Cytochrome P450 catalyzed oxidative hydroxylation of achiral organic compounds with simultaneous creation of two chirality centers in a single C-H activation step

Molecular Basis for Chemoselectivity Control in Oxidations of Internal Aryl-Alkenes Catalyzed by Laboratory Evolved P450s

P450 enzymes naturally perform selective hydroxylations and epoxidations of unfunctionalized hydrocarbon substrates, among other reactions. The adaptation of P450 enzymes to a particular oxidative reaction involving alkenes is of great interest for the design of new synthetically useful biocatalysts. However, the mechanism that these enzymes utilize to precisely modulate the chemoselectivity and distinguishing between competing alkene double bond epoxidations and allylic C-H hydroxylations is sometimes not clear, which hampers the rational design of specific biocatalysts. In a previous work, a P450 from Labrenzia aggregata (P450LA1) was engineered in the laboratory using directed evolution to catalyze the direct oxidation of trans-β-methylstyrene to phenylacetone. The final variant, KS, was able to overcome the intrinsic preference for alkene epoxidation to directly generate a ketone product via the formation of a highly reactive carbocation intermediate. Here, additional library screening along this evolutionary lineage permitted to serendipitously detect a mutation that overcomes epoxidation and carbonyl formation by exhibiting a large selectivity of 94 % towards allylic C-H hydroxylation. A multiscalar computational methodology was applied to reveal the molecular basis towards this hydroxylation preference. Enzyme modelling suggests that introduction of a bulky substitution dramatically changes the accessible conformations of the substrate in the active site, thus modifying the enzymatic selectivity towards terminal hydroxylation and avoiding the competing epoxidation pathway, which is sterically hindered.

Photo-Induced Generation of Oxygenated Quaternary Centers via EnT Enabled Singlet O2 Addition to C3-Maleimidated Quinoxaline: A Reagent-Less Approach

Demonstrated here is an external photo-sensitizer-free (auto-sensitized) singlet oxygen-enabled solvent-dependent tertiary hydroxylation and aryl-alkyl spiro-etherification of C3-maleimidated quinoxalines. Such "reagent-less" photo-oxygenation at Csp3-H and etherification involving Csp3-H/Csp2-H are unparalleled. Possibly, the highly π-conjugated N-H tautomer allows the substrate to get excited by irradiation, and subsequently, it attains the triplet state via ISC. This excited triplet-state sensitized molecule then transfers its energy to a triplet-state oxygen (3O2) generating reactive singlet oxygen (1O2) for hydroxylation and spirocyclization depending on the solvent used. In HFIP, the generated alkoxy radical accepts a proton via HAT giving hydroxylated product. In contrast, in an aprotic PhCl it underwent a radical addition at the ortho-position of the C2 aryl to provide spiro-ether. An unprecedented orthogonal spiro-etherification was observed via the displacement of o-substitutents for ortho (-OEt, -OMe, -F, -Cl, -Br) substituted substrates. The order of ipso substitution follows the trend -OMe>-OEt>-F>-H>-Cl>-Br. Both these oxygenation reactions can be carried out with nearly equal ease using direct sunlight without the requirement of any elaborate reaction setup. Demonstration of large-scale synthesis and a few interesting transformations have also been realized. Furthermore, several insightful control experiments and quantum chemical computations were performed to unravel the mechanism.

Choose Your Own Adventure: A Comprehensive Database of Reactions Catalyzed by Cytochrome P450 BM3 Variants

Cytochrome P450 BM3 monooxygenase is the topic of extensive research as many researchers have evolved this enzyme to generate a variety of products. However, the abundance of information on increasingly diversified variants of P450 BM3 that catalyze a broad array of chemistry is not in a format that enables easy extraction and interpretation. We present a database that categorizes variants by their catalyzed reactions and includes details about substrates to provide reaction context. This database of >1500 P450 BM3 variants is downloadable and machine-readable and includes instructions to maximize ease of gathering information. The database allows rapid identification of commonly reported substitutions, aiding researchers who are unfamiliar with the enzyme in identifying starting points for enzyme engineering. For those actively engaged in engineering P450 BM3, the database, along with this review, provides a powerful and user-friendly platform to understand, predict, and identify the attributes of P450 BM3 variants, encouraging the further engineering of this enzyme.

