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. Author manuscript; available in PMC: 2014 Apr 1.
Published in final edited form as: Curr Opin Chem Biol. 2012 Dec 24;17(2):189–196. doi: 10.1016/j.cbpa.2012.11.019

Figure 4.

Figure 4

Cobalt complexes that undergo bioreductive activation. A) Co(III)(LNN′O)2 undergoes reduction to the more labile Co(II) counterpart to yield an active proteasome inhibitor [40,41*]. In the presence of the reducing agent ascorbic acid, one of the LNN′O ligands of Co(III)(LNN′O)2 is lost and replaced by a solvent (DMF) molecule, as identified by mass spectrometry. The activated complex is thought to bind to the active site of the proteasome to elicit inhibition. Scheme adapted from ref [31] with permission. B) The fluorescence of coumarin-343 (c343) is quenched upon coordination to Co(III)/cyclam. When the complex encounters the reducing environment of a hypoxic spheroid core, the complex undergoes reduction, releasing the fluorophores and restoring fluorescence. The process is monitored by fluorescence confocal microscopy [51*].