Hernan A. Nunez

Carbon-13-enriched carbohydrates. Preparation of aldononitriles and their reduction with a palladium catalyst

Abstract Cyanide condenses with aldoses at 25° in aqueous solution between pH 7.0–9.0 to produce aldononitriles in high yield. These nitriles may be reduced catalytically over palladium-barium sulfate (5%) at pH 4.2 ± 0.1 and 25° to yield the corresponding aldoses in 60–90% yield, depending on the structure of the nitrile. 1-Amino-1-deoxyalditols are produced in approximately 10% yield, and their formation is favored when hemiacetal formation is hindered in the parent aldose. Generally, the product epimeric aldoses can be separated from contaminating by-products and from each other by ion-exchange and adsorption chromatography. This procedure has been applied to the preparation of [1- 13 C]-enriched pentoses and hexoses.

Complete structure elucidation of a trisaccharide from a patient with mannosidosis by carbon-13 nuclear magnetic resonance spectrometry.

Abstract Through the exclusive use of 13 C NMR data a relatively complex oligosaccharide was completely characterized in terms of its sugar composition, ring forms, anomeric configurations, sequence, and interresidue linkage positions. Thus, the unique structure of a trisaccharide from a patient with α-mannosidosis was deduced to be Man p α 1–3Man p β1–4 N -acetylglucosamine. The study demonstrated that the empirical approach of matching chemical shifts between those of known and unknown structures and the use of chemical shift-predictive rules, obtained from a series of related compounds, can be successfully applied to the elucidation of carbohydrate structure in spite of the spectral complexities derived from the multiplicity of similar chemical shifts. This study also demonstrates that as more structure-chemical shift relationships are established with carbohydrates, the easier it will be to use 13 C NMR for their characterization.

Glycerol-, inositol-, and reducing end hexose-containing oligosaccharides in human urine

Ten previously unreported oligosaccharides have been purified from the urines of human subjects using a combination of gel filtration, ion exchange, and thin-layer chromatographies. Their structures were determined by direct probe mass spectrometry, methylation analysis, and proton NMR spectroscopy of the permethylated oligosaccharide alditols.On the basis of composition, the oligosaccharides could be divided into three groups. Five oligosaccharides containing glycerol were characterized as glucosylα1-1′glycerol; glucosylβ1-1′glycerol; galactosylβ1-1′glycerol; glucosyl-1-1′(fucosyl-1-2′)glycerol and/or fucosyl-1-1′(glucosyl-1-2′)glycerol; and glucosyl-1-1′(galactosyl-1-2′)glycerol or galactosyl-1-1′(glucosyl-1-2′)glycerol. Four inositol-containing oligosaccharides were characterized as galactosylβ1 (fucosylα1)inositol,N-acetylgalactosaminylα1 (fucosylα1)inositol, fucosylα1-2galactosylβ1 (N-acetylgalactosaminylα1)inositol and fucosylα1-2galactosylβ1-4-N-acetylglucosaminylα1(N-acetylgalactosaminylα1)inositol. Finally, galactosylα1-3(fucosylα1-2)galactosylβ1-6galactosylα1-4(fucosylα1-3)glucose, an oligosaccharide with glucose at its reducing end, was tentatively identified. The significance and possible origins of the carbohydrate structures are discussed.

STRUCTURAL ANALYSIS OF GLYCOCONJUGATES BY MASS SPECTROMETRY OF PERMETHYLATED DERIVATIVES AND BY 13C NMR SPECTROSCOPY

Abstract The carbohydrate portion of mammalian glycosphingolipids varies in the number of glycose residues, their composition, and the sequence, linkages and anomeric configuration between the sugars. This structural diversity makes possible a very large number of substances; this and also evidence for the occurrence of closely related isomers with different immunological specificities suggests an urgent need for additional fractionation procedures and methods of structural analysis. Such techniques as high performance liquid chromatography, and field desorption and chemical ionization mass spectrometry are reviewed and the results of studies using fuco-pentaose I and glucosylceramide as model compounds are presented. The 90.5 MHz, proton decoupled, natural abundance carbon-13 nuclear magnetic resonance spectra have been obtained for glucosylceramide, lactosylceramide, globotriglycosylceramide and globoside. Single lines were observed for most of the sugar, sphingosine and fatty acyl carbon components. A comparison of their resonances with those of simpler model compounds and other glycolipids allowed the determination of the sugar anomeric configuration, the intersugar linkage position and the configuration of the sugar ring structure. These studies also permitted the estimation of fatty acyl composition in terms of degree of unsaturation and chain length from chemical shift assignments and integration values of specific nuclei. Preliminary results of studies involving the uptake and conversion of 1-13C-mannose into virally transformed hamster (NIL-HSV) cell metabolites are also discussed.