cas 57794-08-8, (1S,2S)-TRANS-1,2-CYCLOHEXANEDIOL

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Enantiotopic Discrimination by Coordination-Desymmetrized meso-Ligands
The first examples of enantiopure catalysts that are chiral merely due to coordination of different metal ions at enantiotopic positions of an achiral meso-ligand are reported. These catalysts exhibit a pseudo-Cs symmetry and are able to catalyze reactions demanding simultaneous involvement of two catalytic sites. The latter was demonstrated by application in the asymmetric ring-opening of meso-epoxides.
Li, Yutang,Lidskog, Anna,Armengol-Relats, Helena,Pham, Thanh Huong,Favraud, Antoine,Nicolas, Maxime,Dawaigher, Sami,Xiao, Zeyun,Ma, Dayou,Lindb?ck, Emil,Strand, Daniel,W?rnmark, Kenneth
p. 1575 - 1579
(2020/02/04)

SYNTHESIS AND APPLICATION OF CHIRAL SUBSTITUTED POLYVINYLPYRROLIDINONES
Chiral polyvinylpyrrolidinone (CSPVP), complexes of CSPVP with a core species, such as a metallic nanocluster catalyst, and enantioselective oxidation reactions utilizing such complexes are disclosed. The CSPVP complexes can be used in asymmetric oxidation of diols, enantioselective oxidation of alkenes, and carbon-carbon bond forming reactions, for example. The CSPVP can also be complexed with biomolecules such as proteins, DNA, and RNA, and used as nanocarriers for siRNA or dsRNA delivery.
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Paragraph 0046; 0047; 0049

(2020/11/24)

Olefin reaction in the catalyst and the olefin production
PROBLEM TO BE SOLVED: To provide a catalyst for obtaining an olefin in high selectivity with a vicinal diol as a raw material.SOLUTION: A catalyst for olefination reaction for use in a reaction to produce an olefin by a reaction of a polyol, having two adjacent carbon atoms each having a hydroxy group, with hydrogen comprises: a carrier; at least one oxide selected from the group consisting of oxides of the group 6 elements and oxides of the group 7 elements supported on the carrier; and at least one metal selected from the group consisting of silver, iridium, and gold supported on the carrier.SELECTED DRAWING: None
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Paragraph 0147; 0149

(2020/10/31)

Aromatic Donor-Acceptor Interaction-Based Co(III)-salen Self-Assemblies and Their Applications in Asymmetric Ring Opening of Epoxides
Aromatic donor-acceptor interaction as the driving force to assemble cooperative catalysts is described. Pyrene/naphthalenediimide functionalized Co(III)-salen complexes self-assembled into bimetallic catalysts through aromatic donor-acceptor interactions and showed high catalytic activity and selectivity in the asymmetric ring opening of various epoxides. Control experiments, nuclear magnetic resonance (NMR) spectroscopy titrations, mass spectrometry measurement, and X-ray crystal structure analysis confirmed that the catalysts assembled based on the aromatic donor-acceptor interaction, which can be a valuable noncovalent interaction in supramolecular catalyst development.
Liang, Jian,Soucie, Luke N.,Blechschmidt, Daniel R.,Yoder, Aaron,Gustafson, Addie,Liu, Yu
supporting information
p. 513 - 518
(2019/01/14)

Organic salts and merrifield resin supported [PM12O40]3? (M = Mo or W) as catalysts for adipic acid synthesis
Adipic acid (AA) was obtained by catalyzed oxidation of cyclohexene, epoxycyclohexane, or cyclohexanediol under organic solvent-free conditions using aqueous hydrogen peroxide (30%) as an oxidizing agent and molybdenum- or tungsten-based Keggin polyoxometalates (POMs) surrounded by organic cations or ionically supported on functionalized Merrifield resins. Operating under these environmentally friendly, greener conditions and with low catalyst loading (0.025% for the molecular salts and 0.001–0.007% for the supported POMs), AA could be produced in interesting yields.
Pisk, Jana,Agustin, Dominique,Poli, Rinaldo
(2019/02/26)

Well-confined polyoxometalate-ionic liquid in silicic framework for environmentally friendly asymmetric di-hydroxylation of olefins
Chiral 1,2-diols with a high yield could be directly prepared from asymmetric di-hydroxylation of olefins via an eco-friendly and enduring catalyst, in which abundant "chiral pools" of polyoxometalate-ionic liquid were target-designed into the silicic framework (POM-ILS) and well stabilized in aqueous media.
Liang, Dong,Wang, Yan,Wang, Sifan,Song, Chengkun,Shi, Yonghe,Liu, Qinghao,Zhu, Hailin,Li, Xia,Liu, Laishuan,Zhu, Na
p. 6102 - 6106
(2019/03/12)

Epoxidation of cyclohexene with H2O2 over efficient water-tolerant heterogeneous catalysts composed of mono-substituted phosphotungstic acid on co-functionalized SBA-15
A series of Keggin-type heteropolyacid-based heterogeneous catalysts (Co-/Fe-/Cu-POM-octyl-NH3-SBA-15) were synthesized via immobilized transition metal mono- substituted phosphotungstic acids (Co-/Fe-/Cu-POM) on octyl-amino-co-functionalized mesoporous silica SBA-15 (octyl-NH2-SBA-15). Characterization results indicated that Co-/Fe-/Cu-POM units were highly dispersed in mesochannels of SBA-15, and both types of Br?nsted and Lewis acid sites existed in Co-/Fe-/Cu-POM-octyl-NH3-SBA-15 catalysts. Co-POM-octyl-NH3-SBA-15 catalyst showed excellent catalytic performance in H2O2-mediated cyclohexene epoxidation with 83.8% of cyclohexene conversion, 92.8% of cyclohexene oxide selectivity, and 98/2 of epoxidation/allylic oxidation selectivity. The order of catalytic activity was Co-POM-octyl-NH3-SBA-15?>?Fe-POM-octyl-NH3-SBA-15?>?Cu-POM-octyl-NH3-SBA-15. In order to obtain insights into the role of -octyl moieties during catalysis, an octyl-free catalyst (Co-POM-NH3-SBA-15) was also synthesized. In comparison with Co-POM-NH3-SBA-15, Co-POM-octyl-NH3-SBA-15 showed enhanced catalytic properties (viz. activity and selectivity) in cyclohexene epoxidation. Strong chemical bonding between -NH3 + anchored on the surface of SBA-15 and heteropolyanions resulted in excellent stability of Co-POM-octyl-NH3-SBA-15 catalyst, and it could be reused six times without considerable loss of activity.
Jin, Manman,Niu, Qingtao,Guo, Zhenmei,Lv, Zhiguo
(2019/07/31)

Calix[8]arene as New Platform for Cobalt-Salen Complexes Immobilization and Use in Hydrolytic Kinetic Resolution of Epoxides
Eight cobalt-salen complexes have been covalently attached to a calix[8]arene platform through a flexible linker by a procedure employing Click chemistry. The corresponding well-defined catalyst proved its efficiency in the hydrolytic kinetic resolution (HKR) of various epoxides through an operative bimetallic cooperative activation, demonstrating highly enhanced activity when compared to its monomeric analogue. As an insoluble complex, this multisite cobalt-salen catalyst could be easily recovered and reused in successive catalytic runs. Products were isolated by a simple filtration with virtually no cobalt traces and without requiring a prior purification by flash chromatography.
Abdellah, Ibrahim,Martini, Cyril,Dos Santos, Amandine,Dragoe, Diana,Guérineau, Vincent,Huc, Vincent,Schulz, Emmanuelle
p. 4761 - 4767
(2018/10/02)

