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1. Protoglobin‐Catalyzed Formation of cis ‐Trifluoromethyl‐Substituted Cyclopropanes by Carbene Transfer

   https://doi.org/10.1002/anie.202208936  

   Schaus, Lucas; Das, Anuvab; Knight, Anders M.; Jimenez‐Osés, Gonzalo; Houk, K. N.; Garcia‐Borràs, Marc; Arnold, Frances H.; Huang, Xiongyi (December 2022, Angewandte Chemie International Edition)

   Abstract Trifluoromethyl‐substituted cyclopropanes (CF₃‐CPAs) constitute an important class of compounds for drug discovery. While several methods have been developed for synthesis oftrans‐CF₃‐CPAs, stereoselective production of correspondingcis‐diastereomers remains a formidable challenge. We report a biocatalyst for diastereo‐ and enantio‐selective synthesis ofcis‐CF₃‐CPAs with activity on a variety of alkenes. We found that an engineered protoglobin fromAeropyrnum pernix(ApePgb) can catalyze this unusual reaction at preparative scale with low‐to‐excellent yield (6–55 %) and enantioselectivity (17–99 % ee), depending on the substrate. Computational studies revealed that the steric environment in the active site of the protoglobin forced iron‐carbenoid and substrates to adopt a pro‐cisnear‐attack conformation. This work demonstrates the capability of enzyme catalysts to tackle challenging chemistry problems and provides a powerful means to expand the structural diversity of CF₃‐CPAs for drug discovery. 

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2. Synthesis and crystal structure of a bench-stable pyridinium ketene hemiaminal: 1-(1-ethoxyethenyl)-2-[methyl(phenyl)amino]pyridin-1-ium trifluoromethanesulfonate

   https://doi.org/10.1107/S2056989023005741  

   Krevlin, Z; Bote, I; Crespo, M; Lam, C; McMillen, C; Majireck, M (August 2023, Acta Crystallographica Section E Crystallographic Communications)

   The novel bench-stableN-quaternized keteneN,O-acetal, C₁₆H₁₉N₂O⁺·CF₃O₃S⁻, was synthesized and its structure determined. The title compound is a rare example of a pyridinium ketene hemiaminal for which a crystal structure has been determined, joining the 2-chloro-1-(1-ethyoxyethenyl)pyridin-1-ium trifluoromethanesulfonate salt from which it was synthesized. The cationic species of the title compound can be defined by three individually planar fragments assembling into a non-coplanar cation. The phenyl substituent extending from the amino nitrogen atom and the ethyoxyvinyl substituent extending from the pyridine N atom are oriented on the same side of the molecule and maintain the closest coplanar relationship of the three fragments. Supramolecular interactions are dominated by C—H...O interactions from the cation to the SO₃side of the trifluoromethanesulfonate anion, forming a two-dimensional substructure. 

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3. Selective Synthesis using ETFBO: A New Strategy for the Preparation of Hexahydro‐1 H ‐pyrrolo[1,2‐ c ]imidazol‐1‐one.

   https://doi.org/10.1002/ajoc.202300318  

   Faillace, Martín S; Ceballos, Noelia M; Shustova, Natalia B; Peláez, Walter J (August 2023, Asian Journal of Organic Chemistry)

   Abstract In this work, we report the regiospecific and stereoselective synthesis of novel pyrrolo thioxoimidazolidinones with promising biological activities due to the inherent pharmaceutical properties of thioxoimidazolidinone core. The reaction of different thioxoimidazolidinones withtrans‐4‐ethoxy‐1,1,1‐trifluorobut‐3‐en‐2‐one (ETFBO) yields bicyclic 1,3‐diaza heterocycles bearing the trifluoromethyl (CF₃) moiety. Our investigation involved both depth experimental analysis and theoretical calculations to fathom out the mode of reaction of this building block and elucidate the underlying mechanism operating for the observed reactions. Remarkably, this unusual mechanism retained the ethanol moiety from the building block in the final products, deviating from conventional nucleophilic reactions reported in the literature. 

