Structure simplification of the Securinine skeleton reveals the importance of BCD ring system for the cytotoxic activity on HCT116 and HL60 cell lines.

Function-oriented molecular editing of the polycyclic scaffold of securinine led to the preparation of a library of simplified analogs that have been evaluated for their cytotoxicity potential against HCT116 and HL60 human cell lines. Chemical diversity at the C14 position (securinine numbering) was generated through the site-selective γ-iodination followed by Pd-catalyzed Sonogashira and Suzuki-Miyaura reactions. To explain the selectivity in the iodination step, a reaction mechanism has been proposed. Surprisingly, the piperidine ring (ring A) of the securinine skeleton has been found to be irrelevant for the cytotoxic activity. Based on this finding, the pharmacophoric core of securinine could be simplified to the key BCD motif. The nature of the substituent at the nitrogen can vary from a methyl or an isobutyl group to a benzyl or a carbamate moiety. Interestingly, the N-benzyl substituted simplified analog exhibited the same cytotoxic activity as the parent compound securinine. This functional group tolerance paves the way for the installation of reactive handles for the synthesis of molecular probes for target identification.