Umbellamin,ein neues «dimeres» Indolalkaloid 130. Mitteilung über Alkaloide [1]

Umbellamine (f; C₄₁H₄₈N₄O₄), a «dimeric» indole-indoline alkaloid, was isolated from the root bark of Hunteria umbellata (K. SCHUM .) HALL . F.; it is probably identical with the alkaloid hunterine (structure unknown) of NeUSS & CONE [14]. Thermolysis yielded (+)-eburnamenine (II), whereas a detailed mass spectrometric study of I, of its O-methyl and O-acetyl derivatives, and also of the derived diol V revealed the presence of a phenolic hydroxy-pseudoakuammigine group as second part, the benzene nucleus of the latter being linked to the C-14 atom of the eburnamenine component (present in the dihydrom form). The n.m.r. study of umbellamine and of its derivatives showed that the phenolic hydroxy group is either at C-10′ or C-11′ and that the dihydroeburnamenyl residue is connected to C-11′ or C-10′ of the pseudoakuammigine residue. A choice between these alternatives was possible by investigation of the hydroxylated base IX arising from the latter component, and obtained in small quantities by treatment of umbellamine with zinc or tin in acid. Its constitution, deduced by uv., n.m.r. and mass spectrometry, suggested that the hydroxy group is fixed at C-11′. If this is correct, the dihydrocburnatnenyl residue is linked to C-10′ of the pseudoakuarnmigine residue. Thus we propose formula I for umbellamine.