370 NITROGEN BASES 



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 poisonous to animals, are not toxic to the 

 plants themselves. 



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

 the mechanism of the photochemical synthesis of certain alka- 

 loids which differs fundamentally from the opinions of Pictet.f 

 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 ; 

 a compound of the formula I, could be formed by the inter- 

 action of these two substances according to the equation — 



NHj . CHj . CH2 . CH2 . CHNH2 . COOH + CH2O = 



IOH\ 



)NCH3 + NH3 + CO., 



CHj . CHOHn 



CH^— CH^ 



This compound would yield the alkaloid hygrine (IV.) 

 by condensation with acetone dicarboxylic acid and subse- 

 quent elimination of carbon dioxide : — 



NCH3 COOH 



CHj CHOH + CH2 . CO . CH2 . COOH 



I I 



CHj — CHj 



II. 

 NCH3 COOH 



CH2 CH . CH . CO . CHa . COOH + H^O -> 



i I 



CH2 — CH2 



III. 



* Robinson : " Journ. Chem. Soc. Lond.," 1917, lil» 762, 876. 

 t Loc. cit. 



