An Fe complex for 19F magnetic resonance-based reversible redox sensing and multicolor imaging

We report a first-in-class responsive, pentafluorosulfanyl (-SF5)-tagged F-19 MRI agent capable of reversibly detecting reducing environments via an Fe-II/III redox couple. In the Fe-III form, the agent displays no F-19 MR signal due to paramagnetic relaxation enhancement-induced signal broadening; however, upon rapid reduction to Fe-II with one equivalent of cysteine, the agent displays a robust F-19 signal. Successive oxidation and reduction studies validate the reversibility of the agent. The -SF5 tag in this agent enables 'multicolor imaging' in conjunction with sensors containing alternative fluorinated tags and this was demonstrated via simultaneous monitoring of the F-19 MR signal of this -SF5 agent and a hypoxia-responsive agent containing a -CF3 group.