Untersuchung der 13c-kernresonanz-spektren der acht isomeren 1,6-anhydro-β-D-hexopyranosen

The signals of the ¹³C-n.m.r. spectra of the eight isomeric 1,6-anhydro-β-D-hexopyranoses having the ¹C₄ conformation were assigned by comparison with the spectra of selectively deuterated derivatives and by observation of the substituent effect of the O-isopropylidene derivatives. Of the two substituted C atoms in the O-isopropylidene derivatives, the signal of the equatorially substituted C atom was shifted to a lower field more strongly than that of the carbon atom bearing an axial substituent. The chemical shifts and their calculation with empirical parameters are discussed.     

1H- and 13C-N.M.R. spectra of eledoisin and intermediate oligopeptides.

The 1H- and 13C-n.m.r. spectra of eledoisin and minor oligopeptides were measured and assigned. The proton spectra were interpreted on the basis of homonuclear decoupling, chemical shift criteria and spectra simulation. The information obtained was used in the assignment of the 13C spectrum via heteronuclear 1H-13C. The steric arrangement of proline residue was deduced from the 13C spectrum. Moreover the similarity of the 13C spectrum of eledoisin with that of component oligopeptides suggests that no considerable conformational change occurs in the undecapeptide relative to the component fragments.     

Properties of C-N.M.R. spectra of O-(1-carboxyethylidene) derivatives of methyl β-d-galactopyranoside: models for determination of pyruvic acid acetal structures in polysaccharides

¹³C-N.m.r. spectra were recorded of compounds containing O-(1-carboxyethylidene) groups linked to galactopyranose and fucopyranose derivatives. These compounds are useful as aids in determination of the positions and configurations of pyruvic acid acetal substituents in polysaccharides. Chemical shifts of non-protonated acetal carbons depend on whether the acetal ring is 5-membered (δ_c 107–109.5) or 6-membered (δ_c 100.5–102.4). The C-3 signals of 3,4-(1-carboxyethylidene) acetals are typical, being at δ_c 81 and in the case of the barium salt of the methyl β-d-galactopyranoside derivative. The exact value depends on the configuration, whether it is as in 6 (δ_c 81.1) or 5 (δ_c 80.4). The CH₃ signals of proton-n.m.r. spectra are also diagnostically useful, falling at δ 1.97 and 2.07 respectively. (The foregoing shift-values are pH-dependent). The pyruvylated galactan from the snail, Pomacea lineata, was shown to contain some residues that could be assigned a structure corresponding, in the positions of acetal substitution and acetal configuration, to structure 6. Compound 6 (barium salt) is of interest as its ¹³C-n.m.r. spectrum lacks non-protonated carbonyl and acetal carbon resonances, when obtained by the usual procedures. While this is principally because of long T₁ values, the non-protonated acetal carbon signals are comparatively broad, possibly through slow conformational interchange. In the case of the carbonyl resonance, the lack of sensitivity is because of a low n.O.e. value of 1.4, approximately one half that of other carbon atoms in the molecule.     

The 13C-N.M.R. spectra of disaccharides of D-glucose, D-galactose, and L-rhamnose as models for immunological polysaccharides.

Complete assignments of the 13C-n.m.r. spectra of disaccharides having beta-glycosidic linkages are presented and discussed. The disaccharides of D-glucose, D-galactose, L-rhamnose, 2-acetamido-2-deoxy-D-glucose, and 2-acetamido-2-deoxy-D-galactose are model compounds for 13C-n.m.r. studies of immunological polysaccharides. Changing the nature of the reducing glucopyranose rings (D-glucose to L-rhamnose) has no important influence on the chemical shifts of the carbons of the non-reducing glucopyranose ring (D-glucose). The converse is also true: the chemical shifts of the carbons of the reducing glucopyranose ring (L-rhamnose) are not noticeably affected by a change of the non-reducing unit (D-glucose to D-galactose or 2-acetamido-2-deoxy-D-glucose).     

