Ketoses 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. ... 

A similar series of reactions was performed on a 6-azido-6-deoxy-2-ketose.246,252 In most of the foregoing syntheses, the piperidine formed is accompanied by the tautomeric furanose. The tautomers can, however, be separated without occurrence of equilibration (which can be induced by changing the pH of the medium). For the ketose derivative 183, the equilibrium mixture includes246 compound 184 and a dehydration product (182). The conformation and anomeric effect in these piperidines have been studied by n.m.r. spectroscopy,253 and their fragmentation pathways have been determined by mass spectrometry.254... 

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... 

Physical methods have been invoked more and more in order to obtain information concerning the keto structure and to determine properties characteristic of this class of sugar. Ultraviolet and infrared spectroscopy have been used for identification of the free carbonyl group, and the latter technique also permits the identification of all 2-ketoses by the... 

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. ... 

Several 4-deoxy-4-nitro ketose derivatives have been synthesized. Three crystalline 2,7-anhydro-4-deoxy-4-nitro-/3-D-heptulopyranoses arose by nitromethane cyclization92 of the dialdehyde (74) produced by periodate oxidation of sedoheptulosan (73), and were assigned93 the D-alio (75), D-gulo (76), and D-altro (77) configurations by nuclear magnetic resonance spectroscopy of the corresponding, peracetylated amino sugars. When the cyclization of 74 was performed in methan-olic medium, a solid mixture of stereoisomeric nitronates was obtained in almost quantitative yield, and it could be partially separated into the individual nitronates, which furnished 75 and 76. The isomer 77... 

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. ... 

Reference is made in Chapter 2 to the use of n.m.r. spectroscopy to identify the tautomeric forms of ketose phosphates present in equilibrium mixtures, while the formation of cyclic phosphites and related derivatives of D-mannitol is dealt with in Chapter 17. 

Through chemoselective esterification of the primary hydroxy group of the 2-ketoses to the corresponding (S)-3,3,3-trifluoro-2-methoxy-2-phenylpropionic acid [(S)-MTPA] esters [17], we opened an easy and reliable way to determine the diastereomeric and enantiomeric excess by NMR spectroscopy. In addition, by correlation with our SAMP-/RAMP-hydrazone method, the absolute configurations can be assigned [16]. 

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. 

Molybdic add catalyzed isomerization of D-tagatose (without boric add) provided a 19 1 ratio (as estimated by NMR spectroscopy) of the ketose and 2-... 

Methyl Ethers.—6-0-Methyl-L-sorbose, 5-O-methyl-D-fructose and -L-sorbose, and 5,6-di-O-methyl-L-sorbose have been synthesized. " U.v. spectroscopy was used to determine the proportion of the acyclic form of these and other ketoses present in methanol solution the extinction coefficient (e = 34.7) for the carbonyl group was determined using 5,6-di-O-methyl-L-sorbose, which cannot cyclize. Of the other ketoses examined, 6-O-methyl-L-sorbose was found to contain the highest proportion (7.4%) of the acyclic form at equilibrium. 

Phosphates and phosphonates of biochemical interest and the forms adopted by ketose phosphates in aqueous solution have been discussed. The p a values of each of the six phosphoric monoester groups of wj o-inositol hexa-phosphate (phytic acid) have been determined by the use of P n.m.r. spectroscopy. The conformation adopted by myo-inositol hexaphosphate in basic and neutral solutions was also discussed. 

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