Post-translational modifications of proteins based on the amino acid residue dehydroalanine (Dha) have been widely adopted in molecular biology to expand their structural and functional capabilities. However, the construction of highly important amide C(sp2)-C(sp3) linkages on peptides through cross-coupling remains unexplored. In this article, we describe a photoredox-catalyzed C(sp2) amidation that enables the mutation of Dha to an asparagine (Asn) motif. This amide installation strategy reported herein will guide us to create more additional derivatives of peptides, which may elucidate the mode of action and address an important area of unmet medical need.