Fructose fructopyranose forms

D-Fructose, a ketohexose, can potentially form either a five-membered (furanose) or a six-membered (pyranose) ring involving formation of an internal hemiketal linkage between C2 (the anomeric carbon atom) and the C5 or C(, hydroxyl group, respectively. The hemiketal linkage introduces a new asymmetrical center at the C2 position. Thus, two anomeric forms of each of the fructo-furanose and fructopyranose ring structures are possible (Figure 9-10). In aqueous solution at equilibrium, fructose is present predominantly in the )3-fructopyranose form. 

It was shown for the sucrose isomerases of more than one strain that the enzyme catalyzes the reaction to both products, whereas isomaltulose (Palatinose ) is the kinetically and trehalulose the thermodynamically preferred product.111,134,157,169 difference in the reaction mechanism between the isomaltulose (Palatinose ) and trehalulose formation is an additional tauto-merization step of the fructose from the fructofuranose to the fructopyranose form in the catalytic pocket of the enzyme, which finally results in the trehalulose formation. ... 

By application of first-order, kinetic equations, B. Anderson and Degn claimed that an equilibrated (25°) aqueous solution of D-fructose contains 31.56% of jS-D-fructofuranose and 68.44% of -D-fructopyranose. N.m.r. studies, however, showed that, at equilibrium, a solution of D-fructose contains /3-D-fructopyranose, -D-fructofuranose, a-D-fructofuranose, and a trace of a-D-fructopyranose the distribution of these isomers was shown by gas-liquid chromatography to be 76,19.5, and 4%, respectively. Based on Anderson and Degn s result, Shallenberger reasoned that, as 0.68 X 1.8 = 1.22 (which approximates the reported sweetness of mutarotated D-fructose ), the furanose form(s) must possess very little sweetness. 

In a previous work, using D-fructose pyran- and furan- forms as inhibitors of D-fructose transport in CHO (Chinese Hamsters Ovary)-GLUT5 cells, Rollin, Holman and co-workers established that both ring forms were tolerated. The approach used was to block each hydroxyl function with allylic ether it was concluded that two sites, 0-2 (pyranose and furanose) and 0-6 (furanose) could be modified and addressed a visualization of vital interactions with the protein. These interactions were considered to occur because the D-fructofuranose form is relatively symmetrical for that reason, the binding site can arise either in anomeric center side or on the other side of the molecule. Hence D-fructopyranose appears to present to GLUT5 transporter by hydroxyl 3, 4, 5 recognition (Fig. 3). 

Several fluoro analogs of ketoses have been reported 1,6-dideoxy-1,6-difluoro-D-fructose was readily obtained from 2,3-O-isopropyli-dene-l,6-di-0-p-tolylsulfonyl-)3-D-fructofuranose by treatment with potassium fluoride in 1,2-ethanediol under a stream of carbon dioxide.96 Surprisingly, although the 6-sulfonyloxy group would be expected to be more reactive than the 1-sulfonyloxy group,97-99 no selectivity was observed. The failure to obtain 1-deoxy-l-fluoro-D-fructopyranose96 from 2,3 4,5-di-0-isopropylidene-l-0-(methylsulfonyl) (or p-nitro-phenylsulfonyl)-/3-D-fructopyranose or phenyl 3,4,5-tri-O-acetyl-l-O-(methylsulfonyl)-/3-D-fructopyranoside by treatment with potassium or sodium fluoride in 1,2-ethanediol, N,N-dimethylformamide, or form-amide at elevated temperatures may be attributed to the fact that nu-... 

When crystalline / -D-fructopyranose is newly dissolved in water, it is twice as sweet as sucrose, but shortly thereafter it is only slightly sweeter. Fructose mutarotates rapidly, and such phenomena have been associated by Isbell (4) with the formation of furanose forms of the sugars. Using a gas chromatographic procedure (5), we have shown (6) that the mutarotation primarily results from the formation of that isomer present in the sucrose molecule or -D-fructofuranose. 

In the synthesis of D-tagatose from the more common D-fructose, 1-O-benzoyl-2,3-O-isopropylidene-P-D-fructopyranose afforded two products identified as l-O-benzoyl-5-0-benzyl-2,3-0-isopropylidene-P-D-fructopyranose (97%) and its 4-O-benzyl isomer (2.8%). The skew-boat 6S4(D) conformation with an oxygen atom at C-5 adopting a quasi-equatorial position is responsible for the unexpected regioselectivity observed [136]. Conformational equilibria may also be a reason for the non-exclusive, though preferential substitution at 0-3 of benzyl 4-0-benzyl-6-deoxy-a-L-talopyranoside (9) [142]. Even in this case, however, no tri-O-benzyl derivative was formed and no starting material 9 remained, the total isolated yield of 10 and 11 being 87%. 

When either 1,3,4,5-tetra-O-acetyl-D-fructopyranose or penta-O-acetyl-A eto-D-fi uctose is treated with a mixture of phosphorus pentachloride and aluminum chloride in acetic anhydride, the product is 1,3,4,5-tetra-O-acetyl-/3-D-fructopyranosyl chloride ( /3-acetochloro-D-fructose ). If, however, 1,3,4,5-tetra-O-acetyl-D-fructose is treated with phosphorus pentachloride in acetic anhydride, without the addition of aluminum chloride, an isomer is formed. This second product is very much more stable than the first, and Brauns noted that, during the quantitative estimation of acetyl, only very small amounts of chlorine were split off by alkali at 0°. Brauns suggested that this compound is an isomeric tetra-O-acetyl-D-fruc-tosyl chloride, and it was considered by Hudson to be a-acetochloro-... 

