4-Azido-L-phenylalanine (4AZP) is an unnatural amino acid analog of L-phenylalanine that contains an azide moiety. 4AZP-labeling is a fast, sensitive, and non-radioactive alternative to the traditional technique for detecting nascent protein synthesis.
4AZP is randomly incorporated into synthesizing protein instead of phenylalanine during translation. The resulting azide-labeled full-length proteins can be detected via copper-catalyzed click reaction (with fluorescent or biotin-labeled alkynes) or copper-free click reaction (with cycloalkynes) and used for subsequent microscopic imaging or purification tasks.