accessible aromatic thiols. We demonstrate that nearly 50 ncAAs with a diverse array of structures can be biosynthesized from these simple small‐molecule precursors by hijacking the cysteine biosynthetic enzymes, and the resulting ncAAs can subsequently be incorporated into proteins via an expanded genetic code. Moreover, we demonstrate that bioorthogonal reactive groups such as aromatic azides and
Treatment of S-p-methoxybenzylcysteine sulfoxide with hydrogen fluoride or methanesulfonic acid in the presence of anisole afforded S-p-methoxyphenylcysteine as a major product, while S-benzylcysteine sulfoxide resisted to the action of these deprotecting reagents in peptide synthesis. Thiophenol was found to be a powerful reducing reagent of the sulfoxides.