Anomeric Hydrogen Research Articles

Structural Characterization and Antifatigue Activity of a Novel Exopolysaccharide Isolated from Marasmius androsaceus

This study aimed at examining the structure-role modeling and antifatigue mechanism of polysaccharides, including M. androsaceus exopolysaccharide 3 (MEPS3), isolated from Marasmius androsaceus fermentation broth. The molecular weight of MEPS3 was 10.47 kDa. Furthermore, monosaccharide analysis showed the presence of mannose, glucose, and galactose in MEPS3 in a molar ratio of 0.08 : 0.34 : 1.46. Mannose, α-galactose, and α-d-glucose anomeric hydrogen signals were detected using nuclear magnetic resonance spectroscopy. MEPS3 was found to contain glyoxylic acid, forming rod-like chains that support high-purity polymerization. The weight-loaded swimming test results showed that MEPS3 treatment reduced lactic acid (LA) levels by 25.72% and increased the lactate dehydrogenase (LDH) activity by 5.67% in the plasma. Furthermore, it lowered malondialdehyde (MDA) levels by 47.09% and increased reactive oxygen species (ROS) and glutathione peroxidase (GSH-Px) levels by 52.42 and 97.03%, respectively, in the plasma. In addition, MEPS3 treatment reduced MDA and ROS levels in the liver by 28.85 and 18.64% while increasing superoxide dismutase (SOD) and GSH-Px levels by 17.41 and 38.13%, respectively. MEPS3 treatment increased the expression of nuclear factor-erythroid 2-related factor 2, glutamate-cysteine ligase, quinone oxidoreductase 1, and heme oxygenase 1 by 22.5, 24.8, 20.3, and 43.1%, respectively, in the liver. These findings demonstrate that MEPS3 effectively alleviates fatigue by removing harmful metabolites and indicate that the antifatigue mechanism is related to the Nrf-2 signaling pathway.

Lactonization Method To Assign the Anomeric Configuration of the 3,4-Unsaturated Congeners of N-Acetylneuraminic Acid.

Assigning the correct configuration at C2 in sialosides is a standing problem because of the absence of an anomeric hydrogen. All different empirical rules that have been proposed over the years lack general applicability. In particular, the correct configuration of several 3,4-unsaturated derivatives of N-acetylneuraminic acid (Neu5Ac), which have been recently shown to be novel sialidase/neuraminidase inhibitors, could only be tentatively assigned by similarity with the reported 3,4-unsaturated 2O-methyl sialosides. In this work, we overcome this problem as we devised a rapid synthetic method to unequivocally resolve the anomeric configuration of the 3,4-unsaturated Neu5Ac derivatives through the synthesis of the corresponding unreported unsaturated 1,7-lactones. Moreover, we discovered a diagnostic 13C nuclear magnetic resonance signal that allows the formulation of a new empirical rule for the direct assignment of the C2 stereochemistry of these molecules, even when only one of the two C2 epimers is available.

ANTI-HELICOBACTER PYLORI ACTIVITY AND IMMUNOSTIMULATORY EFFECT OF OLIGOSACCHARIDE ISOLATED FROM AVERRHOA CARAMBOLA L.

