Design, synthesis, and biological evaluation of fluorinated analogues of salicylihalamide

Salicylihalamide A (SA), a benzolactone enamide compound, possesses potent cytotoxicity against human tumor cell lines. SA is a selective inhibitor of mammalian vacuolar type H⁺-ATPase (V-ATPase), and is distinct from previously known V-ATPase inhibitors such as bafilomycins and concanamycins that do not discriminate between mammalian and nonmammalian V-ATPases. Because of its potent antitumor activity and structural simplicity, SA is a promising candidate for an anticancer drug. Although a number of structure-activity relation studies using synthetic analogues have been reported, no fluorinated derivative of SA has been evaluated even though selective addition of a fluorine atom into a therapeutic small molecule candidate often enhances pharmacokinetic and physicochemical properties. We designed and synthesized fluorinated analogues of SA and evaluated their V-ATPase inhibitory activities. Compared to the natural product, the synthetic analogues were potent V-ATPase inhibitors, suggesting that these analogues are potential drug candidates and potential molecular probes for mode-of-action studies using fluorine-based analytical methods such as ¹⁹F-NMR spectroscopy.