Efforts to expand chemistry toolbox for DNA-encoded libraries

DNA-encoded library (DEL) technology is a widely accepted platform to discover small molecules that can interact with biological targets. DELs containing millions to billions of compounds can be constructed through cycles of iterative DNA tag ligation and chemical synthesis with a 'spit-and-pool' approach. Unique DNA barcodes attached to each compound and high-throughput sequencing allow affinity selection of DEL in a single tube with minimal amounts of library and protein, and identification of binders from the pool. Development of DNA-compatible reactions, especially reactions can expand the chemical space DEL cover, is an essential component of the technology, and is the focus of this dissertation.This dissertation consists of three DEL methodology projects. In my first project, threonine aldolases (TA) were successfully applied to the synthesis of DNA-conjugated β-hydroxy-α-amino acids. Relative stereoselectivity of the reaction was studied by using TAs of varying stereospecificity. Further diversification of the aldol product was explored to demonstrate the utility of this reaction in DEL. In the following project, utilizing intramolecular benzimidazole formation, a 129-million-member macrocyclic library composed of a privileged benzimidazole core, a dipeptide sequence (natural or non-natural), and linkers of varying length and flexibility was designed and synthesized. Finally, on-DNA tetrahydroisoquinoline synthesis via phosphate catalyzed biomimetic Pictet-Spengler reaction was developed. With DNA-conjugated 3-hydroxyl phenylalaninamide, the reaction showed robust conversion and wide aldehyde scope. The formed tetrahydroisoquinoline could be further diversified by utilizing secondary amine and phenol functional groups, whch would lead to 2- or 3- cycle DELs.--Author's abstract