Abstract
We report a first-in-class responsive, pentafluorosulfanyl (-SF(5))-tagged (19)F MRI agent capable of reversibly detecting reducing environments via an Fe(II/III) redox couple. In the Fe(III) form, the agent displays no (19)F 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 (19)F signal. Successive oxidation and reduction studies validate the reversibility of the agent. The -SF(5) tag in this agent enables 'multicolor imaging' in conjunction with sensors containing alternative fluorinated tags and this was demonstrated via simultaneous monitoring of the (19)F MR signal of this -SF(5) agent and a hypoxia-responsive agent containing a -CF(3) group.