Phosphonium betaines derived from hexafluoro-1,4-naphthoquinone: Synthesis and cytotoxic and antioxidant activities

Fluorinated derivatives of 1,4-naphthoquinones are highly potent inhibitors of Cdc25A and Cdc25B phosphatases; they suppress the growth of tumor cells. Four derivatives of phosphonium betaines derived from hexafluoro-1,4-naphthoquinone: (triphenyl[5,6,7,8-tetrafluoro-1-oxido-4-oxo-3-(phenylimino)-3,4-dihydronaphthalen-2-yl]phosphonium) (4), ((3,5-difluorophenyl)(methyl)phenyl(5,6,7,8-tetrafluoro-3-oxido-1,4-dioxo-1,4-dihydronaphthalen-2-yl)phosphonium) (5), ((2,5-difluorophenyl)(methyl)phenyl(5,6,7,8-tetrafluoro-3-oxido-1,4-dioxo-1,4-dihydronaphthalen-2-yl)phosphonium) (6) and ((3,5-difluorophenyl)diphenyl(5,6,7,8-tetrafluoro-3-oxido-1,4-dioxo-1,4-dihydronaphthalen-2-yl)phosphonium) (7) were synthesized for the first time. Their cytotoxicity toward human mammary adenocarcinoma, human myeloma, hamster and murine and fibroblasts as well as their antioxidant and mutagenic effects on a Salmonella tester strain were analyzed. All four substances showed comparable IC50 values in terms of suppression of tumor cell growth, which were from two- to ninefold lower comparing with those of fibroblasts. To identify the features of spatial orientation and noncovalent interactions of the new phosphonium betaines in the binding site of Cdc25B, a molecular docking analysis was carried out. It showed that the interactions of the analyzed compounds with a Cdc25B model binding site are characterized by the presence of a large number of acceptors (fluorine and oxygen atoms, forming halogen and hydrogen bonds) and by participation of pi-systems and phosphorus in specific electrostatic interactions that may result in inhibition of enzymes of the Cdc25 family. In addition, compounds 5 and 6 (especially the latter) were found to be effective antioxidants protecting bacterial cells from H2O2-induced and spontaneous and mutagenesis at significantly lower concentrations (IC50 = 0.09 to 1.8 μM) than those of derivatives 4 and 7 (86–92 μM). Taking into account these data (together with the good cytotoxic effect on cancer cells comparing with normal mammalian cells) we can propose compounds 5 and 6 as possible useful inhibitors of tumor cell growth and antioxidants.