Design, Synthesis, and Biological Investigation of Epothilone B Analogues Featuring Lactone, Lactam, and Carbocyclic Macrocycles, Epoxide, Aziridine, and 1,1-Difluorocyclopropane and Other Fluorine Residues

Despite previous studies within the epothilone field, only one member of this compound family, ixabepilone, made it to approval for clinical use. Recent advances in organic synthesis and medicinal chemistry allow further optimization of lead epothilone analogues aiming to improve their potencies and other pharmacological properties as part of the quest for discovery and development of new anticancer drugs, including antibody–drug conjugates as potential targeted cancer therapies. Herein, we report the design, synthesis, and biological evaluation of a series of new epothilone B analogues equipped with novel structural motifs, including fluorine-containing residues, 12,13-difluorocyclopropyl moieties, mono- and dimethylated macrolactones, and 1-keto macrocyclic systems, as well as two N-substituted ixabepilone analogues in which the 12,13-epoxide and macrolactam NH moieties were replaced, the former with a substituted aziridine moiety and the latter with an NCO-alkyl residue (imide or carbamate). Biological evaluation of these analogues revealed a number of exceptionally potent epothilone B analogues, demonstrating the potency enhancing effects of the fluorine residues and the aziridinyl moiety within the structure of the epothilone molecule and providing new and useful structure–activity relationships within this class of compounds.