CHAPTER 1
Part I MONO-, DI-, AND TRI-SACCHARIDES AND THEIR DERIVATIVES
By B. E. Davison R. J. Ferrier N. R. Williams
1 Introduction
The general terms of reference remain the same as for previous volumes in this series. In order to minimize the time required for editorial collation, the previous system of numbering diagrams and references sequentially throughout Part I has been discarded in favour of each chapter carrying its own set of diagram and reference numbers as in Part II. We hope this alteration will not detract too seriously from the usefulness of the report. We have attempted to maintain the previous policy of providing a generous system of cross-references between chapters.
More than one thousand references quoted in Part I clearly reflect the continued high level of interest in the chemistry of carbohydrates, and the report demonstrates the particular interest now being shown in the synthesis of natural and analogous glycosides and disaccharides (Chapter 3), carbohydrate antibiotics (Chapter 18), and of course nucleosides (Chapter 19), which together account for over one-third of all the references cited.
Texts published this year of general interest to carbohydrate chemists have included issues in the Advances in Carbohydrate Chemistry and Biochemistry series, which are prefaced by appreciations of the late Professors E. J. Bourne and E. L. Hirst; these texts include review articles on 1,6-anhydro sugars, cyclic acetals of aldoses and aldosides, the Koenigs-Knorr reaction, carbohydrate boronates, and the biosynthesis of sugars in antibiotics. Extensive surveys of carbohydrate derivatives are also included in several books devoted to antibiotics.
2 Free Sugars
A review of aspects of the structure and reactivity of carbohydrates has appeared. The free-radical telomerization of vinylene carbonate (1,3-dioxal-2-one) with polyhalomethanes has been dealt with in a review; telomers so derived may be converted to aldoses containing from three to eight carbon atoms (see below). Ab initio SCF calculations have been used to predict the electron distribution, the electrostatic molecular potential around the oxygens, and the hydration and cation binding schemes of C3-endo-gg-ribose. The latter were correlated with recent experimental results.
1 Isolation and Synthesis
Melibiose, raffinose, glucose, and fructose were detected in developing rice (strain IR29), whereas in strain IR28 sucrose, glucose, fructose, raffinose, maltose, melibiose, glucodifructose, maltotriose, and higher oligosaccharides were found. More free sugars were present in the developing grain than when it was mature. Bran contains a higher proportion of raffinose and fructose than does milled rice. The free sugars, water-soluble gums, and hemicelluloses present in barley grains were compared before and after malting. Sugars detected were arabinose, xylose, galactose, glucose, fructose, maltose, and sucrose, levels of which increase on malting. The hydrolysate of the extracellular polysaccharides of Rhizobium (strain CB756) was shown to contain 6-deoxy-L-talose, 3-O-methyl-D-glucose, and 6-O-methyl-D-galactose. D-Gal-actofuranose was found to be present in the capsular polysaccharide of Klebsiella serotype K41.
Per-C-deuteriated D-glucose has been synthesized using the sequence shown in Scheme 1. A simple synthesis of L-idose from (1) by sequential treatment with sodium borohydride, sodium methoxide, and acid has been reported. Also prepared were L-idose di(ethylthio)acetal and 1-deoxy-L-iditol.
The polymerization of formaldehyde has been studied using various catalysts and complexing co-catalysts. When a bed of NaX-zeolite spheres was used, aqueous formaldehyde at 95 °C gave an initial conversion to formose sugars of 50% at pH 5 — 7. Rapid irreversible catalyst deactivation then occurred due to the presence of formic acid produced in the undesired Cannizaro reaction. The problem was overcome by incorporation of 0.86 cm3 sodium hydroxide per cm3 formaldehyde into the combined feed to the reactor thus maintaining pH 10 — 12. Conversion only fell from 95% to 92% during 3 h. Catalysts suitable for use in homogeneous polymerization were prepared from calcium hydroxide and glucose or dihydroxyacetone, and their physical and chemical properties were investigated. ESCA and i.r. analysis suggest a loosely structured dynamic mixture of species derived by co-ordination between the alkaline earth hydroxide and the hydroxylated compound. When the catalyst was used with formaldehyde in 2H2O no C — 2H bonds were formed, showing that water does not participate in the formose reaction and that the latter occurs within the complex. When glucose was used as the complexing co-catalyst with calcium hydroxide in a tank reaction, the Canni-zaro reaction was reduced to ~ 2% with near-complete conversion to formose sugars. Although calcium hydroxide is a good catalyst for the Cannizaro reaction, the calcium hydroxide-glucose complex is not.
Cold-plasma decomposition of methane–water mixtures produced simple organic compounds containing formaldehyde; on apatite surfaces under u. v. irradiation and at various pH values erythrose, ribose, glucose, glucuronic acid, and cellobiose were obtained. Ammonia was found to favour the synthesis of sugars when used to create alkaline media. (The authors report all these sugars as D-enantiomers but no evidence for optical purity is presented.)
