Alcaloides Indoliques. V. Structure de la Voacarpine

Voacarpine, a minor alkaloid obtained from Voacanga chalotiana Pierre ex Stapf (Apocynaceae), is shown to have the tautomeric structure VII ⇆ VIII. The non basic O,N‐diacetyl‐ and O,N‐ditosyl derivatives are true 2‐acyl‐indoles (IX, X). Isovoacarpine, isomeric with voacarpine, is obtained by acid treatment followed by neutralization; it is also a carbinolamine compound. On acetylation, it gives a monoacetyl derivative. UV, IR, NMR and mass spectra of voacarpine and derivatives are discussed.