Configuration of the acetal carbon atom of pyruvic acid acetals in some bacterial polysaccharides

The configuration at the acetal carbon atom of pyruvic acid acetals present in some extracellular bacterial polysaccharides has been investigated. Assignment of the absolute configuration was made by comparing signals in the ¹³C- and ¹H-n.m.r. spectra of the polysaccharides with those of model substances. The S-configuration was demonstrated in eight polysaccharides in which pyruvic acid is linked to O-4 and O-6 of D-glucopyranosyl or D-mannopyranosyl residues. The R-configuration was demonstrated in four polysaccharides in which pyruvic acid is linked to O-4 and O-6 of D-galactopyranosyl residues. Consequently, in each of these acetals, which form 1,3-dioxane rings, the methyl group is equatorial and the carboxyl group axial. The S-form was further demonstrated in four polysaccharides in which the pyruvic acid is linked to O-3 and O-4 of D-galactopyranosyl groups.     

Preparation and N.M.R. studies of pyruvic acid and related acetals of pyranosides: configuration at the acetal carbon atoms

Stereoisomeric pairs of pyruvic acid and related acetals linked to the 3,4- and 4,6-positions, respectively, of the anomeric methyl d-galactopyranosides and the corresponding acetals linked to the 4,6-positions of the anomeric methyl d-glucopyranosides have been prepared by conventional methods, and their structures have been assigned. Their ¹H- and ¹³C-n.m.r. spectra have been recorded. The differences in chemical shifts obtained for stereoisomeric pairs of acetalic CH₃ groups are of sufficient magnitude to make possible the unequivocal determination of the stereo-chemistry of pyruvic acid acetals in naturally occurring polysaccharides.     

Structural investigation of the capsular polysaccharide from Klebsiella serotype K-34 and its characterization by N.M.R. spectroscopy

The repeating unit of the capsular polysaccharide from Klebsiella type K-34 has been established by methylation, partial hydrolysis, and Smith degradation to consist of a hexasaccharide repeating-unit built up of four l-rhamnose, one d-glucose, and one d-galacturonic acid residues. The anomeric configurations of the linkages was determined by proton and ¹³C-n.m.r. spectroscopy at each step of the degradation procedures. Further evidence for the configurations of the glycosidic linkages involved the use of proton T₁ relaxation-times and oxidation by chromium trioxide. The data allowed assignment of the following structure for the repeating unit:     

A 13C-N.M.R.-Spectral study of a gel-forming,branched (1→3)-β-d-glucan, (lentinan) from lentinus edodes, and its acid-degraded fractions. Structure,and dependence of conformation on the molecular weight

The structure and conformation of lentinan, an anti-tumor, branched (1→3)-β-d-glucan from Lentinus edodes, and its acid-degraded, lower molecular-weight fractions have been investigated by ¹³C-n.m.r. spectroscopy. It is found that their ¹³C-n.m.r. spectra are considerably changed, depending on the molecular weight. The conformational behavior as studied by ¹³C-n.m.r. spectroscopy is consistent with that revealed by a study of the shift in the absorption maximum of Congo Red complexed with lentinan and its acid-degraded fractions. It is found that the water-soluble fraction II (mol. wt. 3,640) gives rise to well-resolved ¹³C-n.m.r. spectra; the ¹³C-signals are assigned to (1→3)-β-d-glucan and branch points at C-6. The branched structure is also confirmed by examination of the ¹³C-n.m.r. spectra of the compounds in dimethyl sulfoxide. For the gel state of the fractions of higher molecular-weight, lentinan (mol. wt. 1,000,000) and fraction IV (mol. wt. 16,200), however, ¹³C-n.m.r. spectra of considerably attenuated signal-amplitude are observed. The fact that the ¹³C-signals of the β-d-(1→3)-linked main chain and side chains are completely suppressed is explained as a result of immobilization caused by their taking an ordered conformation. The ¹³C-resonances observed in the gel state, which are assigned to β-d-(1→6)-linkages, are unequivocally assigned to the side chains (of disordered conformation). Finally, the ordered conformation of both the β-d-(1→3)-linked main chain and side chains is identified as the single-helix conformation, which tends to form multiple helixes as junction zones for gel structure.     

Hydrogenolysis of the isomeric 1,2:4,6-di-O-benzylidene-α-d-glucopyranose derivatives with the LiAlH4AlCl3 reagent

Both isomers of 1,2:4,6-di-O-benzylidene-α-d-glucopyranose (and their 3-O-acetyl and 3-O-benzyl derivatives) have been prepared and their ¹H- and ¹³C-n.m.r. spectra assigned. The mode of hydrogenolysis of the dioxolane ring in these isomers by the LiAlH₄AlCl₃ reagent is determined by the configuration at the acetal carbon and is independent of the electronic character of the two oxygen atoms.     

