Fructoside ring structure

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... 

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. 

Fructosides, D-, ring structure of, 5 Fucopyranoside, methyl 2,3-di-O-methyl-/3-D-, 271... 

Because sucrose is hydrolyzed by enzymes that specifically assist hydrolysis of both a glycosides (such as yeast a-glucosidase) and /3-fructosides (such as invertase), it is inferred that the glucose residue is present as an a glucoside and the fructose residue as a /3 fructoside. If so, the remaining uncertainty in the structure of sucrose is the size of the rings in the glucose and fructose residues. 

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