Aldoses spectroscopy

The initiating reaction between aldoses and amines, or amino acids, appears to involve a reversible formation of an N-substituted aldosyl-amine (75) see Scheme 14. Without an acidic catalyst, hexoses form the aldosylamine condensation-product in 80-90% yield. An acidic catalyst raises the reaction rate and yet, too much acid rapidly promotes the formation of 1-amino-l-deoxy-2-ketoses. Amino acids act in an autocat-alytic manner, and the condensation proceeds even in the absence of additional acid. A considerable number of glycosylamines have been prepared by heating the saccharides and an amine in anhydrous ethanol in the presence of an acidic catalyst. N.m.r. spectroscopy has been used to show that primary amines condense with D-ribose to give D-ribopyrano-sylamines. ... 

M.J. Lizak, K. Mori, P.F. Kador, Determination of aldose reductase activity in the eye by localized magnetic resonance spectroscopy, J. Ocul. Pharmacol. Then 17 (2001) 475-483. 

Water is the only solvent in which the composition of sugars has been systematically explored. Stevens1674 has determined the composition of several aldoses in pyridine-d5 by -n.m.r, spectroscopy at 300 MHz. There are scattered data on solutions in organic solvents (mainly pyridine, dimethyl sulfoxide, and N,N-dimethylformamide), but only rarely have four (or more) components of such solutions been quantitatively determined. The data that have been encountered are collected in Table VII undoubtedly, there are others that have been missed. 

The composition of many aldoses and two ketoses has been determined14 by, 3C-n.m.r. spectroscopy the results agreed well with those from previous determinations made from H-n.m.r. spectra. 

The isomerisation of aldoses and ketoses by hydride transfer, although suggested for enzymic isomerisations of aldoses and ketoses (rather than their phosphates), and having precedent in the metal ion-catalysed isomerisations of ot-hydroxy ketones, was considered to be the less common route until the paradigmal aldose-ketose isomerisation, that of glyceraldehyde to dihydrox-yacetone, was examined by NMR spectroscopy. Identification and analysis of all products of the reaction in D2O permitted concentrations to be chosen which minimised side-reactions. A useful feature of the system was that it was possible to integrate the areas of proton resonances in the CHD and CH2... 

At the temperatures commonly used in mass spectroscopy, this method is only valuable for the identification of such derivatives of D-fructose as the methyl ethers and acetates, but permits differentiation of ketoses from aldoses. ... 

Reaction of such compounds as ethyl acetoacetate or 2,4-pentanedione with D-fructose gives /3-substituted furan derivatives this is in contrast with the a-substituted compounds obtained from aldoses. The mechanism of reaction is identical in both cases, and the structure has been proved by degradation methods and by infrared and ultraviolet spectroscopy. With sucrose as the starting material, a mixture of a- and /8-substituted compounds was obtained in the ratio of 65 35. 

The conformations of the peracetylated aldose diethyl dithioacetals in chloroform solution have been examined by n.m.r. spectroscopy, and the term sickle was introduced to designate the conformation generated from the extended, planar, zigzag form by rotation through 120° about an internal carbon-carbon bond. Such a sickle arrangement is adopted in solution by the D-xylose (8) and D-ribose (9) diethyl... 

The a-furanose (0.6%) and p-furanose (0.3%) forms of o-mannose and the P-furanose form (0.14%) of D-glucose have been detected in aqueous solutions by taking advantage of the high resolving power of n.m.r. spectroscopy. The tautomeric forms adopted by ketoses and their biologically important phosphoric esters at equilibrium have also been discussed. The proportion of carbonyl form present in the equilibrium mixture of each of 23 aldoses and 10 ketoses has been estimated from the c.d. spectrum obtained with a highly sensitive circular dichro-meter. An attempt to calculate the probable specific rotations of a- and P-d-fructofuranose is mentioned in Chapter 21. ... 

The individual 2-C-(hydroxymethyl)aldoses were obtained after a combined separation of the epimers via their phenylhydrazones followed by chemisorption chromatography on a cation-exchange resin in the Ba form [50]. Then, on treatment with molybdic acid at increased temperature, 2-C-(hydroxymethyl)-D-mannose (16c) rearranged to D- /Mco-hept-2-ulose (15 c) as expected. Under similar conditions, 2-C-(hydroxymethyl)-D-glucose (15 d) was transformed to d-ma o-hept-2-ulose (16d). The analysis of the reaction equilibria by NMR spectroscopy revealed the presence of small quantities of the respective starting branched-chain aldoses 15d (3.5%) and 16c (8%). The same equilibria were also obtained from the side of the model ketoses 15 c and 16 d. Thus, for example, the equilibrium of the sugars 15c and 16c at their total 2% concentration in a 0.2%... 

Molybdic acid catalyzed isomerization of D-tagatose (without boric acid) provided a 19 1 ratio (as estimated by NMR spectroscopy) of the ketose and 2-C-(hydroxymethyl)-D-xylose. Surprisingly, D-psicose on treatment with molybdic acid under otherwise identical reaction conditions, even after prolonged reaction times, did not lead to the formation of 2-C-(hydroxymethyl)-D-arabi-nose as expected. The co-application of boric acid, either in this case or in the case of D-tagatose, does not shift the equilibria towards the corresponding 2-C-hydroxymethyl)aldoses. 

The products from perbenzylation (BnBr-KOH-DMSO) of six aldoses have been determined by - C-n.m.r. spectroscopy. After chromatographic removal of dibenzyl ether, the 8-pyranoside could be Isolated in yield from D-xylose, D-glucose, and D-mannose ... 

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