Halogenating enzymes in organic synthesis

Enzymes are remarkably efficient catalysts. They have high substrate specificity and, contrary to common belief, many are robust and will work well at elevated temperatures and in organic co-solvents.  

All this makes enzymes viable options as catalysts in organic syntheses. The use of haloperoxidase (HPO) enzymes provides undergraduates with a good introduction both to the importance of biological molecules in chemistry and the rapidly expanding field of natural organohalogens, many of which show great potential as therapeutic agents.^1,2

The syntheses we have chosen are well established and will be familiar to undergraduate chemistry students (see reactions (i)-(vii)). We use the enzyme bromoperoxidase (BPO) from the red coralline seaweed Corallina officinalis. This organism is readily available, though in fact many types of seaweed contain the BPO enzyme and it is usually possible to obtain a suitable organism from any coastal region. To put the experimental work into context for the students, we begin by telling them about the chemical properties of the haloperoxidases and their roles in biological systems.