Synthesis and Photophysical Properties of Benzotriazole-Derived Unnatural α-Amino Acids.

The synthesis of a new class of benzotriazole-derived α-amino acid is described using a highly efficient nucleophilic aromatic substitution of ortho-fluoronitrobenzenes with l-3-aminoalanine and a polymer-supported nitrite reagent-mediated diazotization and cyclization of the subsequent 1,2-aryldiamines as the key steps. Further functionalization of the benzotriazole unit by preparation of halogenated analogues and Suzuki-Miyaura cross-coupling with aryl boronic acids allowed the synthesis of α-amino acids with conjugated side chains. Analysis of the photophysical properties of these α-amino acids revealed that incorporation of electron-rich substituents results in charge-transfer-based, fluorescent compounds with MegaStokes shifts.