It is D-fructofuranose, not D-fructopyranose, that is utilized, at least by bakers yeast.303,304 As with D-glucose, the initial step in the intracellular utilization of either D-fructofuranose305 or D-mannose is phosphorylation by the constitutive hexokinase306 (see Ref. 307 for a review). The D-fructose 6-phosphate formed is an intermediate of both the glycolytic pathway and the pentose cycle. D-Mannose phosphate isomerase (EC 5.3.1.8) effects the conversion of D-mannose 6-phosphate into D-fructose 6-phosphate,308,309 or D-mannose 6-phosphate is epimerized to D-glucose 6-phosphate.308... 

At mutarotational equilibrium in water, D-fructose (51) exists preponderantly as the j8-D-pyranose anomer in the 1C(d) conformation. A 1,2-alkylidene acetal (52) is formed in the same way as for L-sorbose, but this monoacetal has cts-disposed hydroxyl groups at C-4 and C-5 that react readily, forming a l,2 4,5-di-0-alkylidene-)8-D-fructopyranose (53). No evidence is available to indicate that the 1,2-alkylidene acetal might rearrange to a 1,3-alkylidene acetal, and it is to be expected that the activation energy for this isomerization would exceed that for formation of an acetal at 0-4 and 0-5. 

Lobry de Bruyn and Alberda van Ekenstein obtained a di-O-meth-ylene-D-fructose by treating a mixture of D-fructose and paraformaldehyde with either 50% sulfuric acid or 75% phosphoric acid. The diacetal, which melted at 92° and had [aJi, -34.9° in water, did not reduce Fehling solution nor react with phenylhydrazine, but it did form a monoacetate, from which the parent diacetal could be recovered by saponification. By analogy with 2,3 4,5-di-0-isopropyli-dene-)8-D- ctopyranose (2) ([a]o —33.7°), the dimethylene acetal may be formulated as 2,3 4,5-di-0-methylene-j8-D-fructopyranose (95). 

The glucose-lysine Amadori compounds monofructosy1-lysine and dlfructosy1-lysine have been Isolated, and the kinetics of their formation studied. 1-Deoxy-l-tolylamino-D-fructopyranose has been obtained by amlnatlon of fructose with g -toluldine, and shown to form an acyclic oxime and, on reaction with glycine ethyl ester, the glycosylamlne derivative (3). ... 

Previous assignments of bands characteristic of furanose and pyranose forms (Mathlouthi, Carbohydr. Res., 1980, 7, 225) were shown to be incorrect since these bands co-occur in the spectra of crystalline -D-fructopyranose. Prom the intensity of the carbonyl absorption in fructose solutions (the 0 -deuterated form in D-O) relative to that of diethyl ketone, it was concluded that 0.9 of fructose was present as the open-chain form. From a study of the i.r. spectra of peracetylated aryl glycosides, the value of bands in the 800-1000 cm region for differentiating a- and 6-anoraers has been reassessed. The relative intensities of C-O-C stretching vibrations in the 1000-1100 cm region and a band near 300 cm for -anomers only were suggested as criteria for... 

Acetonation of a mixture of 1-deoxy-5,6-0-isopropylidene-D-arabino- and -D-xylo-hexulose. obtained by hydroxylation of 1,3,4-trideoxy-5,6-0-isopropylidene-D-glycero-hex-3-enulose, gave 1-deoxy-2,3 4>5-(ii-0-isopropylidene-y3-D-fructopyranose and 1 -deoxy-2,3 4,6-di-0-isopropylidene-/-D-sorbofuranose. The same two products were formed when acetonation was carried out on a mixture of 1-deoxy-D-fructose and -D-sorbose obtained from hydroxylation of 1,3,4-tri-deoxy-D-glycero-hex-3-9nulose. 

Complexes formed between D-fructose and Mg have been shown to have the structure Mg(6-D-fructopyranose)halide2 and to Involve... 

These furanose derivatives undergo mutarotation in a manner similar to the aldofuranose compounds. The ketohexoses form pyranose derivatives via the OH unit at C6 (in violet). d-Sorbose (47), for example, will form a-d-sorbopyranose (51) and P-d-sorbopyranose (52), and d-fructose (46) will form a-d-fructopyranose (53) and P-d-fructopyranose (54). 

D-Fructose condenses with acetone 2a, 171) to form two isomeric di-0-isopropylidene-D-fructoses. The first derivative upon methylation yields a monomethyl derivative which on partial hydrolysis gives a mono-0-isopropylidene-mono-O-methyl-D-fructose and on complete hydrolysis a mono-O-methyl-D-fructose which is convertible to the same osazone as 3-0-methyl-D-glucose. The methoxyl group is therefore at carbon 3. The mono-O-isopropylidene-3-O-methyl-D-fructose, after methylation and acid hydrolysis of the 0-isopropylidene and glycosidic methoxyl group yields a tri-O-methyl-D-fructopyranose the ring structure is demonstrated by further methylation to tetra-O-methyl-D-fructopyranose of known struc-... 

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