The octodiose present in apramycin has been prepared as its di-isopropyl-idene-monobenzyl derivative (2), using the synthesis shown in Scheme 2.
Oxidation of 1,2:4,5-di-O-isopropylidene-D-xylitol, which is produced together with the 2,3:4,5-di-O-isopropylidene isomer on acetonation of D-xylitol, gave the 3-oxo-derivative, acid-hydrolysis of which gave D-erythro-3-pentulose. The same publication describes the synthesis of L-threo-3-pentulose: 2,4,5-tri-O-acetyl-1,3-O-benzylidene-L-arabinitol was hydrolysed with acid, partially acetylated to give 1,2,4,5-tetra-O-acetyI-L-arabinitol, oxidized with DMSO–phosphorus pentoxide and finally hydrolysed. The same group has described the syntheses of D-manno-3-heptulose, by oxidation of 1,2:3,4:6,7-tri-O-isopropylidene D-glycero-D-manno-heptitol (from volemitol) followed by hydrolysis, D-ido-3-heptulose prepared in the same way from the D-glycero-L-galacto-heptitol analogue, D-glycero-L-galacto-heptose by oxidation of 2,3:4,5: 6,7-tri-O-isopropylidene-D-glycero-D-galacto heptitol, D-glycero-D-ido-heptose by oxidation of 2,3:4,5:6,7-tri-O-isopropylidene-D-glycero-D-ido -heptitol, and D-glycero-D-galacto-heptose by oxidation of the tri-O-isopropylidene derivative of perseitol.
Heating dihydroxyacetone in aqueous solution at pH 5 produced a complex mixture containing substituted pyranones, dipyranones, substituted quinones, hydroxylated benzenes and toluenes, and the sugar derivatives (3), (4), and (5). The syntheses from telomerization of vinylene carbonate of racemic D-glycero-L-gulo-, D-glycero-D-ido-heptose, and D-threo-D-ido -octose in reasonable yield has been reported.
2 Physical Measurements
The viscosity behaviour of the ternary systems of sodium or potassium halides (0.125-3 M) in aqueous solutions of D-xylose (0.4 M) at 25, 30, 35, and 40 °C has been determined and Monlik's equation [(η/ηG)2 = M + KC2 where C = molar concentration, η = viscosity of solution and M and K are constants] was shown to hold beyond the Einstein region. The rigid molar volume and the apparent B values (related to tertiary structure of ion–water mixtures or molecule–water mixtures) were computed using the Breslau–Miller treatment. A study of the viscosity changes of sucrose solution on addition of neutral and charged detergents showed that the former decreased viscosity and the latter caused an increase. From a study of the viscosity of concentrated solutions of polyhydroxy non-electrolytes (glucose, sucrose, mannitol, and sorbitol) in relation to solute–solvent interaction, it has been concluded that local water structure at microscopic level can account for the temperature variation of the Vand–Einstein constant. A universal equation for the behaviour of such solutions was derived.
The adsorption of fructose and glucose on X-zeolites has been shown to depend on the type of cation in the zeolite, the extent of cation exchange, and the solvent used. The findings enabled efficient separations of monosaccharides, monosaccharides from disaccharides, and of monosaccharides from related alditols by column chromatography using sodium calcium X-zeolite as the stationary phase. Electrocapillary measurements were used to determine the interfacial adsorption of D-ribose, 2-deoxy-D-ribose, and D-ribose-5-phosphate at a mercury electrode in a sodium fluoride (0.5 M)-di-sodium hydrogen phosphate (0.01 M) electrolyte. Each was found to be only weakly absorbed, the 5-phosphate, as expected, mainly at the positive electrode. Areas occupied by molecules at monolayer surface saturation suggest that sugars are absorbed with the average plane of the sugar ring parallel to the electrode surface. The more strongly absorbed nucleosides in comparison were absorbed with the bases in a flat orientation (i.e. ring parallel to the electrode surface) and the sugar mainly perpendicular to the surface.
Mutorotation continues to receive attention. Studies of the mutarotation of 2,3,4,6-tetra-O-methyl-α-D-glucopyranose in aqueous dioxan and aqueous DMSO by optical rotation over a wide range of water concentration, with and without catalysts, have shown that the uncatalysed reaction transition-state contains one mole of sugar and two moles of water in an acyclic bonded structure (6). In the pyridine-catalysed reaction one mole of water may be replaced by one mole of pyridine (Scheme 3). The evidence suggests that the reaction takes place by an intimate step-wise mechanism rather than synchronously.
