Fructosides

The specificity of levansucrase98 is dependent not only on the d-fructoside but also on the aldoside residue of the substrate. Neither inulin nor methyl D-fructofuranoside was hydrolyzed by levansucrase, and even when these two substrates were hydrolyzed by inulase (prepared from inulin-fermenting Torula yeast) or by yeast invertase respectively, no levan formation occurred with levansucrase. However, neither methyl D-fructofuranoside nor inulin inhibited levan formation from sucrose by levansucrase. No levan was formed from potassium D-glucose... 

I. E. Baciu, H. J. Jordening, J. Seibel, and K. Buchholz, Investigations of the transfructosylation reaction by fructosyltransferase from B. subtilis NCIMB 11871 for the synthesis of the sucrose analogue galactosyl-fructoside, J. Biotechnol., 116 (2005) 347-357. 

D-Glucose-l-D-fructoside + D-sorbose, D-glucose- l-i/-sorboside + D-fructose... 

D-Glucose-l-D-xyloketoside + D-fructose D-glucose-1-D-fructoside + D-xyloketose... 

As may be seen from Fig. 2, it seems impossible to accommodate at the surface of the enzyme simultaneously a molecule of sucrose and of L-sorbose in such a way as to permit a switch of the fructosidic linkage... 

The indifference of /3-fructofuranosidase towards substitution in the afructon part of sucrose is contrasted by its extreme sensitivity towards any change in the structure and configuration of the fructon. Change from the furanose to the pyranose ring structure in methyl /3-D-fructoside is incompatible with the action of /3-fructofuranosidase.60... 

This enzyme [EC 3.2.1.7], also referred to as 2,l-j8-o-fructan fructanohydrolase and inulase, catalyzes the en-dohydrolysis of 2,l-j8-D-fructosidic linkages in inulin. 

Fig. 2.—Partial hydrolysis of fructofnranoside sirups with invertase. Plot I, change in specific rotation of the entire methyl fructoside sirup plot II, same for benzyl fructoside sirup plot III, change in calculated specific rotation of fructose from methyl fructoside plot IV, same for fructose liberated from benzyl fructoside sirup.

When the original methyl D-fructofuranoside sirup was fermented with yeast, the unstable beta isomer was selectively eliminated and the residue yielded a crystalline methyl D-fructoside melting at 81° and with [a] D +93° in water. The ring structure of this new isomer was proved to be furan by methylation to the liquid tetramethyl derivative, of [a] °D +129.4°, and subsequent hydrolysis to 1,3,4,6-tetramethyl-D-fructofuranose (structure IX) with the correct specific rotation of +29.8° in water. Both the methyl D-fructoside and its fully methylated derivative were therefore of the alpha configuration, since the latter was more dextrorotatory than the tetramethyl-D-fructose and also since the former was more dextrorotatory than the isomer, of [a] D —51°, unstable to invertase. Similar work with the benzyl D-fructofuranoside sirup produced the crystalline alpha isomer, melting point 89°, [a] D +45.7° in water, the liquid tetramethyl derivative, [a] D +83.3° in chloroform and, after acid hydrolysis of the latter, 1,3,4,6-tetramethyl-D-fructofuranose. 

The fructosylation of elymoclavine (9) by C. purpurea was described in [42] (Fig. 8). This reaction is mediated by the transfructosylating activity of p-fructofur-anosidase in sucrose-containing media. Beside mono- (10) and difructoside, higher fructosides (tri- and tetra-) (11) are also formed [43] (Fig. 9). 

Glycosylating Claviceps strains (mostly C. fusiformis) produce most elymoclavine in the form of p-fructofuranosides, which complicates the isolation of elymoclavine. The hydrolysis of fructosides by HCl is not suitable for a large scale process due to the aggressive nature of the acid solution and losses of elymoclavine. A more elegant method is a bioconversion employing the high invertase activity... 

The interesting physiological effects of alkaloid fructosides [41] stimulated the preparation of other glycosides, such as galactosides, glucosides, A-glucosami-nides, and complex alkaloid glycosides. 

The Lewis acid catalyzed C-glycosylation method is probably one of the most efficient to prepare C-glycosides of ketoses, the anomeric carbocation intermediate being in this case more stabilized by a further substituent. We applied this procedure to synthesize C-fructosides [15] (Scheme 8).The reaction of methyl... 

The above-mentioned procedure for the synthesis of C-fructosides has been used to synthesize the bisphosphono analog of / -D-fructose 2,6-bisphos-phate [ 16], which is, as reported in Sect. 2.3, an important activator of glycolysis and inhibitor of gluconeogenesis. To prepare the target molecule we first attempted the conversion of the firee hy iroxyl group of 21 into an iodide which in turn can be easily converted into a phosphonate. However, this conversion... 

Different electrophiles, such as I2, Br2, NBS, NIS, PhSeCl or metachloperoxy-benzoic acid have been used in the cyclization of glycoenitols [34], but the best stereochemical results have been obtained with mercuric salts and iodine. Iodine however can give rise to a debenzylation with formation of the more favored 5-member cyclization product. This is the case for 72 which, when treated with iodine, affords the C-fructosidic structure 83 [35] (Scheme 23). 

Glycosides that contain glucose are called glucoside. Similarly, when the sugars are fructose or galactose, the glycosides are called fructoside or galactoside, respectively. 

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