Sustainable Nonenantioselective Production and Stereochemical Characterization of the Lignin-Derived Chiral Building Block 3-Carboxymuconolactone.

To promote the comprehensive utilization of renewable lignocellulosicbiomass, a practical technology for the nonenantioselective production of 3-carboxymuconolactone (3CML), a lignin-derived chiral building block, is presented. Although an engineered Pseudomonas putida strain with plasmids containing bacterial and fungal genes was previously used to convert lignin-derived aromatic compounds into optically pure 4S-3CML, using the enantiomeric pair 4S-3CML and 4R-3CML as polymer building blocks in appropriate blending ratios can be expected to afford novel materials such as polylactic acid with tunable physical properties for targeted applications. Therefore, in this study, P. putida was engineered to convert vanillic acid, the major aromatic compound derived from lignin, into 3-carboxy-cis,cis-muconate, which was then chemically converted into racemic 3CML under acidic conditions. Using a chiral high performance liquid chromatography-circulardichroism system, racemic 3CML was stereochemically characterized on the basis of the enantiomers. A one-pot process for the production of racemic 3CML was established by combining fed-batch fermentation with subsequent acidic treatment using a jar fermenter, affording 6.6 g/L 4S-3CML and 7.2 g/L 4R-3CML in a high yield of 93.1%. The developed process can be consistently performed at 28°C without requiring pressure or metal reagents and allows using a reduced volume of solvent, offering clear advantages for industrial applications.