Cobalamin-Dependent Apparent Intramolecular Methyl Transfer for Biocatalytic Constitutional Isomerization of Catechol Monomethyl Ethers.

Isomerization is a fundamental reaction in chemistry. However, isomerization of phenyl methyl ethers has not been described yet. Using a cobalamin-dependent methyl transferase, a reversible shuttle concept was investigated for isomerization of catechol monomethyl ethers. The methyl ether of substituted catechol derivatives was successfully transferred onto the adjacent hydroxy moiety. For instance, the cobalamin-dependent biocatalyst transformed isovanillin to its regioisomer vanillin with significant regioisomeric excess (68% vanillin). To the best of our knowledge, isomerization by methyl transfer employing a methyl transferase has not been reported before.

Asymmetric Synthesis of (R)-1-Alkyl-Substituted Tetrahydro-ß-carbolines Catalyzed by Strictosidine Synthases.

Stereoselective methods for the synthesis of tetrahydro-ß-carbolines are of significant interest due to the broad spectrum of biological activity of the target molecules. In the plant kingdom, strictosidine synthases catalyze the C-C coupling through a Pictet-Spengler reaction of tryptamine and secologanin to exclusively form the (S)-configured tetrahydro-ß-carboline (S)-strictosidine. Investigating the biocatalytic Pictet-Spengler reaction of tryptamine with small-molecular-weight aliphatic aldehydes revealed that the strictosidine synthases give unexpectedly access to the (R)-configured product. Developing an efficient expression method for the enzyme allowed the preparative transformation of various aldehydes, giving the products with up to >98 % ee. With this tool in hand, a chemoenzymatic two-step synthesis of (R)-harmicine was achieved, giving (R)-harmicine in 67 % overall yield in optically pure form.

Heterogeneous Pd catalysts as emulsifiers in Pickering emulsions for integrated multistep synthesis in flow chemistry.

Within the "compartmentalised smart factory" approach of the ONE-FLOW project the implementation of different catalysts in "compartments" provided by Pickering emulsions and their application in continuous flow is targeted. We present here the development of heterogeneous Pd catalysts that are ready to be used in combination with biocatalysts for catalytic cascade synthesis of active pharmaceutical ingredients (APIs). In particular, we focus on the application of the catalytic systems for Suzuki-Miyaura cross-coupling reactions, which is the key step in the synthesis of the targeted APIs valsartan and sacubitril. An immobilised enzyme will accomplish the final product formation via hydrolysis. In order to create a large interfacial area for the catalytic reactions and to keep the reagents separated until required, the catalyst particles are used to stabilise Pickering emulsions of oil and water. A set of Ce-Sn-Pd oxides with the molecular formula Ce0.99-x Sn x Pd0.01O2-δ (x = 0-0.99) has been prepared utilising a simple single-step solution combustion method. The high applicability of the catalysts for different functional groups and their minimal leaching behaviour is demonstrated with various Suzuki-Miyaura cross-coupling reactions in batch as well as in continuous flow employing the so-called "plug & play reactor". Finally, we demonstrate the use of these particles as the sole emulsifier of oil-water emulsions for a range of oils.

Functional tuning of the catalytic residue pKa in a de novo designed esterase.

AlleyCatE is a de novo designed esterase that can be allosterically regulated by calcium ions. This artificial enzyme has been shown to hydrolyze p-nitrophenyl acetate (pNPA) and 4-nitrophenyl-(2-phenyl)-propanoate (pNPP) with high catalytic efficiency. AlleyCatE was created by introducing a single-histidine residue (His144 ) into a hydrophobic pocket of calmodulin. In this work, we explore the determinants of catalytic properties of AlleyCatE. We obtained the pKa value of the catalytic histidine using experimental measurements by NMR and pH rate profile and compared these values to those predicted from electrostatics pKa calculations (from both empirical and continuum electrostatics calculations). Surprisingly, the pKa value of the catalytic histidine inside the hydrophobic pocket of calmodulin is elevated as compared to the model compound pKa value of this residue in water. We determined that a short-range favorable interaction with Glu127 contributes to the elevated pKa of His144 . We have rationally modulated local electrostatic potential in AlleyCatE to decrease the pKa of its active nucleophile, His144 , by 0.7 units. As a direct result of the decrease in the His144 pKa value, catalytic efficiency of the enzyme increased by 45% at pH 6. This work shows that a series of simple NMR experiments that can be performed using low field spectrometers, combined with straightforward computational analysis, provide rapid and accurate guidance to rationally improve catalytic efficiency of histidine-promoted catalysis. Proteins 2017; 85:1656-1665. © 2017 Wiley Periodicals, Inc.

Asymmetric Biocatalytic Amination of Ketones at the Expense of NH3 and Molecular Hydrogen.

A biocatalytic system is presented for the stereoselective amination of ketones at the expense of NH3 and molecular hydrogen. By using a NAD(+)-reducing hydrogenase, an alanine dehydrogenase, and a suitable ω-transaminase, the R- as well as the S-enantiomer of various amines could be prepared with up to >99% ee and 98% conversion.