Objective: The main goals of the study were to isolate oligosaccharide as a secondary metabolite from indigenous fruit, Averrhoa carambola L. (star fruit), and analyze its anti-Helicobacter pylori and immunostimulatory potential.
 Methods: The oligosaccharide (S3W) isolated using adsorption chromatography was partially characterized using tandem mass spectrometry in atmospheric pressure chemical ionization/electron spray ionization (APCI/ESI) positive and negative mode and nuclear magnetic resonance. The use of microtiter well method determined anti-H. pylori activity in the form of percentage inhibition of microbial growth, while the determination of the immunostimulatory potential of S3W implemented a protection of DNA, buccal cells, and macrophages against damage by oxidant and N-nitroso-N- methylurea (MNU) and percentage splenocyte proliferative potential.
 Results: S3W was a (1→2) β-heptaglucosaccharide with (4→6) α-branching at every second residue. APCI/ESI-positive mode showed B and A fragmentation patterns, while the negative mode showed abundance of A and C fragments. Anomeric hydrogen displayed integration values at 4.8 and 4.2 ppm indicating the presence of α-glucopyranose and β-glucopyranose. The compound protected DNA from oxidant-induced fragmentation. It expressed anti-H. pyloric activity with an IC50 value of 10.71 μg/ml. At 20 μg/ml, S3W protected buccal cells and macrophages significantly from damage due to oxidants and MNU carcinogens, while >50% splenocyte proliferation was induced as compared to that of an untreated control group.
 Conclusion: Our studies constitute the first report on the significant immunostimulatory activity of the oligosaccharide isolated from star fruit. The study, thus, supports its application as a therapeutic potential in curbing gastric diseases caused by H. pylori.

Reductive Radical Cascades Triggered by Alkoxyl Radicals in the β-Cyclodextrin Framework.

The generation and fate of 2I-VII,3I-VII,6II-VII-icosa- O-methyl-β-cyclomaltoheptaos-6I- O-yl radical under reductive conditions is described. Two radical cascade reactions are involved: the main one is triggered by a 1,8-HAT of the hydrogen at 5VIIC. The radical can reach the anomeric hydrogen at 1VC three sugar units ahead using a six-step sequence. The different hydrogen donor ability of the group 14 hydrides permits one to selectively stop the cascade at 5VIIC, 2VIC, and 4VIC to obtain β-CD with a β-l-Ido p unit, acyclic hepta-, and hexa-saccharide structures, respectively.

Anomeric proportions of d-glucopyranose at the equilibrium determined from 1H NMR spectra II. Effects of alkali metal chlorides, CaCl2 and BaCl2 on the anomeric equilibrium at 25.0 °C

The isomeric proportions of saccharides are important information to discuss the properties of the saccharides such as the solvation states, structures, functions and so on in aqueous solutions. However, the isomeric composition, which is one of the fundamental properties of saccharides in the aqueous solution, has not been fully explored experimentally. Successively to our previous study on the anomeric proportion of d-glucopyranose in the aqueous solution [J. Mol. Liq., 232 (2017) 408–415.], the salt effect on these anomeric proportions at 25.0°C were investigated by 1H NMR measurement for the cases of all alkali metal chlorides, CaCl2 and BaCl2. The experimental conditions were; the glucose concentration was from 0.1wt% to 1.0wt% and the salt molality was from 0.1molkg−1 to 0.5molkg−1. At first, the optimal experimental conditions were confirmed in terms of the irradiation power and the target frequency of the presaturation pulse in 1H NMR measurement. The 1H NMR spectra measured under the optimal conditions with adequate accumulation number allowed us to determine the anomeric proportions within the error of 0.0004. The anomeric proportions of α-glucopyranose in the presence of each salts were determined from peak areas corresponding to the anomeric hydrogens of α- and β- d-glucopyranoses. For all kinds of the salts, the anomeric proportion increased consistently and the slope of the proportion decreased gradually with increasing glucose concentration at a given molality of the salts. The anomeric proportions at the infinite dilution of glucose were determined from these concentration dependences of glucose, and then the Gibbs energies of reaction for the anomerization ΔrG° were estimated from these results. The effects of the salts on ΔrG° were divided into two groups: (1) ΔrG° increased when LiCl, NaCl and CaCl2 were added, and (2) ΔrG° decreased when KCl, RbCl, CsCl and BaCl2 were added. The plots of ΔrG° against the ionic radius of the cations clearly illustrated this result, that is, ΔrG° for these two groups fell on the quite different cation radius dependences. ΔrG° of the first group of the salts were greater than that of the salt free system. ΔrG° for each molality of the salts linearly decreased with the cation radius, and became ΔrG° of the salt free glucose aqueous solution around 0.17nm irrespectively to the salt molality. On the other hand, ΔrG° of the second group of the salts were less than that of the salt free system. ΔrG° for each molality of the salts linearly decreased with the cation radius, and became ΔrG° of the salt free solution around 0.08nm irrespectively to the salt molality.

