Azidophenylalanine (4-azido-L-phenylalanine) is an unnatural amino acid derivative of L-phenylalanine, featuring an azide group at the para position of the phenyl ring. It is a bioorthogonal click-chemistry reagent that can be genetically incorporated into proteins via expanded genetic code techniques for site-specific labeling and functionalization. The compound serves as a vibrational reporter for local protein environments due to its azide group and is used in photo-crosslinking for protein interaction studies.
Chemical properties Azidophenylalanine has the molecular formula and a molecular weight of 206.20 g/mol. Its IUPAC name is (2S)-2-amino-3-(4-azidophenyl)propanoic acid. It appears as an off-white solid and is soluble in water, DMSO, and DMF.
As with many other azides, the isolated compound exhibits explosive properties. It is light-sensitive and should be stored at -20 °C in the dark.
Synthesis A chromatography-free synthesis of azidophenylalanine has been reported. It starts from L-phenylalanine and includes iodination to form 4-iodo-L-phenylalanine, followed by Boc protection, Cu(I)-catalyzed azidation using sodium azide (NaN3), deprotection with sulfuric acid, and purification by recrystallization. This method avoids explosion risks associated with earlier approaches.
Research uses As an analog of L-phenylalanine, azidophenylalanine is incorporated into proteins during translation in place of phenylalanine. The azide group enables bioorthogonal reactions, such as copper-catalyzed or strain-promoted azide-alkyne cycloadditions, for protein modification.
Azidophenylalanine is employed in metabolic labeling to detect nascent protein synthesis as a non-radioactive alternative to traditional methods. It facilitates site-specific protein labeling for microscopic imaging, purification, and FRET studies. Applications include photochemical control of fluorescent proteins, synthesis of ligands for metal complexation in EPR/NMR, and probing protein dynamics during folding or catalysis. It is incorporated using orthogonal tRNA/synthetase pairs in systems like E. coli.
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