Production of Niraparib using Imine Reductases

This proposal aims to develop a multi enzymatic synthetic route to a key intermediate of the PARP inhibitor (S)-niraparib, a drug used to treat ovarian cancer. Initial results have demonstrated the feasibility of our enzymatic approach but also highlighted the need for improvement in the enzymatic activities in order to develop an efficient synthesis required by industry.

GSK recently purchased the company Tesaro and with it the rights to their drug molecule (S)-niraparib. The current synthetic route to the intermediate was initially developed by Merck and involves an eight step synthesis. With our proposed route this would be reduced to just five steps to access the same intermediate, this reduction in complexity of the synthetic route would improve lead times for the delivery of the final drug molecule. Additionally, the route proposed within this project also avoids the use of aluminium trichloride mediated Friedel-Crafts acylation required by the Merck Synthetic route.

The key objectives within this project will be to improve the activities of the IRED and HDNO enzyme involved. The HDNO enzyme, previously worked on by the Turner group, was optimised for alternative model substrates therefore will require re-engineering to ensure that it is fit for purpose within this process. The meta-IRED-358 will also need to be engineered to increase its specific activity towards the substrates defined within this application. In addition, both enzymes will need to be engineered to work in the desired process conditions. GSK have recently published a landmark paper in which they engineered an IRED for reductive amination with both improved substrate loading, low pH tolerance and enhanced thermostability. By applying the same techniques to our meta-IRED-358 we will look to enhance the thermostability, solvent and pH tolerance of both enzymes. Once the enzymes have been engineered we will work with GSK to develop a process that can be used at pilot scale.

The Turner group at the University of Manchester has recently discovered a new group of NADPH-dependent oxidoreductases (meta-IREDs) that are able to catalyse three distinct chemical reactions within a single active-site, namely imine formation, conjugate (C=C) reduction and imine reduction. When presented with a 3-aryl-substituted-5,6-dihydropyridinium substrate, the products with these meta-IREDs are the fully reduced chiral 3-aryl-substituted piperidines which are obtained in high yield and e.e. (>98%). The 3-aryl substituted piperidine is a key motif present in a number of active pharmaceutical ingredients (APIs) including the GSK drug niraparib (Zejula), a recently launched PARP (poly ADP ribose polymerase) inhibitor for the treatment of ovarian cancer. The Turner group have now developed a new synthesis of a key chiral building block for niraparib using one of these newly discovered meta-IREDs. This synthesis is shorter than the current manufacturing route employed by GSK and hence represents an opportunity to develop a 2nd generation approach based upon engineered biocatalysts.

This proposal outlines the process we intend to implement to engineer a biocatalytic cascade for the efficient synthesis of Niraparib, a recently approved treatment for ovarian cancer treatment.

The first synthetic route initially developed by Merck and involves an eight step synthesis to obtain the key intermediate, we propose a shorter five step route that eliminates the need for certain harsh chemicals such as aluminium trichloride. The reduction in overall complexity of the synthetic strategy will improve the lead time for delivery of the final drug molecule, thus allowing more rapid production and availability in the market.

This project not only aligns with the "Principles of Green Chemistry", but will aid in the enhancement of industrial biotechnology through the development of a novel biocatalysts for application. The application-guided collaborative research outlined in this proposal aims to aid bridging the gap between academic and industrial application of IRED and HDNO enzymes beyond their biological purpose. This interdisciplinary research combines methods from synthetic biology, biocatalysis and analytical chemistry and will encourage the training of researchers working at the interface of these technologies, feeding into the UK and EU industrial sector for future endeavours.