Carbohydrate Chemistry Volume 7

A Review of the Literature Published during 1973

By J. S. Brimacombe

The Chemical Society

Copyright © 1975 The Chemical Society
All rights reserved.
ISBN: 978-0-85186-062-6

Contents

Part I Mono-, Di-, and Tri-saccharides and their Derivatives,
1 Introduction, 3,
2 Freesugars, 5,
3 Glycosides, 13,
4 Ethers and Anhydro-sugars, 31,
5 Acetals, 40,
6 Esters, 45,
7 Halogenated Sugars, 57,
8 Amino-sugars, 66,
9 Hydrazones and Osazones, 78,
10 Miscellaneous Nitrogen-containing Compounds,
11 Thio- and Seleno-sugars, 91,
12 Derivatives with Nitrogen, Sulphur, or Phosphorus in the Sugar Ring, 97,
13 Deoxy-sugars, 101,
14 Unsaturated Derivatives, 104,
15 Branched-chain Sugars, 115,
16 Aldehyde-sugars, Aldosuloses, and Diuloses, 123,
17 Sugar Acids and Lactones, 128,
18 Inorganic Derivatives, 135,
19 Cyclitols, 138,
20 Antibiotics, 143,
21 Nucleosides, 153,
22 Oxidation and Reduction,
23 N.M.R. Spectroscopy and Conformational Features of Carbohydrates, 177,
24 Other Physical Methods, 186,
25 Polarimetry, 191,
26 Separatory and Analytical Methods, 192,
27 Alditols, 195,
Part II Macromolecules,
1 Introduction, 201,
2 General Methods By R. J. Sturgeon, 203,
3 Plant and Algal Polysaccharides By R. J. Sturgeon, 215,
4 Microbial Polysaccharides By R. J. Sturgeon, 253,
5 Glycoproteins, Glycopeptides, and Animal Polysaccharides By R. 0. Marshall, 295,
6 Enzymes By J. F. Kennedy, 356,
7 Glycolipids and Gangliosides By R. J. Sturgeon, 471,
8 Chemical Synthesis and Modification of Oligosaccharides, Polysaccharides, Glycoproteins,, 496,
Erratum, 586,
Author Index, 587,

CHAPTER 1

Introduction

The general terms of reference remain those set out in the Introduction to Volume 1 (p. 3) and the arrangement of subject matter follows that of previous Reports in this series.

The synthesis of α-glycopyranosides has continued to attract a great deal of attention, no doubt prompted by Umezawa’s contention {Bull. Chem. Soc. Japan, 1969, 42, 529) that ‘the preparation of α-glycopyranosides in high yields still remains the most important problem of carbohydrate chemistry’. Lemieux’s group has described (Chapter 3) their approach to this problem, via the nitrosyl chloride-glycal procedure, in an eagerly awaited series of papers. Other varied and equally novel approaches to the synthesis of α-glycopyranosides are also covered in Chapter 3. A timely article by Schuerch entitled ‘Systematic Approaches to the Chemical Synthesis of Polysaccharides’ has summarized the problems encountered in the stepwise synthesis of complex oligo- and poly-saccharides of known anomeric configuration.

The considerable interest in nucleosides has been sustained, with reports divided between synthetic (Chapter 21) and conformational (Chapter 23) aspects. The formation of halogenated sugar moieties on treatment of nucleosides with 2-acetoxyisobutyryl chloride (bromide) has opened up a very promising route to deoxy, epoxy, and unsaturated derivatives thereof (Chapters 7 and 21). Antibiotics containing rare sugars have received their customary attention (Chapter 20), and a number of exceedingly complex structures have been elucidated (e.g. everheptoses A and B, and the megalo-micins) and, in some cases, synthesized (e.g. showdomycin).

Recent progress in the application of physical methods to the study of carbohydrates is dealt with in Chapters 23 — 26. In particular, Hall’s group has demonstrated the potential value of longitudinal nuclear relaxation times as probes for structural assignments of carbohydrates. Geminal 13C-1H couplings at C-1 also appear to offer useful information on the anomeric configuration of monosaccharides. The application of X-ray crystallography to carbohydrate chemistry has shown a predictable increase. Free-energy calculations by Rao for the aldohexopyranose penta-acetates have suggested a smaller value (0.9 kcal mol-1) for the anomeric effect of the acetoxy-group than hitherto assumed. A recent explanation of the anomeric effect in monosaccharide derivatives has revived and updated an earlier concept in which non-bonding electrons on the ring-oxygen atom are delocalized by mixing of p-orbital with an antibonding σ-orbital of the C-1-X bond (‘superjacent orbital control’) in the α-anomer.