Theoretical study of the formation of metal-oxo species of the first transition series with the ligand 14-TMC: driving factors of the "Oxo Wall"

Terminal metal-oxo species of the early transition metal series are well known, whereas those for the late transition series are rare, and this is related to the "Oxo Wall". Here, we have undertaken a theoretical study on the formation of metal-oxo species from the metal hydroperoxo species of the 3d series (Cr, Mn, Fe, Co, Ni, and Cu) with the ligand 14-TMC (1,4,8,11-tetramethyl-1,4,8,11-tetraazacyclotetradecane) via O⋯O bond cleavage. DFT calculations reveal that the barrier for O⋯O bond cleavage is higher with the late transition metals (Co, Ni, and Cu) than the early transition metals (Cr, Mn, and Fe), and the formed late metal-oxo species are also thermodynamically less stable. The higher barrier may be due to electronic repulsion because of the pairing of d electrons. In the late transition metal series, the electron goes into an antibonding orbital, which decreases the bond order and hence decreases the possibility of metal-oxo formation. Computed structural parameters and spin densities suggest that valence tautomerism occurs in the late transition metal-oxo species which remain as a metal-oxyl. Our findings support the concept of the "Oxo Wall".

Fishing for Catalysis: Experimental Approaches to Narrowing Search Space in Directed Evolution of Enzymes

Directed evolution has transformed protein engineering offering a path to rapid improvement of protein properties. Yet, in practice it is limited by the hyper-astronomic protein sequence search space, and approaches to identify mutagenic hot spots, i.e., locations where mutations are most likely to have a productive impact, are needed. In this perspective, we categorize and discuss recent progress in the experimental approaches (broadly defined as structural, bioinformatic, and dynamic) to hot spot identification. Recent successes in harnessing protein dynamics and machine learning approaches provide new opportunities for the field and will undoubtedly help directed evolution reach its full potential.

Highly Enantioselective Catalytic Lactonization at Nonactivated Primary and Secondary γ-C-H Bonds

Chiral oxygenated aliphatic moieties are recurrent in biological and pharmaceutically relevant molecules and constitute one of the most versatile types of functionalities for further elaboration. Herein we report a protocol for straightforward and general access to chiral γ-lactones via enantioselective oxidation of strong nonactivated primary and secondary C(sp3)-H bonds in readily available carboxylic acids. The key enabling aspect is the use of robust sterically encumbered manganese catalysts that provide outstanding enantioselectivities (up to >99.9%) and yields (up to 96%) employing hydrogen peroxide as the oxidant. The resulting γ-lactones are of immediate interest for the preparation of inter alia natural products and recyclable polymeric materials.

C-H Bonds as Functional Groups: Simultaneous Generation of Multiple Stereocenters by Enantioselective Hydroxylation at Unactivated Tertiary C-H Bonds

Enantioselective C-H oxidation is a standing chemical challenge foreseen as a powerful tool to transform readily available organic molecules into precious oxygenated building blocks. Here, we describe a catalytic enantioselective hydroxylation of tertiary C-H bonds in cyclohexane scaffolds with H2O2, an evolved manganese catalyst that provides structural complementary to the substrate similarly to the lock-and-key recognition operating in enzymatic active sites. Theoretical calculations unveil that enantioselectivity is governed by the precise fitting of the substrate scaffold into the catalytic site, through a network of complementary weak non-covalent interactions. Stereoretentive C(sp3)-H hydroxylation results in a single-step generation of multiple stereogenic centers (up to 4) that can be orthogonally manipulated by conventional methods providing rapid access, from a single precursor to a variety of chiral scaffolds.

