The utilization of CO2 as a carbon source for organic synthesis meets the urgent demand for more sustainability in the production of chemicals. Herein, we report on the enzyme‐catalyzed para‐carboxylation of catechols, employing 3,4‐dihydroxybenzoic acid decarboxylases (AroY) that belong to the UbiD enzyme family. Crystal structures and accompanying solution data confirmed that AroY utilizes the recently discovered prenylated FMN (prFMN) cofactor, and requires oxidative maturation to form the catalytically competent prFMNiminium species. This study reports on the in vitro reconstitution and activation of a prFMN‐dependent enzyme that is capable of directly carboxylating aromatic catechol substrates under ambient conditions. A reaction mechanism for the reversible decarboxylation involving an intermediate with a single covalent bond between a quinoid adduct and cofactor is proposed, which is distinct from the mechanism of prFMN‐associated 1,3‐dipolar cycloadditions in related enzymes.

Dwindling petroleum feedstocks and increased CO(2)-concentrations in the atmosphere currently open the concept of using CO(2) as raw material for the synthesis of well-defined organic compounds. In parallel to recent advances in the chemical CO(2)-fixation, enzymatic (biocatalytic) carboxylation is currently being investigated at an increased pace. On the one hand, this critical review provides a concise overview on highly specific biosynthetic pathways for CO(2)-fixation and, on the other hand, a summary of biodegradation (detoxification) processes involving enzymes which possess relaxed substrate specificities, which allow their application for the regioselective carboxylation of organic substrates to furnish the corresponding carboxylic acids (145 references).

The stereoselective addition of water across C = C bonds transforms prochiral alkenes to nonracemic alcohols and represents a major challenge in synthetic organic chemistry. In general, alkene hydration is an equilibrium reaction slightly favoring the alcohol side in 1,4-additions and somewhat disfavored on isolated C = C bonds. [1] Acid-catalyzed alkene hydration, which follows the rule of Markovnikov, usually proceeds with low regioselectivity and is often accompanied by rearrangement yielding regioisomeric product mixtures; with a few exceptions, [2] no generally applicable protocol has been developed so far. Likewise, base-catalyzed 1,4-addition of water to a,b-unsaturated (Michael) acceptors is impeded by the poor nucleophilicity of water. [3] Overall, an astonishingly limited number of asymmetric alkene-hydration protocols are reported: 1) The stereoselective hydration of a,b-unsaturated carboxylic acids by using a heterobimetallic chiral biopolymer (wool-Pd II -Co II ) catalyst furnished bhydroxy carboxylic acids in high optical purities, [4] and 2) the asymmetric syn-hydration of a,b-unsaturated acyl imidazoles while applying a DNA-based Cu II catalyst yielded b-hydroxy carbonyl compounds with moderate ee values. [5] To compensate for the insufficient nucleophilicity of water, indirect methods using strong nucleophiles (alkoxides, Nsilyloxycarbamates, oximes, silicon and boron reagents) have been employed, which require cumbersome reductive or oxidative follow-up chemistry to yield the desired b-hydroxy carbonyl compounds. [3]