Structural and Computational Insight into the Catalytic Mechanism of Limonene Epoxide Hydrolase Mutants in Stereoselective Transformations
Directed evolution of limonene epoxide hydrolase (LEH), which catalyzes the hydrolytic desymmetrization reactions of cyclopentene oxide and cyclohexene oxide, results in (R,R)- and (S,S)-selective mutants. Their crystal structures combined with extensive theoretical computations shed light on the mechanistic intricacies of this widely used enzyme. From the computed activation energies of various pathways, we discover the underlying stereochemistry for favorable reactions. Surprisingly, some of the most enantioselective mutants that rapidly convert cyclohexene oxide do not catalyze the analogous transformation of the structurally similar cyclopentene oxide, as shown by additional X-ray structures of the variants harboring this slightly smaller substrate. We explain this puzzling observation on the basis of computational calculations which reveal a disrupted alignment between nucleophilic water and cyclopentene oxide due to the pronounced flexibility of the binding pocket. In contrast, in the stereoselective reactions of cyclohexene oxide, reactive conformations are easily reached. The unique combination of structural and computational data allows insight into mechanistic details of this epoxide hydrolase and provides guidance for future protein engineering in reactions of structurally different substrates.
Sun, Zhoutong,Wu, Lian,Bocola, Marco,Chan, H. C. Stephen,Lonsdale, Richard,Kong, Xu-Dong,Yuan, Shuguang,Zhou, Jiahai,Reetz, Manfred T.
supporting information
p. 310 - 318
(2018/01/17)

One-Pot Enzymatic Synthesis of Cyclic Vicinal Diols from Aliphatic Dialdehydes via Intramolecular C?C Bond Formation and Carbonyl Reduction Using Pyruvate Decarboxylases and Alcohol Dehydrogenases
An enzymatic cascade reaction was developed for one-pot enantioselective conversion of aliphatic dialdehydes to chiral vicinal diols using pyruvate decarboxylases (PDCs) and alcohol dehydrogenases (ADHs). The PDCs showed promiscuity in catalysing the cyclization of aliphatic dialdehydes through intramolecular stereoselective carbon-carbon bond formation. Consequently, 1,2-cyclopentanediols in three different stereoisomeric forms and 1,2-cyclohexanediols in two different stereoisomeric forms could be prepared with high conversion and stereoisomeric ratio from the respective initial substrates, glutaraldehyde and adipaldehyde. These cascade reactions represent a promising approach to the biocatalytic synthesis of important chiral vicinal diols. (Figure presented.).
Zhang, Yan,Yao, Peiyuan,Cui, Yunfeng,Wu, Qiaqing,Zhu, Dunming
supporting information
p. 4191 - 4196
(2018/09/25)

Synthesis of titanium containing MCM-41 from industrial hexafluorosilicic acid as epoxidation catalyst
The industrial by-product hexafluorosilicic acid was investigated as silicate source for titanium containing MCM-41 (Si/Ti–MCM-41) synthesis. An extended and detailed study, which includes the effects of several factors such as the state and content of Ti, surfactant/Si ratio and template removal technique on the physicochemical properties and catalytic activity of Si/Ti–MCM-41, is presented; The Si/Ti–MCM-41 was also characterized by powder X-ray diffraction, N2 adsorption-desorption, fourier transform infrared spectroscopy, ultraviolet-visible spectrophotometer, thermal gravimetric measurements, X-ray fluorescence and scanning electron microscopy. The results show that the specific surface area and pore volume of the molecular sieve reach 1040 m2 g?1 and 0.74 cm3 g?1 under the hydrothermal conditions of the Si/Ti mole ratio equal to 60, CTAB/Si mole ratio to 0.81, hydrothermal temperature at 343 K and time for 3 h. The catalytic performance shows that samples have higher activity and selectivity for cyclohexene epoxidation to produce cyclohexene oxide. With the reaction temperature 333 K and mole ratio of cyclohexene/tertiary butyl peroxide hydrogen equal to 1, the highest cyclohexene conversion and epoxide selectivity is 79.23% and 95%, respectively. The catalyst activity has not obvious change with two times recycles.
Liu, Tieliang,Jin, Fang,Wang, Xianqiao,Fan, Yangchun,Yuan, Ming
p. 316 - 323
(2017/09/30)

Micro reaction device reverse 1, 2-cyclohexanediol method
The invention discloses a micro reaction device reverse 1, 2-cyclohexanediol method, the method mixes oxidation of hydrogen aqueous solution and formic acid, results in epoxy reagent, then reacts in sequence with cyclohexene and caustic soda solution in a micro reactor of a micro reaction device, the solution works without any catalyst in the reaction process, compared with available technologies, the method works without the intermediate cyclohexene oxide and catalyst, the production rate of the product obtained is high, the by-product is reduced, the 1, 2-cyclohexanediol can be applied in serialized and automated production.
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Paragraph 0010; 0023-0039

(2017/04/03)

Towards a global greener process: from solvent-less synthesis of molybdenum(vi) ONO Schiff base complexes to catalyzed olefin epoxidation under organic-solvent-free conditions
Nine Schiff base ligands derived from o-hydroxyaldehydes (2-hydroxybenzaldehyde, 2-hydroxy-3-methoxybenzaldehyde, 2-hydroxy- 1-naphthaldehyde) and nine corresponding dioxomolybdenum(vi) complexes, cis-[MoO2L(CH3OH)] or cis-[MoO2L(CH3OH)]·CH3OH and dinuclear [MoO2L]2, have been prepared using the conventional solution-based method as well as mechanochemically, by liquid assisted grinding (LAG). All products have been characterised by means of IR spectroscopy, thermal analyses and also by powder and five molybdenum complexes by single crystal X-ray diffraction. The crystal structure analysis of mononuclear complexes reveal distorted octahedral Mo(vi) coordination by ONO donor atoms from a dianionic tridentate Schiff base ligand, two oxido oxygen atoms from the MoO22+ moiety and an oxygen atom from the MeOH molecule trans to the oxido oxygen atom. Due to the trans effect of the oxido oxygen atom, Mo-O(MeOH) is the longest bond distance within the Mo coordination sphere and it expected to be the point of maximum reactivity of the complexes. All complexes have been studied as pre(catalysts) for the epoxidation of cis-cyclooctene, cyclohexene and (R)-limonene using aqueous tert-butyl peroxide (TBHP) as the oxidant and in the absence of an organic solvent.
Cindri?, Marina,Pavlovi?, Gordana,Katava, Robert,Agustin, Dominique
p. 594 - 602
(2017/02/05)

Assessing the stereoselectivity of: Serratia marcescens CECT 977 2,3-butanediol dehydrogenase
α-Hydroxy ketones and vicinal diols constitute well-known building blocks in organic synthesis. Here we describe one enzyme that enables the enantioselective synthesis of both building blocks starting from diketones. The enzyme 2,3-butanediol dehydrogenase (BudC) from S. marcescens CECT 977 belongs to the NADH-dependent metal-independent short-chain dehydrogenases/reductases family (SDR) and catalyses the selective asymmetric reductions of prochiral α-diketones to the corresponding α-hydroxy ketones and diols. BudC is highly active towards structurally diverse diketones in combination with nicotinamide cofactor regeneration systems. Aliphatic diketones, cyclic diketones and alkyl phenyl diketones are well accepted, whereas their derivatives possessing two bulky groups are not converted. In the reverse reaction vicinal diols are preferred over other substrates with hydroxy/keto groups in non-vicinal positions.
Médici, Rosario,Stammes, Hanna,Kwakernaak, Stender,Otten, Linda G.,Hanefeld, Ulf
p. 1831 - 1837
(2017/07/15)

