Phenylethylisoquinoline alkaloids

Colchicine 6.175) is an alkaloid with a unique tropolone ring, and on the face of it appears to be quite unrelated to any other alkaloid. 

Phenylalanine, by way of cinnamic acid, serves in Colchicum species as the source of ring A plus carbon atoms 5, 6, and 7. The seven carbons of the tropolone ring arise from tyrosine which loses C-1 and C-2 from the side-chain labels from and [3- C]-labelled 

The answer came from the elucidation of the structure of androcymbine, an alkaloid isolated from a relative of Colchicum. The dienone structure (6.173) was assigned to androcymbine. Androcymbine could then be thought of as arising from the phenethyliso- 

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The photolysis of arenediazonium salts has been widely used for intramolecular cyclizations in the synthesis of 1-phenylethylisoquinoline alkaloids by Kametani and Fukumoto (review 1972). An example is the photolysis of the diazonium ion 10.73, which resulted in the formation of O-benzylandrocymbine (10.74) (Kametani et al., 1971). The mechanism of this cyclization is obviously quite complex, since the carbon (as cation or radical ) to which the diazonio group is attached in 10.73 does not react with the aromatic CH group, but with the tertiary carbon (dot in 10.73), forming a quinone-like ring (10.74). In our opinion the methyl cation released is likely to react with the counter-ion X- or the solvent. 

Aladesanmi AI, Kelley CJ, Leary ID (1983) The Constituents of Dysoxylum lenticellare, I. Phenylethylisoquinoline, Homoerythrina, and Dibenzazecine Alkaloids. J Nat Prod 46 127... 

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