10′-Fluorovinblastine and 10′-Fluorovincristine: Synthesis of a Key Series of Modified Vinca Alkaloids

A study on the impact of catharanthine C10 and C12 indole substituents on the biomimetic Fe­(III)-mediated coupling with vindoline led to the discovery and characterization of two new and substantially more potent derivatives, 10′-fluorovinblastine and 10′-fluorovincristine. In addition to defining a pronounced and unanticipated substituent effect on the biomimetic coupling, fluorine substitution at C10′, which minimally alters the natural products, was found to uniquely enhance the activity 8-fold against both sensitive (IC₅₀ = 800 pM, HCT116) and vinblastine-resistant tumor cell lines (IC₅₀ = 80 nM, HCT166/VM46). As depicted in the X-ray structure of vinblastine bound to tubulin, this site resides at one end of the upper portion of the T-shaped conformation of the tubulin-bound molecule, suggesting that the 10′-fluorine substituent makes critical contacts with the protein at a hydrophobic site uniquely sensitive to steric interactions.