Carbohydrate Chemistry Volume 8

A Review of the Literature Published During 1974

By J. S. Brimacombe

The Chemical Society

Copyright © 1976 The Chemical Society
All rights reserved.
ISBN: 978-0-85186-072-5

Contents

Part I Mono-, Di-, and Tri-saccharides and their Derivatives,
1 Introduction, 3,
2 Free Sugars, 5,
3 Glycosides, 12,
4 Ethers and Anhydro-sugars, 28,
5 Acetals, 39,
6 Esters, 44,
7 Halogenated Sugars, 57,
8 Amino-sugars, 61,
9 Hydrazones, Osazones, and Related Compounds, 71,
10 Miscellaneous Nitrogen-containing Compounds, 83,
11 Thio- and Seleno-sugars, 88,
12 Derivatives with Nitrogen, Sulphur, or Phosphorus in the Sugar Ring, 91,
13 Deoxy-sugars, 91,
14 Unsaturated Derivatives, 95,
15 Branched-chain Sugars, 102,
16 Aldehydo-sugars, Aldosuloses, Dialdoses, and Diuloses, 111,
17 Sugar Acids and Lactones, 116,
18 Inorganic Derivatives, 121,
19 Cyclitols, 126,
20 Antibiotics, 130,
21 Nucleosides, 138,
22 Oxidation and Reduction, 159,
23 N.M.R. Spectroscopy and Conformational Features of Carbohydrates, 163,
24 Other Physical Methods, 174,
25 Polarimetry, 181,
26 Separatory and Analytical Methods, 183,
27 Alditols, 186,
Part II Macromolecules,
1 Introduction, 191,
2 General Methods By R. J. Sturgeon, 193,
3 Plant and Algal Polysaccharides By R. J. Sfurgeon, 202,
4 Microbial Polysaccharides By R. J. Sturgeon, 225,
5 Glycoproteins, Glycopeptides, and Animal Polysaccharides By R. D. Marshall, 262,
6 Enzymes By J. F. Kennedy, 328,
7 Glycolipids and Gangliosides By R. J. Sturgeon, 390,
8 Chemical Synthesis and Modification of Oligosaccharides, Polysaccharides, Glycoproteins, Enzymes, and Glycolipids By J. F. Kennedy, 401,
Author Index, 460,

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.

It has been a particularly active year in monosaccharide chemistry, judging from the increase in the number of papers abstracted, with interest fairly evenly divided between synthetic and stereochemical aspects of the subject. The search for a protecting group that, like the trityl group, can be removed as a stable cation in glycosylation reactions but that can also etherify secondary hydroxy-groups has culminated in the use of the 2,3-diphenyl-2-cyclopropen-l-yl group (Chapter 4). Reference is made in Chapters 4 and 6 to a kinetic approach for calculating all ratios of rate constants characterizing the reaction of a diol (e.g. methyl 3-acetamido-3,6-dideoxy-α-D-glucopyranoside) with an alkylating or an acylating reagent; the information obtained helps to define the factors influencing the reactivity of a particular hydroxy-group and the relations between these factors, and avoids the misleading results that are sometimes given by product analysis alone.

From a synthetic viewpoint, it is pertinent to note that sulphonyloxy-groups at C-2 of β-D-glycopyranosides can be displaced with nucleophiles (Chapter 6). Syntheses of a number of interesting branched-chain sugars (e.g. aldgarose, vinelose, and 3-C-hydroxymethyl-D-riburonic acid) (Chapter 15) and of dihydro-streptomycin (Chapter 20) have been reported. The elegant chemical and physical studies used in elucidating the structure of sisomicin, a novel amino-glycoside antibiotic, make rewarding reading. The torrent of publications on nucleosides (Chapter 21) remained unabated in a year that has seen syntheses of the first 1′,2′-unsaturated purine and pyrimidine nucleosides.

Recent progress in the applications of physical techniques to the study of carbohydrates is dealt with in Chapters 23 — 26. Improvements in instrumentation have allowed structural information to be obtained from the natural-abundance C n.m.r. spectra of monosaccharides and the diagnostic potential of spin-lattice relaxation times to be more fully explored (Chapter 23). Seventy or so new crystal and molecular structures of carbohydrate derivatives were published during 1974 (see Chapter 24), providing a wealth of information against which currently-held concepts and the results of theoretical calculations can be tested.

