Fructose structure

With the aim to explore this model of interaction, Rollin and co-workers have developed a method using the OZTs moieties to block the D-fructose structure and analogues. The OZT structures can be regarded as analogues of D-fructose... 

Ans. All four structures represent the same compound, a-o-fructose. Structures I and II use slightly different ways of representing the CHj carbons. Structure III is rotated 180° in the plane of the paper relative to structure II. Structure IV is rotated 180° out of the plane of the paper relative to structure III. 

The four kelohexoses are fructose, sorbose, allulose and tagatose. See glucose for example of isomerization between open chain and cyclic structures in a typical hexose molecule. 

Figure 6.24 The function of the enzyme phosphofructokinase. (a) Phosphofructokinase is a key enzyme in the gycolytic pathway, the breakdown of glucose to pyruvate. One of the end products in this pathway, phosphoenolpyruvate, is an allosteric feedback inhibitor to this enzyme and ADP is an activator, (b) Phosphofructokinase catalyzes the phosphorylation by ATP of fructose-6-phosphate to give fructose-1,6-bisphosphate. (c) Phosphoglycolate, which has a structure similar to phosphoenolpyruvate, is also an inhibitor of the enzyme.

In a similar manner, ketones can react with alcohols to form hemiketals. The analogous intramolecular reaction of a ketose sugar such as fructose yields a cyclic hemiketal (Figure 7.6). The five-membered ring thus formed is reminiscent of furan and is referred to as a furanose. The cyclic pyranose and fura-nose forms are the preferred structures for monosaccharides in aqueous solution. At equilibrium, the linear aldehyde or ketone structure is only a minor component of the mixture (generally much less than 1%). 

Therapeutic Function Fluid and nutrient replenisher Chemical Name Fructose Common Name Levulose and fruit sugar Structural Formula h... 

The structure of human muscle fructose-1,6-bisphosphate aldolase, as determined by X-ray crystallography and downloaded from the Protein Data Bank. (PDB ID 1ALD Gamblin, S. J., Davies, G. J., Grimes, J. M., Jackson, R. M., Littlechild, J. A., Watson, H. C. Activity and specificity of human aldolases. J. Mol. Biol. v219, pp. 573-576, 1991.)... 

Because i.-fructose is the enantiomer of D-fructose, simply look at the structure of n-fructose and reverse the configuration at each chirality center. 

There is another aspect of the structure of glucose and fructose. They, like other simple sugars, can exist as a straight chain but this form is in equilibrium with a cyclic structure. In solutions the latter form prevails. Reaction (2) shows both forms of glucose. 

Draw a structural formula for the fructose molecule (remember that fructose is an isomer of glucose). Explain why fructose cannot be oxidized to a six-carbon acid. 

Fractional crystallization, 413 Freezing point lowering, 325, 393 Freon, 362 Frequency of light, 246 relation to wave length, 251 Fructose, 423 Fumaric acid, 428 properties, 308 structure, 316... 

The literature in this field is confusing because of a somewhat haphazard method of nomenclature that has arisen historically. This is compounded by some mistakes in structure determination, reported in early papers, and which are occasionally quoted. The first part of this chapter deals with nomenclature and with a brief overview of early work. Subsequent sections deal with the formation and metabolism of di-D-fructose dianhydrides by micro-organisms, and the formation of dihexulose dianhydrides by protonic and thermal activation. In relation to the latter topic, recent conclusions regarding the nature of sucrose caramels are covered. Other sections deal with the effects of di-D-fructose dianhydrides upon the industrial production of sucrose and fructose, and the possible ways in which these compounds might be exploited. An overview of the topic of conformational energies and implications for product distributions is also presented. 

Table 1 contains a list of the dihexulose dianhydrides currently in the literature, together with some mixed fructose-glucose dianhydrides. Trivial and IUPAC names are included. Each entry has a proposed abbreviation. Because of the great similarity of structure between all the compounds in Table I, these abbreviations are used, rather than numbers, in the context of this chapter. Thus, 1 is named as ot-D-Fru/-l,2 2,1 - 3-D-Frup, 2 as (3-D-Fru/-l,2 2,3 - 3-D-Fru/, and 3 as 3-D-Frup-1,2 2,l -ot-L-Sor/>. 

The new compounds were assigned structures by examination of their 13C NMR spectra and of the H NMR spectra of the peracetates. A similar mechanism to that previously postulated for fructose and inulin,31 and involving a sor-bofuranosyl fluoride was suggested for the formation of these isomers. In both Refs. 31 and 80, formation of the 2,3-linkage was associated with more-rigorous conditions. 

---