Isolation and identification of specialized metabolites from Strychnos species using molecular networking

For over two centuries [1], plants of the Strychnos genus, including approximately 200 species and belonging to the Loganiaceae family [2], were studied in depth for their varied therapeutic properties (e.g. treatments for fever, snakebites and stomach aches [3]), as well as for their tetanizing and curarizing properties [4]. However, this genus, so rich in promising bioactive metabolites, has not yet revealed its full phytochemical content. To this end, as part of my research project, the molecular networking workflow [5], described in the Figure 1, was applied to explore the phytochemical contents of 44 crude extracts from 28 Strychnos species, to unveil known metabolites not yet described in some species as well as to detect and identify unknown molecules active against malaria in various species, including S. longicaudata trunk barks, and S. usambarensis leaves. Strychnine, a well-known metabolite of the genus, was identified by molecular networking in 7 species not yet described as strychnine producers in the literature. These identifications were confirmed using a variety of techniques, including TLC, HPLC, NMR, MS, and MS/MS [6].
The dichloromethane extract of S. longicaudata trunk barks, despite showing a promising antiplasmodial activity (4.94 ± 2.51 µg/mL for the chloroquine-sensitive 3D7 strain of Plasmodium falciparum), was few studied to date. The purifications led us to identify alstonine as the extract's major metabolite. The antiplasmodial activity observed for alstonine was moderate (19.0 ± 5.28 µM for chloroquine-sensitive 3D7 strain of Plasmodium falciparum) and, therefore, it does not explain the initial activity. Further purifications are therefore in progress to identify the other unknown metabolites. Finally, the exploration of the alkaloidic extract content from antiplasmodial leaves of S. usambarensis [7] revealed the presence of minor alkaloids with m/z masses superior to 900 (for example, 943.8 m/z, and 944.4 m/z). To our knowledge, such a mass was never described previously in the literature for an alkaloid isolated from S. usambarensis. Therefore, purifications were performed using open column, and preparative and analytical HPLC techniques. NMR and MS/MS analyses provided us interesting structural information on the metabolite with a mass of 944.4 m/z. Future purifications and analyses will enable us to confirm the structure.