Enantioselective Single and Dual α-C-H Bond Functionalization of Cyclic Amines via Enzymatic Carbene Transfer

Cyclic amines are ubiquitous structural motifs found in pharmaceuticals and biologically active natural products, making methods for their elaboration via direct C-H functionalization of considerable synthetic value. Herein, we report the development of an iron-based biocatalytic strategy for enantioselective α-C-H functionalization of pyrrolidines and other saturated N-heterocycles via a carbene transfer reaction with diazoacetone. Currently unreported for organometallic catalysts, this transformation can be accomplished in high yields, high catalytic activity, and high stereoselectivity (up to 99:1 e.r. and 20,350 TON) using engineered variants of cytochrome P450 CYP119 from Sulfolobus solfataricus. This methodology was further extended to enable enantioselective α-C-H functionalization in the presence of ethyl diazoacetate as carbene donor (up to 96:4 e.r. and 18,270 TON), and the two strategies were combined to achieve a one-pot as well as a tandem dual C-H functionalization of a cyclic amine substrate with enzyme-controlled diastereo- and enantiodivergent selectivity. This biocatalytic approach is amenable to gram-scale synthesis and can be applied to drug scaffolds for late-stage C-H functionalization. This work provides an efficient and tunable method for direct asymmetric α-C-H functionalization of saturated N-heterocycles, which should offer new opportunities for the synthesis, discovery, and optimization of bioactive molecules.

The Synthetic Approaches to 1,2-Chlorohydrins

This short review highlights the hitherto realised synthetic approaches towards organic 1,2-chlorohydrins by functionalisation of alkenes (i.e., 1,2-chlorohydroxylation), which is the most prominent access route to this class of compounds. Also, some other synthetic approaches involving the reduction of α-chloroketones, the epoxide opening ring by chloride anions and the utilisation of Grignard reagents for the synthesis of these compounds and chlorination of allylic alcohols are highlighted. Finally, enzymatic reactions for the formation of chlorohydrins are briefly summarised followed by a short view on natural products containing this moiety.

1 Introduction

2 Applications for the Synthesis of 1,2-Chlorohydrins

2.1 Chlorohydroxylation of Alkenes

2.2 Reduction of Chloroketones

2.3 Metalorganic Reagents

2.4 Epoxide Ring Opening

2.5 Chlorination of Allylic Alcohols

2.6 Biochemical Methods

2.7 Selected Applications in Natural Product Total Synthesis

3 Conclusion

Synthesis and Characterization of Bimetallic Nanoclusters Stabilized by Chiral and Achiral Polyvinylpyrrolidinones. Catalytic C(sp3)-H Oxidation

Second-generation chiral-substituted poly-N-vinylpyrrolidinones (CSPVPs) (-)-1R and (+)-1S were synthesized by free-radical polymerization of (3aR,6aR)- and (3aS,6aS)-5-ethenyl-tetrahydro-2,2-dimethyl-4H-1,3-dioxolo[4,5-c]pyrrol-4-one, respectively, using thermal and photochemical reactions. They were produced from respective d-isoascorbic acid and d-ribose. In addition, chiral polymer (-)-2 was also synthesized from the polymerization of (S)-3-(methoxymethoxy)-1-vinylpyrrolidin-2-one. Molecular weights of these chiral polymers were measured using HRMS, and the polymer chain tacticity was studied using ¹³C NMR spectroscopy. Chiral polymers (-)-1R, (+)-1S, and (-)-2 along with poly-N-vinylpyrrolidinone (PVP, MW 40K) were separately used in the stabilization of Cu/Au or Pd/Au nanoclusters. CD spectra of the bimetallic nanoclusters stabilized by (-)-1R and (+)-1S showed close to mirror-imaged CD absorption bands at wavelengths 200-300 nm, revealing that bimetallic nanoclusters' chiroptical responses are derived from chiral polymer-encapsulated nanomaterials. Chemo-, regio-, and stereo-selectivity was found in the catalytic C-H group oxidation reactions of complex bioactive natural products, such as ambroxide, menthofuran, boldine, estrone, dehydroabietylamine, 9-allogibberic acid, and sclareolide, and substituted adamantane molecules, when catalyst Cu/Au (3:1) or Pd/Au (3:1) stabilized by CSPVPs or PVP and oxidant H₂O₂ or t-BuOOH were applied. Oxidation of (+)-boldine N-oxide 23 using NMO as an oxidant yielded 4,5-dehydroboldine 27, and oxidation of (-)-9-allogibberic acid yielded C6,15 lactone 47 and C6-ketone 48.