Hydrogen Bonding-Assisted Enhancement of the Reaction Rate and Selectivity in the Kinetic Resolution of d,l-1,2-Diols with Chiral Nucleophilic Catalysts
An extremely efficient acylative kinetic resolution of d,l-1,2-diols in the presence of only 0.5 mol% of binaphthyl-based chiral N,N-4-dimethylaminopyridine was developed (selectivity factor of up to 180). Several key experiments revealed that hydrogen bonding between the tert-alcohol unit(s) of the catalyst and the 1,2-diol unit of the substrate is critical for accelerating the rate of monoacylation and achieving high enantioselectivity. This catalytic system can be applied to a wide range of substrates involving racemic acyclic and cyclic 1,2-diols with high selectivity factors. The kinetic resolution of d,l-hydrobenzoin and trans-1,2-cyclohexanediol on a multigram scale (10 g) also proceeded with high selectivity and under moderate reaction conditions: (i) very low catalyst loading (0.1 mol%); (ii) an easily achievable low reaction temperature (0 °C); (iii) high substrate concentration (1.0 M); and (iv) short reaction time (30 min). (Figure presented.).
Fujii, Kazuki,Mitsudo, Koichi,Mandai, Hiroki,Suga, Seiji
supporting information
p. 2778 - 2788
(2017/08/23)

Structure-Guided Triple-Code Saturation Mutagenesis: Efficient Tuning of the Stereoselectivity of an Epoxide Hydrolase
The directed evolution of enzymes promises to eliminate the long-standing limitations of biocatalysis in organic chemistry and biotechnology - the often-observed limited substrate scope, insufficient activity, and poor regioselectivity or stereoselectivity. Saturation mutagenesis at sites lining the binding pocket with formation of focused libraries has emerged as the technique of choice, but choosing the optimal size of the randomization site and reduced amino acid alphabet for minimizing the labor-determining screening effort remains a challenge. Here, we introduce structure-guided triple-code saturation mutagenesis (TCSM) by encoding three rationally chosen amino acids as building blocks in the randomization of large multiresidue sites. In contrast to conventional NNK codon degeneracy encoding all 20 canonical amino acids and requiring the screening of more than 1015 transformants for 95% library coverage, TCSM requires only small libraries not exceeding 200-800 transformants in one library. The triple code utilizes structural (X-ray) and consensus-derived sequence data, and is therefore designed to match the steric and electrostatic characteristics of the particular enzyme. Using this approach, limonene epoxide hydrolase has been successfully engineered as stereoselective catalysts in the hydrolytic desymmetrization of meso-type epoxides with formation of either (R,R)- or (S,S)-configurated diols on an optional basis and kinetic resolution of chiral substrates. Crystal structures and docking computations support the source of notably enhanced and inverted enantioselectivity.
Sun, Zhoutong,Lonsdale, Richard,Wu, Lian,Li, Guangyue,Li, Aitao,Wang, Jianbo,Zhou, Jiahai,Reetz, Manfred T.
p. 1590 - 1597
(2016/03/15)

Multiparameter Optimization in Directed Evolution: Engineering Thermostability, Enantioselectivity, and Activity of an Epoxide Hydrolase
The challenge of optimizing several parameters in the directed evolution of enzymes remains a central issue. In this study we address the thermostability, enantioselectivity, and activity of limonene epoxide hydrolase (LEH) as the catalyst in the hydrolytic desymmetrization of cyclohexene oxide with formation of (R,R)- and (S,S)-cyclohexane-1,2-diol. Wild type LEH shows a thermostability of T5030 = 41 °C and an enanioselectivity of 2% ee (S,S). Two approaches are described herein. In one strategy, the mutations generated previously by Janssen, Baker, and co-workers for notably increased thermostability are combined with mutations evolved earlier for enhanced enantioselectivity. Although highly enantioselective R,R and S,S variants (92-93% ee) with increases in T5030 by 10-11 °C were obtained, relative to wild type LEH the tradeoff in activity was significant. The second strategy based on the simultaneous optimization of both parameters using iterative saturation mutagenesis (ISM) with minimized tradeoff in activity proved to be superior. Several notably improved variants were observed, a reasonable "compromise" being R,R- and S,S-selective LEH variants (80-94% ee) showing enhanced thermostability by 5-10 °C and still reasonable levels of activity. Analysis of the X-ray structure of the S,S variant (94% ee) with and without diol product sheds light on the origin of altered stereoselectivity.
Li, Guangyue,Zhang, Hui,Sun, Zhoutong,Liu, Xinqi,Reetz, Manfred T.
p. 3679 - 3687
(2016/07/06)

Mixing and matching chiral cobalt- and manganese-based calix-salen catalysts for the asymmetric hydrolytic ring opening of epoxides
Homochiral oligomeric salen macrocycles possessing aromatic spacers have been prepared as new calix-salen derivatives. The corresponding cobalt and manganese complexes were synthesized and characterized, and their catalytic activities have been studied in the challenging hydrolysis of meso epoxides. While manganese calix-salen complexes were not active in the studied reactions, the dual heterobimetallic system, using an equimolar combination of cobalt and manganese calix-salen derivatives proved to be more enantioselective than the sole cobalt system. Furthermore, as heterogeneous complexes, the catalytic mixture could be easily recovered by simple filtration and successfully reengaged in subsequent catalytic runs. Interestingly, no need for cobalt reactivation was noticed to maintain maximum efficiency of this dual system. The matched Co/Mn dual catalyst was also used to promote the dynamic hydrolytic kinetic resolution of epibromohydrin.
Dandachi, Hiba,Zaborova, Elena,Kolodziej, Emilie,David, Olivier R.P.,Hannedouche, Jér?me,Mellah, Mohamed,Jaber, Nada,Schulz, Emmanuelle
p. 246 - 253
(2017/03/01)

Comparing Different Strategies in Directed Evolution of Enzyme Stereoselectivity: Single- versus Double-Code Saturation Mutagenesis
Saturation mutagenesis at sites lining the binding pockets of enzymes constitutes a viable protein engineering technique for enhancing or inverting stereoselectivity. Statistical analysis shows that oversampling in the screening step (the bottleneck) increases astronomically as the number of residues in the randomization site increases, which is the reason why reduced amino acid alphabets have been employed, in addition to splitting large sites into smaller ones. Limonene epoxide hydrolase (LEH) has previously served as the experimental platform in these methodological efforts, enabling comparisons between single-code saturation mutagenesis (SCSM) and triple-code saturation mutagenesis (TCSM); these employ either only one or three amino acids, respectively, as building blocks. In this study the comparative platform is extended by exploring the efficacy of double-code saturation mutagenesis (DCSM), in which the reduced amino acid alphabet consists of two members, chosen according to the principles of rational design on the basis of structural information. The hydrolytic desymmetrization of cyclohexene oxide is used as the model reaction, with formation of either (R,R)- or (S,S)-cyclohexane-1,2-diol. DCSM proves to be clearly superior to the likewise tested SCSM, affording both R,R- and S,S-selective mutants. These variants are also good catalysts in reactions of further substrates. Docking computations reveal the basis of enantioselectivity.
Sun, Zhoutong,Lonsdale, Richard,Li, Guangyue,Reetz, Manfred T.
p. 1865 - 1872
(2016/11/06)

