272 NITROGEN BASES 



oline and isoquinoline, and it thus becomes possible to account 

 for the origin of the pyridine and quinoline rings which occur 

 in alkaloids, by assuming them to have been produced as 

 above from pyrrole or indole rings, which are the normal con- 

 stituents of protein (e.g. proline, histidine, tryptophane, etc.). 



In support of these views, Pictet states that he was able 

 to isolate by steam distillation from various leaves,* etc., 

 treated with sodium carbonate, a number of simple bases which 

 he calls proto-alkaloids ; these include pyrrolidine and methyl 

 pyrroline 



CH 2 CH a CH=CH 



CH 2 CH 2 CH a CH 2 



\ / \ / 



NH NCH 3 



Pyrrolidine Methyl pyrroline 



whose origin from the protein molecule is readily intelligible, 

 in view of the fact that a similar ring occurs in proline, the 

 cleavage product of a number of proteins. It is assumed that 

 these proto-alkaloids are subsequently methylated, rearranged 

 and condensed as described above to form the more complex 

 alkaloids. 



It has been suggested by Pictet that the secretion of 

 alkaloids by plants is merely due to the inability of such 

 plants to get rid of their nitrogenous products of metabolism 

 by any other means than by converting them into alkaloids, 

 which, though poisonbus to animals, are not toxic to the 

 plants themselves. 



Robinson, from his work on tropinone,f offers a theory of 

 the mechanism of the photochemical synthesis of certain alka- 

 loids which differs fundamentally from the opinions of Pictet,J 

 The raw materials formaldehyde, ammonia, amino acids, and 

 acetone dicarboxylic acid for building up alkaloids either 

 occur as such in the plant or in a combined state. These 

 highly reactive bodies undergo a series of comparatively 

 simple transformations ultimately leading to the alkaloid. 

 Thus the condensation of formaldehyde with a diamino acid 

 such as ornithine would account for the pyrrolidine group; 



* The leaves used were those of tobacco, carrot, parsley and coco, 

 f Robinson: "Journ. Chem. Soc., Lond.," 1917, III, 762, 876. 

 %Loc. cit. 