Directed evolution of cytochrome P450DA hydroxylase activity for stereoselective biohydroxylation

A colorimetric high throughput screening method was developed based on a dual-enzyme cascade and used for the directed evolution of cytochrome P450 hydroxylase activity.

Homogeneous oxidation of C–H bonds with m-CPBA catalysed by a Co/Fe system: mechanistic insights from the point of view of the oxidant

A Co/Fe system efficiently catalyses the oxidation of C–H bonds with m-CPBA. The nitric acid promoter hampers the m-CPBA homolysis, suppressing the free radical activity. Experimental and computational data evidence a concerted oxidation mechanism.

Site and Enantioselective Aliphatic C-H Oxidation with Bioinspired Chiral Complexes

Selective oxidation of aliphatic C-H bonds stands as an unsolved problem in organic synthesis, with the potential to offer novel paths for preparing molecules of biological interest. The quest for reagents that can perform this class of reactions finds oxygenases and their mechanisms of action as inspiration motifs. Among the numerous families of synthetic catalysts that have been explored, complexes with linear tetraazadentate ligands combining two aliphatic amines and two aromatic amine heterocycles display a structural versatility proven instrumental in the design of C-H oxidation reactions showing site and enantioselectivities, not accessible by conventional oxidants. This manuscript makes a review of recent advances in the field.

Engineering P450 TamI as an Iterative Biocatalyst for Selective Late-Stage C-H Functionalization and Epoxidation of Tirandamycin Antibiotics

Iterative P450 enzymes are powerful biocatalysts for selective late-stage C-H oxidation of complex natural product scaffolds. These enzymes represent useful tools for selectivity and cascade reactions, facilitating direct access to core structure diversification. Recently, we reported the structure of the multifunctional bacterial P450 TamI and elucidated the molecular basis of its substrate binding and strict reaction sequence at distinct carbon atoms of the substrate. Here, we report the design and characterization of a toolbox of TamI biocatalysts, generated by mutations at Leu101, Leu244, and/or Leu295, that alter the native selectivity, step sequence, and number of reactions catalyzed, including the engineering of a variant capable of catalyzing a four-step oxidative cascade without the assistance of the flavoprotein and oxidative partner TamL. The tuned enzymes override inherent substrate reactivity, enabling catalyst-controlled C-H functionalization and alkene epoxidation of the tetramic acid-containing natural product tirandamycin. Five bioactive tirandamycin derivatives (6-10) were generated through TamI-mediated enzymatic synthesis. Quantum mechanics calculations and MD simulations provide important insights into the basis of altered selectivity and underlying biocatalytic mechanisms for enhanced continuous oxidation of the iterative P450 TamI.

Structural Basis for Selective Oxidation of Phosphorylated Ethylphenols by Cytochrome P450 Monooxygenase CreJ

