Hexulose solution

Meyerhof and Schulz86 studied this reaction in trisodium phosphate solution, and regarded it as coming to a triose-hexose equilibrium containing 92 % of hexose. Berl and Feazel67 examined the kinetics of hexose formation from trioses in alkaline solution, and noted that 75-90% of hexulose is formed from DL-glycerose alone, but that the yield is lower (about 60%) when dihydroxyacetone is added in equivalent quantity. Paper chromatog-... 

The composition of aqueous solutions of D-arahino-2-hexulose (d-fructose) has also been studied by laser-Raman spectroscopy.45 (The composition of solutions of D-fructose appears to have been determined by more methods, and more often, than that of any other sugar.20)... 

It is well known, however, that substituents favor cyclic as against acyclic forms,76 and electron-attracting substituents on the a-carbon atom increase the tendency of carbonyl groups to react with hydroxyl groups (for example, the ratio of aldehydrol to aldehyde in aqueous solution is —1.2 1 for acetaldehyde77 at 25°, and 17.5 1 for glycolalde-hyde78 at 35°). Hence, whereas 6-hydroxy-2-hexanone is found only in the acyclic form, aqueous solutions of the 1-deoxyhexuloses contain only 5% of this form at equilibrium, and those of the hexuloses contain less than 1% (see Table IV). 

These conclusions are borne out by the data on some phosphorylated ketoses83 that cannot form pyranoses or furanoses. 5,6-Dideoxy-D-fhreo-hexulose 1-phosphate (1) contains 96% (by i.r.) or 91% (by n.m.r.) of the keto form, and D-en/fhro-pentulose 1,5-bisphosphate (2) contains 84% (by i.r.) or 88% (by n.m.r. spectroscopy80 ) in aqueous solution in the hydrates, there would be 1,3-parallel interactions. There are no such interactions in the hydrate of l,5-dihydroxy-2-pentanone 1,5-bisphosphate (3), but here one of the carbon atoms vicinal to the carbonyl group carries no hydroxyl group, and there is 84% of the keto form in equilibrium. l,3-Dihydroxy-2-propanone phosphate has two neighboring hydroxyl groups and no 1,3-parallel interactions only 55% is in the keto form and 45% is present as the hydrate.83,84... 

V. Composition in Aqueous Solution Ketoses 1. Hexuloses and Pentuloses... 

The composition of aqueous solutions of all of the 2-hexuloses, of several 3-hexuloses, 2-pentuloses, and their deoxy derivatives, and some of the hexulosonic acids is shown in Table IV. 

The composition of 6-0-methyl-D-ii/ to-2-hexulose (6-O-methyl-D-tagatose) in aqueous solution at 35° is 21% of a-furanose, 69% of/ -fura-nose, and 10% of the keto form.15 The ratio of a- to / -furanose for 6-0-methyl-D-psicose was found to be — 2.4 1 that of a- to / pyranose for 5-O-methyl-D-psicose, —1.25 1 the proportion of the keto form was not determined.13... 

The refining of solutions containing D-fructose requires careful control in order to prevent such side reactions as the epimerization of D-fructose (D-arafoino-hexulose) to D-psicose (D-rifeo-hexulose). Such processes, in which the use of weakly basic ion-exchange resins is important, have been described by Khaleeluddin and coworkers.48... 

If, in an attempt to obtain free 6-amino-6-deoxy-L-xt/Io-hexulose, the isopropylidene compound 80 is hydrolyzed at 65° with 2 M hydrochloric acid, an almost quantitative yield of 3-hydroxy-2-pyrldinemeth-anol (86) hydrochloride is obtained instead. The formation of 86 can result only through the intermediate 6-amino-6-deoxy-L-xyfo-hexulo-pyranose (83). The furanose (81) first formed is in equilibrium with the pyranose (83). The latter is dehydrated in acid solution to 82 which, under acid catalysis, rearranges to the intermediate 84. In the following steps, the allylic hydroxyl groups on C-4 and C-5 are readily removed, and aromatization to the pyridine derivative (86) ensues. 

If a solution of the furanose hydrochloride 81 is made alkaline, immediate ring expansion to the pyranose form (83) occurs. This compound is stable in alkaline solution, but yields the p)oidine derivative (86) on mild acidification. The size of the hemiacetal ring of 6-amino-6-deoxy-L-xylo-hexulose accordingly shows an interesting dependence on pH in solution in strong acids, the furanose (81) is formed in alkaline solution, the pyranose (83) is present and in neutral solution, or in weakly acidic solutions, the reaction to the pyridine derivative (86) occurs. 

