Deux nouveaux alcaloïdes quaternaires isolés à partir des feuilles du Strychnos usambarensis GILG du Rwanda: Nb-méthyl hydroxy-10 et hydroxy-11 usambarines

Two new isomeric bis-indole alkaloids have been isolated from Strychnos usambarensis leaves. They are phenolic dimers of the "usambarine (usambarane) type" and correspond to the Nb-methyl-derivatives of 10- and 11-hydroxy-usambarine. The structure elucidation and the stereochemistry of these molecules are discussed from their spectroscopic properties (UV,IR,MS, CD , NMR). TLC comparison with quaternarized 10- and 11-hydroxy-usambarine provides a corroborative structural proof. The separation of the two alkaloids by "DCCC" (Droplet Counter current Chromatography) gives a new example of the application of this suitable technique for the separation of polar coumpounds that it is always very difficult to purify and separate.