Klaus Bock

Carbon-13 Nuclear Magnetic Resonance Spectroscopy of Monosaccharides

Publisher Summary This chapter provides an overview of the 13 Carbon-nuclear magnetic resonance ( 13 C-NMR) spectroscopy of monosaccharides. The 13 C-NMR spectroscopy has become increasingly important as a tool for the characterization and structural elucidation of sugars and their derivatives. Although 13 C-NMR is closely related to 1 H-NMR spectroscopy, especially when both types of spectra are recorded with Fourier-transform instruments, the two techniques are sufficiently different to be valuable complements to each other. In many cases, in particular when dealing with complex molecules such as polysaccharides, the amount of information obtainable from 1 H-NMR spectra is limited as compared to that revealed by 13 C- NMR spectra. This chapter provides an almost complete collection of 13 C- NMR chemical shifts of monosaccharides, their methyl glycosides, and acetates, along with the examples of shift data for as many different types of monosaccharide derivative as possible. It also provides details on sampling techniques and assignment techniques, and discusses the identity of monosaccharides, their structure determination, and conformational analysis .

Carbon-13 Nuclear Magnetic Resonance Data for Oligosaccharides

Publisher Summary This chapter presents a compilation of 13 C-nuclear magnetic resonance (NMR) data for oligosaccharides in the form of tables. The literature-survey presented in the chapter covers most of the data of 1982, and all of the information given had been measured for solutions in D 2 O unless stated otherwise. The data for peracetates of xylobioses and of glucobioses were recorded for solutions in CDCl 3 . All data have been copied from the original articles. For mutarotated mixtures of trisaccharides and larger oligosaccharides, the complete set of data is given for the α anomer, but only the chemical shifts for the reducing end of the anomer are given, provided that all other chemical shifts (for the remaining units) are identical. The sampling and assignment techniques used for the measurement of 13 C-NMR spectra of oligosaccharides are identical to those for monosaccharides. Particularly for oligosaccharides, it is important to measure the spectra at the same temperature—that is, with a precision better than ±0.5 p.p.m., when data are to be compared accurately.

A conformational study of hydroxymethyl groups in carbohydrates investigated by 1H NMR spectroscopy

Abstract It is generally acknowledged that information about carbohydrate conformation is important for the understanding of interaction between carbohydrates and other biomolecules, such as proteins.1–5 The major part of oligosaccharides involved in the interactions are made up of hexopyranoses, and the overall conformation can be described by the rotation of the glycosidic linkages and the bonds to the exocyclic groups,6,7 e.g., the hydroxymethyl groups and N-Acetyl groups. The conformation of the hydroxymethyl group is of interest for interactions involving the hydroxyl group at this position.2,8,9 Furthermor, the conformation of the C5-C6 linkage determines the overall shape of oligosaccharides with glycosidic linkages to 06.10–27 The conformational preferences of the hydroxymethyl group in mono and oligosaccharides have therefore been the subject of several investigations including both experimental and theoretical studies, as will be discussed in the following.

The conformational properties of sucrose in aqueous solution: intramolecular hydrogen-bonding

Abstract A detailed analysis is presented of the nuclear ( 1 H and 13 C) magnetic resonance (n.m.r.) properties of sucrose, using both D 2 O and dimethyl sulfoxide- d 6 as solvents, based on measurements of coupling constants, chemical shifts, T 1 relaxation times, and nuclear Overhauser enhancements. Molecular modelling (HSEA calculations) suggests a strong conformational preference about the glycosidic linkages that is near to that for sucrose in the crystalline state, and this conformational rigidity is fully supported by the n.m.r. data, in terms of lack of influence of changes in concentration and temperature on the relevant n.m.r. parameters. The restricted rotation for the 1-hydroxymethyl group of the fructose residue is related to the persistence of the intramolecular hydrogen-bond between O-1 f and O-2 g . The presence of this bond was established for solutions in (CD 3 ) 2 SO by the observation of isotopic chemicashifts on partial deuteration of the hydroxyl groups. The orientation of the 6-hydroxyl methyl group of the fructose residue is not that present in the crystalline state but, in (CD 3 ) 2 SO, it may be intramolecularly hydrogen-bonded, as was demonstrated by titration of the hydroxyl groups with CD 3 OD. Observations are made regarding hydrophobic topographies common to sucrose, saccharin, and 1-chloro-1-deoxysucrose, which may have a bearing on sweetness.

The complex carbohydrate structure database

The Complex Carbohydrate Structure Database (CCSD) and CarbBank, an IBM PC/AT (or compatible) database management system, were created to provide an information system to meet the needs of people interested in carbohydrate science. The CCSD, which presently contains more than 2000 citations, is expected to double in size in the next two years and to include, soon thereafter, all of the published structures of carbohydrates larger than disaccharides.