Thio-D-fructofuranose (88) was prepared from 5-(9-tosyl-l,3-(9-isopropylidcnc-o -L-sorbopyranose (87) by the standard sequence of reactions shown in Scheme 26. The H and C NMR spectra of 88 in aqueous solution show only tlie signals of the furanose a and p anomers in the ratio of 11 89, whereas tlie NMR spectra of D-fructose in D2O show the presence of the -pyranose, -furanose, a-furanose, and a-pyranose in the ratio of 6 3 1 trace, respectively. Partial hydrolysis or methanolysis of 90, prepared from 1,6-di-O-tosyl-D-fructofuranose (89), gave 3,6-anhydro-l-deoxy-6-thio-D-oraZ)W7o (or D-yv/o)-hexulose (91). Nucleophilic attack of the ring sulfur atom on C-3... 

Another feature common to all hexoses is their fragmentation to trioses and related products (such as lactic acid, l-hydroxy-2-propanone, and pyruvaldehyde). l-Hydroxy-2-propanone is formed by heating a solution of D-fructose in potassium acid phosphate buffer solution of pH 6.7 it was proposed that an intermediary 3,4-enediol (s) rearranges to a /3-diketone, which yields (t) by fragmentation of the molecule. Studies by Wolfrom and Schumacher and by Blair and Sowden showed that this mechanism, followed by recombination and aldolization, accounts for some of the observed products. The identification of L-a 2/io-hexulose and DL-a yZo-hexulose was conclusive in this respect, but deuterium studies by Sowden and Thompson proved the minor role of this recombination mechanism in the transformations. 

In alkaline solution, D-arofetno-hexulose phenylosazone is oxidized by atmospheric oxygen to give a product which, from chemical degradative evidence, was assigned the revised (but still inaccurate) structure (70). Although the nuclear magnetic resonance spectrum of the derived tri-... 

The tautomeric equilibria of aldopentoses, aldohexoses and hexuloses in DMSO have been examined by C-n.m.r. spectroscopy the mutarotation kinetics of aqueous D-glucose have been investigated by i.r. methods, and Raman spectroscopic data on the tautomeric transformations of glucose in aqueous solution over a wide pH range confirmed that the ring-chain tautomerism depends on pH." The ring shapes of the two fiiranose and two pyranose forms of psicose in aqueous solution, riiown by n.m.r. spectroscopy to be present in almost equal proportions, have been analyzed by MM3."... 

In this context, it appears to be of relevance to briefly mention some comparable reaction systems for ketose epimerization. Petrus and his group, as well as Petrus, Serianni and co-workers, recently reported the stereospecific molybdic acid catalyzed isomerization of 2-hexuloses to branched-chain aldoses [55-57]. Upon treatment with a catalytic amount of molybdic acid in aqueous solution, the 2-ketohexoses, o-fructose, L-sorbose and o-tagatose, underwent a stereospecific intramolecular rearrangement to give the corresponding 2-C-hydroxyme-thylaldoses, 2-C-hydroxymethyl-D-ribose (o-hamamelose), 2-C-hydroxymethyl-L-lyxose and 2-C-hydroxymethyl-o-xylose, respectively (see Petrus, Petrusova and Hricovfniova, this vol.). 

The photochemical and thermal Isomerization of D-arablno-hexulose phenylosazone In solution between the N- and 0-chelate forms (20) and (21) respectively, has been studied In detail, the photo-reaction being a fast efficient method for the synthesis of the 0-chelate. Lifetimes and quantum yields have been reported for... 

A variety of alditol-l-yl substituted heteiocyclic derivatives have been synthesized. The tetiazole derivative (94) was derived riom maltose, and convened into the corresponding 1,3,4-oxadiazoles (95) on acetylation or benzoylation. Reaction of l-arylamino- or 1-alkylamino-l-deoxy-D-arabino-hexuloses with cyanamide gave the imidazole derivatives (96). Fructosazine (97) and deoxyfiructosazine (98) were simultaneously formed by self-condensation of 2-amino-2-deoxy-D-glucose in neutral to basic aqueous solutions, and were shown to have DNA strand breaking activity. Condensation of 2-amino-2-deoxy-D-glucose with aryl isocyanates gave adducts such as (99) that exist in solution as (R,5)-mixtures in which the (R)-fonn predominates. ... 

Angyal s group has reported a detailed n.m.r. study of the tautomeric equilibria of the 2-hexuloses and some of their derivatives in aqueous solution -all the resonances in the n.m.r. spectra were assigned with the aid of specifically deuteriated compounds. The proportions of the anomeric furanoses and pyranoses present in solutions of the 2-hexuloses at equilibrium in deuterium oxide at 27 °C are shown in the Table (cf. Volume 8, p. 172), and the results were discussed in terms of conformational analysis. 

Table Equilibrium compositions (%) of solutions of the 2-hexuloses in deuterium oxide at 27 C...

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