A new type of literature coverage in the carbohydrate field has appeared with the publication of the volume on ‘Carbohydrates’ in the first series of biennial reviews in the MTP International Review of Science. This publication aims to provide critical and well-documented articles covering actively developing areas of carbohydrate chemistry.

A brief obituary in Volume 31 of Carbohydrate Research has paid tribute to Dr. H. G. Fletcher, jun. (1917 — 1973).

The February and June issues of Carbohydrate Research were dedicated to Professor V. Deulofeu and Dr. L. Long, jun., respectively, in celebration of their seventieth birthdays.

CHAPTER 2

Free Sugars

Reviews have been published on the chemistry of formose, and on the physical properties of aqueous solutions of sucrose, D-glucose, and D-fructose.

Isolation and Synthesis

Two reports have appeared describing the free sugar, cyclitol, and alditol contents of cannabis from various sources; the components identified included arabinose, D-manno-heptulose, altro-heptulose (sedoheptulose), D-glycero-D-manno-octulose, myo-inositol, quebrachitol, glycerol, ery-thritol, arabinitol, and xylitol. A number of free sugars, alditols, and glycosyl-alditols isolated from Sphacelia sorghi honeydew have been identified.

L-Threose has been synthesized from (+)-tartaric acid, and D-erythrose has been obtained by the oxidation of D-fructose with silver carbonate on Celite. A synthesis of 2-deoxy-DL-erythro-pentose from non-carbohydrate precursors is shown in Scheme 1. A simple synthesis of L-gulose from D-mannose has been achieved, the key step being a displacement with sodium acetate on the dimethanesulphonate (1) (Scheme 2). An improved synthesis of D-altrose (as methyl α-D-altropyranoside, see Chapter 5) has also been described. Acetolysis of 2,3-O-isopropylidene-L-rhamno-furanose or its diacetate gave a mixture of acetates, which, after deacetylation, gave L-quinovose (55%) as well as L-rhamnose, but epimerization at C-2 did not occur in L-rhamnopyranose derivatives.

The first application of the Ivanov reaction in carbohydrate chemistry has resulted in a synthesis of the 1-deoxy-l-C-phenylketose (2) (Scheme 3). A synthesis of D-manno-5-heptulose (4) from a D-fructose derivative (3) is shown in Scheme 4; the unusual method of vicinal bishydroxylation is necessary since such conventional reagents as potassium permanganate or 3-chloroperbenzoic acid either failed or gave more-complex reaction products. The related 2-deoxy-D-arbino-5-heptulose should be accessible by way of the product (5) of hydrogenolysis.

Physical Measurements

A number of papers have described mutarotational studies. Polarography has been used in a kinetic study of the mutarotation of D-xylose. The mutarotation of D-galactose and D-mannose has been examined in aqueous solution at 25 °C by calorimetric methods; β-D-galactopyranose is more stable than the a-anomer by 1300 [+ or -] 50 J mol-1, and for D-mannopyranose, the α-anomer is more stable than the β-form by 1900 [+ or -] 80 J mol-11. The mutarotation of D-glucose in DMF at 70 °C was completed in a few hours, when three components (4.7, 42.5, and 52.8%) were present. Mass spectrometry of the trimethylsilylated derivatives showed the major products to be pyranoses and the minor product(s) to be a furanose or a mixture of furanoses. From studies of the mutarotation of D-glucose in DMSO, it was proposed that the proton-catalysed reaction occurs in stepwise fashion, whereas the solvent-catalysed reaction may involve a concerted process. A series of oxy-acids has been examined as catalysts for the mutarotation of 2,3,4,6-tetra-O-methyl-D-glucopyranose; thermo-dynamic data were reported for catalysis by diphenyl hydrogen phosphate, benzenephosphinic acid, trichloroacetic acid, benzoic acid, 2-pyridone, 2-aminopyridine, and picric acid in benzene solution.

The kinetics of the base-catalysed transformations of D-glucose, D-mannose, and D-fructose have been interpreted in terms of anionic intermediates, rather than an SN2 pathway as recently proposed (E. R. Garrett and J. F. Young, J. Org. Chem., 1970, 35, 3502). In the acid-catalysed transformation of D-glucose into D-fructose, an intramolecular hydrogen-transfer from C-2 to C-l was demonstrated by tritium-labelling studies (Scheme 5). The pseudo-equilibria between D-glucose, D-mannose, and D-fructose were displaced in favour of D-fructose in the presence of equi-molar proportions of areneboronic acids.

