Biocatalytic production of 3-hydroxypropionic acid precursors using a regioselective Baeyer-Villiger monooxygenase

Baeyer-Villiger monooxygenases (BVMOs) are versatile biocatalysts that catalyse the oxidation of ketones to esters with high regio- and enantioselectivity, operating under mild reaction conditions while reducing hazardous waste. Some BVMOs can convert cellulose-derived alkyl levulinates to 3-acetoxypropionates (3-APs), which are key intermediates in the production of 3-hydroxypropionic acid (3-HP), a versatile building block chemical. In this study, a BVMO from Acinetobacter radioresistens (Ar-BVMO) was tested as a biocatalyst for the conversion of three marketed alkyl levulinates: methyl, ethyl and butyl levulinate. The enzyme showed 4-fold higher catalytic efficiency (k_cat/K_M) and enhanced regioselectivity for the desired 3-AP product (4:1 ratio) when using butyl levulinate as a substrate. Escherichia coli whole-cells over-expressing Ar-BVMO were exploited to increase the product yield, achieving 85% conversion in 9 h. To further improve the sustainability of this biotransformation, butyl levulinate was obtained via microwave-assisted alcoholysis of pulp, a renewable cellulose feedstock, achieving 92.7% selectivity. Despite challenges posed by poor solubility of the resulting mixture in aqueous environment, Ar-BVMO in cell lysates was able to fully convert butyl levulinate within 24 h, efficiently producing 3-HP precursors without additional purification steps. These findings highlight the feasibility of this chemoenzymatic approach to convert cellulose-based raw materials to platform chemicals.