Chiral-Substituted Poly-N-vinylpyrrolidinones and Bimetallic Nanoclusters in Catalytic Asymmetric Oxidation Reactions
A new class of poly-N-vinylpyrrolidinones containing an asymmetric center at C5 of the pyrrolidinone ring were synthesized from l-amino acids. The polymers, particularly 17, were used to stabilize nanoclusters such as Pd/Au for the catalytic asymmetric oxidations of 1,3- and 1,2-cycloalkanediols and alkenes, and Cu/Au was used for C-H oxidation of cycloalkanes. It was found that the bulkier the C5 substituent in the pyrrolidinone ring, the greater the optical yields produced. Both oxidative kinetic resolution of (±)-1,3- and 1,2-trans-cycloalkanediols and desymmetrization of meso cis-diols took place with 0.15 mol % Pd/Au (3:1)-17 under oxygen atmosphere in water to give excellent chemical and optical yields of (S)-hydroxy ketones. Various alkenes were oxidized with 0.5 mol % Pd/Au (3:1)-17 under 30 psi of oxygen in water to give the dihydroxylated products in >93% ee. Oxidation of (R)-limonene at 25 °C occurred at the C-1,2-cyclic alkene function yielding (1S,2R,4R)-dihydroxylimonene 49 in 92% yield. Importantly, cycloalkanes were oxidized with 1 mol % Cu/Au (3:1)-17 and 30% H2O2 in acetonitrile to afford chiral ketones in very good to excellent chemical and optical yields. Alkene function was not oxidized under the reaction conditions. Mechanisms were proposed for the oxidation reactions, and observed stereo- and regio-chemistry were summarized.
Hao, Bo,Gunaratna, Medha J.,Zhang, Man,Weerasekara, Sahani,Seiwald, Sarah N.,Nguyen, Vu T.,Meier, Alex,Hua, Duy H.
supporting information
p. 16839 - 16848
(2017/01/10)

Whole-Cell-Catalyzed Multiple Regio- and Stereoselective Functionalizations in Cascade Reactions Enabled by Directed Evolution
Biocatalytic cascade reactions using isolated stereoselective enzymes or whole cells in one-pot processes lead to value-added chiral products in a single workup. The concept has been restricted mainly to starting materials and intermediate products that are accepted by the respective wild-type enzymes. In the present study, we exploited directed evolution as a means to create E. coli whole cells for regio- and stereoselective cascade sequences that are not possible using man-made catalysts. The approach is illustrated using P450-BM3 in combination with appropriate alcohol dehydrogenases as catalysts in either two-, three-, or four-step cascade reactions starting from cyclohexane, cyclohexanol, or cyclohexanone, respectively, leading to either (R,R)-, (S,S)-, or meso-cyclohexane-1,2-diol. The one-pot conversion of cyclohexane into (R)- or (S)-2-hydroxycyclohexanone in the absence of ADH is also described.
Li, Aitao,Ilie, Adriana,Sun, Zhoutong,Lonsdale, Richard,Xu, Jian-He,Reetz, Manfred T.
p. 12026 - 12029
(2016/11/16)

Uncovering Key Structural Features of an Enantioselective Peptide-Catalyzed Acylation Utilizing Advanced NMR Techniques
We report on a detailed NMR spectroscopic study of the catalyst-substrate interaction of a highly enantioselective oligopeptide catalyst that is used for the kinetic resolution of trans-cycloalkane-1,2-diols via monoacylation. The extraordinary selectivity has been rationalized by molecular dynamics as well as density functional theory (DFT) computations. Herein we describe the conformational analysis of the organocatalyst studied by a combination of nuclear Overhauser effect (NOE) and residual dipolar coupling (RDC)-based methods that resulted in an ensemble of four final conformers. To corroborate the proposed mechanism, we also investigated the catalyst in mixtures with both trans-cyclohexane-1,2-diol enantiomers separately, using advanced NMR methods such as T1relaxation time and diffusion-ordered spectroscopy (DOSY) measurements to probe molecular aggregation. We determined intramolecular distance changes within the catalyst after diol addition from quantitative NOE data. Finally, we developed a pure shift EASY ROESY experiment using PSYCHE homodecoupling to directly observe intermolecular NOE contacts between the trans-1,2-diol and the cyclohexyl moiety of the catalyst hidden by spectral overlap in conventional spectra. All experimental NMR data support the results proposed by earlier computations including the proposed key role of dispersion interaction.
Procházková, Eli?ka,Kolmer, Andreas,Ilgen, Julian,Schwab, Mira,Kaltschnee, Lukas,Fredersdorf, Maic,Schmidts, Volker,Wende, Raffael C.,Schreiner, Peter R.,Thiele, Christina M.
supporting information
p. 15754 - 15759
(2016/12/16)

Performance, Structure, and Mechanism of ReOx-Pd/CeO2 Catalyst for Simultaneous Removal of Vicinal OH Groups with H2
The ceria-supported rhenium catalyst modified with palladium (ReOx-Pd/CeO2 (Re = 2 wt %, Pd/Re = 0.25)) is still the best catalyst for simultaneous hydrodeoxygenation. Higher Re loading amount decreased the activity. The simultaneous hydrodeoxygenation of cyclic vicinal diols occurs with high cis-stereoselectivity. ReOx-Pd/CeO2 catalysts were characterized by means of XRD, TEM, H2-TPR, XAFS, XPS, Raman, and DFT calculations. The Re species on ReOx-Pd/CeO2 (Re = 2 wt %, Pd/Re = 0.25) catalyst after reduction and after stoichiometric reaction of 1,2-hexanediol to 1-hexene were ReIV and ReVI, and the ReIV species were converted to ReVI through the stoichiometric reaction. The Re species on ReOx-Pd/CeO2 are proposed to be randomly located on the CeO2 surface, and probably only monomeric Re species have catalytic activity for simultaneous hydrodeoxygenation. This model can explain the higher activity of Re = 2 wt % catalyst than those of higher Re loading catalysts. The reaction is proposed to proceed by the tetra/hexavalent redox cycle of the Re center in the catalysis followed by hydrogenation.
Ota, Nobuhiko,Tamura, Masazumi,Nakagawa, Yoshinao,Okumura, Kazu,Tomishige, Keiichi
p. 3213 - 3226
(2016/07/06)

Enantioselective Cascade Biocatalysis via Epoxide Hydrolysis and Alcohol Oxidation: One-Pot Synthesis of (R)-α-Hydroxy Ketones from Meso- or Racemic Epoxides
A new type of cascade biocatalysis was developed for one-pot enantioselective conversion of a meso- or racemic epoxide to an α-hydroxy ketone in high ee via an epoxide hydrolase-catalyzed hydrolysis of the epoxide, an alcohol dehydrogenase-catalyzed oxidation of the diol intermediate, and an enzyme-catalyzed cofactor regeneration. In vitro cascade biotransformation of meso-epoxides (cyclopentene oxide 1a, cyclohexene oxide 1b, and cycloheptene oxide 1c) was achieved with cell-free extracts containing recombinant SpEH (epoxide hydrolase from Sphingomonas sp. HXN-200), BDHA (butanediol dehydrogenase from Bacillus subtilis BGSC1A1), and LDH (lactate dehydrogenase form Bacillus subtilis) or NOX (NADH oxidase from Lactobacillus brevis DSM 20054), respectively, giving the corresponding (R)-α-hydroxycyclopentanone 3a, (R)-α-hydroxycyclohexanone 3b, and (R)-α-hydroxycycloheptanone 3c in 98-99% ee and 70-50% conversion with TTN of NAD+-recycling of 5500-26000. Cascade catalysis with mixed cells of Escherichia coli (SpEH) and E. coli (BDHA-NOX) converted 100-300 mM meso-epoxides 1a-1c to (R)-α-hydroxy ketones 3a-3c in 98-99% ee and 85-57% conversion. Cells of E. coli (SpEH-BDHA-NOX) coexpressing all three enzymes were also proven as good catalysts for the cascade conversion of 100-200 mM meso-epoxides 1a-1c, giving (R)-α-hydroxy ketones 3a-3c in 98-99% ee and 79-52% conversion. The cascade biocatalysis for one-pot synthesis of α-hydroxy ketone in high ee was also successfully demonstrated with a racemic epoxide (1,2,3,4-tetrahydronaphthalene-1,2-oxide 1d) as the substrate. By using two whole-cells based approaches, (R)-α-hydroxytetralone 3d was obtained in 99% ee and 49-40% conversion from 20 to 5 mM racemic epoxide 1d. Preparative cascade biotransformation of cyclohexene oxide 1b gave (R)-α-hydroxycyclohexanone 3b in 98% ee with 70% isolated yield. The developed new type of cascade biocatalysis is enantioselective, green, and often high yielding. The concept might be generally applicable to produce other useful enantiopure α-hydroxy ketones from the corresponding meso- or racemic epoxides by cascade catalysis using appropriate enzymes. (Chemical Equation Presented).
Zhang, Jiandong,Wu, Shuke,Wu, Jinchuan,Li, Zhi
p. 51 - 58
(2015/04/27)

