12'-Methylthiovinblastine Dihydrochloride

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 (IC(50) = 800 pM, HCT116) and vinblastine-resistant tumor cell lines (IC(50) = 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 the 10'-fluorine substituent makes critical contacts with the protein at a hydrophobic site uniquely sensitive to steric interactions.

Four low-level impurities were detected during the development and scale up of the synthesis of ALB 109564(a). These impurities were isolated and characterized in order to determine how they originated in the drug substance. The information allowed the elimination of one impurity and a significant reduction in the relative abundance of the other three. A fifth impurity was detected in an accelerated stability study sample of the drug substance. The degradant was found to be the free acid resulting from the hydrolysis of the methyl ester within the indoline moiety of ALB 109564(a). The characterization of this impurity allowed for changes in the handling of the drug substance which minimized the formation of the impurity.