Anomeric Carbon Atom Research Articles

Measurement of carbon-13-proton coupling-constants in oligosaccharides by two-dimensional carbon-13 N.M.R. spectroscopy

A two-dimensional, n.m.r. experiment, 13C two-dimensional J spectroscopy, has been used to facilitate the measurement of 1H- 13C couplings in spectra of oligosaccharides. One-bond, 13C- 1H coupling-constants ( 1 J CH) have been determined for all of the 13C resonances of raffinose [ O-α- d-galactopyranosyl-(1→6)-α- d-glucopyranosyl β- d-fructofuranoside], and for the anomeric carbon atoms of a single tetrasaccharide repeating-unit [ O-α- d-galactopyranosyl-(1→2)- O-α- l-rhamnopyranosyl-(1→3)- O-β- l-rhamnopyranosyl-(1→4)- l-rhamnopyranose] of the cell-wall polysaccharide of Klebsiella type K32 bacteria.

Catalysis by β-glucosidase A3of Aspergillus wentii

(1)α-Deuterium kinetic isotope effects on Vmax. for hydrolysis of both β-D-glucopyranosylpyridinium ions and aryl β-D-glucopyranosides are in the range kH/kD 1.08–1.14, indicating that bond-breaking limits the rate of hydrolysis of both sets of substrates. The variation of kcat with aglycone acidity, expressed by log kcat=A+βlgpKa, is governed by a βlg value of –0.96 ± 0.19 for the N-glycosides and –0.05 ± 0.05 for the O-glycosides. The latter, low value of |βlg| is evidence for extensive proton donation to the oxygen at the transition state, even for the departure of acidic aglycones. The dependence of rate on protonation of a group of pKa < 6 required by this idea is indeed observed. (2) Comparison of log kcat values with spontaneous hydrolysis rates indicates that nucleophilic and non-covalent interactions accelerate C–N bond cleavage in the ES complex by a factor of 10(8 + 0.3[pka]N) for glucosyl pyridinium salts where [pKa]N is the pKa of the pyridine. On the assumption that these interactions are similar for O-glucosides, proton donation to the aglycone oxygen atom can be estimated to contribute a rate-enhancement of 10(0.1 + 0.7[pKa]O), where [pKa]O is that of the free phenol. (3)D-Glucono-δ-lactone and 5-amino-5-deoxy-D-gluconolactam are bound 102.8 and 102.2 times, respectively, more tightly than β-D-glucopyranose, because of their analogy to a transition state in which α-deuterium kinetic isotope effects have shown the anomeric carbon atom to have substantial sp2 character. (4) Cationic inhibitors are bound 102.5–103.5 times more tightly than directly comparable neutral ones, if the positive charge resides on the equatorial substituent at C-1, but protonated 2-amino-2-deoxyglucose is bound no more tightly than glucose. This indicates the presence of a negative charge in the El complex near C-1 on the α face of the pyranose ring (an aspartate residue previously identified by covalent labelling) which is partly compensated by a positive charge near C-2.

The non-bonded interactions in D-glucose and β-maltose: an ab initio study of conformations produced by empirical force-field calculations

Minimal basis set SCF-MO computations on conformations of α- D-gluco-pyranose, β- D-glucopyranose, and β-maltose resulting from empirical energy minimisation reproduce known trends in relative energy. Analysis of electron population and molecular orbital valency-state energy leads to separation of atoms into classes, two for oxygen, three for carbon, and two for hydrogen, the classes being correlated with the chemical environments of the atoms. Partitioning of the total energy into two-centre terms gives a quantification of non-bonded interactions, leading to potential energy curves for interactions of all types of atom present. Peculiar details of the electronic structure at and around the anomeric carbon atoms are noted: C(1s) chemical shift is insensitive to configuration, but depends on conformation.