An account of the development of Haworth’s concepts of ring conformation and of neighbouring-group effects has appeared. General reviews of recent developments in the chemistry of monosaccharides and of the total synthesis of monosaccharideshave been published, and other specialized reviews have dealt with the applications of electrochemicaland photochemical processes to carbohydrates and their derivatives.

The October issue of Carbohydrate Research was dedicated to the memory of Professor W. Z. Hassid, and the July issue was dedicated to Dr. H. S. Isbell in honour of his seventy-fifth birthday.

CHAPTER 2

Free Sugars

Reviews have appeared on the ionization of carbohydrates in the presence of metal hydroxides and oxides, and on the enolization and oxidation reactions of reducing sugars. Formose sugars have continued to receive attention, and their synthesis and utilization have been reviewed. A unifying mechanism for the formose reaction has been developed based on observed rate phenomena; the mechanism explains why almost any base, regardless of valence, catalyses the formose reaction and the accompanying Cannizzaro reactions of formaldehyde. The same paper reported that Ca(OH)+ is the actual catalytic species for the formose reaction, and another paper has reported that rare-earth hydroxides, especially gadolinium hydroxide, inhibited the reaction. The formose reaction has also been followed potentiometrically; changes in the oxidation-reduction potential curve could be related satisfactorily to the postulated phases of the reaction.

Isolation and Synthesis

Glucose, fructose, 2- and 3-O-methylfucose, rhamnose, sedoheptulose, sucrose, mannitol, and laminitol have been identified in ethanolic extracts of the brown seaweed Desmarestia aculeata, and the hyaluronate-peptide of vitreous humour has been shown to contain arabinose, fucose, and a 7-deoxyheptose (either 7-deoxy-L-glycero-D)-manno-heptose or 7-deoxy-L-glycero-D-gluco-heptose).

L-Erythrulose (L-glycero-tetrulose) has been obtained by the oxidation of erythritol with Acetobacter suboxydans and by the degradation of calcium D-threo-2,5-hexodiulosonate in either neutral or slightly acidic media. d-Arabinose has been transformed into D-lyxose by the steps shown in Scheme 1, and L-lyxose was similarly obtained from L-arabinose. The same principle was utilized in a synthesis of L-ribose from D-ribono-1,4-lactone (see Scheme 2). The latter synthesis was adapted to prepare D-[5-13C]ribose from L-erythrose by way of the enantiomer of the lactone (1). D-Ribose and D-lyxose (as derivatized glycosides) have also been obtained from L-glutamic acid by the procedure shown in Scheme 3, hydroxylation of each of the unsaturated glycosides (2) occurring from the side opposite to the anomeric methoxy-group.

L-Galactose, L-mannose, and L-talose have been obtained from the appropriate 1-deoxy-1-nitro-L-alditols by an improved procedure, oxidative decomposition with hydrogen peroxide in the presence of molybdate ions replacing the classical procedure involving treatment of the sodium salts with dilute sulphuric acid. The epimerization of D-galactose with molybdic acid is claimed to afford a convenient synthesis of D-talose, which was obtained in 16% yield; a small amount (2.4%) of D-gulose was also formed. D-[2-3H]Glucose has been prepared by enzymic methods from D-fructose in tritiated water, and the hexose was sub-sequently converted into D-[2-3H]xylose. Dephosphorylation of the hexose phosphate produced by Methylococcus capsulatus has been shown to give D-arabino-hex-3-ulose (3) and not D-allulose as previously supposed. Self-condensation of DL-glyceraldehyde 3-phosphate in the presence of ethylenediamine has furnished DL-fructose 1,6-diphosphate. A Wittig reagent was used in the preparation of 6-deoxy-D-galacto-heptose, by way of the enol ether derivative (4). The D-mannono-1,4-lactone diacetal (5) has been used to prepare D-manno- heptulose (6) and a related 1-deoxy derivative (7) thereof (see Scheme 4).

