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A new alkaloid from Voacanga africana was identified as the hydroxyindolenine derivative ( 6 ) of voacangine, and its structure was proven by synthesis. A rearrangement product of 6 , the pseudoindoxyl 9 , was also encountered and characterized. Two additional new alkaloids, the hydroxyindolenine ( 7 ) and pseudoindoxyl ( 10 ) derivatives of voacristine were synthesized. Mass spectra of all compounds are presented and interpreted.

Conopharyngine, the major alkaloid present in the leaves of Tabernaemontana (Conopharyngia) pachysiphon var. cumminsi (Stapf) H. Huber was isolated and identified by Thomas & Starmer (1963). The same alkaloid has also been found in the stem bark of a Nigerian variety of the same species by Patel & Poisson (1966) and in the stem bark of Conopharyngia durissima by Renner, Prins & Stoll (1959). Conopharyngine is an indole alkaloid of the voacanga type, being 18-carbomethoxy-12,13dimethoxyibogamine (Fig. 1) and is thus closely related to voacangine and coronaridine.

Voacangine (3), ibogaine (2), voacamine (7), vobtusine (10), voacristine (1), iboluteine (4), vobasine (6), 18′-decarbomethoxyvoacamine (9) and voaluteine (5) are shown to be present in the crude extract from the bark of Voacanga thouarsii , Roem. et Schult. var. obtusa Pichon. All are known compounds. The absolute configuration C-17 R is proposed for the spirannic carbon atom of the pseudoindoxyle (5). Applied to voacristine (1), Brewster's method shows C-20 to have the S -configuration.

The indole alkaloids harmane, harmine, ibogaine, iboxygaine and ibogaline caused tremor in mice when injected intracerebrally. Harmol, voacangine, voacristine and conopharyngine were inactive in this respect. Chemical structure strongly influences tremorigenic potency which is increased by a methoxy group and reduced or abolished by a hydroxy or carbomethoxy group. The great importance of chemical structure for tremorigenic power of indole alkaloids points to specific receptors for these drugs in the brain.

From the root bark of the apocynacea Hedranthera barteri (Hook. f.) Pichon were isolated the known indole alkaloids vobtusine (1), voacamine (2), callichiline (3), voacangine (4) and conoflorine (5), as well as the unknown plant bases amataine, goziline and owerreine, and also beninine and 1, 2-dehydrobeninine. The structures of the two last mentioned alkaloids were shown in an earlier publication to be 6 and 7, respectively. Amataine, goziline and owerreine are bis-indole alkaloids, which on the basis of their chemical and spectroscopic (especially mass spectroscopic) properties have been assigned the structures 8, 9 and 10, respectively.

—From Stemmadenia Donnell-Smithii and S. Galeottiana , the following new alkaloids were isolated: (+)-quebrachamine (IV), an optical isomer of the known (−)-quebrachamine; iso voacangine (IIIa), a position isomer of voacangine (Ia), voacamine, tabernanthine (IIIb) and ibogamine.

Voaluteine is shown to be the ψ-spiro-indoxyl related to voacangine and is thus probably an artefact. Its formation from voacangine by oxidation reactions has been investigated. Experiments on the formation of β-hydroxyindolenines from indoles via their Grignard derivatives and oxygen are described.