Fructose fructofuranose forms

Difructose anhydride II reacts with one mole of per-iodic acid. Hydrolysis of its methyl derivative indicates that two different trimethyl-D-fructoses are formed whose combined specific rotations in water amount to between + 20° and + 30°. If we assume that this anhydride, like the other two derived from inulin, is made up of D-fructofuranoses, the facts that have been mentioned allow only three possible structures for this anhydride. 

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). 

Figure 9.24 Traditional Fisher and Haworth projections of the ketose, fructose. Fructose can form a five-C ring called a furanose when the C-2 keto group reacts with the hydroxyl on C-5, as shown in a-D-fructofuranose.

However, when fructose is linked with itself or with other sugars or when it is phosphorylated, it assumes the furanose form. Fructose 1,6-bisphosphate is present in the j8-fructofuranose form, with a 4 1 ratio of P- toa-anomeric forms. 

Fructose also forms five-membered cyclic hemiacetals. j8-D-Fructofuranose, for example, is found in the disaccharide sucrose (Section 17.7A). 

In the molecule of sucrose, glucose is present in the a-glucopyranose form and fructose in the y3-fructofuranose form. The two sugars are joined by their two reducing groups and as a result sucrose has no reducing properties. 

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. 

Difructose anhydride I was first prepared by Jackson and Goergen.18-70 These authors found a molecular weight of 307 for the anhydride and 574 for the acetate, values which indicate its difructose anhydride composition. Almost simultaneously, Irvine and Stevenson71 prepared the acetate of what they believed to be an anhydrofructose by the action of concentrated nitric acid on inulin acetate. This anhydride was later shown72 to be identical with the difructose anhydride I of Jackson and Goergen. Hexamethyldifructose anhydride I waB hydrolyzed by Haworth and Straight7 and the trimethyl-D-fructose that was formed was identified as 3,4,6-trimethyl-D-fructofuranose by quantitative conversion... 

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-... 

Sucrose (4.5, common sugar) is an acetal formed from glucose (4.3) and fructose (4.4) ignoring terms which indicate the absolute stereochemistry, a more complete name for sucrose is 2a-glucopyranose-2p-fructofuranose. 

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. 

This is one example of the second criterion mentioned previously. However, the other OH substituents, depending upon the furanose ring conformation, are either eclipsed or in the anti conformation. In the former they are disposed to form a strong intramolecular hydrogen bond in the latter they are incapable of such bonding. Further evidence to support the contention that free / -D-fructofuranose is nearly tasteless is seen in the thermal mutarotation (3) of D-fructose. As the temperature of D-fruc-... 

A five-membered cyclic sugar ring is called a furanose. Fructose prefers a fu-ranose ring system, and is formally named fructofuranose. Like glucose, fructose can cyclize and can form either an alpha anomer or a beta anomer. Notice that,... 

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