L-ANAP is a genetically encodable and polarity-sensitive fluorescent unnatural amino acid (Uaa). In Vitro: L-ANAP is a fluorescent, noncanonical amino acid which can be used for specific fluorescent labeling^[1]. L-ANAP is a genetically encodable and polarity-sensitive fluorescent unnatural amino acid (Uaa). Fluorescent Uaas, including L-dansylalanine, L-(7-hydroxycoumrin-4-yl)ethylglycine and L-ANAP, are of particular interest for molecular and cellular biology, which may complement and enchance the widely used fluorescent proteins (FPs)^[2].