Amygdalin, also contains a benzaldehyde group, but there is linked with it a hydrocyanic acid group; hence, this glucoside is usually classed with the cyanophoric glucosides (see [page 86]).
THE ACID GLUCOSIDES
The most common example of this group is gaultherin, C14H18O8, which is found in the bark of the black birch and is a combination of glucose with methyl salicylate. Both the glucoside itself and the methyl salicylate ("oil of wintergreen") which is derived from it are used as remedies for rheumatism.
Jalapin, C44H56O16 (glucose and jalapinic acid), and convolvulin, C54H96O27 (glucose + rhodeose + convolvulinic acid), are glucosides of very complex organic acids, found in jalap resin, which are used in medicine as cathartics or purgatives.
THE OXY-CUMARIN GLUCOSIDES
Cumarin itself is widely distributed in plants. No glucoside containing cumarin as such has yet been isolated; but several glucosides of its oxy-derivatives are known. The following are common ones:
Skimmin, C15H16O8 (glucose and skimmetin), is found in Skimmia japonica; æsculin, C15H16O9 (glucose and æsculetin), is found in the bark of the horse-chestnut, Æsculus hippocastanum, and its isomer, daphnin (glucose and daphnetin), in several species of Daphne; and fraxin, C16H18O10 (glucose and fraxetin), is found in the bark of several species of ash.
The structural arrangement of the oxy-cumarin groups which are found in these glucosides is shown in the following formulas. It is not known to which OH group the sugar is attached, in each case.
Scopolin, C22H28O14, found in Scopolia japonica, contains two glucose molecules united to a monomethyl ether of æsculin; while limettin, found in certain citrus trees, is the dimethyl ether of æsculin.