ALKALOIDS 1 69 



quinoline may be no more complex than that of the smaller berberine 

 type of isoquinoline. The former is a dimer of a simple benzyliso- 

 quinoline; the latter probably involves an N-methyl phenyl condensa- 

 tion of the simple benzylisoquinoline. 



There seem to be an unusually large number of highly specu- 

 lative statements relevant to the systematic implications of the 

 alkaloids. Arguments based on criteria of simplicity versus complexity 

 of the alkaloids may be quite subtle in nature. Often it is difficult to 

 evaluate an argument fully because the logic, as applied in a chemical 

 reference-framework, may be sound, but not in accord with the bio- 

 logical facts. The following discussion by Wenkert (1959) provides an 

 example: 



On the basis of the rapidly emerging patterns of the biosynthesis of 

 plant products, both theoretical and experimental, it is possible to 

 categorize, albeit yet crudely, natural substances into two classes, one 

 based to a large extent on acetate and, hence, on genetically and 

 enzymatically easy routes, and the other founded to a major degree on 

 non-acetate material, i.e. substances farther along in the tricarboxylic 

 acid cycles and hence, enzymatically difficult, circuitous routes. If it be 

 assumed that the evolution of life processes, i.e. the structure and 

 mechanism of enzymes, through geologic time proceeded from simple 

 to more complex patterns, a correlation of paleobotany with the 

 chemistry of natural products would be on hand. Substances originat- 

 ing from acetate would be expected present in the oldest plants. On 

 this basis the structure of Lycopodium alkaloid annotinine is no sur- 

 prise, nor is the discovery of triterpenes from petroleum and coal 

 deposits. 



Despite specific reference to the tricarboxylic acid intermediates to 

 illustrate the "non-acetate" pathways, we infer from the main body 

 of the paper that Wenkert is considering the acetate-mevalonate 

 family (Chapter 13) of compounds on the one hand and the shikimate- 

 prephenate family (Chapter 11) on the other. The former lead to such 

 compounds as the carotenoids, terpenes, essential oils, and sterols; the 

 latter lead to indoles, aromatic amino acids, hgnins, and tannins. In 

 certain water-soluble plant pigments (flavonoids) there is a partial 

 contribution from each pathway (Chapter 11). Alkaloids of both 

 affinities are known as well as some unrelated to either (for example, 

 the purine derivatives). Perhaps purines, by the criterion above, 

 should be expected in the more ancient plants since it is generally be- 

 lieved that the earhest hving organisms formed polynucleotides con- 

 taining purines. However, alkaloids of the purine type are found 

 in coffee. 



