The structure of guettardine 1, an indole alkaloid isolated from the bark of Guettarda heterosepala (Rubiaceae), was determined from an analysis of its MS, 1H and 13C NMR spectral data, and by a chemical correlation with dihydrocorynantheol 7. Guettardine 1 can be considered to be an intermediate between the Corynanthé and the cinchonamine groups of alkaloids which are precursors of quinine and its derivatives. © 1984.