Description Fmoc-L-Photo-Phe-OH is a diazirine-containing, Fmoc-protectedphenylalanine amino acid and multifunctional photo-crosslinker. Its incorporation into peptides or small-molecule probes and tools allows for photoaffinity labeling of cellular targets and protein-protein interactions upon UV light (∼360 nm) irradiation to form a covalent bond. This and othermultifunctional probe building blockswill continue to accelerate drug discovery research for probing cellular mechanisms, target ID/validation, and understanding traditionally undruggable targets. An unprotected version is also available as 907340.