Synthetic Efforts Toward the Complete Synthesis of a C6 Alkyl Substituted Aziridinomitosene
Don L. Warner
Mitomycin C (MC) is a clinically used anti-cancer therapeutic. MC functions by covalently alkylating DNA to form interstrand crosslinks (ICLs), which arrests transcription and replication within the cell, initiating cell death. MC requires reductive activation before undergoing DNA alkylation, resulting in the generation of reactive oxygen species (ROS). It is believed the redox cycling that generates ROS contributes to MC's high level of undesired side effects, thus limiting its clinical utility. Aziridinomitosenes (AZMs) are a class of compounds similar in structure to MC, however several synthetic analogs have been shown to form ICLs without prior reductive activation. Like MC, AZMs contain reactive functional groups at C1 (an aziridine) and at C10 (a carbamate) that are responsible for DNA binding. Several AZMs containing additional electrophilic centers at the C6 and C7 positions have been investigated, and these sites are thought to play a role in ICL formation. Prior research has demonstrated that methyl substitution at either position increases the AZM’s effectiveness in cancer cell-killing studies. The increase in potency is hypothesized to result from either the methyl's increased lipophilicity (compared to hydrogen), or, alternatively, from the increase in steric hindrance that mitigates the AZM's overall reactivity. In order to test these hypotheses, the synthesis of C6/C7 alkyl substituted AZMs are currently being undertaken. Starting with the enolate alkylation of γ-butyrolactone, synthetic approaches towards AZMs proceed through the addition of key structural features, which include an aziridine at C1, formation of a tetracyclic core, and addition of a carbamate at C10. Synthetic efforts toward the complete synthesis of a C6 ethyl and C6 benzyl substituted AZM are presented herein.