Synthesis and Evaluation of Cereblon-Recruiting HaloPROTACs

The development of proteolysis-targeting chimeras (PROTACs) is a useful approach to develop new therapeutics. PROTACs work by tagging proteins for degradation by the ubiquitin-proteasome system (UPS) in the cell. Especially, in this work, we use Halotag, a genetically modified bacterial dehalogenase that forms covalent bonds with ligands functionalized with terminal chlorohexyl moieties. Reported here the development of bifunctional HaloPROTAC ligands that recruit the cereblon (CRBN) E3 ubiquitin ligase to degrade target proteins fused with a HaloTag in the cell. The dissertation will start with a review of the ubiquitin-proteasome system (UPS) system, PROTACs, and induced protein degradation. Next, I will discuss the synthesis and evaluation of CRBN Recruiting HaloPROTACs for degrading proteins. In this collaborative effort, we found that the CRBN-recruiting HaloPROTAC demonstrated higher activities in inducing the degradation of HaloTagged EGFP than an existing VHL-recruiting ligand at sub-micromolar concentrations of the compound. We hypothesize that we can expand the use of the HaloPROTAC system various cell and tissue types for validating the degradation targets for therapeutic discovery. The final chapter of this dissertation is a brief review on the elucidation of the UPS cascade system and a report on the synthesis of unnatural amino acids for the synthesis of ubiquitin conjugates(diUBs) as activity-based probes for deubiquitinating enzymes.