Quantitative Functionalization of the Tyrosine Residues in Silk Fibroin through an Amino‐Tyrosine Intermediate

Abstract Here, a reaction sequence that can be used to quantitatively modify the tyrosine residues in silk protein from B. mori silkworms is demonstrated. A primary amine is installed ortho to the hydroxyl group on the tyrosine ring using a diazonium coupling reaction followed by reduction of the azo bond. The resulting amine is then acylated using carboxylic acid or NHS‐ester derivatives at room temperature and neutral pH conditions. The silk derivatives are characterized using 1 H NMR, UV–vis spectroscopy, ATR‐FTIR, and a unique method to follow this reaction sequence using isotopically labeled reagents and 2D NMR spectroscopy is also used. This study further demonstrates that this sequence can be used to install alkyne or azide functional groups which can undergo further bio‐orthogonal cycloaddition reactions under mild conditions. Finally, methods to carry out these modifications on solid silk microparticles and electrospun mats are also described.