Abstract
Broad substrate tolerance and excellent regioselectivity, as well as independence from sensitive cofactors have established benzoic acid decarboxylases from microbial sources as efficient biocatalysts. Robustness under process conditions makes them particularly attractive for preparative‐scale applications. The divalent metal‐dependent enzymes are capable of catalyzing the reversible non‐oxidative (de)carboxylation of a variety of electron‐rich (hetero)aromatic substrates analogously to the chemical Kolbe‐Schmitt reaction. Elemental mass spectrometry supported by crystal structure elucidation and quantum chemical calculations verified the presence of a catalytically relevant Mg2+ complexed in the active site of 2,3‐dihydroxybenoic acid decarboxylase from Aspergillus oryzae (2,3‐DHBD_Ao). This unique example with respect to the nature of the metal is in contrast to mechanistically related decarboxylases, which generally have Zn2+ or Mn2+ as the catalytically active metal.
Highlights
Broad substrate tolerance and excellent regioselectivity, as well as independence from sensitive cofactors have established benzoic acid decarboxylases from microbial sources as efficient biocatalysts
I) ortho-carboxylation of phenols in analogy to the KolbeSchmitt process[3] is catalyzed by metal-dependent o-benzoic acid decarboxylases (o-BDs), which excel due to their high stability, and by an unusually broad substrate portfolio.[6] ii) Side-chain carboxylation at the vinyl group of phydroxystyrenes, for which no chemical protocol exists, is feasible with metal-independent phenolic acid decarboxylases.[7] iii) More recently, the (ATP-independent) pcarboxylation of phenols and the decarboxylation of electronrich heterocyclic and acrylic acid derivatives was shown to be catalyzed by prenylated FMN-dependent decarboxylases.[8]
We investigated the metal dependence of 2,3-dihydroxybenzoate decarboxylase from Aspergillus oryzae
Summary
Homepage: http://biocatalysis.uni-graz.at [+] These authors contributed to this work. I) ortho-carboxylation of phenols in analogy to the KolbeSchmitt process[3] is catalyzed by metal-dependent o-benzoic acid decarboxylases (o-BDs), which excel due to their high stability, and by an unusually broad substrate portfolio.[6] ii) Side-chain carboxylation at the vinyl group of phydroxystyrenes, for which no chemical protocol exists, is feasible with metal-independent phenolic acid decarboxylases.[7] iii) More recently, the (ATP-independent) pcarboxylation of phenols and the decarboxylation of electronrich heterocyclic and acrylic acid derivatives was shown to be catalyzed by prenylated FMN-dependent decarboxylases.[8] Some of these enzymes display a remarkable substrate acceptance, stability-problems of their prenylated. We investigated the metal dependence of 2,3-dihydroxybenzoate decarboxylase from Aspergillus oryzae (2,3-DHBD_Ao)[15] by determination of its crystal structure, metal ion analysis by inductively coupled plasma tandem mass spectrometry (ICPMS/MS) and the catalytic energy profile by quantum chemical calculations.
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