Physical Measurements

In a detailed paper, Capon and Walker have discussed the kinetics and mechanism of the mutarotation of D-xylose and a series of 6-substituted D-glucoses catalysed by the hydroxonium ion, water, and organic bases. Electron-withdrawing substituents at C-6 decreased the rate of mutarotation catalysed by the hydroxonium ion and by water, whereas the rate of the based-catalysed mutarotations was enhanced. On the other hand, electron- withdrawing substituents at C-2 decreased the rate of mutarotation in all cases, except for that of 2-amino-2-deoxy-D-glucose hydrochloride catalysed by lutidine, which occurred at a slightly faster rate than that of 2-deoxy-D-arabino-hexose. The authors favour the mechanisms outlined in Scheme 5. A concerted mechanism, in which the ring-oxygen atom carries a substantial positive charge in the transition state (8), was proposed for the water-catalysed reaction. Intramolecular catalysis was found in the mutarotations of 6-deoxy-D-gluco-hepturonic acid (9) and 6-O-(o-hydroxy-phenyl)-D-glucose (10). Other papers on mutarotation have included a study on trimethylsilylated sugars by g.l.c. and mass spectrometry, kinetic and thermo-dynamic studies on (β-D-arabinopyranose involving catalysis by various amino-alcohols, and studies on D-glucose in DMF and in water-DMF mixtures; furanose forms (ca. 4.5% at 70 °C) were shown to be involved in the mutarotation of D-glucose in DMF. A value of 10.3 kcal mol-1 has been calculated for the energy barrier to anomerization of α-D-glucopyranose.

Isotopic exchange equilibria have shown that the binding of the hydroxy-protons of gem-diols is tighter than in simple alcohols; similar conclusions were reached for free sugars and, without proof, the effect was ascribed to the hemi-acetal function. However, no control experiments were performed with either vicinal diols or polyhydroxy-systems. The interactions of electrolytes with D-glucitol, D-glucose, glycerol, D-mannitol, and sucrose have been measured by conductometric studies; D-glucose and sucrose were found to associate with the electrolytes, whereas D-glucitol interacted only rarely and D-mannitol and glycerol not at all.

Examination of the volatile products (H2, D2, and HD) of γ-irradiated, crystalline mono- and di-saccharides with unlabelled and labelled hydroxy-groups indicated that transfer from exchangeable positions occurred at an early stage of the irradiation. A number of γ-irradiated saccharides emitted light when dissolved in water; trapped free radicals are considered to be responsible for the emission, and an attempt was made to correlate the e.s.r. spectra with the lyoluminescence.

The redox potentials of free radicals formed by the reactions of D-ribose and 2-deoxy-D-erythro-pentose with hydroxy-radicals have been studied; at least two radicals, with different redox potentials, were formed at pH 7. An investigation of the photochemistry of glyceraldehyde and 1,3-dihydroxyacetone by CIDNP (Chemically Induced Dynamic Nuclear Polarization) has demonstrated the occurrence of the radical processes shown in Scheme 6. CIDNP signals were not shown by tetroses and pentoses. Glycosyl azides have been demonstrated to undergo photolysis with the formation of the corresponding lower aldose (see also Chapter 10).

U.v. absorptions in the region 265 — 310nm have been observed during the reactions of formaldehyde with aldoses, ketoses, and alditols in aqueous solutions of sodium hydroxide; in aqueous solutions of calcium hydroxide, absorptions were observed in the region 325 — 336 nm, and may be due to the formation of complexes with the enol forms.

Theoretical calculations on β-D-gIucopyranose using the CNDO/2 method have predicted the most stable conformer (4C1) to have five hydrogen bonds between the hydroxy-groups and the adjacent oxygen atoms.

The kinetics of oxidation of D-ribose with chloramine-T in alkaline solution have been studied, and the postulated mechanism involves a trimolecular rate-determining step between OC1-, OH-, and the anion of β-D-ribose.

Reactions

The molybdate-catalysed epimerization of D-galactose has already been mentioned. Bilik and his colleagues have also reported on related epimerizations of erythrose and threose, to give a 3 : 4 mixture of the two tetroses, and the epimerizations of L-arabinose to L-ribose, of D-xylose to D-lyxose, and of L-xylose to L-lyxose. Equilibrations of D-fructose, D-sorbose, D-tagatose, and D-psicose in the presence of molybdate ions were also examined. The epimerization and degradation of D-glucose in dilute solutions of sodium hydroxide have been studied, and optimum conditions for its degradation to D-arabinose were determined. Radiolysis of frozen, aqueous solutions of hexoses at — 78 °C led to isomerization and to the formation of pentoses.