The X-ray crystal structure of 6-deoxy-α- l-sorbofuranose. Conformational analysis of ketohexofuranosides and their comparison with ribofuranosides and arabinofuranosides

The crystal and molecular structure of 6-deoxy- l-sorbose have been determined by the application of multisolution methods and refined to an R-index of 0.063 for 560 reflections, using three-dimensional intensity data collected on a Picker automatic diffractometer. The compound crystallizes in the space group P2 12 12 1 with unit-cell dimensions a = 18.470 (10), b = 7.636 (10), and c = 5.371 (8) Å; Z = 4. The molecule occurs as the α-furanose form, which is also the preponderant tautomer in solution. The puckering of the furanoid ring is C-3′- exo-C-4′- endo ( 3 T 4) [equivalent to C-2′- exo-C-3′- endo ( 2 T 3) in the numbering for d-ribose], with P and τ m angles of -6.5 and 42.7° respectively. Conformational analysis of the known ketofuranosides shows that the 3 T 4 ( 2 T 3 in d-ribose numbering) puckering mode, which is typical of α-nucleosides, is favored, in contrast to the favored 3 T 2 or 2 T 3 puckering mode for the β- d-ribonucleosides and β- d-arabinonucleosides. The conformational differences among furanoid rings are mainly influenced by the configuration at the anomeric carbon atom. The favored orientation about the C-2′-C-1′ bond (O-5′-C-2′-C-1′-O-1′)of the ketofuranosidesis — gauche. All four hydroxyl groups are involved in donor-acceptor hydrogen bonding, and O-4′-8 appears to be involved in a bifurcated hydrogen bond to O-2′ and O-3′ of neighboring molecules.

ChemInform Abstract: THE KOENIGS‐KNORR REACTION

Publisher Summary This chapter focuses on Koenigs–Knorr reaction used for the synthesis of glycosides. The Koenigs–Knorr reaction is applicable to the preparation of both aryl and alkyl glycosides, and is widely used for the synthesis of glycosides having complex groups attached to the anomeric carbon atom—particularly oligosaccharides. The procedure involves the treatment of a per- O acylated glycosyl halide with an alcohol in the presence of a heavy-metal salt or an organic base as the acid acceptor; the latter enhances the rate of reaction and also prevents side reactions. It is noted that under the usual reaction-conditions the more-stable anomer is obtained, and the less stable anomer can be prepared only by a kinetically controlled reaction. Per- O -acylated glycosyl bromides react faster than the corresponding chlorides, and are therefore preferred for most reactions. Silver carbonate or silver oxide is commonly used as the acid acceptor in the Koenigs–Knorr reaction. Mercury (II) acetate instead of a silver salt has been also used.

The beta-glucosidase from Botryodiplodia theobromae Pat. Kinetics of enzyme-catalysed hydrolysis of o-nitrophenyl beta-D-glucopyranoside in dioxan/water.

1. The hydrolysis of o-nitrophenyl beta-D-glucopyranoside by the high-molecular-weight beta-glucosidase (beta-D-glucoside glucohydrolase, EC 3.2.1.21) from Botryodiplodia theobromae Pat. has been studied in the presence of added dioxan. 2. At donor saturation, the maximum rate of hydrolysis in the presence of up to 50%(v/v) dioxan was pH4.3-4.5 (pH of the buffer system in water) in McIlvaine's buffer. 3. Increasing dioxan concentrations progressively decreased the maximum rate of hydrolysis. 4. The rate of enzyme-catalysed reaction was enhanced at high donor concentrations, but inhibited at low donor concentrations in the presence of glycerol, methanol, fructose of sucrose. 5. The hydrolytic reaction was found to proceed with retention of configuration at the anomeric carbon atom. 6. The kinetics of the enzyme-catalysed process in the presence of added acceptors indicated that water was necessary for the maintenance of the active enzyme conformation apart from its acceptor function.

3-β- d-erythrofuranosyl-1-phenylpyrazolo[3,4- b]quinoxaline, a new C-nucleoside analog

Dehydration of the hydroxyalkyl chain of 1-phenyl-3-( d- arabino-tetritol-1-yl)pyrazolo[3,4- b]quinoxaline gave the C-nucleoside 3-β- d-erythrofuranosyl-1-phenyl-pyrazolo[3,4- b]quinoxaline ( 2) in 82% yield. The structure, and the configuration at the anomeric carbon atom, of 2 were elucidated by periodate oxidation, c.d. and n.m.r. spectroscopy, and mass spectrometry. N.m.r.-spectral and c.d. studies revealed that, due to the large size of the heterocyclic base, compound 2 is formed by inversion in the configuration or C-1 of the side chain. The mechanism of the dehydrative cyclization with inversion is discussed.

Improved synthesis of n-octyl-beta-D-glucoside: a nonionic detergent of considerable potential in membrane biochemistry.