Selective oxidation of C-H bonds in alkylphenols holds great significance for not only structural derivatization in pharma- and biomanufacturing but also biological degradation of these toxic chemicals in environmental protection. A unique chemomimetic biocatalytic system using enzymes from a p-cresol biodegradation pathway has recently been developed. As the central biocatalyst, the cytochrome P450 monooxygenase CreJ oxidizes diverse p- and m-alkylphenol phosphates with perfect stereoselectivity at different efficiencies. However, the mechanism of regio- and stereoselectivity of this chemomimetic biocatalytic system remained unclear. Here, using p- and m-ethylphenol substrates, we elucidate the CreJ-catalyzed key steps for selective oxidations. The crystal structure of CreJ in complex with m-ethylphenol phosphate was solved and compared with its complex structure with p-ethylphenol phosphate isomer. The results indicate that the conformational changes of substrate-binding residues are slight, while the substrate promiscuity is achieved mainly by the available space in the catalytic cavity. Moreover, the catalytic preferences of regio- and stereoselective hydroxylation for the two ethylphenol substrates is explored by molecular dynamics simulations. The ethyl groups in the complexes display different flexibilities, and the distances of the active oxygen to H _pro-S and H _pro-R of methylene agree with the experimental stereoselectivity. The regioselectivity can be explained by the distances and bond dissociation energy. These results provide not only the mechanistic insights into CreJ regio- and stereoselectivity but also the structural basis for further P450 enzyme design and engineering.IMPORTANCE The key cytochrome P450 monooxygenase CreJ showed excellent regio- and stereoselectivity in the oxidation of various alkylphenol substrates. C-H bond functionalization of these toxic alkylphenols holds great significance for both biological degradation of these environmental chemicals and production of value-added structural derivatives in pharmaceutical and biochemical industries. Our results, combined with in vitro enzymatic assays, crystal structure determination of enzyme-substrate complex, and molecular dynamics simulations, provide not only significant mechanism elucidation of the regio- and stereoselective catalyzation mediated by CreJ but also the promising directions for future engineering efforts of this enzyme toward more useful products. It also has great extendable potential to couple this multifunctional P450 enzyme with other biocatalysts (e.g., hydroxyl-based glycosylase) to access more alkylphenol-derived high-value chemicals through environment-friendly biocatalysis and biotransformation.

Biosynthesis of chiral cyclic and heterocyclic alcohols via CO/C–H/C–O asymmetric reactions

This review covers the recent progress in various biological approaches applied to the synthesis of enantiomerically pure cyclic and heterocyclic alcohols through CO/C–H/C–O asymmetric reactions.

Catalytic Enantioselective Methylene C(sp3)-H Hydroxylation Using a Chiral Manganese Complex/Carboxylic Acid System

Achieving direct C-H hydroxylation in a highly diastereo- and enantioselective manner is still a challenging goal. This reaction is mainly hindered by the potential for overoxidation of the generated alcohols as well as low stereoselectivity. Herein, we present an enantioselective benzylic C-H hydroxylation catalyzed by a manganese complex, H₂O₂, and a carboxylic acid in 2,2,2-trifluoroethanol. The benzylic alcohols were successfully furnished in excellent diastereoselectivities (up to >95:5) and enantioselectivities (up to 95% ee). As a highlight of this work, high diastereoselectivity of C-H hydroxylation could be achieved by tuning the amount of carboxylic acid additive.

Scalable biocatalytic C-H oxyfunctionalization reactions

Catalytic C-H oxyfunctionalization reactions have garnered significant attention in recent years with their ability to streamline synthetic routes toward complex molecules. Consequently, there have been significant strides in the design and development of catalysts that enable diversification through C-H functionalization reactions. Enzymatic C-H oxygenation reactions are often complementary to small molecule based synthetic approaches, providing a powerful tool when deployable on preparative-scale. This review highlights key advances in scalable biocatalytic C-H oxyfunctionalization reactions developed within the past decade.

Mechanism-Guided Design and Discovery of Efficient Cytochrome P450-Derived C-H Amination Biocatalysts

Cytochromes P450 have been recently identified as a promising class of biocatalysts for mediating C-H aminations via nitrene transfer, a valuable transformation for forging new C-N bonds. The catalytic efficiency of P450s in these non-native transformations is however significantly inferior to that exhibited by these enzymes in their native monooxygenase function. Using a mechanism-guided strategy, we report here the rational design of a series of P450_BM3-based variants with dramatically enhanced C-H amination activity acquired through disruption of the native proton relay network and other highly conserved structural elements within this class of enzymes. This approach further guided the identification of XplA and BezE, two "atypical" natural P450s implicated in the degradation of a man-made explosive and in benzastatins biosynthesis, respectively, as very efficient C-H aminases. Both XplA and BezE could be engineered to further improve their C-H amination reactivity, which demonstrates their evolvability for abiological reactions. These engineered and natural P450 catalysts can promote the intramolecular C-H amination of arylsulfonyl azides with over 10 000-14 000 catalytic turnovers, ranking among the most efficient nitrene transfer biocatalysts reported to date. Mechanistic and structure-reactivity studies provide insights into the origin of the C-H amination reactivity enhancement and highlight the divergent structural requirements inherent to supporting C-H amination versus C-H monooxygenation reactivity within this class of enzymes. Overall, this work provides new promising scaffolds for the development of nitrene transferases and demonstrates the value of mechanism-driven rational design as a strategy for improving the catalytic efficiency of metalloenzymes in the context of abiological transformations.

