Mid-Term Report Summary - MOCOMODELS (Synthesis of mono-dithiolene molybdenum complexes and their evaluation as potential drugs for the treatment of human isolated sulfite oxidase deficiency.)
Two phenotypically indistinguishable fatal diseases (Moco-deficiency (MocoD) and isolated sulfite-oxidase-deficiency (iSOD)) are caused by a failure at different levels of the expression and assembly of a certain group of enzymes. While MocoD patients have been successfully treated by injection of an organic molecule that takes part in the proteins' development there is no cure for iSOD. This project aims to develop a substitute for the very sensitive metal based part of the enzyme, to test its potential to generate an active enzyme together with the biotechnologically produced enzyme-peptide (the apo-enzyme) and to evaluate the semi-synthetic enzyme's applicability as a treatment. In order to achieve these goals the very complex active site structure of the enzymes has been divided on paper into different targets to be modelled independently from each other. Eventually all these different approaches will be combined for generating a chemical copy of the biological active site with as much resemblance as necessary yet with the least possible effort; i.e. we want to determine what actually needs to be modelled to generate a functioning semi-synthetic enzyme and what might be left aside for convenience, stability or handling issues. The work on the organic part of the active site is challenging but the three subprojects dealing with these tasks are well on their way towards delivering the ligand precursors for complex synthesis, i.e. bringing organic and inorganic parts of the active site models together. In course of the research in this regard, known synthetic procedures have been modified and optimised and a misconception in the literature of how a specific set of compounds actually does look like (white instead of brown or red) could be corrected. This is to say that these specific compounds (pyrazine substituted alkynes) had never been isolated in pure form prior to our work. Initial tests of combining apo-enzymes and our chemical active site models were unsuccessful but showed us the direction in which we need to modify these compounds in order to achieve actual binding between chemical and biological part. Work in this respect is under way. A prerequisite for such studies was to synthesise complexes, which are water soluble. This is something, which hasn't been reported in the literature before and it appears as if we were the first to achieve this task by a rather simple method now frequently applied in our labs: the use of simple counter ions instead of the typical bulky ones.
Many complexes made in course of our work were investigated for their catalytic potential and it was found that those with aliphatic (i.e. non-aromatic) substituents on the dithiolene moiety were far more reactive yet also far more labile than those with aromatic substituents. By combining aliphatic and aromatic functions in our substituents we hope to eventually be able to meet the delicate balance between stability and reactivity required for the complexes suitable for re-constituting activity of the apo-enzyme.
In course of the work towards the project's aims two very unexpected, hence unanticipated discoveries were made. We found that a method very frequently used in many labs of different specialisation for the de-protection of dithiolene precursors is actually fully reversible. Given that the side product of the reaction is CO2, this means that the de-protected version of a dithiolene ligand may serve as an effective trap for the greenhouse gas. The second unexpected finding was made while trying to generate dithiolene complexes from alkynes and a molybdenum sulfur complex. Instead of the desired complex a so called pentathiepin (a sulfur rich organic compound) was made. As there are some natural products with this chemical motif having antibacterial and fungicidal properties, we investigated the respective reaction further and were able to synthesise a set of pentathiepins of unprecedented complexity, which even showed interesting DNA binding behaviour. These compounds were then tested for their activity against four different cancer cell lines and it was found that they could very well compete in this respect with carboplatin, a chemotherapeutic agent frequently administered to cancer patients. By accident we may have found a promising new class of compounds well equipped for treating cancer patients.
Many complexes made in course of our work were investigated for their catalytic potential and it was found that those with aliphatic (i.e. non-aromatic) substituents on the dithiolene moiety were far more reactive yet also far more labile than those with aromatic substituents. By combining aliphatic and aromatic functions in our substituents we hope to eventually be able to meet the delicate balance between stability and reactivity required for the complexes suitable for re-constituting activity of the apo-enzyme.
In course of the work towards the project's aims two very unexpected, hence unanticipated discoveries were made. We found that a method very frequently used in many labs of different specialisation for the de-protection of dithiolene precursors is actually fully reversible. Given that the side product of the reaction is CO2, this means that the de-protected version of a dithiolene ligand may serve as an effective trap for the greenhouse gas. The second unexpected finding was made while trying to generate dithiolene complexes from alkynes and a molybdenum sulfur complex. Instead of the desired complex a so called pentathiepin (a sulfur rich organic compound) was made. As there are some natural products with this chemical motif having antibacterial and fungicidal properties, we investigated the respective reaction further and were able to synthesise a set of pentathiepins of unprecedented complexity, which even showed interesting DNA binding behaviour. These compounds were then tested for their activity against four different cancer cell lines and it was found that they could very well compete in this respect with carboplatin, a chemotherapeutic agent frequently administered to cancer patients. By accident we may have found a promising new class of compounds well equipped for treating cancer patients.