Structure and thermal interconversion of cyclobilirubin IX alpha.

One of the two main photoproducts in bilirubin metabolism during phototherapy in neonatal hyperbilirubinaemia is (EZ)-cyclobilirubin. However, it has not yet been possible to come to a final conclusion as to its chemical structure, despite the fact that much effort has been expended on the problem. The present paper demonstrates that (EZ)-cyclobilirubin is formed by the intramolecular cyclization of the C-3-vinyl group with the position at C-7 rather than at C-6, without delta-lactone-ring formation. The evidence comes from 13C-n.m.r. spectra, which indicate that an oxygen-bound quaternary carbon atom is not present, and from 1H-n.m.r. spectra, which indicate that the orientation of the methyl group at C-2 is equatorial; these findings are supported by mass spectra. The existence of both an epimeric relationship at C-7 between (EE)- and (EZ)-cyclobilirubins A and B and of steric isomers of the hydrogen atom and methyl group at C-2 is supported by the fact that the methyl-group protons at C-2 and C-7 are observed as a paired signal in 1H-n.m.r. spectra, and that new signals at C-7, C-2 and C-3 beta appear in 13C-n.m.r. spectra, that mass spectra of (EZ)-cyclobilirubins A and B are extremely similar and that, furthermore, thermal interconversion between (EE)- and (EZ)-cyclobilirubins A and B is observed.     

13C-n.m.r. spectra of some ribitol teichoic acids

Proton-decoupled ¹³C-n.m.r. spectra were determined for D₂O solutions of several wall teichoic acids containing glycosylated ribitol 1,5-diphosphate residues and for their dephosphorylated repeating-units. Assignments were made by correlating the chemical shift values observed with those reported for isolated constituents, allowing for perturbations of the latter resonances because of the presence of O-glycosyl or phosphodiester bonds. Anomeric configurations of hexopyranosyl residues and their position of substitution on ribitol were indicated from the distinctive chemical shifts of the carbons concerned. Three-bond ¹³C³¹P couplings (6–8 Hz) were observed, and two-bond ¹³C³¹P couplings were indicated by broadened signals. The lack of resolution for the latter resonances is probably due to the heterogeneous nature of the polymers.     

Comparison of the 13C-n.m.r. spectra of gangliosides GM1 with those of GM1-oligosaccharide and asialo-GM1

The ¹³C-n.m.r. spectra of asialo-G_M1 and G_M1-oligosaccharide are completely assigned and compared to those previously found for intact G_M1 and for the series G_M4, G_M3, G_M2, G_M1, G_D1a, G_D1b, and G_T1b. Removal of the ceramide residue from G_M1 liberated a free, reducing aldehyde group, which was reflected in a doubling of the ¹³C-n.m.r. signals assignable to the d-glucose residue because of α,β equilibrium. The spectrum of asialo-G_M1 lacks the resonances from the sialic acid residue, as expected; in addition, several resonances from the neutral gangliotetraglycosyl residue shifted to different field positions after removal of sialic acid from G_M1. These resonances include that of C-4 of the inner β-d-galactosyl residue, and C-1 of the 2-acetamido-2-deoxy-d-galactosyl residue that is near the site of attachment of the sialosyl residue. The differences between the chemical shifts of the carbon resonances of oligomeric and monomeric saccharides, termed linkage shifts, provide a quantitative assignment aid. They are ～ $\text{1}\text{3}$ of those for residues linked to sialic acid than those for residues linked to the neutral hexose chain. Correlations among linkage shifts for pairs of glycosidically-linked carbon atoms for asialo-G_M1 and G_M1-oligosaccharide were compared with those for the series of gangliosides G_M4 to G_T1b, and differences are noted for resonances for carbon atoms near the sialic acid residue. The spectrum of ganglioside G_M1b, a positional isomer of G_M1 whose ¹³C-n.m.r. spectrum has not yet been observed, is predicted.     

Proton and carbon-13 nuclear magnetic resonance studies on methyl (methyl d-galactosid)uronates and their per-O-acetyl derivatives

The ¹H- and ¹³C-n.m.r. spectra of the anomeric methyl (methyl d-galactosid)uronates, as well as the ¹H-n.m.r. spectra of their acetyl derivatives, were analyzed. The spectra of the unacetylated d-galactopyranosiduronates showed good correlation with those of the corresponding anomeric d-galactopyranuronic acids and their methyl esters, and with those of the anomeric methyl d-galactopyranosides. From the values of the chemical shifts and coupling constants, it was concluded that the anomeric methyl (methyl d-galactopyranosid)uronates and their corresponding peracetates are in the ⁴C₁(d) conformation. The chemical shifts in the ¹³C-n.m.r. spectra show good correlation with those of the methyl d-galactosides. The signals of the furanose derivatives appear at fields lower than those of the corresponding pyranose compounds.     

