Direct enzymatic synthesis of a deep-blue fluorescent noncanonical amino acid from azulene and serine

Abstract

We report a simple, one‐step enzymatic synthesis of the blue fluorescent noncanonical amino acid β‐(1‐azulenyl)‐l‐alanine (AzAla). Using an engineered tryptophan synthase β‐subunit (TrpB), stereochemically pure AzAla can be synthesized at scale starting from commercially available azulene and l‐serine. Mutation of a universally conserved catalytic glutamate in the active site to glycine has only a modest effect on native activity with indole but abolishes activity on azulene, suggesting that this glutamate activates azulene for nucleophilic attack by stabilization of the aromatic ion.

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