Reshaping an Enzyme Binding Pocket for Enhanced and Inverted Stereoselectivity: Use of Smallest Amino Acid Alphabets in Directed Evolution
Directed evolution based on saturation mutagenesis at sites lining the binding pocket is a commonly practiced strategy for enhancing or inverting the stereoselectivity of enzymes for use in organic chemistry or biotechnology. However, as the number of residues in a randomization site increases to five or more, the screening effort for 95% library coverage increases astronomically until it is no longer feasible. We propose the use of a single amino acid for saturation mutagenesis at superlarge randomization sites comprising 10 or more residues. When used to reshape the binding pocket of limonene epoxide hydrolase, this strategy, which drastically reduces the search space and thus the screening effort, resulted in R,R- and S,S-selective mutants for the hydrolytic desymmetrization of cyclohexene oxide and other epoxides. X-ray crystal structures and docking studies of the mutants unveiled the source of stereoselectivity and shed light on the mechanistic intricacies of this enzyme.
Sun, Zhoutong,Lonsdale, Richard,Kong, Xu-Dong,Xu, Jian-He,Zhou, Jiahai,Reetz, Manfred T.
supporting information
p. 12410 - 12415
(2015/10/12)

Alcohol cross-coupling for the kinetic resolution of diols via oxidative esterification
We present an organocatalytic C-O-bond cross-coupling strategy to kinetically resolve racemic diols with aromatic and aliphatic alcohols, yielding enantioenriched esters. This one-pot protocol utilizes an oligopeptide multicatalyst, m-CPBA as the oxidant, and N,N-diisopropylcarbodiimide as the activating agent. Racemic acyclic diols as well as trans-cycloalkane-1,2-diols were kinetically resolved, achieving high selectivities and good yields for the products and recovered diols.
Hofmann, Christine,Schümann, Jan M.,Schreiner, Peter R.
p. 1972 - 1978
(2015/02/19)

A photoinduced cyclization cascade - Total synthesis of (-)-leuconoxine
A protecting-group-free and enantioselective total synthesis of the monoterpenoid indole alkaloid (-)-leuconoxine was accomplished. The key step comprises a novel photoinduced domino macrocyclization/transannular cyclization involving the Witkop cyclization, for which additional mechanistic evidence is provided. This process furnishes a diaza[5.5.6.6]fenestrane skeleton, which is a hitherto unprecedented structure element.
Pfaffenbach, Magnus,Gaich, Tanja
supporting information
p. 6355 - 6357
(2015/04/22)

Silica microspheres containing high density surface hydroxyl groups as efficient epoxidation catalysts
Uniformly sized silica microspheres were synthesized by a hydrolysis-condensation method. The obtained material was etched with a mild aqueous potassium hydroxide solution for different periods of time to break their Si-O-Si bonds and increases the density of hydroxyl groups on their surfaces. The resulting materials were then used as transition metal-free catalysts for oxidation of olefins in the presence of hydrogen peroxide as a green oxidant. The materials were thoroughly characterized using various physicochemical techniques. These highly populated hydroxyl groups on the surface of silica microspheres were proven to be responsible for excellent conversion (up to 93%) and epoxide selectivity (up to 100%) for various olefins. Quantum mechanical calculations also corroborate the experimental findings. Furthermore, both experimental and theoretical studies show that tertiary silanols were present at the active sites of the catalyst surface and were responsible for olefin epoxidation.
Chandra, Prakash,Doke, Dhananjay S.,Umbarkar, Shubhangi B.,Vanka, Kumar,Biradar, Ankush V.
p. 21125 - 21131
(2015/03/30)

Functionality, Effectiveness, and Mechanistic Evaluation of a Multicatalyst-Promoted Reaction Sequence by Electrospray Ionization Mass Spectrometry
A multicatalytic three-step reaction consisting of epoxidation, hydrolysis, and enantioselective monoacylation of cyclohexene was studied by using mass spectrometry (MS). The reaction sequence was carried out in a one-pot reaction using a multicatalyst. All reaction steps were thoroughly analyzed by electrospray ionization (ESI) MS (and MS/MS), as well as high-resolution MS for structure elucidation. These studies allow us to shed light on the individual mode of action of each catalytic moiety. Thus, we find that under the epoxidation conditions, the catalytically active N-methyl imidazole for the terminal acylation step is partially deactivated through oxidation. This observation helps to explain the lower efficiency of the catalyst in the last step compared to the monoacylation performed separately. All reactive intermediates and products of the reaction sequence, as well as of the side-reactions, were monitored, and we present a working mechanism of the reaction.
Alachraf, M. Wasim,Wende, Raffael C.,Schuler, S?ren M. M.,Schreiner, Peter R.,Schrader, Wolfgang
p. 16203 - 16208
(2015/11/03)

The influences of Al species and Ti species on the catalytic epoxidation over Si/Ti-pillared MCM-36 synthesized from MCM-22
A novel mesopore silica-aluminium material, i.e., Si/Ti-MCM-36 derivatives were prepared with Si/Ti mixed oxide as a pillar. The influences of acidity from Al species and the coordination state of Ti species on the catalytic cylcohexene epoxidation with t-butylhydroperoxide (TBHP) as the oxidant were investigated. The mesoporous structures were confirmed by XRD and N2 ads/desorption experiment. The acidity and surface polarity were characterized by NH3-TPD, 27Al 2D MQ MAS NMR and 29Si MAS NMR. The Ti coordination state was identified with UV-Vis spectra. By using 27Al 2D MQ MAS NMR technique, the Al species from the different eight crystallographically T (Si, Al) positions of MWW zeolite were identified, which are associated with bridging hydroxyl groups such as the Bronsted acid site. It was found that the Si/Ti-MCM-36 samples, whether with tetrahedrally (Td) or octahedrally (Oh) coordinated state Ti species, are all inactive for the cyclohexene epoxidation. A further acid treatment of the Si/Ti-MCM-36 samples can greatly expel Al species from the MWW structure, which largely decrease the acidity and transfer the acid-catalyzed decomposition of t-butylhydroperoxide to Ti catalyzed cyclohexene epoxidation. It shows that not only the amount of Al species but also their framework crystallographic positions have a great influence on the epoxidation activity. Furthermore, the grafting of the tetra-isopropoxide on the acid treated Si/Ti-MCM-36 can increase its hydrophobicity and epoxidation activity. Moreover, the Td TiO4 in the units has been confirmed to be the most active site for the epoxidation reaction.
Jin, Fang,Huang, Shingjong,Cheng, Soofin,Wu, Yuanxin,Chang, Chih-Cheng,Huang, Yu-Wei
p. 3007 - 3016
(2015/05/20)

