D-Fructofuranosides

Attempts to overcome this obstacle have included the use of ethyl 1,3,4,6-tetra-O-benzyl-2-thio-D-fructofuranoside as the glycosyl donor, and use of thiophilic promoters. Predictably, a,(3 mixtures were obtained, with the a anomers predominating. 

In contrast, the corresponding l,3,4,6-tetra-(9-benzoyl-2-thio-D-fructofuranoside produced exclusively the a anomers, demonstrating that there is no difficulty in producing a-D-fructofuranosides as long as the fructosyl donor has a participating 3-0-substituent.86a 

Recourse has therefore been taken to adopt the strategy successfully used for (3-mannosides, employing intramolecular aglycon delivery, namely, using a tether that forces the nucleophile to approach the oxocarbenium intermediate from the (3 

The alcohols used were ethanol, methyl 2,3,4-tri-O-benzyl-a-D-glucopyranoside, and 4-nitrophenylethyl 2-azido-2-deoxy-4,6-0-benzylidene-a-D-mannopyranoside. A range of promoters were tried dimethyl(methylthio)-sulfonium triflate, methyl triflate, iodonium dicollidine perchlorate, and iodonium dicollidine triflate. Yields were in the 30-70% range. 

Subsequently another method was developed for forcing the nucleophile to approach the anomeric center of a fructose oxocarbenium ion from the (3 side, namely to block the furanoside with bridging substituents so as to make a approach impossible. The method is illustrated here in a benchmark synthesis of sucrose 87 

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Fischer projection, monosaccharides acyclic form, 56-57 cyclic forms, 59-60 modified, 60-61 Fluorine chemistry, 18-19 D-Fructofuranosides, degradation, 445 Fructofuranosyl cation, 217 Fructofuranosyl fluorides, 217 Fructose... 

Methyl-D-fructofuranosides, 445 -447 4-Methyl-5-(2-hydroxyethyl)thiazole, 268-269 O-Methylsucroses, degradation, 447 Methyl trifiate, 187... 

Deoxy-4-fluoro- a/flc/o-sucrose (617 4-deoxy-4-fluoro-a-D-galacto-pyranosyl D-fructofuranoside), 2,3,1, 3, 4, 6 -hexa-0-benzyl-4,6-dideoxy-4,6-difluorosucrose (618), 2,3,1, 3, 4, 6 -hexa-0-benzyl-6-deoxy-6-... 

Ci2H22Ou / -d-Fructofuranosyl a-D-glucopyranoside a-D-glucopyranosyl / -D-fructofuranoside (sucrose) SUCROS, 02, 03, 04, 11 31 352... 

Ci8H32016 5 H20 0-a-D-Galactopyranosyl-(l- 6)-0-a-D-glucopyranosyl /J-D-fructofuranoside, pentahydrate (raffinose, pentahydrate) RAFINO 30 455... 

C24H42021-4.4 H20 0-a-Galactopyranosyl-( 1 — 6)-0-a-D-galactopyranosyl-( 1 — 6)-O-a-D-fucopyranosyl /J-D-fructofuranoside, hydrate (stachyose, hydrate) STACHY 34 372... 

However, some carbohydrates with a terminal D-fructofuranose residue are not suitable substrates for levan formation, e. g., methyl /3-d-fructofuranoside and inulin,64 even in the presence of enzymes98 which hydrolyze these substrates. 

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... 

Lespieau, R., Synthesis of Hexitols and Pentitols from Unsaturated Poly-hydric Alcohols, II, 107-118 Levi, Irving, and Purves, Clifford B., The Structure and Configuration of Sucrose (oipta-D-Glucopyranosyl beta-D-Fructofuranoside), IV, 1-35 Liggett, R. W., and Deitz, Victor R., Color and Turbidity of Sugar Products, IX, 247-284... 

The synthesis of (3-D-fructofuranosides is yet another useful application of this concept [293-295]. The latter 1,2-cis-glycosidic linkage is as difficult to establish as in the case of (3-mannosides. In an elegant synthesis of a-D-fucofuranose-containing disaccharides, Plusquellec and coworkers used the IAD concept via p-methoxybenzylidene acetals in combination with a glycosylation protocol via pentenyl glycosides. Here, the intermediate NIS-adduct could be isolated (Scheme 5.108) [295]. 

There is also strong evidence for the type of glycosidic linkage existing in the fructose constituent of the sucrose molecule. Schlubach and Rauchalles18 showed that invertase hydrolyzes sucrose and methyl /3-D-fructofuranoside at approximately the same rate, indicating that... 

The same holds for substitution at C3 and C5 of the fructofuranose moiety of sucrose neither melezitose (XV)61 nor o-D-glucopyranosyl-/3-D-xyloketofuranoside (XVIc)22 is hydrolyzed by yeast saccharase. As might have been expected from the experience with glycosidases, any change in the configuration of the fructon of sucrose results in stereoisomers unhydrolyzable by /3-fructofuranosidase. Thus, methyl and benzyl a-D-fructofuranosides,62 isosucrose (= /3-D-glucopyranosyl-a-D-fructo-... 

The hydrolysis of the a-D-fructofuranoside derivative with Amberlite IRA-400(HO) resin in aqueous acetone gave the I -amino-1 -deoxy-a-0-fructofuranoside in quantitative yield (86MI10). 

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