Synthesis of Fluorescent Dibenzofuran α-Amino Acids: Conformationally Rigid Analogues of Tyrosine.

We report two synthetic strategies for the preparation of dibenzofuran α-amino acids, expanding the structural toolbox of fluorescent probes. The strategies involved dibenzofuran synthesis via a Pd(II)-catalyzed C-O cyclization, alongside an efficient Negishi coupling approach for faster access to analogues. These rigid tyrosine mimics possess enhanced fluorescent properties compared to proteinogenic amino acids as demonstrated by application of the lead compound as a FRET donor for monitoring peptide hydrolysis by a serine protease.