Vanadium complexes have been previously utilised as potent inhibitors of cysteine based phosphatases (CBPs). Herein, we present the synthesis and characterisation of two new fluorescently labelled vanadyl complexes (14 and 15) with bridged di-picolinic acid ligand.These compounds differ significantly from previous vanadyl complexes with phosphatase inhibition properties in that the metal-chelating part is a single tetradentate unit, which should afford greater stability and scope for synthetic elaboration then the earlier complexes. These new complexes inhibit a selection of cysteine based phosphatases (CBPs) in the nM range with some selectivity. Fluorescence spectroscopic studies (including fluorescence anisotropy)were carried out to demonstrate that the complexes are not simply acting as vanadyl delivery vehicles but they interact with the proteins. Finally, we present preliminary fluorescence microscopy studies to demonstrate that the complexes are cell permeable and localise throughout the cytoplasm of NIH3T3 cells.

The development of effective molecular probes to detect and image the levels of oxidative stress in cells remains a challenge. Herein we report the design, synthesis and preliminary biological evaluation of a novel optical probe to monitor oxidation of thiol groups in cysteine-based phosphatases (CBPs). Following orthogonal protecting approaches we synthesised a new vanadyl complex designed to bind to CBPs. This complex is functionalised with a well-known dimedone derivative (to covalently trap sulfenic acids, SOHs) and a coumarin-based fluorophore for optical visualization. We show that this new probe efficiently binds to a range of phosphatases in vitro with nanomolar affinity. Moreover, preliminary flow cytometry and microscopy studies in live HCT116 cells show that this probe can successfully image cellular levels of sulfenic acids -one of the species resulting from protein oxidative damage.

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