Many active small molecule compounds, such as metabolites, natural products, and drug molecules, interact dynamically and reversibly with target proteins in a non-covalent manner. When proteins are inactivated during in vitro studies, this can disrupt their binding interactions. Photoaffinity labeling (PAL) technology is widely used in the fields of small molecule target identification, cellular distribution imaging, and protein labeling. PAL is a common method for covalently capturing small molecule-biomolecule interactions. Under ultraviolet light stimulation, the photoreactive groups on the chemical probes (classification and characteristics are shown in the table below) generate radicals, nitrenes, or carbenes, which can rapidly and covalently label adjacent biomolecules. Among them, the diazirine structure is the most widely used in small molecule photoaffinity bioorthogonal probes due to its strong biocompatibility, small chemical structure, and fast reaction speed.

The representative products are as follows: