Syntheses of Taxuspine C Derivatives as Functional Inhibitors of P-Glycoprotein, an ATP-Associated Cell-Membrane Transporter.

Abstract

UV-Irradiation of taxinine and related compounds in acetonitrile induced a smooth transannulation between the C-3 and C-11 positions without any influence from the C-2, C-9 and C-10 substituents to give tetracyclic taxuspine C derivatives in almost quantitative yields. Photochemical transannular reaction of taxoids possessing a cinnamoyl group in the side-chain was accompanied by an E,Z-isomerization of the cinnamoyl moiety. Cellular accumulation of vincristine, a useful drug for cancer chemotherapy, in multidrug-resistant ovarian cancer cells was found to increase most effectively in the case of 5-O-benzoylated 5-O-decinnamoyltaxuspine C. This indicates that the 5-O-benzoylated taxuspine C derivative may be a promising functional inhibitor of P-glycoprotein, which acts as an ATP-associated efflux pump for cancer chemotherapeutic agents.