ALKALOIDS 



259 



The quinoline alkaloids are usually presumed to arise from anthranilic acid (75) 

 although there seems to be no tracer evidence in support of this view. Some quinoline 

 alkaloids have structures resembling the flavonoids with the substitution of nitrogen for 

 oxygen in the heterocyclic ring. Such a substitution can occur non-enzymatically (77) 

 and suggests that certain alkaloids could be biogenetically related to the flavonoids or 

 other oxygen heterocycles. 



In the formation of several alkaloids such as quinine, emetine, and strychnine a 

 type of reaction apparently occurs which was not foreseen in the original proposals of 

 Robinson, namely the breaking of a six-membered ring. The generality of this pathway 

 has been discussed by Woodward (42), and in cases where an ethyl or vinyl group appears, 

 one can assume that it originally was part of a stx-membered ring. Seven-membered 

 rings (as in strychnine) also seem to arise from the breaking or an expansion of six- 

 membered rings, and six-membered rings may rarely (e.g. quinine) arise from expan- 

 sion of five-membered rings: 



Cc^-^OO 



Some other, quite different, suggestions have been made regarding synthetic path- 

 ways for certain alkaloids. Thomas (78) has suggested a possible relationship between 

 cyclopentanoid monoterpenes and certain indole alkaloids. Conroy (79) has proposed 

 that the Lycopudiiun alkaloids could reasonably arise from polyacetate condensations 

 (cf. Chapter 6). 



Space does not permit consideration of the many experiments which have been 

 carried out to elucidate pathways of biosynthesis for some other alkaloids, but a few 

 references to recent literature are tabulated below: 



ALKALOIDS STUDIED REFERENCE 



Amaryllidaceae alkaloids 80 



morphine alkaloids 81, 82 



hydrastine 83 



colchicine 84, 85 



berberine 86 



Rauwolfia alkaloids 87 



Strycknos alkaloids 88, 89 



GENERAL REFERENCES 



Battersby, A. R. , ed. "Symposium on New Developments in Alkaloid Chemistry", 



Tetrahedron 14 1 (1961). 

 Bentley, K. W. The Alkaloids , Interscience Publishers, N. Y. , 1957. 

 Cromwell, B. T. "The Alkaloids" in Paech and Tracey 4 367. 



