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

Abstract

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: CO 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, CO 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 CO 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.

Fine Bubble‐based CO2 Capture Mediated by Triethanolamine Coupled to Whole Cell Biotransformation

“…The biocatalytic carboxylation of catechol is known to suffer from unfavorable thermodynamics . Up to 12 % conversion is achievable in a typical biotransformation, when applying 10 mM catechol with 1 M KHCO 3 at 30 °C . This challenge can be addressed by the application of amines such as TEA.…”

“…This challenge can be addressed by the application of amines such as TEA. Pesci et al have already shown that TEA acts as a CO 2 mediator with the concentration of 1 M, which shifted successfully the reaction equilibrium towards the carboxylation . In respect to this, TEA was chosen as a suitable model system in which the effect of higher TEA concentrations was in the focus of this study.…”

“…The key aspect of the amine‐mediated biocatalytic carboxylation of phenols by decarboxylases is the utilization of CO 2 . In designing an efficient process involving triethanolamine, the gassing plays a major role .…”

“…Due to the worldwide efforts to reduce greenhouse gas emission, the optimization of existing and development of new technologies for reduction and recycling of CO 2 is of major interest , . The carbon capture technology that uses amines such as triethanolamine (TEA) was shown to be compatible with the enzymatic carboxylation, which is competitive to the Kolbe‐Schmitt reaction . Here, the bound CO 2 , in the form of hydrogen carbonate, is consumed as a sustainable carbon source for the synthesis of carboxylated phenolics (Fig.…”

Carboxylation of Hydroxyaromatic Compounds with HCO3− by Enzyme Catalysis: Recent Advances Open the Perspective for Valorization of Lignin-Derived Aromatics

“…In view of industrial applications, Kara and coworkers [67] suggested the use of CO 2 in the carboxylation reactions instead of KHCO 3 . In situ formation of the [HCO 3 − ][ + HNR 3 ] salt was favored in the presence of tertiary amines under a CO 2 atmosphere.…”