CHAPTER 1
Introduction and General Aspects
Boons has edited a multi-author book 'Carbohydrate Chemistry' which deals mainly with many topics of interest to synthetic chemists concerned with mono- and oligo-saccharide chemistry, while David has authored one which serves as a basis for studies of the carbohydrates for chemists, biochemists and biologists.
IUPAC-IUBMB recommended rules for the nomenclature of glycolipids have appeared.
Advances in Carbohydrate Chemistry and Biochemistry, Vol. 53 has chapters dealing with tin-containing intermediates in carbohydrate chemistry, synthesis aspects of selenium-containing sugars and antibodies with specificity for monosaccharide and oligosaccharide units of antigens. It also records appreciations of the work of John E. Hodge, Allene R. Jeanes and Harriet L. Frush.
Reviews of general significance have been written on the transformation of D-fructose, L-sorbose and isomaltulose, i.e. the most accessible ketoses, into starting materials for industrial synthesis, and the use of carbohydrate 'building blocks' for the synthesis of Pharmaceuticals. A review of papers covering advances in protecting group chemistry published in 1997 includes sections on the protection of diols, amines, carboxylic acids and phosphates – all with significance for carbohydrate chemists.
Many reviews relevant to the topics covered in the body of the Reports are referred to at the beginning of the chapters; others to have appeared relate to: cyclodextrins (a complete issue of Chemical Reviews has been devoted to them), the chemistry of neutron capture therapy (sugar derivatives having linked carboranes are the significant compounds), biosensing with polymer vesicles having biorecognition molecules on their surfaces (sialic acids, for example) and carbohydrate-selectin interactions (including the identification of the Sia Lex groups which determine the binding).
Two other somewhat general topics to have been reviewed are the production of enantiopure bioactive molecules by biotransformations (e.g. cyclopen-tene and cyclohexa-1,3-diene derivatives), and the use of hypervalent iodine reagents in carbohydrate chemistry (mainly addition and oxidation reactions of glycals).
CHAPTER 2
Free Sugars
1 Theoretical Aspects
The anomeric effects in 2-methoxytetrahydropyran, 2-deoxyribose and glucose have been investigated by use of class II force field calculations, and ab initio quantum mechanical methods including continuum solvation have been employed to study the intrinsic exocyclic hydroxymethyl rotational surface for (β-D-glucopyranose as well as the α/β energy difference for D-glucopyranose.
Mathematical calculations for predicting saccharide–saccharide interactions under vacuum and in aqueous solutions indicated very strong interactions for (β-D-glucopyranose/(β-D-glucopyranose, α-D-glucopyranose/α-D-fucopyranose and sucrose/ (β-D-glucopyranose.
2 Synthesis
Mixtures containing up to 30% aldopentoses were obtained when formaldehyde and catalytic amounts of known intermediates of the prebiotic pathway were incubated with lead salts.
A section on the preparation of ketosugars via ketosugar phosphates was included in a review on the use of aldolases in synthesis. A kinetic study on the aldolase-catalysed condensation of various electrophilic aldehydes with pyruvate (1 -> 2) showed that there is no advantage in the use of preformed phosphates (compounds 1, R = PO32-).
The mechanism of the condensation of sugar-aldehydes and -ketones with Dondoni's reagent [2-(trimethyl)thiazole] has been examined with particular attention to the fact that the reactions of ketosugars are accelerated by addition of equimolar quantities of a free aldose or a non-sugar aldehyde.
Efficient hydrolysis (yields 80–90%) of ethyl thioglycosides has been achieved with BU4NIO4 and 70%> aqueous triflic acid in acetonitrile.
2.1 Tetroses to Hexoses. – L-Threose derivative 3 has been synthesized from l-tartaric acid in four standard steps, as a useful precursor of homochiral, functionalized, long-chain alcohols 4. Further tetrose derivatives suitable for chain-extension, such as 5, have been obtained by radical cleavage of the C-1–C-2 bond in pentofuranose derivatives on exposure to (diacetoxyiodo)benzene and iodine (see Vol. 31, Chapter 2, ref. 7). The syntheses of d- and L-threose- and -erythrose-derivatives modified at the 2-position from D-isoascorbic and L-ascorbic acid via intermediate 6 and its enantiomer, respectively, are referred to in Chapters 5 and 12.
Pentodialdose derivatives 7, obtained from D-glucose by conventional methods, were converted to 5-monodeuterated pentose derivatives 8 with S/R-ratios from 4:1 to 1:7.4 by reduction with UAID4 in the presence of various ligands. The use of these compounds in the preparation of 5'-monodeuterated nucleosides is covered in Chapter 20.
The key operation in the preparation of L-xylose from xylitol was the lipase-mediated enantioselective deacetylation of the racemic cyclic acetal 9 to give the L-enantiomer 10, whereas preparation of the L-fucose precursor 12 involved controlled, lipase-mediated mono-acetylation of the galactitol-derived cyclic acetal 11. Addition of nitromethane to D-xylose by an improved procedure and exposure of the 1-deoxy-1-nitroalditol thus formed to Nef conditions (aq. NaOH, then aq. H2SO4) gave simple access to D-idose. 11C-Labelled aldononitriles, obtained from D-arabinose by chain-elongation with NH411CN on a solid support, furnished D-[1-11C] glucose on reductive hydrolysis with Raney nickel/formic acid (radiochemical yield >95%).
The biosynthesis of apiose is referred to in Chapter 18.
A new method for epimerizing free sugars via 1,2-O-stannylene derivatives has been exploited in a practical synthesis of D-talose from D-galactose. The process is equilibrium driven and favours the structure with an axial OH-group at C-2.
Stereocontrolled, Lewis...
