Gelsemine-type oxindole alkaloids

The humantenine-type Gelsemium alkaloids, which so far include human-tenine, humantenirine, and rankinidine, are oxindole alkaloids with a novel skeleton similar to that of gelsemine but lacking a bond between C-6 and C-20. From a biogenetic viewpoint, humantenine-type alkaloids are less evolved than those of the gelsemine series and might well be immediate precursors of them... 

For reasons of brevity, some skeletal variations are not clearly defined in Figs. 2 and 3 and some have been omitted. In particular, the picraline (Volume VIII, p. 147), the echitamine (Volume VIII, p. 174) 78), and the aspidodasycarpine 53) skeletons have been merged into type If. The new alstophylline type 39, 40) is somewhat hidden in the Id reprepresentation. Gelsemine (Volume VIII, p. 95) has been included in the oxindole type Ic. Type Ila Iboga) includes several closely related rearranged alkaloids (Volume VIII, Chapter 9) which are not shown in Fig. 3. An unusually modified Aspidosperma structure 83) is related to type III6 and is listed as such. 

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