An improved synthesis for the nonionic detergent n-octyl-beta-D-glucoside (detergent 2) is described. The key modification over earlier methods is the utilization of n-octyl alcohol as the limiting reagent in the condensation between bromide 1 and n-octyl alcohol. A 60-70% overall yield of 2 is obtained without isolation of the intermediate. The beta-configuration at the anomeric carbon atom of 2 was confirmed by 100 mHz NMR spectroscopy.

39] Carbohydrate binding sites

Several carbohydrate analogs incorporating haloacetyl or epoxide groups have been synthesized and evaluated as affinity labels for carbohydrate binding sites in proteins. Analogs incorporating photosensitive functions (photoaffinity labels) have also been described. This article deals with the synthesis and properties of representative compounds of the above type, in particular those in which the reactive function is attached to the anomeric carbon atom of the carbohydrate. The glycosylamines (1-amino sugars) are easily accessible by treatment of the appropriate aldose with anhydrous methanol saturated with ammonia. The synthesis of β-D-galactosylamine has been examined in this chapter. Apart from this the chapter also examines Epoxypropyl Glycosides and Photoaffinlty Labels.

Enzymatic studies on a cellulase system of Trichoderma viride. IV. Purification and properties of a less-random type cellulase.

A cellulase [EC 3.2.1.4] component was purified from a crude cellulase preparation of Trichoderma viride (Meicelase) by consecutive column chromatography procedures, and was designated as cellulase III. The enzyme was homogeneous on polyacrylamide gel disc electrophoresis. The molecular weight of the enzyme was estimated to be about 45,000 by gel filtration. The optimum pH and temperature of the enzyme were pH 4.5-5.0 and 50 degrees, respectively. The enzyme was stable over the range of pH 4.5-7.5 at 4 degrees for 24 hr, and retained 40% of the original carboxymethylcellulose-saccharifying activity after heating at 100 degrees for 10 min. The enzyme was completely inactivated by 1 mM Hg2+, and partially by 1 mM Ag+ and Cu2+. The enzyme was characterized as a less-random type cellulase on the basis of its action on carboxymethylcellulose. The enzyme split cellohexaose, retaining the beta-configuration of the anomeric carbon atoms in the hydrolysis products. The Km values of cellulase III for cellooligosaccharides decreased in parallel with increase of the chain length of the substrates, while Vmax values showed a tendency to increase. The enzyme produced predominantly cellobiose and glucose from various cellulosic substrates as well as from higher cellooligosaccharides. Cellulase III preferentially attacked the aglycone linkage of p-nitrophenyl beta-D-cellobioside. The enzyme was found to catalyze the rapid synthesis of cellotetraose from cellobiose (condensation action).

Immunochemical studies on methyl α- and methyl β-glucosaminide-azoprotein conjugates

Conjugates consisting of methyl 2( p-azobenzamido)2-deoxy-α- d-glucopyranoside and methyl 2( p-azobenzamido)-2-β- d-glucopyranoside coupled to bovine serum albumin were used as synthetic antigens. Rabbits immunized with artificial antigen provided specific anti-methyl α-glucosaminide or anti-methyl β-glucosaminide anti-hapten sera. Quantitative hapten inhibition was employed to elucidate the specificity of anti-hapten combining sites and to evaluate some structural and configurational features contributing to the immunochemical interaction with the antibody. It is shown that the configuration at the anomeric carbon atom makes a major contribution to the immunochemical specificity of the anti-hapten antibodies against α- and β-methyl glycosides.

Synthesis of Naturally Occurring C-Nucleosides, Their Analogs, and Functionalized C-Glycosyl Precursors

Publisher Summary The C-nucleosides are a group of C-glycosylated heterocycles in which the anomeric carbon atom is attached to the heterocycle by a C-C bond. C-nucleosides have been mainly from fermentation sources, and have been found to exhibit a variety of interesting biological properties. Pyrazomycin has significant antiviral activity. Formycin, formycin B, and oxazinomycins exhibit, in addition, antitumor activity. The biological importance of most of the naturally occurring C-nucleosides has prompted the exploration of synthetic routes leading to these compounds and their analogs. As synthetic targets, the C-nucleosides have deceptively simple structures, and the design of synthetic routes to them must take two important factors into account. Firstly, the methods selected for C-C bond formation at the anomeric center should be stereocontrolled because the structures known thus far are, with two exceptions, β-D-glycosyl compounds. Secondly, the carbon atom attached to the glycosyl group in a C-nucleoside precursor should be appropriately substituted or be amenable to substitution, so as to allow the elaboration of the other heterocyclic portion of the molecule.

