254 



ALKALOIDS 



1. 



2. 



The basic skeletons of alkaloids are derived from common amino acids and 

 other small biological molecules. 



A few simple types of reactions suffice to form complex structures from these 

 starting materials. For example the aldol condensation: 



C = O + HC-X 

 the carbinolamine condensation: 



N-C-OH + H-C-X 



' I I 



OH 

 I r 

 -C-C- 



I I 



VN-C-C + H2O 



as well as simple dehydrations, oxidations, and decarboxylations. (X repre- 

 sents an "activating" group such as carbonyl. ) 



For example the formation of the tropane alkaloid skeleton was pictured as follows: 







II 



CHj-CH 



CHo-CH 

 ^ II 

 



I 

 CH3NH2 ♦ C=0 ^ 



CH2COOH CH2--CH CH2 



I 



I 



NCH, C=0 



I 



CH2COOH CH2-CH CH2 



No specific order of the steps is implied, so that intermediates of many different struc- 

 tures might appear, e.g.: 



OH 



CHo-CH 

 ^ \ 



NCH. 



CHo-CH 



^ \ 

 OH 



CH9--CH=GC00H 

 ^ I 



C=0 

 I 

 CHo — CH=CCOOH 



Succindialdehyde could arise in plants either by a reduction of succinic acid or by an oxi- 

 dative decarboxylation of ornithine. Another pathway starting from ornithine might also 

 be possible and would use one of the amino groups of ornithine in the final tropane skele- 

 ton: 



CH2~"^ CHo 

 NH. 



CHo CHCOOH 



2 I 



NH2 



ornithine 



CH2 



CHo- 



\H2 

 NH2 - 



CCOOH 



II 







GH2 — CH. 



/ 

 CHo — CH. 



NH 



