Maltose anomers

Though the data are not included in Table I, concurrent tests were also made of the action of all the a-amylases on crystalline a-maltose (106) and /3-maltose. The unique saccharifying a-amylase of B. subtilis var. amylosacchariticus showed a-D-glucosyl transferring activity with both maltose anomers, confirming the conclusion of Japanese authors (88, 89, 90, 91). The remaining a-amylases showed no detectable action on either maltose anomer under these conditions. 

Maltose exists in two anomeric forms a-(+)-maltose, [ ]d = +168, and )3-(+)-maltose, = +112. The maltose anomers undergo mutarotation to yield an equi-... 

Maltose and cellobiose are both reducing sugars because the anomeric carbons on the right-hand glucopyranose units have hemiacetal groups and are in equilibrium with aldehyde forms. For a similar reason, both maltose and cellobiose exhibit mutaiotation of a and /3 anomers of the glucopyranose unit on the right. 

Figure 9.17 Alpha and beta anomers of maltose. When only the hydroxyl group on the anomeric carbon of one of the monosaccharide residues is involved in the glyco-sidic linkage, the anomeric hydroxyl group on the other residue is still free. This permits two possible orientations, which are described as either alpha or beta forms of the monosaccharide residue.

The hydrolysis of cellulose, a polysaccharide, sometimes yields the disaccharide cellobiose. When cellobiose, a reducing sugar, is hydrolyzed, two glucose molecules result. Unlike maltose, which we describe in the preceding section, the linkage involves the (3 anomer of the left glucose (see Figure 16-24). 

Using the pure anomers of maltose in the same way, we found that crystalline hog pancreatic a-amylase causes the very rapid synthesis of maltotetraose from a-maltose but not from /3-maltose whereas, crystalline sweet potato /3-amylase causes the very rapid synthesis of the same compound, specifically from /3-maltose. Configurational inversion again marks this latter condensation as glycosyl-hydrogen interchange, or glycosyl transfer. 

Four commonly occurring disaccharides. The configuration about the hemiacetal group has not been specified for lactose, maltose, or cellobiose because both anomers exist in equilibrium. 

An ab initio calculation with a minimal basis set of both a- and 0-glucopyranose as well as p-maltose results in the correct prediction of the energetical order of the two glucose anomers as well as the two conformations of p-maltose [80], But the less favored conformer contains an energy which is higher by a factor of approximately 6 compared to the results of the FF300 calculation (cf. below). 

P-Glycosides.12 Hemithioortho esters such as 1 are reduced by Bu3SnH (AIBN) mainly to P-glucosides (2). The method can also produce the maltose dissacharide 4 as a 10 1 mixture of anomers. The effect of anomeric C2-substituents is not clear. 

Draw the structures of the individual mutarotating a and (i anomers of maltose. 

In the structure for maltose shown in Example 2.23, no configuration is given for the anomeric carbon of the glucose unit on the right the structure represents the state of maltose in solution—a mixture of a and (3 anomers. In crystalline maltose, the anomeric hydroxyl is a, and maltose can be described as a-D-glucosyl-(l — 4)-a-D-glucose. 

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