Anomeric proton

The NMR spectrum of methyl kasugaminide in deuterium oxide at 100 Me is shown in Figure 3. The anomeric proton at C-l linking with methoxyl group is shown as a doublet at 4.57 p.p.m. indicating one proton at C-2. The weak coupling, 1.6 c.p.s., is possible between protons in cis relation (28) or in equatorial-equatorial relation (6) at C-l and C-2 of the six-membered ring. 

According to van deer Veen (27) and Rao and Foster (17 the anomeric proton line positions for a-D-glycopyranosides (H equatorial) appear in the region of 4.8 to 5.5 p.p.m., while for / -D-glycopyranosides (Hi axial), the peaks appear at 4.4 to 4.6 p.p.m. The chemical shift of the anomeric proton of methylkasugaminide (5) is located at 4.57 p.p.m. and thus the proton must be axial, excluding structure 8b and 8c in which the anomeric proton is equatorial. Structure 8a is thus completely in agreement with the NMR spectra. 

On the other hand, the NMR spectrum (Figure 6) of kasuganobiosa-mine (4) shows that the anomeric proton signal is located at 5.02 p.p.m., therefore the configuration of the proton is assigned to the equatorial configuration or the same ground (17,27). 

Consequently, the glycosidic linkage in kasuganobiosamine must be -configuration, showing conversion of the anomeric proton during methanolysis. 

The P.M.R. spectrum of an equilibrated aqueous solution of 2-deoxy-D-arafoino-hexopyranose was first measured by Lenz and Heeschen (37) who reported values for the chemical shifts of the anomeric protons and... 

One of the most interesting stereospecific dependences which followed from the original study (38,39) of O-acetylated hexopyranose and pento-pyranose derivatives was that of the anomeric proton shifts. In general it was found that the axially oriented anomeric protons gave resonances to higher field than the equatorially oriented protons. Many subsequent studies of pyranose derivatives (24,40) and of inositol derivatives (43)... 

Table IV. Comparison of Anomeric Proton (Hi) Chemical Shifts for Free and Acetylated D-gluco and D-mannopyranoses With Those of Related 2-Deoxy Sugar Derivatives. Effect of Replacing an Axial or an Equatorial C2-Methylene Proton With a Hydroxy or Actetoxy Substituent...

The first observations on the stereochemical dependence of spin-lattice relaxation-rates of carbohydrate molecules, beginning in " 1972, provided a general survey of the nonselective relaxation-rates of the anomeric protons of monosaccharide derivatives, oligosaccharides, and some polysaccharides. 

Nonselective Spin-Lattice Relaxation Rates (s ) for the Anomeric Protons of Monosaccharides and Derivatives"... 

Scheme 1.—Occurrence of Ring Protons Expected to Have a Major Influence on the Relaxation Rates (R,) of the Anomeric Protons (H-1) of Aldopyranoses and Derivatives (4-25, Table I) in the C, or C4, Conformation.

The relaxation data for the anomeric protons of the polysaccharides (see Table II) lack utility, inasmuch as the / ,(ns) values are identical within experimental error. Obviously, the distribution of correlation times associated with backbone and side-chain motions, complex patterns of intramolecular interaction, and significant cross-relaxation and cross-correlation effects dramatically lessen the diagnostic potential of these relaxation rates. 

Figure 2.17 Application of the reverse DEPT pulse sequence to monitor C-labeled glucose by mouse liver-cell extract. (A) Normal FT spectrum. (B) Reverse DEPT spectrum showing the a- and )3-anomeric proton resonances. (C) Two different CH2 proton resonances, a and b, appear after 1.5 h of metabolism. (D) Edited H spectrum confirming that the CH2 resonances arise from metabolic products. (Reprinted from J. Magn. Resonance 56, Brooks et al., 521, copyright 1984, Academic Press.)...

Applying the reverse DEPT pulse sequence to monitor C-labeled glucose by mouse liver-cell extract is shown in Fig. 2.17. The a- and /3-anomeric proton resonances are shown in the starting material these are transformed to CH.2 proton resonances in the metabolite. 

Fig. 2. Changes in relative intensity of anomeric proton resonances during hydrolysis of pentaGalU-ol by A. niger PGII H-lp of triGalUA, O H-la of trigalUA, O.

A new NMR method for the determination of the anomeric configuration in mono- and disaccharides has been described.18 The protocol is based on the different cross-correlated relaxation between proton chemical shift anisotropy (CSA) and dipolar relaxation for the a and (3 anomers of sugars. Only the ot-anomers show the presence of CSA (HI or Hl )-proton dipole (H1-H2 or Hl -H2 ) in the longitudinal relaxation of the anomeric protons. The method is of special interest for cases in which vicinal coupling constants between HI and H2 in both anomers a and (3 are similar and small, such as D-mannose, and the non-ambiguous description of the anomeric configuration needs additional measurements. 

In addition to well-resolved one-dimensional (ID) 1H and 13C spectra, which are usually sufficient for monitoring synthetic steps, HR-MAS techniques can be applied to two-dimensional (2D) homonuclear and heteronuclear experiments, which allow a wealth of structural information to be obtained. H,13C HMQC (heteronuclear multiple quantum coherence) spectra are particularly useful in the analysis of solid support-bound oligosaccharides, since the anomeric protons exhibit characteristic resonances. Such a spectrum of a polymer-bound trisaccharide glycal is shown in Figure 8.4. 

We have characterized a resin-bound pentasaccharide by HR-MAS techniques. A comparison of the solution spectrum of the resin-cleaved pentasaccharide with the HR-MAS spectrum of the resin-bound pentasaccharide is shown in Figure 8.5. It is immediately obvious that the HR-MAS technique provides data of a quality similar to that of the solution technique, but in both cases, only four of the five anomeric protons are visible. However, a 2D homonuclear total correlation spectroscopy (TOCSY) spectrum (Fig. 8.6) of the resin-bound pentasaccharide allowed us to clearly observe the overlapped anomeric protons (demonstrating a resolution of 4.4 Hz). 

Fig. 3 a 1 3 syn-diaxial interactions established by OH2ni and OH5m with the vicinal OH3ni group are dependent on the ring 111 conformation, b Dependency exhibited by the intraresidue NOEs on temperature for the different sugar units. Selective NOEs obtained upon inversion of the three anomeric protons at 313 K (left) and 293 K (right)... 

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