Synthesis of mechanism probes and potential Inhibitors for Tryptophan 2, 3-dioxygenase and Indoleamine 2, 3-dioxygenase enzymes

摘要

In biological terms, the kynurenine pathway is considered as a one of the major degradation pathway of tryptophan (L-Trp) in which the first and rate-limiting step in this pathway is the oxidation of L-Trp to N-formylkynurenin (NFK). In spite of the fact that many mechanism have been proposed to explain how the transformation occurs, the mechanism of this oxygen-dependent reaction has not yet been determined. Nonetheless, this type of unique reaction is catalysed by two heme-containing dioxygenase enzymes:- tryptophan 2,3-dioxygenase (TDO), and indoleamine 2,3-dioxygenase (IDO), and due to the fact that the overexpression of these enzymes leads to degradation of this amino acid to NFK. From a clinical point view, the breakdown of L-Trp through this pathway leads to the production of a variety of secondary metabolites, such as quinolic acid, anthranilic acid (AA), and 3-hydroxyanthranilic acid (3-HAA). These compounds, amongst others are implicated in a broad range of diseases such as cataract formation, neurological disorders and suppression of T-cells proliferation. In this context, both enzymes apparently present as significant targets for drug intervention. As a result, developing new inhibitors for these enzymes is ongoing. The current work has included the synthesis, purification and characterisation of some heterocyclic compounds. Generating these compounds has relied on indole derivatives as a core component; other species such as alkenes have been used as precursors for generating a cyclopropane ring after the amine groups of the main indole derivatives had been protected by various protection groups. However, a number of difficulties were encountered when trying to remove some of these groups. In application terms, some of these species have been employed as potential inhibitors for both TDO and IDO, in presence of tryptophan as a substrate. The kinetic assays carried out here have shown that there is a slight change in the slope (velocity) for some of these compounds with the enzyme IDO in the presence of L-Trp. as a substrate. This might imply a reduction in enzyme activity, which could mean some of our compounds were slightly effective, at least to some degree, as inhibitors, whilst others had no effect on the same enzyme. In case of TDO, due to the fact that the amount of protein obtained after purification was insufficient, just a very few of these compounds were tested with this enzyme, however no action was observed.