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Paper | Regular issue | Vol 29, No. 7, 1989, pp.1343-1348
Published online, 1st January, 1970
DOI: 10.3987/COM-89-4988
On the Protonation Site of Rauwolfia Alkaloids in Highly Concentrated Sulphuric and Solutions

María A. Muñoz, Carmen Carmona, Jose Hidalgo, Manuel Balón, and Manuel López-Poveda

*Departamento de Química Física, Instituto de Ciencias de los Materiales, Universidad de Sevilla-C.S.I.C., 41012-Sevilla, Spain


13C-Nmr spectroscopy has been used to investigate the protonation site of the Rauwolfia alkaloids yohimbine, reserpine and reserpiline in highly concentrated sulphuric acid solutions (~189M H2SO4). The chemical shifts which occur upon protonation reveal unambiguously that the alkaloids protonate on C-7, the β-position with respect to their indole ring, and suggest that the indoleninium cations of the methoxy-substituted alkaloids have principally an enamine structure.