A new crystalline phase of D-glucose has been obtained from aqueous solution; it may be a hydrated form of β-D-glucopyranose, since it was transformed into stable α-D-glucopyranose monohydrate at 32 — 38 °C. Conditions have been determined for the preparation of ferric-D-fructose and ferric-D-fructose-D-glucose complexes that could be isolated and redissolved to give neutral solutions; studies with labelled substrates showed that no interconversion of D-fructose and D-glucose occurred in the complexes. The yellow colour that accompanies the degradation of sugars with acid has been attributed to further oxidation of 5-(hydroxymethyl)-2-furaldehyde and 2-furaldehyde to γ-unsaturated dicarbonyl compounds, whose broad absorption bands extend into the violet region of the visible spectrum. The conversions of D-[2-3H]xylose and D-[2-H3]glucose with acid into 2-furaldehyde and the 5-(hydroxymethyl) derivative thereof, respectively, involve transfer of hydrogen from C-2 to C-1, since the formyl groups of the products were found to be labelled with tritium.

Intraveneous administration of C-labelled D-psicose to rats resulted in its virtual complete excretion in the urine, whereas a large part of D-psicose was metabolized by intestinal micro-organisms following oral feeding.

CHAPTER 3

Glycosides

O-Glycosides

Reviews on flavonoid glycosides (232 references) and on the synthesis of citrus flavonoid glycosides (65 references) have appeared.

Synthesis. — The problems of glycoside synthesis, in particular with methods involving glycosyl halides and 1,2-orthoesters, have been discussed.

The products of Fischer methanolysis of D-galacturonic acid have been monitored by g.l.c. Esterification occurred most rapidly, and was succeeded by the formation in sequence of furanosides and pyranosides. Interestingly, small proportions of the dimethyl acetals of D-galacturono-6,3-lactone and D-galacturonic acid were detected as kinetically controlled products early in the methanolysis. Specific points relating to the Fischer method of glycosidation have been made: acetic acid is recommended instead of hydrogen chloride for glycosidation of the 2-pentuloses, and molecular sieves can usefully be employed to remove the water liberated in the reaction. It was claimed that methyl α-D-gluco- and -manno-pyranosides can be obtained in ca. 89% yield using this modification. However, the preparation of the former glycoside with this efficiency cannot be a one-step operation, since it exists only to the extent of 66% in equilibrium with its isomers. Treatment of sucrose in 30% aqueous ethanol with yeast invertase has afforded a means of obtaining ethyl β-D-fructofuranoside. A sophisticated treatment of the methanolysis of D-glucose has produced a computer program that predicts the yields of the four isomeric glycosides at any stage of the reaction.

It is unusual for sugar derivatives with free hydroxy-groups at C-1 to be used in glycoside synthesis, except in the Fischer reaction. However, 2,3,4,6-tetra-O-acetyl-D-glucopyranose has been used to prepare the compound (11) (with boron trifluoride as catalyst), and the condensation of 2-amino-2-deoxy-D-galactose with either D-glucuronic acid or D-mannurono-6,3-lactone in the presence of hydrochloric acid gave the 6-linked disaccharide derivatives (12). In the absence of an acid catalyst, N-linked disaccharides were formed (see Chapter 10). Similarly, treatment of methyl α-D-glucopyranoside in p-dioxan with an excess of 2,3,4,6-tetra-O-methyl-D-glucopyranose in the presence of perchloric acid and Drierite gave a mixture of di- and tri-saccharides, demonstrated to contain mainly 1,1- and 1,6-linked disaccharides, and 1,2- and 1,6-linked trisaccharides.

Acylated glycosyl halides have continued to be used extensively as glycosylating agents. Bromides are usually considered to have the most suitable characteristics for glycosylations, whereas iodides have been used infrequently. However, it has been shown that benzoylated glycopyranosyl iodides, prepared in situ from the chlorides, reacted with the lower alcohols in acetonitrile in the presence of 2,6-lutidine to give mixtures of glycosides containing a high proportion of α-glycosides. It was suggested that this modification could be useful for the synthesis of oligosaccharides. Another interesting innovation has utilized crown ethers and related compounds to help solubilize the salts used in the reactions; thus, the use of dibenz-[18]-crown-6 with silver nitrate facilitated the synthesis of β-glycosides from 2,3,4,6-tetra-O-acetyl-α-D-glucopyranosyl bromide. However, when the bicyclic aminopolyether (13) was used in conjunction with silver nitrate, the products contained substantial proportions of glycosyl nitrates (especially with sterically hindered alcohols).

(Continues…)Excerpted from Carbohydrate Chemistry Volume 8 by J. S. Brimacombe. Copyright © 1976 The Chemical Society. Excerpted by permission of The Chemical Society.
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