Common sugars, spectrum

When the extract is passed over an anion-exchange resin, approximately 40-45 percent of the solids are retained on the resin and the remainder passes through. Infrared absorption spectra of the two fractions are presented in Figure 3. The neutral fraction shows absorption of infrared at 3 microns (hydroxyl), 5.9 microns (aldehydic carbonyl), and at 9-10 microns (C-O-C and C-O-H), with little absorption at 3.4 microns (C-H stretch). This spectrum resembles that of the common simple sugars when scanned as a melt between NaCl optics. 

Shown in Fig. 3.3 (C) is the N-NMR spectrum ofHMWDOM isolated from a depth of 15 m near Hawaii. The one major resonance in the spectrum corresponds to amideN (124 ppm >90% ofthe total N). Surface water samples sometimes show a minor resonance near 24 ppm (<10% of the total N), which corresponds to amine N. Amides are commonly present in biological systems within peptide bonds. Other amide containing biochemicals that may be common in oceanic environments include N-acetyl amino sugars such as Af-acetyl glucosamine, iV-acetyl muramic... 

Natural sialic acids (Schauer 1982 1991) are derivatives of 5-amino-3,5-dideoxy- D-glycero-D-galacto-nonu osonic acid 12.1. This awkward name has been replaced by neuraminic acid . The most common derivative is N-acetyl-neuraminic acid 12.2 whose configuration is easy to memorize because, in the Fischer representation, 12.3, it is presented as an aldolic condensation product of N-acetylmannosamine (2-acetamido-2-deoxy-D-mannose) and pyruvic acid. When the expression sialic acid is used without any other precision, it is in reference to derivative 12.2. It exists in the free state or glycosidated in the d-conformation, which allows an equatorial disposition of the three-carbon side chain. Structure 12.2 represents the stable /3-anomer of the free sugar with an axial anomeric hydroxyl group and all-equatorial non-anomeric substituents. An X-ray spectrum of this crystallized /3- anomer confirms this conformation and reveals, moreover, that the side chain has the zig-zag conformation with two... 

The methods of assignments are now demonstrated using the triterpenoid saponin 1 from Nothpanax davidii as an example. As described above, the anomeric proton resonances are usually well separated, they are commonly used as a spectral window in the analysis of HNMR spectrum of sugar moieties of saponins. 

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