Agreement with the above findings on water dependence is reported by Sørenson et al. for high water concentrations only; at low water concentrations (≤ 11 M) the order with respect to water falls to one for dioxan and acetonitrile but increases to 3.7 in DMSO. This behaviour parallels a decrease and increase respectively in both activation energy and entropy of activation for the two groups of solvents. The data were shown to be compatible with concerted proton transfer via water catalyst molecules on the basis of known properties of mixed solvents and modern quantum theories of proton transfer reactions in polar media. An investigation of the isotope effect in acid-catalysed mutarotation of D-glucose using polarography has shown that the effect may be used to establish the existence of general or special catalysis by acid, or whether there is a pre-equilibrium involving the participation of protons. The rate constants, and hence isotope effects, were calculated for the systems NaClO4-HClO4, at pH 3 — 3.5 in water, heavy water, water–acetone, and heavy water–acetone. The effect of ethanol on optical rotation, velocity of mutarotation, and equilibrium constant of lactose has been reported. The specific rotation is less in ethanol than in water and there is a linear relationship between the percentage ethanol in aqueous ethanol and the final specific rotation. Equilibrium studies on the α: β anomer ratio have shown that there is a direct relationship between the proportion of ethanol in water and the amount of α-anomer in the mixture. Similarly mutarotation is slower in ethanol–water than in water alone; lower α : β ratios were obtained showing that the rate of conversion of α to β was decreased more than the reverse reaction.
The effect of the crystal habit-forming impurities, raffinose, dextrose, and potassium chloride on the growth of sucrose crystals from various seeds has been studied. A mechanism for the oxidation of D-galactose by Nessler's reagent in alkaline media via the enediol has been proposed on the basis of kinetic measurements. The reaction is zero-order with respect to HgII and first-order with respect to galactose. The rate is inversely proportional to the concentration of iodine ion.
The presence of 1.6% septanose form in solutions of D-idose has been detected using 13C n.m.r. in 2H2O solution at 37 °C. A report on the diffusion of glucose, maltose, and maltotriose in cross-linked gels at different gel concentrations and degrees of cross-linking suggests that diffusion velocity is restricted not only by interaction between diffusing substances and gel components but also by steric hindrance of the gel matrix. The lyoluminescence of irradiated solid carbohydrates in ice has been suggested to be due to the formation of singlet oxygen species. The difficulties in invoking such species in light emission studies are discussed. The rise in conductivity on flash photolysis of oxygenated aqueous hydrogen peroxide solutions at pH 5 of meso-erythritol, D-xylitol, D-glucitol, myo-inositol, D-glucose, and methyl α-D-gluco-pyranoside has been measured as a function of time. All showed transient conductivity decaying within several hundred milliseconds, which was attributed to formation of hydroperoxy radicals which dissociate to give protons and O[•.bar]2. The precursors of hydroperoxy radicals were thought to be sugar α-hydroperoxy compounds. Polyols were found to show two first-order processes, k [??] 200 and 3000 s-1, whereas D-glucose shows three parallel first-order processes, k [??] 400, 2700, and > 70 000 s-1; the separate reactions were assumed to be due to the different points of attachment of the hydroperoxy radical with the fastest rate for D-glucose being due to the C-1 adduct and the slowest due to that at C-6. Dehydration of β-D-glucose and β-D-xylose in the presence of Cr3+, Al3+, Ti3+, Ga3+, and In3+ to yield 5-hydroxymethylfurfural and furfural respectively has been shown to proceed by a unimolecular mechanism. As part of the continuing studies on molybdic acid transformations of free sugars the kinetics of the isomerization of DL-glyceraldehyde to dihydroxyacetone at pH 3.1 and 70 °C have been shown to be first order with respect to the trioses, but the results did not distinguish between an enediol mechanism or an intramolecular hydride transfer. A case in which an intramolecular C-1 to C-2 hydride transfer did occur has been reported for the conversion of D-threo-pentulose to D-xylose under acid-catalysis. This is in line with other aldose–ketose conversions (see Vol. 9, p.8). The thermo-gravimetric analysis of α-lactose hydrate has shown that α-lactose first loses its water of crystallization, followed by a small exotherm, then by the melting endotherm. An anhydride which was characterized by an endotherm at 180 °C and an exotherm at 190 °C was produced by heating in methanol.
3 Reactions
The alkaline degradation of D-glucose produced coloured polymeric and acidic compounds which were isolated and characterized by gel filtration, gel electrophoresis, ion-exchange, and spectral analysis. Another group of workers have studied the stoicheiometry of the alkaline degradation of D-glucose and D-fructose in the temperature range 30 — 70 °C, and shown that almost two moles of alkali are consumed per mole of the carbohydrate. Although the degradation is partly controlled by the dielectric constant of the medium, such additives as acetone and urea have specific effects, presumably due to complex formation characterized by presence of a dark red colour (λmax 320 nm). The reaction of urea with lactose produced lactosyl urea in maximal yield (40%) at pH 2 during 5 days at 50 °C or 4 h at reflux. Some hydrolysis of lactose occurred in the process, giving rise to minor urea–glucose and urea–galactose compounds. Increasing the alkalinity resulted in a reduction of the yield of lactosyl urea and an increase in production of lactulose.
