# A novel ene-reductase from Halomonas elongata for flow biocatalytic synthesis of 3-phenylpropionaldehyde and sustainable indigo-carmine dyeing

## TL;DR

A new enzyme from Halomonas elongata efficiently reduces carbon-carbon double bonds and is used in a biocatalytic process to produce a chemical and a sustainable dye.

## Contribution

A novel halophilic ene-reductase is characterized and applied in a flow biocatalytic system for efficient synthesis.

## Key findings

- The ene-reductase from Halomonas elongata showed high activity across various substrates.
- Flow biocatalytic reduction of cinnamaldehyde achieved a 62-fold process intensification compared to batch.
- An enzymatic cascade converted indole to leuco-indigo with co-production of 2-oxindole.

## Abstract

In order to broaden the toolbox of enzymes available for biocatalytic reductions of carbon-carbon double bonds, we investigated four promising ene-reductases (ERs) stemming from extremophilic organisms or showing homology with thermophilic ERs. The novel ene-reductase from the halophilic organism Halomonas elongata showed consistently high activity across a range of tested substrates. Upon immobilisation of the ERs, the flow biocatalytic ene-reduction of cinnamaldhehyde into 3-phenylpropionaldehyde was successfully achieved with an intensification of the process of 62-fold with respect to batch (2173.9 mg L−1 h−1 and 34.7 mg L−1 h−1, respectively). Additionally, to expand the scope of ERs applications, we describe a proof-of concept of a novel enzymatic cascade to convert indole to indigo using an unspecific peroxygenase, and its subsequent reduction to the water-soluble leuco-indigo. In addition, the co-production of the valuable pharmaceuticals precursor 2-oxindole was demonstrated.

The characterization of novel ene-reductases identifies a halophilic enzyme with remarkable catalytic efficiency. HeOYE could be successfully immobilised for process intensification and applied in a tandem cascade for the synthesis of leuco-indigo. The image was created in full using Bria AI.