Fructofuranoside, benzyl

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-... 

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-... 

Comparisons made with the same invertase solutions showed that the methyl and benzyl / -D-fructofuranosides were hydrolyzed 13.5 and times, respectively, more slowly than sucrose, and that the rates... 

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. 

Although dilute aqueous acid hydrolyzed the methyl and benzyl a-D-fructofuranosides approximately 8 and 16 times as rapidly as sucrose, their method of preparation showed them to be unaffected by any of the enzymes active in a fermenting yeast suspension. Purified yeast invertase, proven free of a-D-glucosidases (maltases), could therefore contain no enzyme capable of hydrolyzing the above two a-D-fructo-furanosides, but did contain constituents that readily cleaved the beta isomers and also sucrose. The latter is accordingly a /S-D-fructofuranos-ide. When the evidence is put in this way, the present uncertainties as to whether purified invertase preparations include one or a number of /3-D-fructofuranosidases, and whether or not sucrose, methyl and... 

Two crystalline benzyl fructosides have been prepared by Purves and Hudson. By treating crystalline methyl a-D-fructofuranoside with benzyl alcoholic hydrogen chloride they obtained a mixture which was partially hydrolyzed by invertase. Acetylation of the unhydrolyzed part gave a crystalline tetraacetate which was deacetylated to crystalline... 

Benzyl dimethyl-a-D-fructofuranoside Methyl dimethyl-a-D-fructofuranoside liquid +57.1 Dioxan 95... 

Of other promoters tried, NIS also gave high yields of disaccharides, whereas methyl triflate, NBS, NCS and silver aluminium silicate gave inferior results. The benzoylated donor always gave stereospecifically the a-linked fructofuranoside, whereas the benzylated donors gave a/ -mixtures with the a-product generally in excess. The a/ -ratio and yield were independent of the anomeric configuration of the donor. 

As a first attempt, the synthesis of sucrose was tried using the fully benzylat-ed donor 65 a and the commercially available crystalline 2,3,4,6-tetra-O-benzyl-a-D-glucopyranose as acceptor. The conditions were optimised to give as much fructofuranoside as possible and at the same time not to cause anomerisation of the glucose acceptor. As found earher with this approach, it was not possible to obtain a really good a/)S-ratio for the furanosidic linkage. Only a 20% yield of perbenzylated sucrose was achieved, the main product (50%) being the a,a-isomer [104]. 

As we have argued before, if the primary effect of electron-withdrawing phosphorus aryl substituents is to accelerate the final reductive elimination, then the enhancement of enantioselectivity may result because one of the diastereomers of the benzylic complex (Fig. 4) may be disproportionately affected. The precise factors favoring a particular diastereomer (its formation or its decomposition) are presently unclear, but the results with the a-methyl fructofuranoside ligand frame strongly suggest the importance of a stereoelectronic component. For example, the effect of electronic asymmetry may reflect the importance of a trans... 

Benzyl a-D-fructofuranoside was synthesized, and obtained in pure form, by the addition of zinc bromide (as the catalyst) to a solution of the corre-... 

When the ortho ester (7) is treated with benzyl alcohol and fused zinc bromide, benzyl 1,3,4,6-tetra-O-benzoyl-a-D-fructofuranoside (10) is formed this is readily saponified to the free fructoside (11). 

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. 

Although there were a number of kinetic studies of the acid-catalyzed hydrolysis of sucrose (containing a ketofuranoside) [35-38] and of methyl and benzyl fructofuranoside [39], the first systematic kinetic and mechanistic study of acid-catalyzed hydrolysis of glycofuranosides was reported by Capon and Thacker [40] (see Table 3.8). 

Heidt LJ, Purves CB (1944) Thermal rates and activation energies for the aqueous acid hydrolysis of a- and p-methyl, phenyl and benzyl-D-glucopyranosides, a- and p-methyl and P-benzyl-D-fructopyranosides, and a-methyl-D-fructofuranoside. J Am Chem Soc 66 1385-1389... 

The thermolysis of sucrose in DMSO has been shown to yield a fructofuranosyl carbonium ion and a-D- lucose, which subsequently anomerizes. If the latter is generated in the presence of benzyl alcohol, benzyl o - and 3-fructofuranosides result. The carbonium ion was thought to be the precursor for the formation of 2,6-anhydrofructofuranose in thermolysis reactions of sucrose. 

O -Benzoyl-1,2-0 -isopropylidene- p-D-fructopyranose, 1-62 1-0-Benzyl-3-deoxy-3-fluoro-D-fructose, D-74 l-Bromo-l-deoxy-2,3 4,5-di-0-isopropylidene-p-D-fructopyranose, B-67 Butyl p-D-fructofuranoside, F-84... 

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