Strychnobaillonine, an unsymmetrical bisindole alkaloid with an unprecedented skeleton from Strychnos icaja roots

A reinvestigation of the roots of Strychnos icaja resulted in the isolation of a new bisindole alkaloid named strychnobaillonine (1) with original C-17–N-1′ and C-23–C-17′ junctions, in addition to sungucine, bisnordihydrotoxiferine, and strychnohexamine (2). Compound 1 showed potent activity against the chloroquine-sensitive 3D7 strain of Plasmodium falciparum in vitro with an IC50 value of 1.1 μM. The structures of the compounds were defined by detailed spectroscopic analyses, especially 1H and 13C NMR, DEPT, HSQC, COSY, NOESY, HMBC, and HRESIMS. The proposed absolute configuration was based on biosynthetic considerations and spectroscopic data (CD, NMR) supported by molecular modeling.