Favorable Conformations of 2-Amino-2-deoxy-d-hexopyranose Derivatives

Abstract The conformational free energies of 2-amino-2-deoxy (hydrochloride) and 2-acetamido-d-deoxy derivatives of d-glucose, d-galactose, and d-mannose were calculated by using the empirical potential functions. The most stable conformations of these amino sugars were obtained for α- and β-anomers in the Cl and 1C chair forms through the procedure of searching for the energy minimum. The results of the energy calculations indicate that the increased anomeric effect in the protonated and N-acetylated amino derivatives in an aqueous solution is mainly due to the electrostatic interaction between the positive-charged amino group on C(2) and the hydroxyl group on the anomeric carbon atom, C(1).

Enzymatic studies on a cellulase system of Trichoderma viride. III. Transglycosylation properties of two cellulase components of random type.

Two highly purified cellulases [EC 3.2.1.4], II-A, and II-B, were obtained from the cellulase system of Trichoderma viride. Both cellulases split cellopentaose retaining the beta-configuration of the anomeric carbon atoms in the hydrolysis products at both pH 3.5 and 5.0. The Km values of cellulases II-A and II-B for cellotetraose were different, but their Vmax values were similar and those for cellooligosaccharides increased in parallel with chain length. Both cellulases produced predominantly cellobiose and glucose from various cellulosic substrates as well as from higher cellooligosaccharides. Cellulase II-A preferentially attacked the holoside linkage of rho-nitrophenyl beta-D-cellobioside, whereas cellulase II-B attacked mainly the aglycone linkage of this cellobioside. Both cellulases were found to catalyze the synthesis of cellotriose from rho-nitrophenyl beta-D-cellobioside by transfer of a glucosyl residue, possibly to cellobiose produced in the reaction mixture. They were also found to catalyze the rapid synthesis of cellotetraose from cellobiose, with accompanying formation of cellotriose and glucose, which seemed to be produced by secondary random hydrolysis of the cellotetraose produced. The capacity to synthesize cellotetraose from cellobiose appeared to be greater with cellulase II-B than with cellulase II-A.

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 crystal structure of N-acetylneuraminic acid methyl ester monohydrate

The crystal structure of the methyl ester of N-acetylneuraminic acid monohydrate has been determined from three-dimensional X-ray diffraction data. The crystals are orthorhombic, space group P212121, with unit-cell constants a=7.954+ 1, b= 11.675+4, c= 16.974+2 ~. The structure was solved using the tangent formula and refined by block-diagonal least-squares techniques to R=0.042. The three bulky substituent groups, the N-acetyl, the glycero and the methyl ester groups, are all equatorially bonded to the pyranose ring while the hydroxyl group at the anomeric carbon atom C(2) is in the axial position. An extensive system of seven interand one intramolecular hydrogen bonds holds the molecules quite rigidly in the crystal lattice, resulting in an average overall isotropic temperature factor coefficient of only 2.7 ,~2.

Conformational studies of -glucans.

AbstractA study of the effect of linkage on the possible conformations of di‐and polysaccharides of α‐D‐glucose and also the probable intramolecular hydrogen bonds has been made. The differences in the nature of linkage is shown to effect the energetically preferred conformations; (1 → 2) linkages lead only to righthanded helical conformations, (1 → 3) linkages lead to extended as well as both left and righthanded helical conformations; (1 → 4) linkages lead to both right‐and lefthanded wide helical conformations. The possible hydrogen bonds between adjacent residues are also dependent on the nature of the linkage. A comparison of the conformational data of α‐D‐glucans with those of β‐D‐glucans has indicated that the favored conformations and hydrogen bonds between contiguous residues in the chain are influenced by the configuration at the anomeric carbon atom in all the three types of polysaccharides. From the energy calculations a probable conformation (ϕM = −10°, ψM = −30°, ϕN = −23°, ψN = −19°) has also been proposed for crystalline mycodextran in conformity with x‐ray data. This conformation contains two types of hydrogen bonds between contiguous residues one between 0–2 and 0–3 atoms at (1 → 4) linkage and the other between 0−2 and 0–4 atoms at (1 → 3) linkage in the chain. The conformation of maltose unit (−10°,−30°) that is likely to occur in the crystalline mycodextran coincides with the minimum energy conformation of maltose.

