214 PRACTICAL ORGANIC AND BIO-CHEMISTRY 



GLUCOSIDES. 



In addition to the carbohydrates there also occur in nature a large 

 number of compounds which contain glucose, more rarely other sugars, 

 e.g. galactose, rhamnose and disaccharides, combined with other organic 

 compounds, especially those belonging to the aromatic series. These 

 are the glucosides. Glucosides have also been prepared in the labora- 

 tory from glucose, mannose, maltose, etc. Two isomers are generally 

 thus obtained, termed the a- and /3-glucosides. The chief of the syn- 

 thetical glucosides are the a- and /3-methyl glucosides which are pre- 

 pared by the action of hydrochloric acid upon a solution of glucose 

 in methyl alcohol. They are derived from a- and /3-glucose by the 

 replacement of the hydrogen atom in the hydroxyl group attached to 

 the carbon atom which possesses aldeydic properties : 



CH 2 OH 



H-OOH 



CH 3 0-C-H 



a-methyl glucoside. /3-methyl glucoside. 



These two glucosides, besides having different physical properties, be- 

 have differently towards the enzymes, maltase and emulsin. Maltase 

 hydrolyses the a-glucoside, but not the /3-glucoside, emulsin hydrolyses 

 the /3-glucoside, but not the a-glucoside. The natural glucosides are, 

 in general, hydrolysed only by emulsin and would be derivatives of 

 /3-glucose, i.e. y8-glucosides. 



The three best-known glucosides are probably 



,CN O.C 6 H U 5 



/ 



4 65 . 



\CH 3 OH \O.C 13 H 21 10 



Salicin. Amygdalin. Arbutin. 



Salicin is a combination of glucose with saligenin or salicylic alcohol. 



