Glucose, <7 anomer glycosides

Hydrolysis of maltose forms two molecules of glucose. The Cl - O bond is cleaved in this process, and a mixture of glucose anomers forms. The mechanism for this hydrolysis is exactly the same as the mechanism for glycoside hydrolysis in Section 27.7B. 

Figure 9.6 Anomeric forms of D-glucose and D-fructose. The alpha and beta anomers are named with reference to the configuration of the glycosidic hydroxy] group associated with the oxygen bridge.

An observed effect of certain substituents on the conformation and stability of glycosides. In the case of a- and /3-glucosides, when the substituent attached to the anom-eric position of o-glucose is a nonpolar alkyl group, such a substituent will favor the equatorial position /3). However, if the substituent is polar, the a-position i.e., axial) is favored. Thus with polar moieties, a-glucosides exhibit greater stability than /3-glucosides. 

The stereochemistry of the C-glycosidic products, obtained with the above-mentioned procedure, depends on the structure of the starting sugar and on the experimental conditions. In general, base catalyzed cyclizations afford a mixture of anomers, which on prolonged reaction time is converted into the thermodynamic product. For example, in the case of 4,6-O-isopropylidene-D-glucose,... 

At the completion of the reaction, the excess n-pentenyl alcohol can be recovered by distillation and saved for future glycosidation. As expected, the reaction gives a mixture of anomers. For example, the ot/p ratio for glucose is 2 1, whereas mannose gives almost exclusively the a-product [6],... 

Sucrose (cane sugar) is a disaccharide in which the glycosidic link involves the anomer C-l of a-D-glucose and the anomeric C-2 of fructose. Sucrose (a-D-glucopyranosyl(l —> 2) (3-D-fruc.tofuranoside a-D-Glc(l —> 2) (3-D-Fru) does not have a reducing end because the reducing ends of both the constituent monosaccharides are involved in glycosidic bond formation (Section 4, Appendix). 

---