Iron- and cobalt-catalyzed C(sp3)–H bond functionalization reactions and their application in organic synthesis

This review highlights the developments in iron and cobalt catalyzed C(sp³)–H bond functionalization reactions with emphasis on their applications in organic synthesis, i.e. natural products and pharmaceuticals synthesis and/or modification.

A Benchmark of Density Functional Approximations For Thermochemistry and Kinetics of Hydride Reductions of Cyclohexanones

The performance of density functionals and wavefunction methods for describing the thermodynamics and kinetics of hydride reductions of 2-substituted cyclohexanones has been evaluated for the first time. A variety of exchange correlation functionals ranging from generalized gradient approximations to double hybrids have been tested and their performance to describe the facial selectivity of hydride reductions of cyclohexanones has been carefully assessed relative to the CCSD(T) method. Among the tested methods, an approach in which single-point energy calculations using the double hybrid B2PLYP-D3 functional on ωB97X-D optimized geometries provides the most accurate transition state energies for these kinetically-controlled reactions. Moreover, the role of torsional strain, temperature, solvation, noncovalent interactions on the stereoselectivity of these reductions was elucidated. Our results indicate a prominent role of the substituent on the cis/trans ratios driven by the delicate interplay between torsional strain and dispersion interactions.

Enantioselective aliphatic C-H bond oxidation catalyzed by bioinspired complexes

Enantioselective aliphatic C-H bond oxidation simultaneously installs functionality and chirality into hydrocarbon units, converting in a single step readily available, inexpensive and typically inert hydrocarbons into precious building blocks for organic synthesis. The reaction remains however an open problem eager for catalyst development and improvement. Metal complexes reproducing structural and reactivity aspects of oxygenases are emerging as promising homogeneous catalysts for this class of reactions. The present work reviews the current status of field, analyzing the difficulties of the reaction, discussing principles of catalyst design, and critically highlighting the limitations of the current state-of-the-art methodologies.

Selective aerobic oxidation reactions using a combination of photocatalytic water oxidation and enzymatic oxyfunctionalisations

Peroxygenases offer attractive means to address challenges in selective oxyfunctionalisation chemistry. Despite their attractiveness, the application of peroxygenases in synthetic chemistry remains challenging due to their facile inactivation by the stoichiometric oxidant (H₂O₂). Often atom inefficient peroxide generation systems are required, which show little potential for large scale implementation. Here we show that visible light-driven, catalytic water oxidation can be used for in situ generation of H₂O₂ from water, rendering the peroxygenase catalytically active. In this way the stereoselective oxyfunctionalisation of hydrocarbons can be achieved by simply using the catalytic system, water and visible light.

Use of bioconjugation with cytochrome P450 enzymes

Bioconjugation, defined as chemical modification of biomolecules, is widely employed in biological and biophysical studies. It can expand functional diversity and enable applications ranging from biocatalysis, biosensing and even therapy. This review summarizes how chemical modifications of cytochrome P450 enzymes (P450s or CYPs) have contributed to improving our understanding of these enzymes. Genetic modifications of P450s have also proven very useful but are not covered in this review. Bioconjugation has served to gain structural information and investigate the mechanism of P450s via photoaffinity labeling, mechanism-based inhibition (MBI) and fluorescence studies. P450 surface acetylation and protein cross-linking have contributed to the investigation of protein complexes formation involving P450 and its redox partner or other P450 enzymes. Finally, covalent immobilization on polymer surfaces or electrodes has benefited the areas of biocatalysis and biosensor design. This article is part of a Special Issue entitled: Cytochrome P450 biodiversity and biotechnology, edited by Erika Plettner, Gianfranco Gilardi, Luet Wong, Vlada Urlacher, Jared Goldstone.

