Proton chemical shifts structural-reporter groups

Comparison of the spectral data for 1 and 2 shows that the chemical shifts of the GlcNAc structural-reporter groups, that is, H-l and the N-acetyl-CH3-protons, are slightly, but significantly, influenced, whereas the /1>2 value is but little affected by the extension of 1 with a Fuc group. For the Fuc group, the resonances of its H-l, H-5, and CH3-group protons are characteristic. The /1<2 value (3.75 Hz) of Fuc is... 

H Chemical Shifts" of Structural-reporter Groups of Constituent Monosaccharides, and of Amino Acid Protons for Glyco-asparagines... 

The chemical shifts of the structural-reporter groups of Gal-6 and GlcNAc-5 are in full accord with those observed for the corresponding protons in the diantennary oligosaccharide 7 (see Table IV). The chemical shift and the line width of the H-l doublet of GlcNAc-5 differ considerably from those observed for GlcNAc-5 in the spectrum of 17 (see Fig. 18a). The chemical shifts of the H-l and H-2 atoms of Man-4 reflect the incompleteness of the branching core (compare with 6, 7, 19, and 20 see Tables IV and VIII). 

It must be emphasized that the extension of a triantennary structure with a NeuAc group a-(2— 6)-linked to Gal-8 can be unambiguously established on the basis of both the unique set of chemical shifts for its H-3c, H-3e, and N-acetyl protons, as well as its specific effects upon the chemical shifts of the structural-reporter groups of GlcNAe-7 and Gal-8 (compare Table XIII). 

The chemical shifts of H-l and of the N-acetyl protons of GlcNAc-1 deviate from those for 8 (see Table V) and 33 (see Table X), illustrating ffie effect of the peptide moiety (Asn-Ser as against Asn-Lys) on the chemical shifts of the structural-reporter groups of this residue. 

The effects of attachment of NeuAc in a-(2— 3) linkage to Gal are restricted to the structural-reporter groups of the N-acetyllactosamine unit to which Gal belongs as the chemical shifts of corresponding protons of these units in the asialo upper and lower branch of a dian-tennary structure differ only slightly (compare compounds 7, 8, and 15 see Tables IV, V, and VII), it is advisable to utilize the combination of the three effects just mentioned, in order to establish unambiguously the upper- or lower-branch position of NeuAc in -(2—>3) linkage to Gal. 

Fig. 36.—Structural-reporter-group Regions of the Resolution-enhanced, 500-MHz, H-N.m.r. Spectrum of a Mixture Containing Compounds 49,50, and 51 in the Ratios of 12 2 3. [The bold numbers in the spectrum refer to the corresponding residues in the structures, and die italic numbers to the compounds in the mixture. Signals of corresponding protons in the various components of this mixture coincide, unless otherwise indicated. The relative-intensity scale, as well as the chemical-shift scale, of the N-acetyl-proton region and the Fuc CH3-proton region (b), differ from those of the other parts (a) of the spectrum, as indicated. The HOD resonance, as well as the H-l signal of Man-3, have been omitted from the spectrum.]...

Figure 5.1 shows representative H-NMR spectra of compounds 19 and 24. The position of the amide NH in Fc-[GluOEty 25 is further downfield compared with Fc-GluOEt 19. Such a downfield shift of ami NH is garerally the result of H-bonding. The use of different solvents has an effect on the position of the chemical shift, especially for species that have the tendency to form H-bonds with the solvent. It was observed that the amide NH of the monosubstimted 17-19 was shifted further down-field in CDClj as compared with DMSO-d6 (Tables 5.1 and 5.2). Kraatz previously reported the effect of protic solvents on the NH proton chemical shifts in a series of Fc-peptides that were attributed to strong H-bonds between the solvent and the amide moiety, which also affected the electronic structure of the Fc group [28]. 

The aniline-zinc porphyrin interaction has also been exploited to form dimers. Hunter (60) reported the dimerization of porphyrins functionalized at one meso position with ortho or meta aniline groups (47, 48, Fig. 15). Both compounds showed concentration-dependent H NMR spectra with large upfield shifts for the aniline protons. The dimerization constants are 160 and 1080 M-1 respectively for 47 and 48, and these values are an order of magnitude higher than the association constants of simple reference complexes (K — 10 and 130 M 1 respectively), which is indicative of cooperative self-assembly. The complexa-tion-induced changes in chemical shift were used to obtain three-dimensional structures of the dimers. 

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