E.s.r. studies have been performed on radicals formed by irradiation of solutions of glycolaldehyde and glyceraldehyde in aqueous acetone, and also on D-glucose, 2-deoxy-D-erythro-pentose, and 2-deoxy-D-arabino-hexose.

The effect of reducing and non-reducing sugars on the conductance of electrolyte solutions has been examined. Thermal transformations and rearrangements of β-cellobiose and αα-trehalose have been investigated by a number of physical methods. Anomerization, dehydration, condensation, and polymerization were all observed, and polymers formed contained both furanoid and pyranoid rings and unsaturated components. A kinetic study of the thermal decomposition of D-glucose and D-fructose at 300 °C has been reported.

A model for the hydration of monosaccharides has been established on the basis of O n.m.r. and dielectric-relaxation measurements; the model was used to explain the dependence of the conformational equilibrium of D-ribose on temperature. SCF-MO calculations have been made on the electronic distribution in α- Land β-D-glucopyranoses, β-D-arabinopyranose, 2-deoxy-β-D-erythro-pentopyranose, and the enediol form of D-erythro-pentulose. In both anomers of D-glucopyranose, the charge on O-1 was calculated to be greater than that on the ring-oxygen atom, in keeping with its preferential protonation in acid solution, but the difference is greater for the β-form. The role of the enediol form of D-erythro-pentulose in the fixation of carbon dioxide was discussed.

Reactions

Alkaline solutions of hydrogen peroxide have been found to degrade both aldoses and ketoses; aldohexoses and aldopentoses give six and five moles of formic acid, respectively, whereas ketohexoses give one mole of glycolic acid and four moles of formic acid. The reaction probably involves initial addition of a hydroperoxide anion at the reducing centre, followed by fragmentation and subsequent repetition of this sequence (Scheme 6), the final carbon-fragment appearing as formaldehyde, which is further oxidized to formic acid. Experiments at different pH values suggested a free-radical mechanism, rather than an ionic mechanism, and this is supported by the observation that iron salts accelerate the reactions.

Up to 51% incorporation of non-labile tritium occurred on tritium-atom bombardment of crystalline D-glucose. The distribution of the tritium was determined; none was detected at C-2, but twice the expected amount of tritium was found at C-5.

A number of deoxyhexuloses and deoxyhexodiuloses were formed by γ-irradiation of oxygen-free solutions of D-glucose and D-fructose. γ-Irradiation of frozen, aqueous solutions of sugars resulted in epimeriza-tions; for example, D-arabinose, L-lyxose, and D(?)-xylose were detected after irradiation of D-ribose. D-Fructose and lactose, which are known to be particularly sensitive to degradation by γ-irradiation in solution, have been shown to be equally sensitive in the solid phase.

The reactions of D-glucose and maltose with alkaline-earth hydroxides in the presence of ethylenediamine and 2-aminoethanol have been examined. Epimerizations at C-2 and C-3 were observed on heating hexoses near to their melting points in the presence of such basic catalysts as calcium hydroxide or sodium carbonate. A model reactor utilizing poly(4-vinylbenzeneboronic acid) resins for optimizing the formation of D-fructose from D-glucose has been described. Transformations and degradations of sugars in acidic solutions have been studied. Treatment of D-glucose with cold, concentrated sulphuric acid gave a polymer of sulphated D-glucose residues. Isomerizations occurred when aqueous solutions of 4-O-methyl-D-glucuronic acid at pH 7 were heated to 100 °C, and the products observed were 3-O-methyl-D-lyxo-5-hexulosonic acid (47%), 3-O-methyl-L-ribo-5-hexulosonic acid (12%), 4-O-methyl-D-man-nuronic acid (4%), and 3-0-methyl-L-ribo-4-hexulosonic acid (1%).

Tryptophan and D-xylose reacted to give the heterocyclic compounds (6) and (7) when heated at 160 °C in neutral, aqueous solution. In continuing their work on the reactions of sugars with monocyclic aromatic systems in the presence of hydrogen fluoride, Micheel’s group have described the properties of a number of their products. One, a compound C27H24 from D-mannose and toluene, has the unusually high optical rotation of [α] D20 — 1264°. A second paper has reported the reaction of D-glucose with toluene to give optically active derivatives of hydrindane (see Scheme 7).

