Comprehensive insights into the production of long chain aliphatic aldehydes using a copper-radical alcohol oxidase as biocatalyst

Abstract

The oxidation of alcohols is a cornerstone reaction in chemistry, notably in the flavor and fragrance industry where long-chain aliphatic aldehydes are major odorant compounds. In a context where greener alternatives are sought after, biocatalysis holds many promises. Here, we investigated the ability of the alcohol oxidase from Colletotrichum graminicola (CgrAlcOx)—an organic cofactor-free enzyme belonging to the copper-radical oxidase (CRO) class—to convert industrially relevant long-chain aliphatic alcohols. CgrAlcOx is a competent catalyst for the conversion of octan-1-ol when supported by the accessory enzymes peroxidase and catalase. Detailed examination of the products revealed the occurrence of an overoxidation step leading to the production of carboxylic acid for some aliphatic aldehydes and benzaldehyde derivatives. The partition between aldehyde and acid products varied upon substrate properties (chain length and propensity to form geminal-diols) and enzyme specificity and could be tuned by controlling the reaction conditions. In silico analyses suggested an inhibitory binding mode of long-chain aliphatic geminal-diols and a substrate-induced fit mechanism for a benzyl alcohol derivative. By demonstrating their natural ability to perform long-chain aliphatic alcohol oxidation, the present study establishes the potential of fungal CRO-AlcOx as promising candidates for the green production of flavor and fragrance compounds.