Conventional approaches for the discovery of bioactive small molecules typically follow a cycle of design, synthesis, purification and testing. This workflow usually employs a narrow toolkit of robust chemical reactions, and places equal value on every chemical entity regardless of bioactivity. Consequently, significant effort is invested into designing, making and purifying large numbers of compounds with low levels of bioactivity.
Activity-Directed Synthesis (ADS) places the focus exclusively on bioactive molecules during the discovery phase, using activity to guide syntheses through an iterative discovery cycle. ADS exploits chemistry that may yield multiple product outcomes and are not commonly integrated into traditional discovery workflows. The process is structure-blind and function- driven, permitting the discovery of bioactive small molecules and their associated synthetic routes in parallel, mimicking elements of the process in which small molecule natural products are produced via biosynthetic pathways in nature.
Integration of new chemistries into the ADS workflow would permit exploration of more diverse areas of chemical space using the approach. Organocatalysis was recognised to have potential to generate a wide range of scaffolds in a combinatorial manner and is robust enough to tolerate the miniaturised high-throughput format required for ADS. The potential for the use of organocatalysis in ADS was explored and successfully translated into a micro-scale format for application in ADS. Additionally, protocols were developed to remove undesirable functional groups from product mixtures prior to screening.
The miniaturised organocatalytic chemistry was then applied in ADS to reaction arrays, seeking to use organocatalysis in ADS to discover novel androgen receptor agonists. Different strategies for reaction array design were developed, in addition to protocols for efficient execution of reaction arrays. Both conversion and bioactivity of product mixtures were assessed using a TR-FRET assay and NMR, highlighting issues that significantly decreased the number of reactions that yielded intermolecular products. However, successful identification of bioactive components within product mixtures that were not the result of intermolecular reactions demonstrated the potential for the protocols developed to be successful in identifying bioactive small molecules. Consequently, ADS is now poised to utilise organocatalysis to attempt to generate bioactive molecules for alternative biological targets.
