Straightforward Regeneration of Reduced Flavin Adenine Dinucleotide Required for Enzymatic Tryptophan Halogenation

Mohamed Ismail, Lea Schroeder, Marcel Frese, Tilman Kottke, Frank Hollmann, Caroline E. Paul, Norbert Sewald*

*Corresponding author for this work

Research output: Contribution to journalArticlepeer-review

27 Citations (Scopus)
166 Downloads (Pure)


Flavin-dependent halogenases are known to regioselectively introduce halide substituents into aromatic moieties, for example, the indole ring of tryptophan. The process requires halide salts and oxygen instead of molecular halogen in the chemical halogenation. However, the reduced cofactor flavin adenine dinucleotide (FADH2) has to be regenerated using a flavin reductase. Consequently, coupled biocatalytic steps are usually applied for cofactor regeneration. Nicotinamide adenine dinucleotide (NADH) mimics can be employed stoichiometrically to replace enzymatic cofactor regeneration in biocatalytic halogenation. Chlorination of l-tryptophan is successfully performed using such NADH mimics. The efficiency of this approach has been compared to the previously established enzymatic regeneration system using the two auxiliary enzymes flavin reductase (PrnF) and alcohol dehydrogenase (ADH). The reaction rates of some of the tested mimics were found to exceed that of the enzymatic system. Continuous enzymatic halogenation reaction for reaction scale-up is also possible.

Original languageEnglish
Pages (from-to)1389-1395
JournalACS Catalysis
Issue number2
Publication statusPublished - 2019


  • enzymatic cofactor regeneration
  • FADH
  • flavin-dependent halogenases
  • hydride transfer
  • NADH mimics
  • regioselective chlorination


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