Primary Amine-Based Photoclick Chemistry: From Concept to Diverse Applications in Chemical Biology and Medicinal Chemistry.

ConspectusClick chemistry has significantly impacted many fields. The emergence of photoclick chemistry, which harnesses light-driven processes under mild conditions, has introduced distinct advantages, including precise spatiotemporal control, high selectivity, and elimination of toxic metal catalysts and reagents. These features make photoclick chemistry a highly valuable tool in various fields. Although many exciting applications have been found, the development of photoclick methodologies remains limited, and photoclick chemistry is still in its early stage. Thus, the development of novel and versatile systems is crucial for advancing a wide range of applications and fully realizing their potential.In this Account, we aim to highlight the concept of a novel photoclick chemistry, light-induced Primary Amine and o-Nitrobenzyl Alcohol Cyclization (PANAC), to broaden the potential and applications of photoclick chemistry. Inspired by the abundance and versatility of primary amines in synthetic chemistry, biological systems, and materials science, we introduced the primary amine as a direct and general photoclick handle, while the o-nitrobenzyl alcohol (o-NBA) structure was designed as a molecular plugin to provide easily accessible and modular reactants for the PANAC photoclick reaction. With intrinsic features such as temporal control, reliable chemoselectivity, high efficiency, readily accessible reactants, biocompatibility, operational simplicity, and mild conditions, the developed PANAC photoclick reaction aligns with the core criteria of photoclick chemistry. By leveraging the advantages of PANAC photoclick chemistry and designing various conjugation strategies, we have successfully applied it in various applications, enabling modular synthesis and bioconjugation, including modular functionalization of bioactive small molecules, lysine-specific unprotected peptide cyclization and labeling of native proteins both in vitro and in live cells, and temporal profiling of endogenous kinases and organelle-targeted labeling in living systems. Moreover, by harnessing widespread primary amines and the versatility of PANAC photoclick chemistry, we developed a direct-to-biology platform for proteolysis-targeting chimera (PROTAC) library assembly, accelerating PROTAC degrader discovery, and created structurally diverse DNA-encoded libraries for high-throughput screening and identification of novel bioactive compounds. Furthermore, based on primary-amine-based modular synthesis, a general platform for the efficient and modular assembly of ligand-oligonucleotide conjugations via PANAC photoclick chemistry enables rapid access to therapeutic oligonucleotides. More importantly, PANAC photoclick chemistry enables temporally controlled proteome-wide profiling of biomacromolecule interactions and dynamics through endogenous lysine bioconjugation within complex biological environments. This is exemplified by the spatiotemporal and global profiling of DNA-protein interactions, which enables the discovery of low-affinity transcription factors, as well as by the direct capture of protein-protein interactions (PPIs) and global substrates of lysine-modifying enzymes in live cells, thereby providing a valuable tool for exploring previously unrecognized functional roles of proteins.Collectively, with its versatility and high efficiency, PANAC photoclick chemistry has emerged as an accessible and promising chemical tool across diverse fields. Building on its intrinsic advantages and potential for future development, PANAC photoclick chemistry will open up exciting opportunities for the functional discovery of primary-amine-enabled photoclick connections and inspire innovative solutions to address challenges in areas such as synthetic chemistry, medicinal chemistry, chemical biology, and materials science.