Monosaccharides protonation shifts

Identification of constitutive monosaccharides two-dimensional homonuclear NMR techniques such as DQF-COSY and TOCSY are used to assign chemical-shift values for all C-bonded protons in each individual monosaccharide (96). One-dimensional NMR spectra provide useful information about the chemical shifts and scalar couplings of such well-resolved signals as methyl groups for 6-deoxy monosaccharides (fucose, quinovose, and rhamnose) at 6 1.1-1.3 ppm. 

Introduction to 2-D NMR experiments The purpose of the standard 1-D H NMR experiment is to achieve structure-related information about sample protons (i.e., chemical shifts, spin-spin couplings, and integration data) describing the relative number of protons. Applied to anthocyanins, this information may help to identify the aglycone (anthocyanidin), number of monosaccharides present, and anomeric configuration of the monosaccharides. However, for most anthocyanins, the information gained by a standard 1 -D H NMR experiment is insufficient for complete structure elucidation. In recent years, various 2-D NMR experiments have evolved as the most powerful tools for complete structure elucidation of anthocyanins. 

Influence of oe-(2— 3)-linked and -(2— 6)-linked, Terminal N-Acetylneuraminic Acid Residues on the Chemical Shift of Anomeric and N-Acetyl Protons of Other Monosaccharide Residues Present in a Dianteunary Clycari 4 1 ... 

The most important, practical application of 13C-n.m.r. spectroscopy is probably the simple characterization and identification of organic compounds. Because of the simplicity of proton-decoupled carbon spectra, and the sensitivity of carbon-13 chemical-shifts towards structural changes, carbon spectra are extremely well suited for this purpose (see, for example, Ref. 84), and it is for this reason that the emphasis of the present article has been placed on presenting chemical-shift data of monosaccharides and their derivatives. Such data are also important for structural studies of oligo- and poly-saccharides,3 and for the investigation of such mixtures as those arising from mutarotation85-87 (see Section 11,4) or from other reactions.34... 

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

For the determination of the sequence and substitution positions of the different monosaccharides of a saponin, a series of proton and carbon 2D-NMR techniques can provide valuable information about the usually crowded regions of the conventional ID spectra. Thus, integrated approaches including ID or 2D homonuclear NMR shift-... 

Chemical shifts S) of methyl protons in H-NMR of peracetylated monosaccharides ... 

A very useful source on various NMR techniques and chemical shifts of functionalized carbon atoms that contains tabulated data on monosaccharides is Reference [23]. Specifically correlating functional groups with chemical shifts of protons and the associated carbon is an important tool for elucidating the stmcture of the monosaccharide moiety of many complex oligosaccharides. Since monosaccharides contain one or more chiral centers, absolute configuration must be known in order to predict the conformational shape of the molecules. The outcome of many stereoselective functionalizations of free and partially functionalized monosaccharides depends on conformation. 

Analysis of the monosaccharide signals in the C-NMR spectrum (103.1, 77.9, 75.0, 71.3 and 66.9) and further assignment of all proton and carbon chemical shifts using H- H COSY and HMQC experiments indicated the presence of a xylose residue. The presence of xylose was confirmed by acid hydrolysis of 44 with aqueous 2N trifluoroacetic acid followed by GC analysis of the corresponding peracetylated alditol. The D-configuration was determined by GC analysis of the l-[(S)-A-acetyl-(2-hydroxypropylamino)]-l-deoxy alditol acetate derivative as for... 

The limited dispersion of internuclear orientations of CH vectors between directly bonded carbon and proton atoms in monosaccharide rings means that additional types of RDCs such as DHh> "D< h, and Dcc are required for proper analysis of RDCs. The demand on the number and accuracy of measured RDCs increases for flexible carbohydrates. Attention must be paid to higher order effects caused by the narrow range of 1H chemical shifts of carbohydrates. 

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