Aryl‐Alcohol‐Oxidase‐Mediated Synthesis of Piperonal and Other Valuable Aldehydes

The use of fungal aryl‐alcohol oxidases in biocatalysis is still modest, despite their advantageous capability to produce valuable aldehydes via oxidation of the respective alcohols without the need for costly external cofactors. For biocatalytic application, enzyme stability in the presence of organic solvents used for substrate solubilization has to be investigated, and process limitations due to low oxygen supply and the accumulation of the by‐product H2O2 must be addressed. In this study, we showed that the aryl‐alcohol oxidase PeAAO2 from Pleurotus eryngii P34 remained active and stable in the presence of up to 30% (v/v) various organic solvents and up to 500 mM H2O2. The potential of this biocatalyst was explored based on conversion of piperonyl alcohol to the fragrance compound piperonal. After reaction optimization, product titers of up to 245 mM were achieved within 3 h. Addition of catalase was imperative to re‐introduce O2 as co‐substrate into the reaction, thereby diminishing oxygen limitation. On a preparative scale, space‐time‐yield of 9.5 g/l/h was achieved and 244.6 mg piperonal (85% yield) with >99% purity were isolated via simple crystallization from n‐hexane extract. Under optimized reaction conditions four other substrates, cumic alcohol, 2‐thiophenemethanol, trans,trans‐2,4‐heptadienol and trans‐2‐cis‐6‐nonadienol, at concentrations of up to 300 mM were converted to the corresponding aldehydes within 20 h. Our results demonstrate that PeAAO2 is a versatile and promising biocatalyst for the production of valuable aldehydes.