Highly Enantioselective Catalytic System for Asymmetric Copolymerization of Carbon Dioxide and Cyclohexene Oxide
A new ligand can be easily prepared, and its intramolecular dinuclear zinc complexes act as a high performance catalyst for the asymmetric alternating copolymerization of cyclohexene oxide and CO2under very mild conditions (1 atm CO2, room temperature), affording completely alternating polycarbonates with up to 93.8 % enantiomeric excess (ee) and 98 % yield. A high Mnvalue of 28 600 and a relatively narrow polydispersity (Mw/Mnratio) of 1.43 were also achieved.
Hua, Yuan-Zhao,Lu, Liu-Jie,Huang, Pei-Jin,Wei, Dong-Hui,Tang, Ming-Sheng,Wang, Min-Can,Chang, Jun-Biao
supporting information
p. 12394 - 12398
(2016/08/25)

Enantiomerically enriched tris(boronates): Readily accessible conjunctive reagents for asymmetric synthesis
The catalytic enantioselective diboration of vinyl boronate esters furnishes chiral tris(boronates) in a selective fashion. Subsequent deborylative alkylation occurs in a diastereoselective fashion, both for intermolecular and intramolecular processes.
Coombs, John R.,Zhang, Liang,Morken, James P.
p. 16140 - 16143
(2015/01/09)

Phenolic glycosides from the twigs of Salix glandulosa
As a part of an ongoing search for bioactive constituents from Korean medicinal plants, the phytochemical investigations of the twigs of Salix glandulosa afforded 12 new phenolic glycosides (1-12) and a known analogue (13). The structures of 1-13 were characterized by a combination of NMR methods (1H and 13C NMR, 1H-1H COSY, HMQC, and HMBC), chemical hydrolysis, and GC/MS. The absolute configuration of 13 [(1R,2S)-2-hydroxycyclohexyl-2′-O-trans-p-coumaroyl-β-d- glucopyranoside] was determined for the first time. Compounds 1-3, 6, and 7 exhibited inhibitory effects on nitric oxide production in lipopolysaccharide- activated murine microglial cells (IC50 values in the range 6.6-20.5 μM).
Kim, Chung Sub,Kwon, Oh Wook,Kim, Sun Yeou,Choi, Sang Un,Kim, Jae Yoon,Han, Ji Young,Choi, Soo Im,Choi, Jong Gil,Kim, Ki Hyun,Lee, Kang Ro
p. 1955 - 1961
(2014/10/16)

En route to multicatalysis: Kinetic resolution of trans-cycloalkane-1,2- diols via oxidative esterification
We demonstrate the application of a multicatalyst to the oxidation of a broad variety of aldehydes and subsequent enantioselective esterification of the incipient acids with (±)-trans-cycloalkane-1,2-diols. This reaction operates well with a multicatalyst bearing two independent catalytic moieties that provide monoprotected 1,2-diols in one pot.
Hofmann, Christine,Schuler, Soeren M. M.,Wende, Raffael C.,Schreiner, Peter R.
supporting information
p. 1221 - 1223
(2014/01/17)

Organocatalytic asymmetric hydrolysis of epoxides
The hydrolytic ring opening of epoxides is an important biosynthetic transformation and is also applied industrially. We report the first organocatalytic variant of this reaction, exploiting our recently discovered activation of carboxylic acids with chiral phosphoric acids via heterodimerization. The methodology mimics the enzymatic mechanism, which involves an enzyme-bound carboxylate nucleophile. A newly designed phosphoric acid catalyst displays high stereocontrol in the desymmetrization of meso-epoxides. The methodology shows wide generality with cyclic, acylic, aromatic, and aliphatic substrates. We also apply our method in the first highly enantioselective anti-dihydroxylation of simple olefins.
Monaco, Mattia Riccardo,Prevost, Sebastien,List, Benjamin
p. 8142 - 8145
(2014/08/18)

A broadly applicable and practical oligomeric (salen)Co catalyst for enantioselective epoxide ring-opening reactions
The (salen)Co catalyst (4a) can be prepared as a mixture of cyclic oligomers in a short, chromatography-free synthesis from inexpensive, commercially available precursors. This catalyst displays remarkable enhancements in reactivity and enantioselectivity relative to monomeric and other multimeric (salen)Co catalysts in a wide variety of enantioselective epoxide ring-opening reactions. The application of catalyst 4a is illustrated in the kinetic resolution of terminal epoxides by nucleophilic ring-opening with water, phenols, and primary alcohols; the desymmetrization of meso epoxides by addition of water and carbamates; and the desymmetrization of oxetanes by intramolecular ring opening with alcohols and phenols. The favorable solubility properties of complex 4a under the catalytic conditions facilitated mechanistic studies, allowing elucidation of the basis for the beneficial effect of oligomerization. Finally, a catalyst selection guide is provided to delineate the specific advantages of oligomeric catalyst 4a relative to (salen)Co monomer 1 for each reaction class.
White, David E.,Tadross, Pamela M.,Lu, Zhe,Jacobsen, Eric N.
supporting information
p. 4165 - 4180
(2014/06/09)

Heterobimetallic dual-catalyst systems for the hydrolytic kinetic resolution of terminal epoxides
A heterobimetallic dual-catalyst system based on the preparation and use of various salen complexes has been developed for the hydrolytic kinetic resolution (HKR) of terminal epoxides. A combination of cobalt-salen and manganese-salen complexes, generated from ligands with the same configuration possessing thiophene or pyrrole moieties, produced indeed highly selective catalysts for the hydrolysis of epibromohydrin. This effect could also be extended to other terminal epoxides and to the more challenging ring opening of cyclohexene oxide. Kinetic studies indicated that only one CoIII salen complex was involved in the rate-determining step, which supported a heterobimetallic highly enantioselective pathway based on the crucial existence of in situ generated CoIII-OH species, previously postulated in the literature. The beneficial effect of the presence of additional Mn-complexes was ascribed to the inhibition of the alternative less enantioselective monometallic reaction pathway by epoxide activation.
Hong, Xiang,Mellah, Mohamed,Schulz, Emmanuelle
p. 2608 - 2617
(2014/07/22)

Enantioselective hydrolysis of racemic and meso -epoxides with recombinant escherichia coli expressing epoxide hydrolase from Sphingomonas sp. HXN-200: Preparation of epoxides and vicinal diols in high ee and high concentration
A unique epoxide hydrolase (SpEH) from Sphingomonas sp. HXN-200 was identified and cloned based on genome sequencing and expressed in Escherichia coli. The engineered E. coli (SpEH) showed the same selectivity and substrate specificity as the wild type strain and 172 times higher activity than Sphingomonas sp. HXN-200 for the hydrolysis of styrene oxide 1. Hydrolysis of racemic styrene oxide 1, substituted styrene oxides 3, 5-7, and N-phenoxycarbonyl-3,4-epoxypiperidine 8 (200-100 mM) with resting cells of E. coli (SpEH) gave (S)-epoxides 1, 3, 5-7 and (-)-8 in 98.0-99.5% enantiomeric excess (ee) and 37.6-46.5% yield. Hydrolysis of cyclopentene oxide 9, cyclohexene oxide 10, and N-benzyloxycarbonyl-3,4-epoxypyrrolidine 11 (100 mM) afforded the corresponding (R, R)-vicinal trans-diols 12-14 in 86-93% ee and 90-99% yield. The ee of (1R, 2R)-cyclohexane-1,2-diol 13 was improved to 99% by simple crystallization. These biotransformations showed high specific activity (0.28-4.3 U/mg cdw), product concentration, product/cells ratio, and cell-based productivity. Hydrolysis at even higher substrate concentration was also achieved: (S)-1 was obtained in 430 mM (51 g/Lorg) and 43% yield; (1R, 2R)-13 was obtained in 500 mM (58 g/L) and >99% yield. Gram-scale preparation of epoxides (S)-1, (S)-3, (S)-6 and diols (1R, 2R)-12, (1R, 2R)-13, (3R, 4R)-14 were also demonstrated. E. coli (SpEH) cells showed the highest enantioselectivity to produce (S)-1 (E of 39) among all known EHs in the form of whole cells or free enzymes and the highest enantioselectivities to produce (S)-3, 5, 6, 7, (-)-8, and (R, R)-14 (E of 36, 35, 28, 57, 22, and 28) among all known EHs. The easily available and highly active E. coli (SpEH) cells are the best biocatalysts known thus far for the practical preparation of these useful and valuable enantiopure epoxides and vicinal diols via hydrolysis.
Wu, Shuke,Li, Aitao,Chin, Yit Siang,Li, Zhi
p. 752 - 759
(2013/06/05)