Anomeric proportions of d -glucopyranose at the equilibrium determined from 1 H-NMR spectra I. Investigation of experimental conditions and concentration dependence at 25.0 °C

Abstract Anomeric proportions of d -glucopyranose, defined as the ratio of the amount of substance of α- d -glucopyranose to the sum of that of α- and β- d -glucopyranoses, in aqueous solution were determined from 1H NMR spectra in the concentration range between 0.1 wt% and 10 wt% at 25.0 °C. First of all, experimental conditions were investigated in terms of a time required to equilibrate anomerization and an irradiation power and a target frequency of the presaturation pulse in 1H NMR measurement. Using the optimal condition determined by us, we were able to obtain spectra whose resonant peaks of anomeric protons of d -glucopyranoses were symmetric and baseline were non-distorted. These spectra allowed us to determine the anomeric proportions within experimental error of 0.005. Anomeric proportions of α-glucopyranose in the concentration range from 0.1 wt% to 10 wt% were determined from peak areas corresponding to anomeric hydrogens of α- and β- d -glucopyranose in 1H NMR spectra. The anomeric proportion increased with increasing glucose concentration, though the degree of its increment was not uniform. The steep increase of the proportion was observed in the range between 0.1 wt% and 1 wt% and the increase was gentle between 1 wt% and 6 wt%. The proportion at infinite dilution determined by the least square method using a quadratic curve for the proportions was 0.3598 with a standard error of ± 0.0003, which lead that the Gibbs energy of anomerization of − 1.43 kJ mol− 1. The concentration dependence of the ratio of the activity coefficient for α-glucopyranose to that for β-glucopyranose was estimated from the anomeric proportions and equilibrium constant of the anomerization. The ratio increased with increasing concentration, which shows that the activity coefficient for β-glucopyranose was slightly greater than those for α-glucopyranose at this concentration range.

산성 수용액 조건에서 포도당과 자일로스 반응 산물의1H-NMR 분광분석을 이용한 정량 분석

진한 산 가수분해 반응 중 2차 가수분해 조건에서 포도당과 자일로스의 반응을 수소 핵자기 공명 분광분석을 통하여 정량적으로 분석하였다. 정량분석은 아노머성 수소, 퓨란과 개미산의 특징적인 피크를 이용하여 실시하였다. 진한 산 가수분해의 2차 가수분해 조건에서 포도당의 일부가 5-hydroxymethylfufural (5-HMF) 중간 구조를 거쳐 levulinic acid와 개미산으로 분해되었음을 확인하였다. 자일로스는 furfural 중간 구조를 거쳐 개미산으로 분해가 되었으며, 포도당은 자일로스보다 2차 가수분해 조건에서 산에 의한 퓨란계 화합물의 전이가 느리게 전환되어 단당의 안정성이 높았다. 퓨란계 화합물로 전환된 이후, 산에 민감한 5-HMF는 쉽게 formic acid와 levulinic acid로 전환되었지만, furfural은 formic acid로의 분해 반응이 더디게 진행되어 furfural의 농도가 5-HMF보다 상대적으로 높게 나타났다. Reaction of glucose and xylose to secondary hydrolysis of concentrated acid hydrolysis was quantitatively analyzed by <TEX>$^1H$</TEX>-NMR spectroscopic method. Anomeric hydrogen, furan and formic acid peaks were selected for quantitative analysis. The glucose was converted to the formic acid and the levulinic acid via the 5-hydroxymethylfurfural (HMF) but the xylose was converted to the fufural, which further degraded to the formic acid. The conversion to furans was slower for the glucose than the xylose. But the 5-HMF formed from the glucose was unstable in acidic aqueous medium, resulted in fast conversion to the levulinic acid and the formic acid. The furfural was relatively stable than 5-HMF at acidic aqueous medium.