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4. Electrochemical transformations catalyzed by cytochrome P450s and peroxidases

   https://doi.org/10.1039/D3CS00461A  

   Kumar, Neeraj; He, Jie; Rusling, James F. (July 2023, Chemical Society Reviews)

   Cytochrome P450s (Cyt P450s) and peroxidases are enzymes featuring iron heme cofactors that have wide applicability as biocatalysts in chemical syntheses. Cyt P450s are a family of monooxygenases that oxidize fatty acids, steroids, and xenobiotics, synthesize hormones, and convert drugs and other chemicals to metabolites. Peroxidases are involved in breaking down hydrogen peroxide and can oxidize organic compounds during this process. Both heme-containing enzymes utilize active FeIV[double bond, length as m-dash]O intermediates to oxidize reactants. By incorporating these enzymes in stable thin films on electrodes, Cyt P450s and peroxidases can accept electrons from an electrode, albeit by different mechanisms, and catalyze organic transformations in a feasible and cost-effective way. This is an advantageous approach, often called bioelectrocatalysis, compared to their biological pathways in solution that require expensive biochemical reductants such as NADPH or additional enzymes to recycle NADPH for Cyt P450s. Bioelectrocatalysis also serves as an ex situ platform to investigate metabolism of drugs and bio-relevant chemicals. In this paper we review biocatalytic electrochemical reactions using Cyt P450s including C–H activation, S-oxidation, epoxidation, N-hydroxylation, and oxidative N-, and O-dealkylation; as well as reactions catalyzed by peroxidases including synthetically important oxidations of organic compounds. Design aspects of these bioelectrocatalytic reactions are presented and discussed, including enzyme film formation on electrodes, temperature, pH, solvents, and activation of the enzymes. Finally, we discuss challenges and future perspective of these two important bioelectrocatalytic systems. 

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5. Metal-Ligand Tautomerism, Electron-Transfer, and C(sp3)-H Activation by a 4 Pyridinyl-Pincer Iridium Hydride Complex

   https://doi.org/10.26434/chemrxiv-2023-8sbll-v2  

   Bhatti, Tariq; Kumar, Akshai; Parihar, Ashish; Emge, Thomas; Hasanayn, Faraj; Goldman, Alan (March 2023, ChemRxiv)

   The para-N-pyridyl-based PCP pincer ligand 3,5-bis(di-tert-butylphosphinomethyl)-2,6-dimethylpyridine (pN-tBuPCP-H) was synthesized and metalated to give the iridium complex (pN tBuPCP)IrHCl (2-H). In marked contrast with its phenyl-based congeners (tBuPCP)IrHCl and derivatives, 2-H is highly air sensitive and reacts with oxidants such as ferrocenium, trityl cation, and benzoquinone. These oxidations ultimately lead to intramolecular activation of a phosphino-t-butyl C(sp3)-H bond and cyclometalation. Considering the greater electronegativity of N than C, 2-H is expected to be less easily oxidized than simple PCP derivatives; DFT calculations of direct one-electron oxidations are in good agreement with this expectation. However, 2-H is calculated to undergo metal-ligand-proton tautomerism (MLPT) to give an N-protonated complex that can be described with resonance forms representing a zwitterionic complex (negative charge on Ir) and a p-N-pyridylidene (remote NHC) Ir(I) complex. One-electron oxidation of this tautomer is calculated to be dramatically more favorable than direct oxidation of 2-H (G° = 31.3 kcal/mol). The resulting Ir(II) oxidation product is easily deprotonated to give metalloradical 2• which is observed by NMR spectroscopy. 2• can be further oxidized to give cationic Ir(III) complex, 2+, which can oxidatively add a phosphino-t butyl C-H bond, and undergo deprotonation to give the observed cyclometalated product. DFT calculations indicate that less sterically hindered complexes would preferentially undergo intermolecular addition of C(sp3)-H bonds, for example, of n alkanes. The resulting iridium alkyl complexes could undergo facile -H elimination to afford olefin, thereby completing a catalytic cycle for alkane dehydrogenation that is driven by one-electron oxidation and deprotonation, enabled by MLPT. 

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