Target-guided synthesis is an approach to drug discovery that uses the
biological target as a template to direct synthesis of its own best inhibitors from
small molecule fragments. The process bridges the gap between chemical synthesis
of drug candidates and their biological binding assay, merging the two operations
into a single process whereby the active site or a binding pocket within the structure
of the biological target directly controls the assembly of the best inhibitor in situ.
Two different approaches to target-guided synthesis, the thermodynamic approach,
making use of reversible reactions, and the kinetic approach, which uses an
irreversible reaction, have been employed to discover novel, isoform selective
inhibitors of the glutathione transferase (GST) enzyme family – possible drug targets
in cancer and parasitic disease treatments.
The thermodynamic approach described in this thesis uses the
aniline-catalysed reversible acyl hydrazone formation reaction to create a dynamic
covalent library of bivalent ligands designed to bind the dimeric structure of GST. In
the presence of GST one of the bivalent ligands was selectively amplified at the
expense of the other library members. This ligand was shown, via biological assays,
to be a specific inhibitor for one isoform of GST, the mu isoform mGSTM1-1.
A kinetic approach has also been investigated as a way to identify novel
bivalent GST inhibitors utilising the Huisgen 1, 3 dipolar cycloaddition reaction. An
azide and alkyne fragment library was designed to bind across the dimeric GST
structure. The inhibitor structures are therefore bivalent, containing two anchoring
fragments known to bind to the GST active site, linked by a triazolopeptide spacer.
The triazole provides the click chemistry disconnection, enabling rapid in situ
screening of candidate alkyne and azide fragments for inhibitor discovery. Whilst the
in situ reaction with GST yielded inconclusive results, a number of the triazole
products were found to have low nanomolar inhibitory activity towards GST