The Hunteria Alkaloids

The full paper on the X-ray crystallographic analysis of hunter-burnine j8-methiodide has appeared (28). 

A new dimeric hypotensive alkaloid has been reported from Hunteria eburnea Pichon (29). Hunteriamine, C39H48N4O2 CH2 was amorphous and gave crystalline salts (perchlorate, mp 279°-281° decomp. [a]jj -1-29° in MeOH pif 6.50 hydrochloride, mp 310°-315° decomp. [a]p -f27° in MeOH pA 6.56 hydroiodide, mp 300°). The alkaloid has a UV-spectrum typical of a 2,3-dialkyl-5-hydroxyindole and a bathochro-mic shift was observed in base. In the IR-spectrum OH/NH bands were 

Hunterburnine a- and j8-methochlorides and huntrabrine metho-chloride have been isolated from the closely related plant, Pleiocarpa mutica Benth. (3d). The mass spectra of hunterburnine a- and /3-metho-chlorides have been studied along with other quaternary salts (31). Both 

Dihydrobumamicine has been synthesized (Chart V) but could not be compared (32) with the same derivative of the natural product because none of the latter remained from structural studies (33). The action of lead tetraacetate in benzene transformed dihydrocorynantheine into 7-acetoxy-7H-dihydrocorynantheine (XXVI mp 180°-181°) which was converted into its methiodide (mp 206° decomp.). Hydrolysis of the methiodide in refluxing aqueous acetic acid containing sodium acetate gave the 2-acylindole XXVII (mp 153°-155° or 208°-209°) which gave the expected UV-spectrum in ether but in a more polar solvent (ethanol) 

The structure elucidation of pleiocarpamine, a yohimbinoid alkaloid of H. eburnea, and its relationship to mavacurine (34) is discussed elsewhere in this volume. 

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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. 

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