Enhanced rate and selectivity by carboxylate salt as a basic cocatalyst in chiral N-heterocyclic carbene-catalyzed asymmetric acylation of secondary alcohols
The rate and enantioselectivity of chiral NHC-catalyzed asymmetric acylation of alcohols with an adjacent H-bond donor functionality are remarkably enhanced in the presence of a carboxylate cocatalyst. The degree of the enhancement is correlated with the basicity of the carboxylate. With a cocatalyst and a newly developed electron-deficient chiral NHC, kinetic resolution and desymmetrization of cyclic diols and amino alcohols were achieved with extremely high selectivity (up to s = 218 and 99% ee, respectively) at a low catalyst loading (0.5 mol %). This asymmetric acylation is characterized by a unique preference for alcohols over amines, which are not converted into amides under the reaction conditions.
Kuwano, Satoru,Harada, Shingo,Kang, Bubwoong,Oriez, Raphael,Yamaoka, Yousuke,Takasu, Kiyosei,Yamada, Ken-Ichi
supporting information
p. 11485 - 11488
(2013/09/02)

Enantioselective biooxidation of racemic trans-cyclic vicinal diols: One-pot synthesis of both enantiopure (S,S)-cyclic vicinal diols and (R)-α-hydroxy ketones
Highly regio- and enantioselective alcohol dehydrogenases BDHA (2,3-butanediol dehydrogenase from Bacillus subtilis BGSC1A1), CDDHPm (cyclic diol dehydrogenase from Pseudomonas medocina TA5), and CDDHRh (cyclic diol dehydrogenase from Rhodococcus sp. Moj-3449) were discovered for the oxidation of racemic trans-cyclic vicinal diols. Recombinant Escherichia coli expressing BDHA was engineered as an efficient whole-cell biocatalyst for the oxidation of (±)-1,2-cyclopentanediol, 1,2-cyclohexanediol, 1,2-cycloheptane-diol, and 1,2-cyclooctanediol, respectively, to give the corresponding (R)-α-hydroxy ketones in >99% ee and (S,S)-cyclic diols in >99% ee at 50% conversion in one pot. Escherichia coli (BDHA-LDH) co-expressing lactate dehydrogenase (LDH) for intracellular regeneration of NAD+ catalyzed the regio- and enantioselective oxidation of (±)-1,2-dihydroxy-1,2,3,4- tetrahydronaphthalene to produce the corresponding (R)-α-hydroxy ketone in >99% ee and (S,S)-cyclic diol in 96% ee at 49% conversion. Preparative biotransformations were also demonstrated. Thus, a novel and useful method for the one-pot synthesis of both vicinal diols and α-hydroxy ketones in high ee was developed via high Copyright
Zhang, Jiandong,Xu, Tingting,Li, Zhi
supporting information
p. 3147 - 3153
(2013/12/04)

Lipophilic oligopeptides for chemo- and enantioselective acyl transfer reactions onto alcohols
Inspired by the extraordinary selectivities of acylases, we envisioned the use of lipophilic oligopeptidic organocatalysts for the acylative kinetic resolution/desymmetrization of rac- and meso-cycloalkane-1,2-diols. Here we describe in a full account the discovery and development process from the theoretical concept to the final catalyst, including scope and limitations. Competition experiments with various alcohols and electrophiles show the full potential of the employed oligopeptides. Additionally, we utilized NMR and IR-spectroscopic methods as well as computations to shed light on the factors responsible for the selectivity. The catalyst system can be readily modified to a multicatalyst by adding other catalytically active amino acids to the peptide backbone, enabling the stereoselective one-pot synthesis of complex molecules from simple starting materials.
Mueller, Christian E.,Zell, Daniela,Hrdina, Radim,Wende, Raffael C.,Wanka, Lukas,Schuler, Soeren M. M.,Schreiner, Peter R.
p. 8465 - 8484
(2013/09/24)

Two alternative routes for 1,2-cyclohexanediol synthesis by means of green processes: Cyclohexene dihydroxylation and catechol hydrogenation
In this paper we compare two different reactions, aimed at the synthesis of 1,2-cyclohexanediol. Specifically: (a) the direct epoxidation and hydrolysis (dihydroxylation) of cyclohexene to trans-1,2-cyclohexanediol, with an aqueous solution of hydrogen peroxide, and (b) the hydrogenation of catechol to a mixture of cis and trans-1,2-cyclohexanediol, in an attempt to establish green protocols for the synthesis of diols. Both reactions, the dihydroxylation of cyclohexene and the hydrogenation of catechol, were carried out without organic solvents. In the former case, an unprecedented 97.4% yield to the glycol was obtained, by selecting proper reaction conditions and using a tungstic acid/phosphoric acid catalyst, in a biphasic system with a phase-transfer agent. In the second approach, a heterogeneous alumina-supported Ru(OH)x catalyst was used, and a 90% yield to the glycol was obtained. A comparison of the two processes allowed to show the lower environmental impact of the catechol hydrogenation route.
Antonetti, Claudia,Galletti, Anna Maria Raspolli,Accorinti, Pasquale,Alini, Stefano,Babini, Pierpaolo,Raabova, Katerina,Rozhko, Elena,Caldarelli, Aurora,Righi, Paolo,Cavani, Fabrizio,Concepcion, Patricia
p. 21 - 31
(2013/08/23)

Influence of temperature and pressure on cyclic carbonate synthesis catalyzed by bimetallic aluminum complexes and application to overall syn -bis-hydroxylation of alkenes
The effect of moderate temperatures (22-100 °C) and pressures (1-10 bar) on the synthesis of cyclic carbonates from epoxides and carbon dioxide catalyzed by a combination of bimetallic aluminum complexes and tetrabutylammonium bromide is investigated. The combined bimetallic complex and tetrabutylammonium bromide catalyst system is shown to be an order of magnitude more active than the use of tetrabutylammonium bromide alone at all temperatures and pressures studied. At the higher temperatures and pressures used, disubstituted epoxides become substrates for the reaction and it is shown that reactions proceed with retention of the epoxide stereochemistry. This allowed a route for the overall syn-bis-hydroxylation of alkenes to be developed without the use of hazardous metal based reagents. At higher pressures it is also possible to use compressed air as the carbon dioxide source.
Beattie, Christopher,North, Michael,Villuendas, Pedro,Young, Carl
p. 419 - 426
(2013/03/13)

