Shrnutí: | Biomimicry valuably allows the understanding of the essential chemical components required to recapitulate biological function, yet direct strategies for evaluating the roles of amino acids in proteins can be limited by access to suitable, subtly-altered unnatural variants. Here we describe a strategy for dissecting the role of histidine residues in enzyme active sites using unprecedented, chemical, post-translational side-chain-β,γ C-N bond formation. Installation of dehydroalanine (as a "tag") allowed the testing of nitrogen conjugate nucleophiles in "aza-Michael"-1,4-additions (to "modify"). This allowed the creation of a regioisomer of His (iso-His, His
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