Synthetic Chemistry for Tryptophan Tryptophylquinone like Enzyme Cofactors

This thesis describes studies on the synthesis of model compounds based on the tryptophan tryptophanyl quinone (TTQ) cofactor designed to probe the mechanism by which it catalyses primary amine oxidation and the role of the enzyme in assisting the TTQ-facilitated reaction. This project has begun to explore ways of investigating the mechanistic landscape going from small molecule ortho-quinone catalysis through to the corresponding enzymatic reaction to address the proposal that enzyme environment is directly involved in the catalytic activity of the TTQ moiety by facilitating a process known as quantum tunnelling and to determine at what point does the catalytic mechanism „swap‟ from a classical one to a mechanism involving quantum tunnelling?

The principal goal was therefore to establish a synthetic route to novel amino acid building blocks that contained appropriate functionality that could be converted into the key ortho-quinone unit that would mimic TTQ. Such fragments required suitable protecting groups to allow their incorporation into peptide and protein domains. This report describes exploration of two synthetic routes to such molecules, both routes utilising 4-methylphenol that, once modified, incorporates the key ortho-quinone unit.

One approach is the synthesis of a novel TTQ-like amino acid that would allow for insertion into a peptide using well documented procedures. This thesis details a variety of different synthetic approaches to the preparation of such a molecule, including problems in coupling the amino acid moiety with the quinone moiety and utilisation of a range of protecting groups in an attempt to overcome these problems.

An alternative approach is also explored involving the synthesis of an ortho-quinone cassette that incorporates either alkyne or azide functionality and utilisation of the relatively new field of copper-catalysed click chemistry to insert this unit into an enzyme containing a non-natural amino acid with an alkyne or azide-containing side chain. Again details of a variety of different routes involved in attempting to produce such a molecule are given and although the target molecule was not produced a model system was successfully developed and inserted into an alkyne-containing amino acid.