A study of 13CH coupling constants in hexopyranoses

Proton decoupled and undecoupled 13C n.m.r. spectra have been measured on a number of hexopyranoses. The direct coupling constants between the anomeric carbon atoms and protons {1J[13C–H(1)]} were found to be ca. 160 in the β-anomers and ca. 170 Hz in the α-anomers; the difference of ca. 10 Hz between pairs of anomers was found in almost all cases. Chemical shifts and 1J(13CH) values of the other carbon atoms in the pyranose rings were also measured.

The conformational analysis of oligosaccharides by 1H-NMR and HSEA calculation

The application of 1H-nuclear Overhauser enhancement, 1H-spin-lattice-relaxation-time and 1H-chemical shift measurements for the assessment of the conformational preferences of oligosaccharides are briefly reviewed. It is demonstrated that additivity rules, for the correlation of the chemical shifts of similar hydrogen atoms in different oligosaccharides, can be useful in the conformational analysis of oligosaccharides when the differential chemical shifts are greater than 0.1 ppm. These often can be attributed to specific interunit deshielding of a hydrogen atom by an oxygen atom with which it is in strong nonbonded interaction. HSEA calculations are used to demonstrate that differential chemical shifts of less than 0.1 ppm can have origins that are not significant to the overall conformational preferences of the oligosaccharides which are being compared. Both shielding and deshielding effects can arise from a change in the orientation of a substituent group as the result of the introduction of a sugar on a neighboring unit. It is demonstrated that substituent groups, such as hydroxymethyl and acetamido groups, on occasions, should be treated in HSEA calculations as freely rotating about their linkage to a pyranose ring.

A nuclear magnetic resonance spectroscopic investigation of Kdo-containing oligosaccharides related to the genus-specific epitope of chlamydia lipopolysaccharides

The 1H- and 13C-NMR parameters, chemical shifts and coupling constants, for the pentasaccharide of the genus-specific epitope of Chlamydia lipopolysaccharide and related di-, tri-, and tetra-saccharides have been measured and assigned completely using 1D and 2D techniques, and their structures have been confirmed. NOE experiments indicated the preferred conformation of the pentasaccharide and the component oligosaccharides. The 3JH,H demonstrate a change in conformation by rotation of the C-6-C-7 bond of the side chain of the (2----8)-linked Kdo (unit b) in alpha-Kdo-(2----8)-alpha-Kdo-(2----4)-alpha-Kdo-(2----6)-beta-GlcN-(1--- -6)- GlcNol, alpha-Kdo-(2----8)-alpha-Kdo-(2----4)-alpha-Kdo-(2----6)-beta-GlcNAc-(1- ---O)- allyl, and alpha-Kdo-(2----8)-alpha-Kdo-(2----4)-alpha-Kdo-(2----O)-allyl relative to that preferred in alpha-Kdo-(2----4)-alpha-Kdo-(2----6)-beta-GlcNAc-(1----O)-allyl, alpha-Kdo-(2----8)-alpha-Kdo-(2----O)-allyl, alpha-Kdo-(2----4)-alpha-Kdo-(2----O)-allyl, and alpha-Kdo-(2----6)-beta-GlcNAc-(1----O)-allyl, irrespective of the size of the aglycon, e.g., allyl or beta-D-GlcN residues. The conformational results have been substantiated by computer calculations using the HSEA approach.

Preparation of some bromodeoxyaldonic acids

Abstract Reaction of L -ascorbic acid with hydrogen bromide in acetic acid gave 6-bromo-6-deoxy- L -ascorbic acid, which was converted into 5,6-dideoxy- D - glycero -hex-2,3-enono-1,4-lactone. Hexonic acids or their lactones also gave bromo compounds on treatment with HBrAcOH. From D -galactono-1,4-lactone a 6-bromo derivative was obtained. Calcium D -gluconate yielded 2,6-dibromo-2,6-dideoxy- D -mannono-1,4-lactone, whereas D -mannono-1,4-lactone gave 2,6-dibromo-2,6-dideoxy- D -glucono-1,4-lactone.

Iridoid allosides from Viburnum opulus

Abstract Arbutin and four novel iridoid glycoside esters, named opulus iridoids I–IV, have been isolated from foliage of Viburnum opulus (Caprifoliaceae). Each opulus iridoid constitutes an inseparable mixture of two compounds, differing by containing either 2-methyl- or 3-methylbutyric acid in ester linkage at the 1-OH-group in an iridoid glycoside. In all glycosides 2′,3′-di- O -acetyl-β- D -allopyranose is linked through a glycosidic bond to C-11 in the iridoid aglycone. The opulus iridoids differ by the degree of acetylation of the aglycone and by the attachment, in III and IV, of a β- D -xylopyranosyl group at C-4 of the allose moiety. The structures have been elucidated by 1 H and 13 C-NMR spectroscopy and by cleavage of the glycosidic linkage with boron trifluoride etherate in acetic anhydride, yielding the acetates of the cyclized aglycone and of the appropriate mono- or disaccharide. This is the second report of an iridoid attached to a sugar other than glucose and the second time allose has been encountered in higher plants. The systematic position of Viburnum is briefly discussed.