Hunteria alkaloids

Tacamonine, an indole alkaloid of the Iboga type, isolated from Tabermemontana eglandulosa, the root of which is used to treat snake bites in Zaire, bears structural similarity to the Hunteria alkaloids, eburnamonines, which possess vasodilator and hypotensive activities. Its synthesis in racemic and homochiral form was accomplished by incorporating a classic 6-exo-trig radical cyclization in the key step of the synthesis (Scheme 6)71. The radical precursor 6 was constructed in a 7-step synthesis by starting from racemic or chiral propane-1,3-diol. The radical cyclization of 6 produced the piperidinone in 72% yield as a diastereomeric mixture, which was then transformed into tacamonine. 

These feeding experiments seem to suggest that As-pidosperma-Hunteria alkaloids (classes 3 and 5) arise by prior formation of Corynanthe and then Strychnos alkaloids (class I) (Atta-ur-Rahman and Basha, 1983). 

Both antipodes of several Aspidosperma and Hunteria alkaloids are known to occur, but it is uncommon to find more than one in a single plant. 

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