Investigation of hydrogen abstraction from methyl glucoside by active oxygen species under oxygen delignification conditions. Part 1: Study on the anomeric position

Abstract We investigated whether active oxygen species (AOS) abstract the anomeric hydrogen from a carbohydrate model compound, methyl β-d-glucopyranoside (MGPβ) under conditions simulating oxygen delignification in pulp and paper mills (0.5 mol l-1 NaOH, 0.36 mmol l-1 Fe3+, 1.1 MPa O2, 95°C). The simulation involved in situ AOS generation by reaction of 2,4,6-trimethylphenol with O2, so that various types of AOS were operative in the system. MGPβ was degraded slightly more than methyl α-d-glucopyranoside (MGPα) when they were jointly reacted with AOS. Thus, we suggest that the configurational difference in their anomeric positions has some effects on their reactions with AOS. When MGPβ and methyl β-d-(1-2 H)glucopyranoside (MGPβ-1D) were jointly reacted with AOS, MGPβ was degraded slightly more than MGPβ-1D. This difference results from the kinetic isotope effect, indicating that the anomeric hydrogen of MGPβ is undoubtedly abstracted by AOS, although the contribution of this abstraction to the overall degradation of MGPβ has not been clarified yet. MGPβ and MGPβ-1D were also jointly subjected to alkaline hydrogen peroxide treatment (0.5 mol l-1 NaOH, 0.36 mmol l-1 Fe3+, 95°C) in which the oxyl anion radical (O-·), the conjugate base of hydroxyl radical (HO·), is likely only one of the AOS to degrade these compounds. Since no difference in degradation was observed, some AOS other than O-· must participate in anomeric hydrogen abstraction from MGPβ in these oxygen-alkali treatments. When MGPα and methyl α-d-(1-2 H)glucopyranoside were jointly reacted with AOS, almost no difference in degradation was observed. This result suggests that abstraction of the anomeric hydrogen from MGPα by AOS is no more than a very minor reaction. It was confirmed that the anomeric hydrogen of MGPβ is activated towards AOS reaction owing to the anomeric effect, which is in fact a stereoelectronic effect.

Conversion factors for carbohydrate analysis by hydrolysis and 1H-NMR spectroscopy

Conversion factor to calibrate the lower xylan content in carbohydrate compositional analysis in wood by 1H-NMR spectroscopy was investigated. During acid hydrolysis, xylan monomer was dehydrated as furfural, and that furfural was further degraded or condensed in acidic reaction condition. Anomeric hydrogen peaks integration in 1H-NMR spectroscopic method excluded xylose reacted products (such as furfural and their condensed or degraded products). Only 52% of xylose was counted in anomeric hydrogen integration and 62% of xylose was counted in integration of furfural peak and anomeric hydrogen. For accurate carbohydrate compositional analysis by NMR spectroscopic method, furfural and their reacted products should be counted as xylose. Conversion factor for xylose content analysis was introduced from the acid hydrolysis of several different combinations of standard cellulose and xylan. In this study xylan conversion factor 0.66 was obtained based on compared NMR data from the prepared cellulose and xylan mixtures acid hydrolyzed with the same condition for woodmeal and pulps. With corrected xylan content calculation, NMR spectroscopic method gave rather closer carbohydrate composition compared to the other analytical methods.

2′-O-Carbamate-containing oligonucleotides: synthesis and properties

In order to evaluate the effect of a new 2′-carbohydrate modification on the hybridization properties of oligonucleotides, uridine 2′-O-carbamates were synthesized and incorporated into DNA strands. The key intermediate in the synthesis, a mixed succinimide carbonate 2, was treated with various amines to give 2′-O-carbamates 3. Thermal melting studies of modified oligonucleotides revealed that the presence of the 2′-O-carbamate modification significantly destabilized DNA/RNA duplexes. A molecular-modeling study indicated that unfavorable steric interactions between the hydrogen of the NH group from the carbamate substituent and the anomeric hydrogen of the sugar residue on the same strand of the duplex may be the contributing factor causing destabilization.

