TOCSY spectra, polysaccharides

Further 2-D H total correlation spectroscopy (TOCSY) anal3rsis of fire humate from the cellulose treatment indicates that this region is rich in aCH and CH2 of amino acid residues phis CH/CH2 of polysaccharides (Figure 6). These assignments were made based on the proton covalent connectivity and chemical shift information acquired from the TOCSY spectrum, and are in agreement with the 2-D heteronuclear single quantum coherence (HSQC) analysis... 

The proposed ID TOCSY-NOESY experiment is illustrated by the assignment of NOEs from anomeric protons H-lc and H-ld of the polysaccharide 1. Because the resonances of H-lc and H-ld overlapped, this assignment was not possible from a ID NOESY spectrum as shown in fig. 3(b). Although these protons differed in their chemical shifts, it was not possible to separate them by chemical-shift-selective filtration because of the very fast spin-spin relaxation of backbone protons (20-50 ms) in this polysaccharide. Instead, a ID TOCSY-NOESY experiment was performed in which the initial TOCSY transfer from an isolated resonance of H-2c was followed by a selective NOESY transfer from H-lc. The ID TOCSY-NOESY spectrum (fig. 3(c)) clearly separated NOE signals of the H-lc proton from those originating from the H-ld proton and established the linkage Ic —> 6a. 

Fig. 3. Top Resolution-enhanced 600 MHz H NMR spectrum of the octasaccharide repeating unit from Hafnia alvei strain 2 O-specific polysaccharide, (a)-(g) 500 MHz ID TOCSY subspectra with selective excitation of the respective anomeric proton resonances, (h) ID TOCSY subspectrum with the H3eq resonance of the neuraminic acid residue selectively excited. (Reproduced (adapted) with permission from Gamian et al. [25J. Copyright 1991...

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