N.M.R. spectroscopy and calcium binding of sialic acids: N-glycolylneuraminic acid and periodate-oxidized N-acetylneuraminic acid

N.m.r. spectroscopy (¹H- and ¹³C-) of N-glycolylneuraminic acid, and of its interaction product with Ca²⁺ at pH 7, indicated that a 1:1 complex is formed, with a formation constant of 193 M^?1 [compared to 121 M^?1 for N-acetylneuraminic acid (1)]. From analysis of electric-field shifts, an approximate position of the Ca²⁺ ion in the complex is inferred, with the hydroxyl group of the N-glycolyl group providing the additional binding. Compound 1 was oxidized with sodium periodate, and ¹³C-n.m.r. spectroscopy was applied in an attempt to identify the aldehyde formed, and to demonstrate that the loss of the glycerol-1-yl side-chain (carbon atoms 8 and 9) decreases its Ca²⁺ ion-binding capacity.     

Kinetic cyclohexylidenation and isopropylidenation of aldose diethyl dithioacetals

Aldose diethyl dithioacetals react with 1.2 equivalents of 1-ethoxycyclohexene or 2-methoxypropene in N,N-dimethylformamide at 0° with p-toluenesulfonic acid as catalyst to give the five-membered ring acetal attached to the two terminal oxygen atoms as the major product in every case. In most instances, a small proportion of the terminal, six-membered ring acetal was also obtained, and in a few cases, terminal seven-membered ring acetals were also isolated. Cyclohexylidenation at room temperature gave the same products, but isopropyl-idenation at room temperature resulted in certain cases in partial rearrangement. Cyclohexylidenation reactions gave smaller proportions of the minor six- and seven-membered ring products. Structures were established from ¹³C-n.m.r. and mass spectra. The ¹³C-n.m.r. spectra of model cyclohexylidene derivatives were found very similar to those of isopropylidene derivatives previously studied. Two new features useful for structure determination were noted when the spectra of the precursor diols were compared with those of both types of derived acetals; the chemical shift of C-2 of a 1,3-propanediol derivative was shifted upfield by 6–9 p.p.m. on acetalation and the shifts of the diol carbon atoms attached to oxygen were affected according to the type of acetal and ring-size formed. Similar observations were made for methylene acetals.     

The synthesis and N.M.R. spectroscopy of derivatives of 6-amino-6-deoxy-D-galactose-6-15N

Derivatives of 6-amino-6-deoxy-D-galactose-6-¹⁵N have been synthesized by reaction of the 6-deoxy-6-iodo (1) or 6-O-p-tolylsulfonyl derivative of 1,2:3,4-di-O-isopropylidene-α-D-galactopyranose with potassium phthalimide-¹⁵N. The reaction of 1 also yielded an elimination product, 6-deoxy-1,2:3,4-di-O-isopropylidene-β-L-arabino-hex-5-enopyranose. The structures of the 6-amino-6-deoxy-D-galactose derivatives and their precursors were characterized by proton- and ¹³C-n.m.r. spectroscopy, with confirmation of the ¹³C assignments by selective proton decoupling. Selective broadening of the C-1, C-4, C-5, and C-6 resonances of 6-amino-6-deoxy-1,2:3,4-di-O-isopropylidene-α-D-galactopyranose by low concentrations of cupric ion was observed, and studied by computerized measurements of the ¹³C linewidths. The application of this broadening to ¹³C-spectral assignments of amino sugar derivatives is indicated.     

Structural analysis of comb-like,amylose derivatives by 13C-N.M.R. spectroscopy

¹³C-N.m.r. spectra have been recorded for previously reported, comb-like derivatives of amylose produced by orthoester and Helferich condensation of D-glucose to amylose. As known from monomeric studies, the Helferich condensation conditions (the presence of mercury salts) favor α-D-glucosylation, and orthoester condensation conditions favor β-D-glycosylation. It was anticipated that, for these polymer condensations, the Helferich and orthoester condensations would also favor α- or β-D-glycosylation, respectively. The ¹³C-n.m.r. spectra of representative products of the Helferich and orthoester condensations confirmed the presence of 4,6-di-O-substituted α-D-glucopyranosyl residues, and also the degree of polymer linearity derived from independent, analytical data. However, these spectra indicate extensive, if not exclusive, β-D-glycosylation for both the helferich and the orthoester conditions. These results were obtained by using the product from an enzymically synthesized, strictly linear amylose in the Helferich condensation reaction.     

