242 GLUCOSIDES 



are mannosidase and trehalase, while j8-glucosidases are repre- 

 sented by amygdalase and the phenolglucosidase of emulsin, 

 cellobiase, and gentiobiase. 



For a complete elucidation of the constitution of a given 

 glucoside it is necessary to determine not only the nature 

 of the non-sugar residue but also to ascertain which of 

 the hydroxyl groups of the sugar and of the non-sugar 

 residue are involved in the union between the two complexes 

 — more especially if the non-sugar residue contains more than 

 one hydroxyl. For this purpose the glucoside is treated with 

 methyl iodide and silver oxide whereby all the free hydroxyls 

 in the molecule are methylated ; the resulting methylated 

 glucoside is then hydrolysed and the methylated sugar and non- 

 sugar residues are examined ; any free hydroxyl groups now 

 occurring in these products must have been involved in the 

 union of the two complexes, since if present in the original 

 compound they could not have escaped methylation. 



Thus, for example, Irvine and Rose * found that salicin 

 yielded a pentamethyl derivative which on hydrolysis gave 

 rise to 2 : 3 : 5 : 6 tetramethyl glucose f (I.) and a methylated 

 sahgenin (II.) containing a free phenoHc hydroxyl but having 

 a methyl group attached to its alcoholic hydroxyl, from which 

 it follows that the parent glucoside must have had the 

 formula III. : — 



-CHOH 



OH 



CHOMe 

 O I f XHpMe O 



CHOMe 



I 

 CHOMe 



'2^ 



-CH O y 



I ,/ \— CH,OH 



CHOH I 



CHOH 



I 

 CHOH 



I 

 -CH 



CHjOMe CHoOH 



I. II. III. 



2:3:5:6 trimethyl * Salicin 



glucose 



♦Irvine and Rose: "J. Chem. Soc," 1906, 89, 814; Irvine: id., 

 1923, 123, 903. 



t According to Haworth's formula for glucose, the methylated sugar is 

 the 2:3:4:6 tetramethyl derivative ; this formula has been adopted. 



