Halogenation and Dehalogenation

• Published in: Practical Methods for Biocatalysis and Biotransformations 3 p. 1
• Main Authors: Lang, Alexander, Polnick, Stefan, Nicke, Tristan, William, Peter, Patallo, Eugenio P, Naismith, James H, van Pée, Karl‐Heinz
• Format: Book Chapter
• Language: English
• Published: Chichester John Wiley & Sons 2016; John Wiley & Sons, Ltd
• Subjects: Biochemistry; Biochemistry, Biology & Biotechnology; Chemistry & Chemical Engineering; chloroperoxidase; dehalogenation; electrophilic chlorination; enantioselectivity; General References; halogenation; halohydrin dehalogenases; pyrrolnitrin biosynthesis; reactive hypohalogenite; regioselectivity; tryptophan 7‐halogenase PrnA
• ISBN: 111860525X; 9781118605257
• DOI: 10.1002/9781118697856.ch07

The occurrence of many halogenated metabolites suggests that biology possesses halogenating enzymes with a high degree of substrate specificity and the ability to introduce halogen atoms regioselectively. The first halogenase shown to catalyze the regioselective chlorination or bromination of tryptophan was the tryptophan 7‐halogenase PrnA, involved in pyrrolnitrin biosynthesis. Halohydrin dehalogenases catalyze the dehalogenation of vicinal halohydrins and the epoxide ring‐opening reaction with a series of anion nucleophiles. The improved HheAN178A mutant enzyme could transform the toxic vicinal halohydrin 2‐chloro‐1‐phenylethanol (2‐CPE) to reactive epoxide styrene oxide with a high enantioselectivity. This chapter describes the enzymatic generation of the reactive hypohalogenite by use of chloroperoxidase (CPO) from Caldariomyces fumago for the electrophilic chlorination of thymol and its derivative carvacrol. It also describes the procedure of purification and functional reconstitution of the α‐ketoglutarate (α‐KG)‐dependent non‐heme Fe(II) halogenase HctB, as well as the characterization of its substrate and reaction specificities.