Multi-step biocatalytic depolymerization of lignin
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Lignin is a biomass-derived aromatic polymer that has been identified as a potential renewable source of aromatic chemicals and other valuable compounds. The valorization of lignin, however, represents a great challenge due to its high inherent functionalization, what compromises the identification of chemical routes for its selective depolymerization. In this work, an in vitro biocatalytic depolymerization process is presented, that was applied to lignin samples obtained from beech wood through OrganoCat pretreatment, resulting in a mixture of lignin-derived aromatic monomers. The reported biocracking route comprises first a laccase-mediator system to specifically oxidize the Cα hydroxyl group in the β-O-4 structure of lignin. Subsequently, selective β-O-4 ether cleavage of the oxidized β-O-4 linkages is achieved with β-etherases and a glutathione lyase. The combined enzymatic approach yielded an oily fraction of low-molecular-mass aromatic compounds, comprising coniferylaldehyde and other guaiacyl and syringyl units, as well as some larger (soluble) fractions. Upon further optimization, the reported biocatalytic route may open a valuable approach for lignin processing and valorization under mild reaction conditions.
KeywordsBiomass conversion Lignin Ether bond cleavage β-etherase Laccase-mediator system
We thank Dr. Jakob Mottweiler and Prof. Carsten Bolm (Institute of Organic Chemistry, RWTH Aachen University) for the generous provision of lignin model substrates 1 + 2. Additionally, we thank Dr. Christoph Räuber (Institute of Organic Chemistry, RWTH Aachen University) for the preparation of 2D NMR figures.
This work was performed as part of the Cluster of Excellence “Tailor-Made Fuels from Biomass” [grant EXC 236], which is funded by the Excellence Initiative of the German Research Foundation to promote science and research at German universities.
Compliance with ethical standards
Conflict of interest
The authors declare that they have no competing interests.
This article does not contain any studies with human participants or animals performed by any of the authors.
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