3 years ago

Amine-Mediated Enzymatic Carboxylation of Phenols Using CO2 as Substrate Increases Equilibrium Conversions and Reaction Rates

Amine-Mediated Enzymatic Carboxylation of Phenols Using CO2 as Substrate Increases Equilibrium Conversions and Reaction Rates
Andreas Liese, Selin Kara, Lorenzo Pesci, Pavel Gurikov
A variety of strategies is applied to alleviate thermodynamic and kinetic limitations in biocatalytic carboxylation of metabolites in vivo. A key feature to consider in enzymatic carboxylations is the nature of the cosubstrate: CO2 or its hydrated form, bicarbonate. The substrate binding and activation mechanism determine what the actual carboxylation agent is. Dihydroxybenzoic acid (de)carboxylases catalyze the reversible regio-selective ortho-(de)carboxylation of phenolics. These enzymes have attracted considerable attention in the last 10 years due to their potential in substituting harsh conditions typical of chemical carboxylations (100–200 °C, 5–100 bar) with, ideally, greener ones (20–40 °C, 1 bar). They are reported to use bicarbonate as substrate, needed in large excess to overcome thermodynamic and kinetic limitations. Therefore, CO2 can be used as substrate by these enzymes only if it is converted into bicarbonate in situ. In this contribution, we report the simultaneous amine-mediated conversion of CO2 into bicarbonate and the ortho-carboxylation of different phenolic molecules catalyzed by 2,3-dihydroxybenzoic acid (de)carboxylase from Aspergillus oryzae. Our results show that under the newly developed conditions a significant thermodynamic (up to twofold increase in conversion) and kinetic improvement (up to approx. fivefold increase in rate) of the biocatalytic carboxylation of catechol is achieved. Dihydroxybenzoic acid (de)carboxylases catalyze the reversible regio-selective ortho-(de)carboxylation of phenolics using bicarbonate as a carboxylating agent. However, due to the intrinsic thermodynamic constraints, enzymatic approaches necessitate a large excess of bicarbonate. In this study, the authors establish simultaneous amine-mediated conversion of carbon dioxide into bicarbonate and the ortho-carboxylation of different phenols catalyzed by 2,3-dihydroxybenzoic acid (de)carboxylase from Aspergillus oryzae. This work demonstrates that equilibrium conversion values and reaction rates are increased via in situ pre-conversion of carbon dioxide to bicarbonate using amines for the enzymatic carboxylation of catechol.

Publisher URL: http://onlinelibrary.wiley.com/resolve/doi

DOI: 10.1002/biot.201700332

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