Johannes Gross

Regioselective Enzymatic Carboxylation of Phenols and Hydroxystyrene Derivatives

The enzymatic carboxylation of phenol and styrene derivatives using (de)carboxylases in carbonate buffer proceeded in a highly regioselective fashion: Benzoic acid (de)carboxylases selectively formed o-hydroxybenzoic acid derivatives, phenolic acid (de)carboxylases selectively acted at the β-carbon atom of styrenes forming (E)-cinnamic acids.

An Exceptionally DMSO‐Tolerant Alcohol Dehydrogenase for the Stereoselective Reduction of Ketones

A novel short-chain alcohol dehydrogenase from Paracoccus pantotrophus DSM 11072, which is applicable for hydrogen transfer, has been identified, cloned, and overexpressed in E. coli. The enzyme stereoselectively reduces several ketones in a sustainable substrate-coupled approach using 2-propanol (5% v/v) as hydrogen donor. The enzyme maintained its activity in organic co-solvents in biphasic as well as monophasic systems and was even active in micro-aqueous media (1% v/v aqueous buffer). In general, a higher conversion was observed at higher log P values of the solvent, however, DMSO, which exhibits the lowest log P value of all solvents investigated, was not only tolerated but led to a higher conversion and relative activity (110-210%). For example, the conversion after 24 h in 15% v/v DMSO was double that for the reaction performed in buffer. This tolerance to DMSO may be attributed to the ability of the wild-type strain to adapt and grow in media with high sulfur content.

Regioselective Enzymatic β-Carboxylation of para-Hydroxy- styrene Derivatives Catalyzed by Phenolic Acid Decarboxylases

Abstract We report on a ‘green’ method for the utilization of carbon dioxide as C1 unit for the regioselective synthesis of (E)‐cinnamic acids via regioselective enzymatic carboxylation of para‐hydroxystyrenes. Phenolic acid decarboxylases from bacterial sources catalyzed the β‐carboxylation of para‐hydroxystyrene derivatives with excellent regio‐ and (E/Z)‐stereoselectivity by exclusively acting at the β‐carbon atom of the C=C side chain to furnish the corresponding (E)‐cinnamic acid derivatives in up to 40% conversion at the expense of bicarbonate as carbon dioxide source. Studies on the substrate scope of this strategy are presented and a catalytic mechanism is proposed based on molecular modelling studies supported by mutagenesis of amino acid residues in the active site. WILEY-VCH

Regioselective ortho-carboxylation of phenols catalyzed by benzoic acid decarboxylases: a biocatalytic equivalent to the Kolbe–Schmitt reaction

The enzyme catalyzed carboxylation of electron-rich phenol derivatives employing recombinant benzoic acid decarboxylases at the expense of bicarbonate as CO2 source is reported. In contrast to the classic Kolbe–Schmitt reaction, the biocatalytic equivalent proceeded in a highly regioselective fashion exclusively at the ortho-position of the phenolic directing group in up to 80% conversion. Several enzymes were identified, which displayed a remarkably broad substrate scope encompassing alkyl, alkoxy, halo and amino-functionalities. Based on the crystal structure and molecular docking simulations, a mechanistic proposal for 2,6-dihydroxybenzoic acid decarboxylase is presented.

Aerobic oxidation of isosorbide and isomannide employing TEMPO/laccase

The oxidation of the renewable diols isosorbide and isomannide was successfully achieved using a TEMPO/laccase system. Furthermore, various TEMPO-derivatives were tested leading to conversions of up to >99% for the oxidation of isosorbide, isomannide, indanol and a halohydrin to the corresponding ketone.

Regio‐ and Enantioselective Sequential Dehalogenation of rac‐1,3‐Dibromobutane by Haloalkane Dehalogenase LinB

The hydrolytic dehalogenation of rac‐1,3‐dibromobutane catalyzed by the haloalkane dehalogenase LinB from Sphingobium japonicum UT26 proceeds in a sequential fashion: initial formation of intermediate haloalcohols followed by a second hydrolytic step to produce the final diol. Detailed investigation of the course of the reaction revealed favored nucleophilic displacement of the sec‐halogen in the first hydrolytic event with pronounced R enantioselectivity. The second hydrolysis step proceeded with a regioselectivity switch at the primary position, with preference for the S enantiomer. Because of complex competition between all eight possible reactions, intermediate haloalcohols formed with moderate to good ee ((S)‐4‐bromobutan‐2‐ol: up to 87 %). Similarly, (S)‐butane‐1,3‐diol was formed at a maximum ee of 35 % before full hydrolysis furnished the racemic diol product.