Alcaloides Indoliques. VII. Structure de la Voacoline

Abstract

Voacoline, a new minor alkaloid from Voacanga chalotiana Pierre ex Stapf (apocynaceae) is shown to ahve structure I. This structure contains two unusual features : a N,C& indolic group and a hemiketal function. This last feature accounts for the very easy formation of 0-methyl I1 and O-ethylvoacoline 111. A correlation with voachalotine IV, the major alkaloid of the same species, has been achieved by degradation of I to dihydrodeshydroxymethylvoachalotine XIV. UV,IR, NMR and mass spectra of I and some of its derivatives are discussed.La separation des alcaloides totaux de Voacanga chalotiana Pierre ex Stapf (apocynackes) par distribution B contre-courant a 6ttc dCcrite anterieurement (1). La fraction C de cette separation contient au moins trois constituants qui sont mis en evidence par chromatographie sur couche mince. Le plus important d'entre eux peut &tre isole par une nouvelle distribution a contre-courant, par chromatographie sur d i c e ou par cristallisation fractionnee dam l'ether.Cette nouvelle base, la voacoline, se prksente sous forme d'aiguilles incolores, F : 147-147,5" (ether), [LY];~ = -29,8 f 2" (chloroforme, c = 0,5). La teneur en voacoline dans les Ccorces skches de tronc de V. Chalotiana s'elbve a 0,07 % en poids.

Indole Alkaloids. XX. Isolation and Structural Elucidation of Four Minor Alkaloids from Voacanga Chalotiana Pierre Ex Stapf

“…The new alkaloid [4] is therefore named voachalotine oxindole. The mass spectrometry fragmentation of this new type of molecules may be visualised as detailed for [4] in figure 3.…”

“…We wish to report now the isolation and the structural determination of four new minor alkaloids from the same source: polyneuridine [2], akuammidine 131, voachalotine oxindole [4] and 21(? )-hydroxyvoachalotine [5].…”

“…In previous communications we reported the isolation from Voacanga chalotiana Pierre ex Stapf of voachalotine [l], voacarpine [2, 31, vobtusine [2], voamonine [2], voacoline [4] and dehydrovoachalotine [5].…”

“…The IR spectrum (CHCI,) no longer shows hydroxyl absorption but shows an intense band at 1240 cm-' (acetate group). The NB nitrogen atom of [4] must be tertiary as no NB acetylated compound is obtained. Alkaloid [4] gives also a mono-0-tosyl compound, the JR spectrum of which shows two intense bands at 1370 and 1 180 cm-' (sulfonate group).…”

“…The NB nitrogen atom of [4] must be tertiary as no NB acetylated compound is obtained. Alkaloid [4] gives also a mono-0-tosyl compound, the JR spectrum of which shows two intense bands at 1370 and 1 180 cm-' (sulfonate group). It is obvious that in the high mass range (from m/e = 279 to M') the fragmentation ions of the oxindole compounds are shifted 16 mass units to higher masses as compared to the corresponding ions of the indole compounds.…”