Monosaccharide Anomers Mutarotation

Define, by reference to glucose, the meaning of each of the following terms (a) a monosaccharide, (b) mutarotation, (c) a pyranose ring system, (d) anomers and (e) a- and (3-glucosides. 

Monosaccharides undergo mutarotation, the interconversion of a- and /3-anomers in aqueous solution. One can separately prepare pure a-o-glucose and pure /8-o-glucose as crystalline solids. However, addition of either anomer to water results in the same equilibrium mixture of 64 percent a-D-glucose and 36 percent -o-glucose. 

Mechanism 23-1 Formation of a Cyclic Hemiacetal 1108 23-7 Anomers of Monosaccharides Mutarotation 1112 23-8 Reactions of Monosaccharides Side Reactions in Base 1114... 

Nitriles, a-amino, mutarotation of, 13 Nitrogen compounds, of cyclic monosaccharides, 115 — 232 Nojirimycin, 116,132,133 Nomenclature, of enzymes, 306 Nuclear magnetic resonance anomer determination by, 43 characterization of anhydrodeoxyaldi-tolsby, 74,77,79... 

Mutarotation (Section 27.6A) The process by which a pure anomer of a monosaccharide equilibrates to a mixture of both anomers when placed in solution. 

The first term in the denominator of Eq. (66) represents a non-competitive inhibition (compare to Eq. (31)) of the enzyme by the sum of concentrations of A, B and P. This non-specific inhibition could be correlated with an increased viscosity of the reaction medium in the presence of A, B and P147- mi. As the mutarotation of the carbohydrates is fast compared to the enzymatic reaction there was no need for a discrimination between the a,P-anomers or the open-chain form of the monosaccharides. A complete set of kinetic parameters was determined, summarized in Table 7-4. 

See also Sugar Ring Structures, Derivatives of Monosaccharides, Oligosaccharides, Polysaccharides, Anomers, Ouabain, Amygdalin, Mutarotation... 

The monosaccharide D-glucose, whose chemistry is representative of all aldoses containing four or more carbon atoms, exists predominantly in the two pyranosc forms 4 and 5. These are six-membered hemiacetals formed by the reversible cyclization of the acyclic polyhydroxy aldehyde 3 (Eq. 23.1). In the cyclic forms 4 and 5, the ring carbon that is derived from the carbonyl group is referred to as the anomeric carbon atom. The specific rotation, [a] (Sec. 7.5), of a-D-(+)-glucose (4) is +112 whereas that of the -anomer 5 is +19°. When crystals of either pure 4 or pure 5 are dissolved in water, the [a]p changes to an equilibrium value of +52.7°. This process is termed mutarotation. At equilibrium in water, the a- and p-forms are present in the ratio of 36 64 only about 0.03% of D-glucose is in the acyclic form 3. 

The carbon in position 1 is called the anomeric carbon. The location (equatorial or axial) of the oxygen linked to this carlxMi is determined upon cyclization of the monosaccharides and all monosaccharides can exist in two anomeric forms. In the D-pyranoside ring, the a anomer is formed if 01 is axial, and if 01 is equatorial the P anomer is formed both are illustrated in Fig. 2. When an OH group is bound to Cl, the anomers may co-exist and intercOTivert (mutarotation), in relative... 

In the crystalline state, reducing monosaccharides exist exclusively in cyclic structures (a- or P-anomers). In solutions, a balance between the a- and P-anomers and acyclic forms is established as the individual forms interconvert over time. This process, schematically shown in Figure 4.2, is called mutarotation. The mechanism of mutarotation assumes cleavage of the saccharide cyclic forms... 

In case of compounds with a heterocyclic ring, more substituents at the sp carbon atom, change in the location of one of them leads to altered rotation of polarized light. A typical example of such situation includes spontaneous change of rotation of polarized light that takes place in aqueous solutions of optically pure monosaccharides it is called mutarotation and individual interconverting isomers are called anomers. 

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