An interesting investigation has been carried out on the structural requirements necessary for the binding of sugars to the sugar-transport system of human erythrocytes. Studies with various D-glucose derivatives indicated that the sugar is bound as the β-pyranose form by means of hydrogen bonds at C-1 and C-3, and probably at C-4, and possibly at C-6. D-Glucal was shown to be a powerful inhibitor, indicating that a derivative with an appreciably distorted chair conformation can still bind to the sugar-transport system.

CHAPTER 3

Glycosides

O-Glycosides

A review has appeared on the synthesis of linear polyglycosides (polysac-charides) with emphasis on the polymerization of 1,6-anhydrohexoses and cyclic 1,2-orthoesters, and another review has dealt with the preparation of mono- and di-aminoglycosides of 2-deoxystreptamine.

Synthesis. — Phenyl 1-thio-D-glucopyranosides have been shown to be readily solvolysed in the presence of mercury(n) salts to give, with good stereoselectivity, alkyl glycosides of inverted anomeric configuration. The method can be extended to the synthesis of complex glycosides if the hydroxy-groups of the glycosylating reagents are protected by benzylation; in particular, the procedure allowed the synthesis of α-D-glucopyranosides. A further development in the synthesis of α-D-glucosides has utilized a double-displacement at the anomeric centre of 2,3,4,6-tetra-O-benzyl-α-D-glucopyranosyl bromide. Initial nucleophilic attack at C-1 was effected with either triethylamine or triphenylphosphine to give intermediate ammonium and phosphonium salts, which were then treated with methanol. The corresponding sulphonium salt, prepared using dimethyl sulphide, gave an 86% yield of the α-glycoside, and the reactivities of the intermediates to methanolysis were demonstrated to be in the order sulphonium > ammonium > phosphonium salts. The method has not yet been applied to the synthesis of complex α-D-glucopyranosides.

A novel modification to a standard synthesis of glycosides has used glycosyl acetates for the glycosylation of trityl ethers in the presence of allyl bromide and silver perchlorate. It was suggested that the allyl cation formed from these reagents gives allyl acetate and the glycosyl carbonium ion, which is then attacked by the nucleophilic oxygen atom of the trityl ether. Applications of the method are illustrated in Scheme 8.

Another novel development followed from the observation that pyrolysis of the carbonate (8) gave the phenyl glycoside (9) as the main product, together with diphenyl carbonate and the diglycosyl carbonate. Fusion of the carbonate in the presence of a molar proportion of p-nitrophenol gave the p-nitrophenyl β-glycoside in good yield. Various purine β-glyco-sides were obtained similarly; thus, 2-hydroxypyridine and 2-hydroxy-4-methoxypyrimidine gave 0-glycosylated compounds, which were converted into N-glycosylated isomers by treatment with mercury(II) bromide in xylene. Thus, a new route to nucleosides is provided (see also Chapter 21).

Methyl glycosides have continued to receive attention, and detailed studies of the methanolyses of D-fructose and L-sorbose (using C-labelled sugars) have been reported. As with aldoses, furanosides are the main products of kinetic control, but pyranosides are present at equilibrium; no evidence was obtained for the presence of dimethyl acetals. The equilibrium percentages of glycosides (D-fructosides first) were as follows: α-pyranosides, 3, 92; β-pyranosides, 46, 1; α-furanosides, 25, 5; and β-furanosides, 26, 2%. Complete methylation of D-glucose and D-galactose with diazomethane in ether furnished high yields of the β-glycopyranoside tetramethyl ethers, in contrast with the anomeric mixtures of furanosides and pyranosides resulting from methylation of these sugars with methyl iodide and barium oxide. The configuration of the free sugars at C-1 during alkylation with diazomethane is unknown, but the observed products may be derived by preferential reaction of anomeric, equatorial hydroxy-groups. Similar methylations of the penta-acetates of α- and β-D-gluco- and -galacto-pyranoses also gave the methyl β-glycopyranoside tetramethyl ethers selectively, but anomeric mixtures of the furanosides were produced in the cases of α- or β- D-galactofuranose penta-acetates. Treatment of free sugars with benzyl alcohol in benzene containing an acidic cation-exchange resin has afforded a means of obtaining benzyl glycosides; benzyl 2-deoxy-α-D-arabino-hexopyranoside, for example, was prepared by this method.

(Continues…)Excerpted from Carbohydrate Chemistry Volume 7 by J. S. Brimacombe. Copyright © 1975 The Chemical Society. Excerpted by permission of The Chemical Society.
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