糖的构型与核磁数据.ppt

Phytochemistry. Vol. 31. No. page:3307-3330,1992. NMR SPECTROSCOPY IN THE STRUCTURAL ELUCIDATION OF OLIGOSACCHARIDES AND GLYCOSIDES Pawan K. Agrawal The occurrence form of carbohydrate The determination of an oligosaccharide What is the monosaccharide composition? What are the anomeric configuration of each glycosidically linked monosaccharide unit? How are the monosaccharide units linked to one another? What are the appended groups, if any? Conventional method for structural elucidation of carbohydrate Derivatization: 　　　　　　　methylation, 　　　　　　　acetylation, 　　　　　 　　　　　　　trimethylsilylation. （MS or GC-MS） Advantage: provide the substitution position. Disadvantage: no information on the anomeric configuration or sequence of mono saccharides in an oligosaccharide 13ＣNMR, modern method for structural elucidation of carbohydrate Advantage: purity; recovered sample; provide complete structural determination. Disadvantage: poor sensitivity. Representative 1H-NMR and 13C-NMR chemical shifts for oligosaccharides Monosaccharide composition and anomeric configuration α-anomeric proton, 4.8-5.3 ppm (d, J=1-4 Hz) β-anomeric proton, 4.4-4.8 ppm (d, J=6-8 Hz) Attention Vicinal H-H coupling constants Signal line-widths Spectral integration The type and amount of monosaccharide units, compositional ratio. Comparision with model compounds. Anomeric carbon: The rest of the methine and methylene (51-86 ppm ) Methine: 52-57 ppm (amino sugar carbon signals) Aldoses : one methylene at 60-70 ppm Ketoses: two methylene at 60-70 ppm Anomeric configuration13C NMR data for methyl glycopyranosides Exception: mannose, rhamnose 13C NMR data for methyl glycopyranosides sugar C-1 C-2 C-3 C-4 C-5 C-6 α-D-Man 102.2 71.4 72.1 68.3 73.9 62.5 β-D-Man 102.3 71.7 74.5 68.4 77.6 62.6 α-L-Rha 102.1 71.2 71.5 73.3 69.5 17.9 β-L-Rha 102.4 71.8 74.1 73.4 73.4 17.9