Glycosides defined

The generic term glycosides defines all mixed acetals formed by the acetalisation of the cyclic forms of aldoses and ketoses. Glycosyl groups are monosaccharides that have lost their anomeric -OH group the suffix -yl is used to indicate the change that has occurred at C-1. 

Glycosides were originally defined as mixed acetals (ketals) derived from cyclic forms of monosaccharides. 

C5 , then the atom is said to be endo, and if it is on the opposite side it is defined as exo. The conformation about the sugar-base linkage is defined as anti when the torsion angle (chi, 04 -Cl -Nl -C2 for pyrimidines and 041-Cl -N9-C4 for purines) lies near 180° and syn when it lies near 0°. These situations are illustrated in Figure 22. The glycosidic linkage are all anti in B-DNA and A-DNA, but in Z-DNA the guanine bases are in the syn conformation. 

The tea plant, Thea sinensis, has provided a desirable beverage for centuries but it is also used as a colorant. Extracts of tea contain a very complex mixture of glycosides of myricetin, quercitin and kaempferol, epicatechin, epigallocatechins, acyl acids and many other polyphenol compounds.33 In black tea, the above compounds may act as precursors to the poorly defined compounds thearubin and theaflavin. 

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