Fructose fructopyranose

D-Fructose is the sweetest sugar known in naturally occurring carbohydrates, and its intense sweetness is produced only by ) -D-fructopyranose. "... 

Treatment of inulin or D-fructose with liquid HF (neat or diluted with liquid SOj) gave a mixture of six di-D-fructose dianhydrides, including 23, 25, 27, and )3-D-fructofuranosyl ) -D-fructopyranose 2,l 3,2 -dianhydride... 

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. 

A 3-0-benzylated D-fructose derivative was produced from l,2 4,5-di-O-isopropylidene-P-D-fructopyranose under standard conditions (Scheme 26). Transient 3-0-benzylated D-fructose resulting from acidic hydrolysis was reacted with thiocyanic acid without intermediate purification. This sequence afforded a mixture of isomeric spiro-OZT on pyran and furan templates, which was difficult to separate, even if standard acetylation was applied. 

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). 

Though there is no direct evidence that the D-fructofuranose unit in melezitose is of -configuration, the facts that all naturally occurring fructofuranoside sugars known so far are sucrose or sucrose derivatives and that the equilibrium mixture of D-fructose appears to consist almost entirely of /3-o-fructopyranose and /3-D-fructo-furanose, are very suggestive of a /3-configuration. For a full discussion of the problem see C. S. Hudson, Advances in Carbohydrate Chem., II, 1 (1946). 

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-... 

Investigations by Haworth and many others have made it probable that a D-fructopyranose structure is to be assigned to crystalline D-fructose. Formulas III and IV below illustrate the interconversion of... 

HMF has been discovered for the first time in 1895 by Diill and Kiermeyer who independently introduced a method of synthesis of HMF that they named oxy-methylfurfurol [65, 66]. Later, Haworth and Jones studied the mechanism of this reaction and showed that the formation of HMF involved a triple dehydration of hexoses [67]. Other studies performed by Van Dam, Kuster and Antal showed that the dehydration of hexoses (especially fructose and glucose) involved two possible pathways (Scheme 5) [63, 68, 69]. The path 1 involves the dehydration of ring systems (fructopyranose or glucopyranose), while the path 2 is based on acyclic derivatives (glucose and fructose open chain). 

Leucrose, 6-0-(a-D-glucopyranosyl)-p-D-fructopyranose [7158-70-5], is synthesized from sucrose using a dextranase enzyme from Leuconostoc mesenteriodes and a small proportion of fructose (2%). Pfeifer Langen of Germany have developed a production process for leucrose that involves extraction of the enzyme, treatment with 65% aqueous solution of sucrose and fructose (1 2 wt/wt) at 25°C, separation of the product from fructose by ion-exchange column chromatography, and crystallization. The product has not yet been launched on the market as of this writing (1996). 

Study of this reaction has not been limited to cyclic acetals of aldoses and aldosides, and synthetic applications in the ketose series have been developed,273,276,278,278 particularly for isopropylidene acetals of D-fructose. As an illustration of these reactions, two examples are given here. The action of butyllithium on 2,3 4,5-di-0-isopropyli-dene-l-0-methyl-/3-D-fructopyranose (280) gave273 a 30% yield of the 5-enopyranose 282. Abstraction by the base of the axial hydrogen atom from the 6-methylene group, giving the anion 281, was invoked... 

An analogous scheme was revealed in the ammonolysis of 1,3,4,5-tetra-O-benzoyl-jS-D-fructopyranose and 1,3,4,5,6-penta-O-acetyl-keto-D-fructose,37 with formation of the imidazole derivatives 37, 38, 40, 41, and 4(5)-(D-arabino-tetritol-l-yl)imidazole (42), which were identified by paper chromatography. 

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. 

Cognate preparations. l,2 4,5-Di-0-cyclohexylidene-D-fructopyranose. Add 200 g (1.11 mol) of finely powdered dry D-fructose with vigorous stirring to 419 g (440 ml, 4.49 mol) of ice-cooled cyclohexanone containing 30 ml of concentrated sulphuric acid the reaction mixture becomes solid within 30 minutes. Leave the mixture overnight at room temperature, dissolve the product in 500 ml of chloroform and wash the solution with dilute aqueous sodium hydroxide, dilute hydrochloric acid and water and finally dry and evaporate. Solidify the residue by m.p. 145-156°C, Md° —133.5° (cl in CHC13). The yield is 142 g (37%). 

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%. 

Pseudo-p-DL-fructopyranose 180 was found to be nearly as sweet as D-fructose. The D-enantiomer 196 and the L-antipode 207 were also as sweet as D-fructose, but 196 was somewhat sweeter than 207. The small but observable difference in sweetness of 196 and 207 might be due to a stereogeometrical deformation of interrelations between the sweetness eliciting tripartite and a sweet receptor. 

The oxidation of D-fructose with cerium(IV) in sulfuric acid medium is inhibited by an increase in the acidity. A cationic surfactant, CTAB, catalyses the reaction, whereas SDS has no effect. The catalytic role of CTAB has been explained using the pseudophase model of Menger and Portnoy. A mechanism involving the formation of an intermediate complex between /3-D-fructopyranose and Ce(S04)32- has been proposed.61 The oxidation of cycloalkanones with cerium(IV) in sulfuric acid medium showed a negligible effect of acidity. Formation of an intermediate complex, which decomposes in the rate-determining step, has been suggested.62... 

---