Effect of pH on the Biotransformation of (R)-1-(4-bromo-phenyl)-ethanol by using Aspergillus niger as Biocatalyst

Molecular chirality is a fundamental phenomenon that plays an important role in biological processes. Currently, much attention has been focused on the production of chiral alcohols. Chiral alcohols such as (R)-1-(4-bromo-phenyl)-ethanol is important as a useful starting material used in pharmaceutical industries for drug synthesis. There are many factors that influenced the bioconversion and some of the crucial ones include the pH of media, biotransformation time, substrate concentration and agitation speed. All of these factors significantly affect the percentage of enantiomeric excess as well as the percentage conversion of the chiral alcohol. In this work, biocatalytic production of (R)-1-(4-bromo-phenyl)-ethanol was achieved via asymmetric reduction of 1-(4-bromo-phenyl)-ethanone using the shake-flask method at the reaction conditions of 30° C, 1 mmol of substrate, agitation speed of 150 rpm and at various pH’s. Since Aspergillus niger can easily grow and produce enzyme that is suitable in converting the substrate, therefore, it was used as a biocatalyst in the reaction. Based on the results obtained, pH 7 gave the highest enantiomeric excess of 99.9% and conversion of 94.7% for the reduction time of 48 h.