Synthesis of peracetylated d-galactopyranosylidene dihalides

Upon treatment with aluminium trichloride in absolute chloroform, β- d -galactopyranose penta- O -acetate was converted in high yield into tetra- O -acetyl-β- d -galactopyranosyl chloride. In the presence of N -bromosuccinimide in boiling carbon tetrachloride, homolytic substitution of the anomeric hydrogen atom in this β-chloride occurred selectively to afford tetra- O -acetyl-1-bromo-β- d -galactopyranosyl chloride, in admixture with minor amounts of tetra- O -acetyl- d -galactopyranosylidene chloride. Bromine substitution by fluorine took place with a low stereoselectivity in tetra- O -acetyl-1-bromo-β- d -galactopyranosyl chloride when treated with 1.25 equiv silver fluoride in acetonitrile, whereas tetra- O -acetyl- d -galactopyranosylidene fluoride could be prepared in 54 % yield with 3.3 equiv AgF. The gem -difluoride could be deacetylated quantitatively. Upon treatment with 1,4-diazabicyclo〚2.2.2〛octane, peracetylated 1-bromo-β- d -galactopyranosyl chloride underwent 1,2-elimination of hydrogen bromide to afford 2,3,4,6-tetra- O -acetyl- d - lyxo -hex-1-enopyranosyl chloride in 33 % yield. Le traitement du β- d -galactopyranose penta- O -acétylé par le trichlorure d’aluminium dans le chloroforme absolu conduit au chlorure de β- d -galactopyranosyle tétra- O -acétylé. Par bromuration radicalaire en présence de N -bromosuccinimide dans le tétrachlorure de carbone à reflux, le β-chlorure est converti en chlorure de 1-bromo-β- d -galactopyranosyle tétra- O -acétylé et en gem -dichlorure correspondant, produit mineur difficile à séparer. En présence de fluorure d’argent (1,25 equiv) dans l’acétonitrile, le chlorure de 1-bromo-β- d -galactopyranosyle acétylé donne un mélange des chlorofluorosucres correspondants. Avec 3,3 equiv d’AgF, le fluorure de d -galactopyranosylidène tétra- O -acétylé est obtenu avec un rendement de 54 %. La déacétylation de ce gem -difluorure est quantitative. Le chlorure de 1-bromo-β- d -galactopyranosyle tétra- O -acétylé subit, en présence de 1,4-diazabicyclo〚2.2.2〛octane, une élimination d’acide bromhydrique qui conduit au chlorure de 2,3,4,6-tétra- O -acétyl- d - lyxo -hex-1-ènopyranosyle, avec un rendement de 33 % seulement.

Sensitivity of (1)J[C(1)-H(1)] magnitudes to anomeric stereochemistry in 2,3-anhydro-O-furanosides.

The magnitude of the one-bond coupling constant between C(1) and H(1) in 2,3-anhydro-O-furanosides has been shown to be sensitive to the stereochemistry at the anomeric center. A panel of 24 compounds was studied and in cases where the anomeric hydrogen is trans to the epoxide moiety, (1)J[C(1)-H(1)] = 163-168 Hz; and when this hydrogen is cis to the oxirane ring, ((1)J[C(1)-H(1)] = 171-174 Hz. In contrast, for 2,3-anhydro-S-glycosides, the size of the (1)J[C(1)-H(1)] is not sensitive to C(1) stereochemistry. Computational studies on all four methyl 2,3-anhydro-O-furanosides (5-8) demonstrated that (1)J[C(1)-H(1)] was inversely proportional to the length of the C(1)-H(1) bond. A previously reported equation, which relates C(1)-H(1) bond distance and atomic charges to (1)J[C(1)-H(1)] magnitudes, could be used to accurately predict the J values in the alpha-lyxo (5) and beta-ribo (8) isomers. In contrast, with the beta-lyxo (6) and alpha-ribo isomers (7), this equation underestimated the size of these coupling constants by 10-20 Hz.

