Anomers of D-glucose

This enzyme oxidizes a- and P-anomers of D-glucose to the same extent and shows excellent stability and sensitivity about twice that for the methods with immobilized glucose oxidase. In this approach, pyranose oxidase is immobilized on tresylate-poly(vinylalcohol) beads and packed into a stainless column and peroxidase is immobilized on tresylate-hydrophylic vinyl polymer beads and packed into a transparent FITE tube that is used as the CL flow cell. The H202... 

Calculations of the conformations and frequencies of various monosaccharides (a and /3 anomers of D-glucose, D-allose, D-galactose, and d-... 

In the presence of dilute base, D-glucose rearranges to a mixture containing the anomers of D-glucose (—64%), D-fructose (—31%), and D-mannose (3%). This interconversion undoubtedly involves enolization of the hexoses by way... 

Comparison of the Fischer (a) and Haworth (b) projections for a- and /3-D-glucose. The Haworth projection is a step closer to reality. Chair configurations for the two anomers of D-glucose are the most accurate depiction (c) but they are not always used because of the difficulty in drawing. Note that the largest substituent, —CH2OH, is in an equatorial location in both structures. The differences between the two anomers are shown in color. 

Equation I is a simplified one, as it does not take into account the interchange between the enzymically active a anomer of D-glucose and the /3 anomer. The same reservation applies to D-fructose, which exists in four anomeric forms in solution, and which of the four is the... 

Figure 7 G, G, and T hydroxymethyl conformers of both anomers of D-glucose. Under each structure is the anomer designation, the conformer label, and the AMl-SM2 value of AG (kcal/mol).

Figure 27.7 Three-dimensional representations for tx)th anomers of D-glucose...

Glucose has all substituents larger than a hydrogen atom in the more roomy equatorial positions, making it the most stable and thus most prevalent monosaccharide. The p anomer is the major isomer at equilibrium, moreover, because the hemiacetal OH group is in the equatorial position, too. Figure 27.7 shows both anomers of D-glucose drawn as chair conformations. 

Mutarotation. The specific rotations of the a and P anomers of d-glucose are +112 degrees and +18.7 degrees, respectively. Specific rotation, [ a ], is defined as the observed rotation of light of wavelength 589 nm (the d line... 

The monosaccharide carriers of Saccharomyces cerevisiae, and also of Kluyveromyces (Saccharomyces) fragilis, appear from polarimetric measurements to have a higher affinity for the a-D anomers of D-glucose, D-mannose, and D-xylose than for the corresponding /3 anomers.178 Intracellularly, a-D-glucopyranose is a slightly better substrate of hexokinase than the /3 anomer.179... 

H. J. Koch and A. S. Perlin, Synthesis and 13C NMR spectroscopy of D-glucose-3-d. Bond-polarization differences between the anomers of D-glucose, Carbohydr. Res., 15 (1970) 403 -10. 

Mutarotation. The specific rotations of the a and anomers of D-glucose are +112 degrees and +18.7 degrees, respectively. 

Explain how this reaction helps to establish the configuration of the a- and g-anomers of D-glucose. 

Anomers of D-glucose, xylose, galactose, mannose, arabinose, maltose,... 

Studies of the structures of the cyclic hemiacetal forms of D-(-+-)-glucose using X-ray analysis have demonstrated that the actual conformations of the rin are the chair forms represented by conformational formulas 6 and 7 in Fig. 22.3. This shape is exactly what we would expect from our studies of the conformations of cyclohexane (Chapter 4), and it is especially interesting to notice that in the j8 anomer of D-glucose all of the large substituents, —OH and —CH2OH, are equatorial. In the a anomer, the only bulky axial substituent is the —OH at Cl. 

Calculate the specific rotation of invert sugar from the known rotations of the equilibrium mixtures of the anomers of D-glucose and D-fructose. How does this number compare with that determined experimentally ... 

At equilibrium, the (3 anomer of D-glucose predominates, because the —OH group of the anomeric carbon is in the more stable equatorial position of the more stable chair conformation. In a-D-glucose, the —OH group on the anomeric carbon is axial. When remembering the names of D-glucose anomers, some students find it helpful to remember the phrase alpha is axial. 

Scheme 11.15. An example of the Wohl degradation. The anomers of D-glucose (i.e., the isomers that are epimeric at the anomeric carbon) can be considered as the aldehyde rather than the hemiacetals. Formation of the oximes (presumably both ( )- and (Z)-oxime isomers form) followed by acetylation results in elimination to the nitrile. Hydrolysis of the remaining acetates is accompanied by elimination of hydrogen cyanide and formation of an aldehyde with one carbon less than the aldehyde with which the sequence began. Thus, both mannose and glucose yield arabinose.

Further NMR-spectroscopic investigations into the mechanism and reactive species of the D-glucose/o-fructose interconversion by Optisweet P (Miles Kali-Chemie) employing D-(l- C)glucose confirmed that the a-anomer of D-glucose Is the aldose substrate for the enzyme. However, in contrast to prior observations [21], a-D-fructofuranose (not )3-D-glucofuranose) appeared to be the ketose substrate [32]. Very recently, these interpretations have been supported by Col-... 

Figure 5 The pyranose anomers of D-glucose 1 (K) a,-D-glucopyranose and fB) P-z)-glucopyranose. The relative cis- and trans-orientations of the vicinal Cl and C2 hydroxyl groups were inferred by tracking the changes in conductivity of boric acid solutions as these saccharides were added, permitting the absolute structural configuration of the a- and -anomers to be attributedf ...

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