The Immunosuppressive Drug Mycophenolic Acid Does Not Bind Iron(II) Under Conditions Mimicking the Upper Gastrointestinal Environment

Spectroscopic investigation for the interaction of mycophenolate mofetil with ferrous ions

The interaction of mycophenolate mofetil (MMF) with ferrous ions (Fe(2+)) in the solid state, in water, and in polar organic solvents was investigated using (1)H-NMR, (13)C-NMR, IR, and UV-visible (Vis) spectroscopies. A red-purple colored substance was formed after grinding solid MMF and FeSO4·7H2O in a mortar. The IR spectrum of taken as a KBr tablet of the colored substance showed a new absorption band at 1651 cm(-1). Although the color disappeared when the sample was dissolved in water, it persisted in organic solvents such as MeOH or dimethyl sulfoxide (DMSO). The UV-Vis spectrum of a 0.25 mM MeOH solution of MMF showed a new absorption maximum at 507 nm in the presence of Fe(2+) ions, while an aqueous solution of the same mixture showed no significant change from the MMF solution. All the signals in the (13)C-NMR spectrum in DMSO-d6 solution were unambiguously assigned. Upon the addition of 0.5 eq. of Fe(2+) ions, all the carbon signals except those of the 2-morpholinoethyl group almost disappeared, which clearly indicated that the Fe(2+) ions were located far away from the 2-morpholinoethyl groups in the MMF molecules. On the basis of these results, we have concluded that the MMF-Fe(2+) complex is actually formed in the solid state as well as in polar organic solvents such as MeOH or DMSO.