Molecular origin for the thermal stability of Koshihikari rice amylopectin

The non-Newtonian behavior and dynamic viscoelasticity of Koshihikari rice amylopectin (waxy type) in aqueous solution were investigated. The flow curves, at 25°C, of Koshihikari amylopectin showed plastic behavior at various concentrations. The viscosity increased slightly with increase in temperature up to 25°C, then it decreased a little with further increase in the temperature at a concentration of 6%. The dynamic modulus showed very large values and stayed constant during increase in temperature at 2.0 and 4.0%, but a little increase of dynamic modulus was observed at 6.0% solution. The dynamic modulus decreased slightly upon addition of urea (4.0 M) or 85% DMSO and decreased gradually with increase in the temperature. The dynamic modulus, however, was lower in 0.10 M NaOH solution than in aqueous solution and decreased rapidly when the temperature reached 45°C, which was estimated to be a transition temperature. The results obtained support the mode of intramolecular associations within rice amylopectin molecules previously proposed. An anomeric hydrogen atom may take part in an intramolecular van der Waals forces of attraction with an adjacent OH-6 or methylene group of d-glucosyl residue.

Formation of anomeric phosphodiester linkages using H-phosphonate acceptors

A new way of constructing anomeric glycosyl phosphodiester linkages has been explored. Non-anomeric monosaccharide hydrogen phosphonate monoesters ( 5 and 9) have been used as acceptors in couplings using various benzylated galactosyl donors (trichloroacetimidate, thioglycoside, bromo and chloro sugars, 1–4, 7 and 8) and promoters to give, after oxidation, good yields of phosphodiester linked “disaccharides” ( 6 and 10), products usually obtained by using an anomeric hydrogen monophosphonate, a hydroxyl acceptor and pivaloyl chloride as coupling reagent.

Two modes of ligand binding in maltose-binding protein of Escherichia coli. Electron paramagnetic resonance study of ligand-induced global conformational changes by site-directed spin labeling.

Binding of ligands to the maltose-binding protein (MBP) of Escherichia coli often causes a global conformational change involving the closure of its two lobes. We have introduced a cysteine residue onto each of these lobes by site-directed mutagenesis and modified these residues with spin labels. Using EPR spectroscopy, we examined the changes, caused by the ligand binding, in distance between the two spin labels, hence between the two lobes. The binding of both maltose and maltotetraose induced a considerable closure of the N- and C-terminal lobes of MBP. Little closure occurred upon the binding of maltotetraitol or beta-cyclodextrin. Previous study by fluorescence and UV differential absorbance spectroscopy (Hall, J. A., Gehring, K., and Nikaido, H. (1997) J. Biol. Chem. 272, 17605-17609) showed that maltose and a large portion of maltotetraose bound to MBP via one mode (R mode or "end-on" mode), which is physiologically active and leads to the subsequent transport of the ligands across the cytoplasmic membrane. In contrast, maltotetraitol and beta-cyclodextrin bound to MBP via a different mode (B mode or "middle" mode), which is physiologically inactive. The present work suggests that the B mode is nonproductive because ligands binding in this manner prevent the closure of the two domains of MBP, and, as a result, the resulting ligand-MBP complex is incapable of interacting properly with the inner membrane-associated transporter complex.