Alcoholyses of 2, 3, 4-Tri-O-acetyl-α -D-xylopyranosyi and xylothiapyranosyl Bromides

Solvolyses of 2, 3, 4-tri-O-acetyl-α -D-xylopyranosyl [1-o] and xylothiapyranosyl [1-s] bromides in methanol, ethanol and 2-propanol were investigated. Both bromides were solvolyzed through SN1 process (Table 1 and 2). The rate of 2-propanolysis of [1-o] was strongly increased in the presence of added bromide ion (Table 3), and the product analysis showed the presence of considerable amout of α -xyloside, while bromide ion exhibited no such rate acceleration and enhanced production of the α -xylosides in methanol and ethanol (Table 4). Mechanism for 2-propanolysis of [1-o] was discussed, which involved a) the nucleophilic attack of bromide ion to the anomeric carbon atom of [1-o] to give the β -bromide [5], and b) successive solvolysis of [5] via acetoxonium ion intermediate to α - and β -xylosides. Analysis of alcoholysis product mixture from [1-s] showed the α /β -xyloside ratio of more than unity.

The Metabolism of Glyceride Glycolipids: III. BIOSYNTHESIS OF DIGALACTOSYL DIGLYCERIDE BY GALACTOSYL TRANSFERASE PATHWAYS IN BRAIN

Abstract Particulate enzyme preparations of brain from rats greater than 11 days of age catalyze the synthesis of digalactosyl diglyceride from two common precursors, UDP-galactose and diglyceride. Monogalactosyl diglyceride has been implicated as an intermediate in the reaction. Sodium deoxycholate at optimum concentrations is required for the incorporation of UDP-14C-galactose (uniformly labeled) but not for the incorporation of diglyceride-[1,3-14C-glycerol] or exogenous monogalactosyl diglyceride (uniformly labeled 14C-galactose) into digalactosyl diglyceride. Five structurally related bile salts and a variety of other types of detergents do not effectively substitute for deoxycholate. Sodium deoxycholate, which does not serve as a substrate in this reaction, appears to function as a surface-active adjuvant that promotes an interaction between UDP-galactose, enzyme, and an endogenous monogalactosyl diglyceride. Of seven diglycerides tested some preference is shown for dipalmitin as a substrate. Experiments carried out with specific α- and β-galactosidases suggest that the anomeric carbon atom of the galactose to galactose bond of the galactolipid is of the α-configuration. This α-galactosidic bond appears to be unique to the glycolipids thus far characterized and isolated from the central nervous system. The activity of the biosynthetic enzyme is dependent on the age of the rat from which the brain was taken; it is low or nonexistent before about 11 days, but increases sharply after this time until reaching a peak at 16 to 18 days postpartum. Since the age of most active myelination (about 10 to 20 days) in the rat is coincident with the age of highest enzyme activity, a role in the process of myelination is suggested for the enzyme responsible for the synthesis of digalactosyl diglyceride.

Preparation and differentiation of anomeric pairs of steroid tri- O-acetyl- d-glucopyranosiduronic methyl esters and d-glucopyranoside tetraacetates

Twenty-eight steroid tri- O-acetyl-β- d-glucopyranosiduronic methyl esters have been prepared by a standard method, and isomerized to their α- d anomers with titanium tetrachloride. Reduction of seven such pairs with lithium aluminum hydride, followed by re-acetylation, provided the corresponding d-glucopyranoside tetraacetates. The configuration at the anomeric carbon atom assigned in each case was supported by ( a) the anomerization increment, M d α — M d β , which constituted a regular series within the limits of +704 to +985, and ( b) the correspondence between observed and calculated M d values. Members of the anomeric pairs, with the exception of those derived from the isosapogenins, were also differentiated by i.r. spectroscopy, chiefly by a band within the range of 1146–1140 cm − that is displayed only by the α- d anomers. Methyl (tri- O-acetyl-β- d-glucopyranosid)uronates were distinguished from the corresponding β- d-glucopyranoside tetraacetates both by i.r. spectroscopy and mass spectrometry.