Selective oxidation of aliphatic C-H bonds in alkylphenols by a chemomimetic biocatalytic system

Selective oxidation of aliphatic C-H bonds in alkylphenols serves significant roles not only in generation of functionalized intermediates that can be used to synthesize diverse downstream chemical products, but also in biological degradation of these environmentally hazardous compounds. Chemo-, regio-, and stereoselectivity; controllability; and environmental impact represent the major challenges for chemical oxidation of alkylphenols. Here, we report the development of a unique chemomimetic biocatalytic system originated from the Gram-positive bacterium Corynebacterium glutamicum The system consisting of CreHI (for installation of a phosphate directing/anchoring group), CreJEF/CreG/CreC (for oxidation of alkylphenols), and CreD (for directing/anchoring group offloading) is able to selectively oxidize the aliphatic C-H bonds of p- and m-alkylated phenols in a controllable manner. Moreover, the crystal structures of the central P450 biocatalyst CreJ in complex with two representative substrates provide significant structural insights into its substrate flexibility and reaction selectivity.

Highly Enantioselective Oxidation of Nonactivated Aliphatic C-H Bonds with Hydrogen Peroxide Catalyzed by Manganese Complexes

Monosubstituted cycloalkanes undergo regio- and enantioselective aliphatic C-H oxidation with H₂O₂ catalyzed by biologically inspired manganese catalysts. The reaction furnishes the corresponding ketones resulting from oxidation at C3 and C4 methylenic sites (K₃ and K₄, respectively) leading to a chiral desymmetrization that proceeds with remarkable enantioselectivity (64% ee) but modest regioselectivity at C3 (K₃/K₄ ≈ 2) for tert-butylcyclohexane, and with up to 96% ee and exquisite regioselectity toward C3 (up to K₃/K₄ > 99) when N-cyclohexylalkanamides are employed as substrates. Efficient H₂O₂ activation, high yield, and highly enantioselective C-H oxidation rely on the synergistic cooperation of a sterically bulky manganese catalyst and an oxidatively robust alkanoic acid. This represents the first example of nonenzymatic highly enantioselective oxidation of nonactivated methylenic sites. Furthermore, the principles of catalyst design disclosed in this work constitute a unique platform for further development of stereoselective C-H oxidation reactions.

Hydroxylation of anilides by engineered cytochrome P450BM3

Cytochrome P450_BM3mutants achieve selectivepara-hydroxylation of substitutedN-sulfonylanilines under mild conditions.

Control of stereoselectivity of benzylic hydroxylation catalysed by wild-type cytochrome P450BM3 using decoy molecules

The benzylic hydroxylation of non-native substrates was catalysed by cytochrome P450BM3, wherein “decoy molecules” controlled the stereoselectivity of the reactions.

A metalloporphyrin-based porous organic polymer as an efficient catalyst for the catalytic oxidation of olefins and arylalkanes

A metalloporphyrin-based porous organic polymer contains both micropores and mesopores, which are favourable for mass transfer in heterogeneous catalysis.

Immobilization of a Bacterial Cytochrome P450 Monooxygenase System on a Solid Support

Bacterial cytochrome P450s (P450s), which catalyze regio- and stereoselective oxidations of hydrocarbons with high turnover rates, are attractive biocatalysts for fine chemical production. Enzyme immobilization is needed for cost-effective industrial manufacturing. However, immobilization of P450s is difficult because electron-transfer proteins are involved in catalysis and anchoring these can prevent them from functioning as shuttle molecules for carrying electrons. We studied a heterotrimeric protein-mediated co-immobilization of a bacterial P450, and its electron-transfer protein and reductase. Fusion with subunits of a heterotrimeric Sulfolobus solfataricus proliferating cell nuclear antigen (PCNA) enabled immobilization of the three proteins on a solid support. The co-immobilized enzymes catalyzed monooxygenation because the electron-transfer protein fused to PCNA via a single peptide linker retained its electron-transport function.