Degradation of Methyl β-D-Ribopyranoside and Methyl β-D-Xylopyranoside by Oxygen in Aqueous Sodium Hydroxide Solution

Abstract Methyl β-D-ribopyranoside (1) and methyl β-D-xylopyranoside (2) were degraded by oxygen (0.682 MPa partial pressure) in 1.25 M sodium hydroxide at 120°C. The degradations of 1 and 2 were similar to the previously reported degradations of 1,5-anhydroribitol (3) and 1,5-anhydroxylitol (4), respectively.4 Both hydrogen peroxide and stable organic peroxides were detected in the reactions of 1 and 2. The riboside 1 degraded faster than the xyloside 2. This difference in reactivity is proposed to be a function of the relative acidity of the glycosides. Ionization of hydroxyl groups is postulated to be favored in 1, thus facilitating the initiation of the free radical degradation. The degradations of both 1 and 2 exhibited complex kinetics indicating autoinhibited reactions. In spite of the differences in reactivity, glycosidic bond cleavage occurred in approximately 60% of the degradations for both 1 and 2. C-1 radicals, resulting from abstraction of the anomeric hydrogen atom, are proposed to cause the observed autoinhibition via termination reactions with α-hydroxyhydroperoxyl radicals. However, decomposition of the glycosides via C-1 radicals is not believed to constitute a major degradation pathway since the reactivities of 1 and 2 were essentially the same as the analogous 1,5-anhydroalditols, i.e. 3 and 4, respectively. The major acidic degradation products of 1 and 2 were identical, but were formed in different relative ratios. The major acidic products were methoxyacetic acid, lactic acid, glycolic acid, glyceric acid, a methyl 3-C-carboxyfuranoside, and two isomeric 2-C-carboxyfuranosides.

Synthese Et Photochimie Des (Oxo-3)Butyl- α Et β -L-Arabinopyranosides

Abstract (3-Oxo) butyl-l-arabinopyranosides undergo Norrish II type photocyclization giving hydroxyspiroketals with a low stereo-selectivity but with a greater reactivity for α -l-anomers according to stereoelectronic effects for the photolysis of axial anomeric hydrogens.

Virtual coupling in the 1H NMR spectrum of N,N'-diacetyl chitobioside. Application to glycopeptides.

The unexplained line shape for the anomeric hydrogen resonance of the core GlcNAc observed in the 1H NMR spectra of high mannose N-linked glycopeptides (Bruch, R. C., and Bruch, M. D. (1982) J. Biol. Chem. 257, 3409-3413) can be accounted for by virtual coupling. Complete assignment, at various temperatures, of the 360-MHz 1H NMR spectrum of beta-methyl N,N'-diacetyl chitobioside confirms this interpretation. This analysis has revealed the existence of a long range chemical shift perturbation in these glycopeptides which is interpreted as arising from their specific three-dimensional structure.

Determination of glycopeptide primary structure by 360-MHz proton magnetic resonance spectroscopy.

A detailed analysis of the proton magnetic resonance spectral parameters for the anomeric and C2 hydrogen resonances of 63 different glycopeptides and oligosaccharides of known structure reveals a general method for the determination of the primary structure of glycopeptides for most currently known classes of structures. In particular, a two-dimensional display formed by plotting mannosyl C1-H vs. C2-H chemical shifts demonstrates that these pairs of values are sensitive to long-range perturbation by remote substitution by hexoses as well as to direct substitution effects. A total of 41 Cl-H/C2-H chemical shift clusters have been defined which characterize unique structural microenvironments. On the basis, the sequence and branching pattern for most structures can be derived. Corroborative evidence is obtained from an examination of the chemical shifts of the galactosyl and N-acetylglucosaminyl anomeric hydrogens as well as other features of the spectrum.

Photocyclisation des (oxo-3)-butyl glycopyranosides

3-Oxo butyl glycopyranosides undergo Norrish type II photocyclization giving hydroxyspiroketals. The influence of the anomeric configuration and of different substituents at C-2 has been studied. The favored photocyclization of various β-glycosides occurs with retention of configuration and is interpreted in terms of the greater stability of the radical formed by abstraction of the axial anomeric hydrogen atom.