Assignment of configuration at quaternary centres in pairs of 3-C Hydroxymethyl and 3-C methyl branched chain 1,2:4,6-diacetalated aldohexopyranose derivatives using 13C-N.M.R. spectoscopy

The configuration at the C-3 quaternary carbon atoms in two pairs (1 and 2, 3 and 4) of 3-C-hydroxymethyl, branched-chain, 1,2:4,6-diacetalated aldohexo-pyranoses have been determined from their ¹³ C-n.m.r. spectra. The stereochemical assignments were achieved by comparison of the spectra with those of the Z (13) and E isomers (14) of 4-tert-butyl-l-hydroxymethylcyclohexanol and with those of the corresponding diacetalated gluco- and allo-pyranoses (5, 6, 9, and 10). The spectra of 13 and 14 showed that an axial hydroxyl group shielded the α, β, and μ ring carbon atoms more than an axial hydroxymethyl group and that the carbon atom in the latter group was shielded relative to that in an equatorial hydroxymethyl group The spectra of 5, 6, 9, and 10 indicated the effect of an axial HO-3 on the shifts of the carbon atoms in the 1,2-O-alkylidene groups. The stereochemistry of an isomeric pair of 1,2:4,6-di-O-alkylidene-3-C-methyl-aldohexopyranoses (11 and 12) has also been determined.     

Distribution of substituents in O-(2-hydroxyethyl)cellulose: A 13C-N.M.R. approach

O-(2-Hydroxyethyl)cellulose was converted into a mixture of the corresponding d-glucitol derivatives by hydrolysis followed by reduction of the sugars with NaBH₄. On the basis of the spectra of individual O-(2-hydroxyethyl)-d-glucitols, the ¹³C-n.m.r. spectrum of this mixture was assigned to the extent that permitted quantitative analysis in terms of monomer composition of the polymer. The monomer mole-fractions conform to a statistical, kinetic model that assumes that the reactivity of the 3-hydroxyl group of the d-glucosyl residues of cellulose depends on the state of substitution at O-2. The relative rate-constants of the hydroxyl groups in the (hydroxyethyl)ation reaction are k₂:k₃:k₃′:k₆:k_x = 6.0:1.0:4.0:11.1:34.6, indicating that the reactivity of OH-3 increases fourfold upon (hydroxyethyl)ation of OH-2.     

Multi-nuclear (119Sn, 13C, 1H), fourier-transform,N.M.R. studies of di- and tri-butylstannyl ethers of carbohydrates

¹¹⁹Sn-N.m.r. spectra are reported for toluene solutions of the tributylstannyl ethers of 2,3,4,6-tetra-O-methyl-d)-glucose, 1,2:3,4-di-O-isopropylidene-α-d-galactopyranose, methyl 2,3-di-O-methyl-α-d-glucopyranoside, and methyl 4,6-O-benzylidene-α-d-glucopyranoside, and the dibutylstannyl ether of the last sugar. In the reaction of bis(tributyltin) oxide with methyl 4,6-O-benzylidene-α-d-glucopyranoside in toluene, HO-3 is much more reactive than HO-2. The presence of the various tin-containing species is readily apparent from the ¹¹⁹Sn-spectra. The importance of suppressing the nuclear Overhauser effect is demonstrated. The appearance of ¹¹⁹Sn satellites in the ¹³C-n.m.r. spectra demonstrates couplings of the types, ²J(¹¹⁹Sn-O-¹³C) and ³J(¹¹⁹Sn-O-C-¹³C), forthe first time, and, together with the ¹³C-chemical shifts, facilitates the determination of the site of substitution. The ¹¹⁹Sn-chemical shifts show that different states of coordination may be recognised. However, although different sites of substitution produce separate resonances, no simple relationship between shift and position is found. ¹³C-Chemical shifts are reported for methyl 4,6-O-benzylidene-α-d-glucopyranoside and its tributylstannyl ethers, and substituent effects are discussed.