Photoa‹nity labeling enables the direct probing of a target protein through a covalent bond between a ligand and its binding protein. We used carbene-generating phenyldiazirine as a photophore because practical examinations had shown that the phenyldiazirine functioned as the powerful barb on the hook. This review describes improvements of synthetic strategies of the photoa‹nity ligands bearing diazirine. First, we dramatically improved the direct formylation of phenyldiazirine, which was a

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... tical diazirine source, to obtain a versatile diazirine unit. Second, we established"the photoreactive unit technique" for a one-step introduction of phenyldiazirine into peptides, proteins, DNAs, and sugars. Since the photoreactive units can be easily integrated into physiological ligands by chemoselective reaction, the biochemists, who are not familiar with organic synthesis, can prepare the photoa‹nity ligands using their interested ligands. Our improvements would promote the utilization of phenyldiazirine for analyzing biological interfaces, and extend the potential of photoa‹nity labeling as a sensitive means of rapidly elucidating protein structures and proteomic proˆling.