The 5’-phosphatases are a family of metalloenzymes involved in the regulation of phosphoinositide signalling in cells and also implicated in diseases such as cancer, diabetes and neurodegenerative disorders. Even so,only a handful of modulators have been reported to target these enzymes. In this thesis,efforts towards the design of zinc(II)complexes for 5’-phosphatase inhibition are described with further analysis of the interaction between these enzymes and zinc(II). The validation of previous reports that zinc(II) can inhibit the 5’-phosphatases is described and, alongside published evidence that calcium(II) displaced the magnesium(II) co-factor from the 5’-phosphatase active site, was the basis for design and synthesis of zinc(II) complexes. Synaptojanin 1 was chosen as the representative of the 5’-phosphatases for this study due in part to its importance in neurodegenerative disease and the paucity of reported inhibitors for this enzyme.
Iterations of design (with the aid of computational docking), synthesis and testing in vitro with a series based on a zinc(II) cyclen motif yielded poorer than anticipated inhibition of synaptojanin 1. Investigation into the mechanism of zinc(II) mediated inhibition of the 5’-phosphatases using a combination of biochemical, biophysical and computational techniques revealed that, rather than displacing magnesium(II), zinc(II) more likely bound a second metal binding region within the 5’-phosphatase active site. This proposed zinc(II) binding site incorporated residues recently postulated to be important for a 5’-phosphatase mechanism of action involving a “moving” magnesium(II) co-factor. As zinc(II) was inhibitory, the results described in this thesis support this mechanism. Furthermore, the weak inhibitory activity of zinc(II) cyclen towards synaptojanin 1 was found to be via binding to the phosphoinositide substrate I(1,4,5)P3. Considering the tractable synthesis and good aqueous solubility of substituted zinc(II) cyclens reported herein, these motifs might hold promise towards modulation of phosphoinositide signalling by direct binding to phosphoinositides.