GlcNAc beta 1 leads to 3Gal beta 1 leads to 4Glc-ol (3), Gal beta 1 leads to 3GlcNAc beta 1 leads to 3Gal beta 1 leads to 4Glc-ol (4), Gal beta 1 leads to 3GlcNAc(4 comes from 1Fuc alpha) beta 1 leads to 3Gal beta 1 leads to 4Glc-ol (5), Fuc alpha 1 leads to 2Gal beta 1 leads to 3GlcNAc beta 1 leads to 3Gal beta 1 leads to 4Glc-ol (6), Fuc alpha 1 leads to 2Gal beta 1 leads to 3GlcNAc(4 comes from 1Fuc alpha)beta 1 leads to 3Gal beta 1 leads to 4Glc-ol (7), Fuc alpha 1 leads to 2Gal beta 1 leads to 4Glc-ol(3 comes from 1Fuc alpha) (8), and a 1:3 mixture of Fuc alpha 1 leads to 2Gal beta 1 leads to 4Glc-ol (9) and Gal beta 1 leads to 4Glc-ol(3 comes from 1Fuc alpha) (10). Owing to the strong downfield shifts of the resonances of protons linked to acetoxylated carbons, the problems of signal overlap are less severe and the spin systems of all constituent sugar residues can be assigned fully. The sites of glycosidic linkage can be recognized by the high-field position of the signals of protons linked to those sites; for example, type 1 (Gal beta 1 leads to 3GlcNAc) and type 2(Gal beta 1 leads to 4GlcNAc) saccharide chains can be distinguished. The sequence can be established by observing a nuclear Overhauser effect involving the anomomeric and the aglyconic proton.

Structural analysis by mass spectrometry and NMR spectroscopy of the glycolipid sulfate from Halobacterium salinarium and a note on its possible function

The major glycolipid sulfate of the extreme halophile Halobacterium salinarium was isolated and characterised mainly by mass spectrometry and NMR spectroscopy. The mass spectrum of the permethylated, desulfated and trimethylsilylated derivative showed the molecule to be a trihexosyl glycerol C20-diether with the sulfate group on the terminal hexose. A 3-position of the sulfate was indicated by the mass spectrum obtained after acetylation and trimethylsilylation (solvolysis of sulfate and replacement by a trimethylsilyl group). The NMR spectrum of the desulfated permethylated glycolipid gave conclusive evidence for the presence of one beta and two alpha anomeric protons. With the knowledge of degradation data it was possible to assign the beta signal to galactose (terminal hexose), and the alpha signals to glucose and mannose. These data together make it likely that the glycolipid sulfate is identical in structure with the glycolipid from Halobacterium cutirubrum characterised previously (M. Kates and P.W. Deroo, J. Lipid Res., 14 (1973) 438). On the basis of a suggested function of cerebroside sulfate of animal origin (identical polar end with the bacterial glycolipid: beta-galactopyranose-3-sulfate) and the present knowledge of ion transport in Halobacteria, it is proposed that the bacterial glycolipid may function as a selective K+ receptor for the K+ transport from a high-Na+ and low-K+ outside medium.