Fine Control over Site and Substrate Selectivity in Hydrogen Atom Transfer-Based Functionalization of Aliphatic C-H Bonds

The selective functionalization of unactivated aliphatic C-H bonds over intrinsically more reactive ones represents an ongoing challenge of synthetic chemistry. Here we show that in hydrogen atom transfer (HAT) from the aliphatic C-H bonds of alkane, ether, alcohol, amide, and amine substrates to the cumyloxyl radical (CumO^•) fine control over site and substrate selectivity is achieved by means of acid-base interactions. Protonation of the amines and metal ion binding to amines and amides strongly deactivates the C-H bonds of these substrates toward HAT to CumO^•, providing a powerful method for selective functionalization of unactivated or intrinsically less reactive C-H bonds. With 5-amino-1-pentanol, site-selectivity has been drastically changed through protonation of the strongly activating NH₂ group, with HAT that shifts to the C-H bonds that are adjacent to the OH group. In the intermolecular selectivity studies, trifluoroacetic acid, Mg(ClO₄)₂, and LiClO₄ have been employed in a orthogonal fashion for selective functionalization of alkane, ether, alcohol, and amide (or amine) substrates in the presence of an amine (or amide) one. Ca(ClO₄)₂, that promotes deactivation of amines and amides by Ca²⁺ binding, offers, moreover, the opportunity to selectively functionalize the C-H bonds of alkane, ether, and alcohol substrates in the presence of both amines and amides.

Enzymatic hydroxylation of an unactivated methylene C-H bond guided by molecular dynamics simulations

The hallmark of enzymes from secondary metabolic pathways is the pairing of powerful reactivity with exquisite site selectivity. The application of these biocatalytic tools in organic synthesis, however, remains under-utilized due to limitations in substrate scope and scalability. Here, we report how the reactivity of a monooxygenase (PikC) from the pikromycin pathway is modified through computationally guided protein and substrate engineering, and applied to the oxidation of unactivated methylene C-H bonds. Molecular dynamics and quantum mechanical calculations were used to develop a predictive model for substrate scope, site selectivity and stereoselectivity of PikC-mediated C-H oxidation. A suite of menthol derivatives was screened computationally and evaluated through in vitro reactions, where each substrate adhered to the predicted models for selectivity and conversion to product. This platform was also expanded beyond menthol-based substrates to the selective hydroxylation of a variety of substrate cores ranging from cyclic to fused bicyclic and bridged bicyclic compounds.

Oxidation of methane by an N-bridged high-valent diiron–oxo species: electronic structure implications on the reactivity

Methane activation by dinuclear high-valent iron–oxo species: do we need two metals to activate such inert bonds? Our theoretical study using DFT methods where electronic structure details and mechanistic aspects are established answers this intriguing question.

Evolving P450pyr monooxygenase for highly regioselective terminal hydroxylation of n-butanol to 1,4-butanediol

Directed evolution of a P450pyr created I83M/I82T mutant as the first catalyst for highly regioselective terminal hydroxylation of n-butanol to 1,4-butanediol.

Expanding the toolbox of organic chemists: directed evolution of P450 monooxygenases as catalysts in regio- and stereoselective oxidative hydroxylation

Cytochrome P450 enzymes (CYPs) have been used for more than six decades as catalysts for the CH-activating oxidative hydroxylation of organic compounds with formation of added-value products.

A magnetic nanoparticle catalyzed eco-friendly synthesis of cyanohydrins in a deep eutectic solvent

A short and highly efficient synthesis of cyanohydrins in a recyclable and biodegradable magnetic deep eutectic solvent is described.

Biocatalytic route to chiral acyloins: P450-catalyzed regio- and enantioselective α-hydroxylation of ketones

P450-BM3 and mutants of this monooxygenase generated by directed evolution are excellent catalysts for the oxidative α-hydroxylation of ketones with formation of chiral acyloins with high regioselectivity (up to 99%) and enantioselectivity (up to 99% ee). This constitutes a new route to a class of chiral compounds that are useful intermediates in the synthesis of many kinds of biologically active compounds.