These results suggested that our expected product was too reactive to be isolated and was immediately attacked by methanol that was used as solvent for hydrogenolysis, giving rise to the corresponding [alpha]-glycoside with inversion of configuration at the anomeric carbon atom.
Glycosidic bond formation is achieved by a chemical reaction between the anomeric carbon atom (C1) of one monosaccharide molecule and a hydroxy group of another monosaccharide molecule, and results in an oxygen bridge between the two molecules.
The hydroxy group at the anomeric carbon atom of, for example, D-glucose can point either downward or upward, giving rise to the a and [beta]-isomers of D-glucose, respectively.
The peaks are assigned as follows: 173 ppm to the amino acid carbonyls, 105 ppm to the C-1 anomeric carbons of the carbohydrate, 73 ppm to the carbohydrate CHs having secondary hydroxyls, 60 ppm to the C[H.sub.2]s of the carbohydrate ring containing primary alcohol functionality, and 30 ppm to the CH carbons in the protein amino acids.
Comparing the 105-ppm carbons (C-1 anomeric carbons of the carbohydrates), we see that the relaxation data were best fit by a biexponential model for all the samples.
Finally, the region around 100ppm corresponds to the anomeric carbons [C.sub.1]([alpha]) according to Li et al.
As can be noted in the figure, the changes are most evident in regions from 80 to near 1110rpm, which correspond to [C.sub.4] internal carbons of the glucose chain, and to [C.sub.1] or anomeric carbons. The [C.sub.4] resonance in the region ~82ppm of the cross-linked starch is higher than that of the native counterpart, probably due to changes in crystalline conformation produced by the thermal treatment.
and [sup.1.H-NMR spectrum exhibited the presence of eight olefinic protons, one methyl doublet signals, two anomeric proton signals ([delta]HI' 4.39 and [delta]HI" 5.20) confirmed by two anomeric carbons
([delta]CI' 103.20 and [delta]CI" 102.03) indicating that the compound contains two sugar moieties (glucose and rhamnose).
(2005), working with human umbilical cord, using [sup.13]C NMR spectroscopy identified carboxyl and acetamide groups at 173.4 and 144.5ppm, respectively, two anomeric carbons
at 100.1 and 102.7ppm and an acetamide carbon at 22.1ppm.