Fructose specific rotation

Invertase Inverts Sucrose The hydrolysis of sucrose (specific rotation +66.5°) yields an equimolar mixture of D-glucose (specific rotation +52.5°) and D-fructose (specific rotation —92°). (See Problem 4 for details of specific rotation.)... 

Secalin. Secalin has been isolated from the stems of unripe rye.46,68 Schlubach and Bandmann69 studied its structure. The great difficulty they encountered in obtaining the polysaccharide and its acetate in homogeneous form made the determination of physical properties uncertain. However, by hydrolysis of the methyl derivative, they obtained, after separation by means of the /3-naphthoates, tetramethyl-, trimethyl-, and dimethyl-D-fructoses in the proportions of 1 2 1. The trimethyl-D-fructose was identified as 1,3,4-trimethyl-D-fructofura-nose by its melting point and specific rotation. 

It has been mentioned that the mixture of trimethyl-D-fructoses from the acid hydrolysis of hexamethyl-di-D-fructose anhydride III, which are now known to be the 3,4,6- and 1,4,6-trimethyl-D-fructoses, shows a specific rotation near that of pure 3,4,6-trimethyl-D-fructose it is to be inferred accordingly that these two trimethyl-D-fructoses do not differ greatly in rotation. Montgomery76 has synthesized 1,4,6-tri-methyl-D-fructose and found its rotation in chloroform to be [a] d = + 29.7°, a value approximating that of 3,4,6-trimethyl-D-fructose (+ 27.7° in the same solvent). Pertinent also are the respective rotations of the acetone condensation products from these two trimethyl-D-fructoses. Montgomery found that 3,4,6-trimethyl-D-fructose under-... 

Difructose anhydride II reacts with one mole of per-iodic acid. Hydrolysis of its methyl derivative indicates that two different trimethyl-D-fructoses are formed whose combined specific rotations in water amount to between + 20° and + 30°. If we assume that this anhydride, like the other two derived from inulin, is made up of D-fructofuranoses, the facts that have been mentioned allow only three possible structures for this anhydride. 

If di-D-fructose anhydride II has formula XIX, a mixture of 1,3,4-and 1,4,6-trimethyl-D-fructoses would be present in the hydrolytic product. Such a mixture would have a specific rotation of — 10° to — 20° (water) in contrast to the value of + 25 to + 30 found by McDonald and Jackson.76 The rotation of 1,4,6-trimethyl-D-fructose was measured by Montgomery76 in chloroform (+ 29.7°), but it has not been measured directly in water. However, the hydrolysis data of McDonald and Jackson76 for hexamethyl-di-D-fructose anhydride III show that 1,4,6-trimethyl-D-fructose has about the same rotation in water as in chloroform. The argument thus appears to exclude structure XIX. 

The result, [a] D -f-110° with an error of not more than + 2°, showed that prior to mutarotation the D-glucose was the ordinary a-form of rotation approximately - -109°, now known as a-D-glucopyranose. Sucrose, then, was an a-D-glucoside. Inspection of Fig. 1 also shows that after inversion but before mutarotation the sum of the rotations contributed by the a-D-glucose and the D-fructose remained very close to the specific rotation of 66° possessed by the original sucrose. The relationship ... 

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. 

Problem 22.40 Hydrolysis of ( + )-sucrose gives a mixture of d-( + )-glucose ([aji, = 52.7°) and o-(-)-fructose ((ajo = -92.4°) called invert sugar. Calculate the specific rotation of invert sugar. 

One mole of sucrose produces 1 mol each of glucose and fructose, and the specific rotation is one-half the sum of those of the two monosaccharides i.e. 

Sucrose is a disaccharide that is composed of a unit of glucose (acetal form) and a unit of fructose (ketal form) linked through C-1 of glucose and C-2 of fructose, i.e. a 1,2 link. In sucrose, neither glucose nor fructose can exist in open chain form because of the formation of acetal and ketal as shown below. As a result, sucrose is not a reducing sugar, and does now exhibit mutarotation. The specific rotation [a]D of sucrose is +66°. 

Hydrolysis of sucrose yields glucose and fructose with specific rotations [q ]d + 52.5° and —92°, respectively, and makes the resulting mixture laevorotatory (—). This phenomenon of sucrose is called the inversion of sucrose, and the resulting mixture is known as invert sugar, which is the main component of honey, and is sweeter than sucrose itself. 

For levulose or fructose, the variations of specific rotation with temperature and concentration are considerable, but the data are somewhat discordant and uncertain, owing to the difficulty of obtaining this sugar pure and crystalline. The value — 930 given in the table, which is in satisfactory agreement with those adopted for glucose and invert sugar, is deduced for about 10% solutions from the formula ... 

Hudson10 showed that the mutarotation of fructose in water at 30° is eleven times faster than that of glucose. He therefore assumed that in a sucrose solution which is undergoing very rapid inversion with invertase at that temperature, practically all of the fructose has reached equilibrium and exists as a mixture of its a and 0 forms, while the glucose is being liberated in only one form which, however, slowly passes to its a, 0 equilibrium mixture. The drop in rotation between the apparent and real curves of inversion by invertase must therefore be due almost entirely to the mutarotation of glucose. Hudson thus showed that the D-glucose liberated from sucrose by invertase had a specific rotation between [< ]d +100° and +125° and is thus most likely the a-form. 

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