ALKALOIDS 



The alkaloids include a particularly heterogeneous 

 group of nitrogenous compounds, upwards of 1,000 

 in number, mostly from vascular plants (Willaman 

 and Schubert, 1961). A few non-vascular plants and 

 some animals synthesize alkaloids, but the com- 

 pounds are rare in both of these groups. Unlike 

 many classes of naturally occurring substances which 

 may be defined rather precisely in chemical terms, 

 no entirely adequate chemical definition of an alkaloid 

 seems possible because of the variety of alkaloid types 

 in existence. By a general operational definition an 

 alkaloid is considered to be a pharmacologically 

 active compound usually containing a basic group 

 and with a heterocychc nitrogen-containing ring.i It 

 is evident, from such a definition, that alkaloids are 



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