Enhanced asymmetric induction for the copolymerization of CO2 and cyclohexene oxide with unsymmetric enantiopure SalenCo(III) complexes: Synthesis of crystalline CO2-based polycarbonate
Enantiopure metal-complex catalyzed asymmetric alternating copolymerization of CO2 and meso-epoxides is a powerful synthetic strategy for preparing optically active polycarbonates with main-chain chirality. The previous studies regarding chiral zinc catalysts provided amorphous polycarbonates with moderate enantioselectivity, and thus, developing highly stereoregular catalysts for this enantioselective polymerization is highly desirable. Herein, we report the synthesis of highly isotactic poly(cyclohexene carbonate)s from meso-cyclohexene oxide using dissymmetrical enantiopure salenCo(III) complexes in conjunction with bis(triphenylphosphine)iminium chloride (PPNCl) as catalyst. The presence of a chiral induction agent such as (S)-propylene oxide or (S)-2-methyltetrahydrofuran significantly improved the enantioselectivity regarding (S,S)-salenCo(III) catalyst systems. Up to 98:2 of RR:SS was observed in the resultant polycarbonates obtained from the catalyst system based on (S,S)-salenCo(III) complex 4d bearing an adamantyl group on the phenolate ortho position, in the presence of (S)-2-methyltetrahydrofuran. Primary ONIOM (DFT:UFF) calculations, which were performed to investigate the effect of the competitive coordination of (S)-induction agent versus cyclohexene oxide to Co(III) center on enantioselectivity, suggest that the (S)-C-O bond in cyclohexene oxide is more favorable for cleavage, due to the interaction between oxygen atom of (S)-induction agent and (S)-C-H of the coordinated cyclohexene oxide. The highly isotactic poly(cyclohexene carbonate) is a typical semicrystalline polymer, possessing a melting point of 216 °C and a decomposition temperature of 310 °C.
Wu, Guang-Peng,Ren, Wei-Min,Luo, Yi,Li, Bo,Zhang, Wen-Zhen,Lu, Xiao-Bing
supporting information; experimental part
p. 5682 - 5688
(2012/06/04)

Enantiomerically enriched trans-diols from alkenes in one pot: A multicatalyst approach
Multicatalysts consisting of non-natural oligopeptides with distinctly different catalytic moieties create molecular complexity in a multistep one-pot sequence starting from simple alkenes yielding highly enantiomerically enriched trans-diols. The Royal Society of Chemistry 2012.
Hrdina, Radim,Mueller, Christian E.,Wende, Raffael C.,Wanka, Lukas,Schreiner, Peter R.
p. 2498 - 2500
(2012/04/10)

Self-assembly approach toward chiral bimetallic catalysts: Bis-urea-functionalized (Salen)cobalt complexes for the hydrolytic kinetic resolution of epoxides
A series of novel bis-urea-functionalized (salen)Co complexes has been developed. The complexes were designed to form self-assembled structures in solution through intermolecular urea-urea hydrogen-bonding interactions. These bis-urea (salen)Co catalysts resulted in rate acceleration (up to 13atimes) in the hydrolytic kinetic resolution (HKR) of rac-epichlorohydrin in THF by facilitating cooperative activation, compared to the monomeric catalyst. In addition, one of the bis-urea (salen)CoIII catalyst efficiently resolves various terminal epoxides even under solvent-free conditions by requiring much shorter reaction time at low catalyst loading (0.03-0.05amol %). A series of kinetic/mechanistic studies demonstrated that the self-association of two (salen)Co units through urea-urea hydrogen bonds was responsible for the observed rate acceleration. The self-assembly study with the bis-urea (salen)Co by FTIR spectroscopy and with the corresponding (salen)Ni complex by 1HaNMR spectroscopy showed that intermolecular hydrogen-bonding interactions exist between the bis-urea scaffolds in THF. This result demonstrates that self-assembly approach by using non-covalent interactions can be an alternative and useful strategy toward the efficient HKR catalysis.
Park, Jongwoo,Lang, Kai,Abboud, Khalil A.,Hong, Sukwon
supporting information; experimental part
p. 2236 - 2245
(2011/03/22)

Asymmetric trans-dihydroxylation of cyclic olefins by enzymatic or chemo-enzymatic sequential epoxidation and hydrolysis in one-pot
Novel and efficient one-pot enzymatic and chemo-enzymatic synthetic methods are developed for the asymmetric trans-dihydroxylations of cyclic olefins 1a and 1bvia sequential epoxidation and hydrolysis. The Novozym 435 -mediated epoxidation of cyclohexene 1a and subsequent hydrolysis of the intermediate cyclohexene oxide 2a with resting cells of Sphingomonas sp. HXN-200 in one-pot gave (1R,2R)-cyclohexane diol 3a in 84% ee and 95% conversion. trans-Dihydroxylation of N-benzyloxycarbonyl 3-pyrroline 1b with the same enzymatic system gave the corresponding (3R,4R)-N- benzyloxycarbonyl-3,4-dihydroxy-pyrrolidine 3b in 93% ee and 94% conversion. In the one-pot chemo-enzymatic system, epoxidation of N-benzyloxycarbonyl 3-pyrroline 1b by m-CPBA and subsequent hydrolysis of epoxide intermediate 2b with resting cells of Sphingomonas sp. HXN-200 gave the trans-diol (3R,4R)-3b in 92% ee and 94-97% conversion. While the trans-dihydroxylation of cyclohexene 1a to (1R,2R)-cyclohexane diol 3a is reported for the first time, the trans-dihydroxylation of N-benzyloxycarbonyl 3-pyrroline 1b to (3R,4R)-3b with such an enzymatic or chemo-enzymatic system afforded a much higher product concentration than the same reaction with the system using a microorganism containing the two necessary enzymes. The developed one-pot enzymatic and chemo-enzymatic systems for the asymmetric trans-dihydroxylation of olefins are new, easy to prepare, adjust and operate, are high yielding, complementary to Sharpless asymmetric dihydroxylation and particularly useful for the asymmetric synthesis of cyclic trans-diols.
Xu, Yi,Li, Aitao,Jia, Xin,Li, Zhi
experimental part
p. 2452 - 2458
(2011/10/13)

Manipulating the Expression Rate and Enantioselectivity of an Epoxide Hydrolase by Using Directed Evolution
We describe here a strategy to improve the expression efficiency and enantioselectivity of Aspergillus niger epoxide hydrolase (ANEH) by directed evolution. Based on a blue-colony screening system using the LacZα (β-galactosidase α peptide) complementation solubility reporter, several ANEH variants out of 15000 transformants from a random-mutagenesis library were identified that show improved recombinant expression in E. coli. Among them, Pro221Ser was subsequently used as a template for iterative saturation mutagenesis (ISM) at sites around the ANEH binding pocket. Following four rounds of ISM, a highly enantioselective mutant was identified that catalyzes the hydrolytic kinetic resolution of racemic glycidyl phenyl ether with a selectivity factor of E=160 in favor of the (S)-diol compared to WT ANEH characterized by E=4.6. Expression of this mutant is 50 times higher than that of WT ANEH. It also serves as an excellent stereoselective catalyst in the hydrolytic kinetic resolution and desymmetrization of several other structurally diverse epoxides. Copyright
Reetz, Manfred T.,Zheng, Huabao
experimental part
p. 1529 - 1535
(2012/05/31)

Oxidative esterification, thioesterification, and amidation of aldehydes by a two-component organocatalyst system using a chiral N-heterocyclic carbene and redox-active riboflavin
Flavin of the month! Triazolium-derived N-heterocyclic carbenes (NHCs) and a flavin catalyzed the oxidative esterification, thioesterification, and amidation of aldehydes with various alcohols, thiols, and amines, respectively, with O2 as the terminal oxidant (see scheme; R1=aryl; R2, R3=alkyl or aryl). By using a chiral NHC catalyst, the enantioselective acylation promoted the kinetic resolution of racemic alcohols and the desymmetrization of a meso-diol.
Iwahana, Soichiro,Iida, Hiroki,Yashima, Eiji
supporting information; experimental part
p. 8009 - 8013
(2011/08/22)

Manipulating the stereoselectivity of limonene epoxide hydrolase by directed evolution based on iterative saturation mutagenesis
Limonene epoxide hydrolase from Rhodococcus erythropolis DCL 14 (LEH) is known to be an exceptional epoxide hydrolase (EH) because it has an unusual secondary structure and catalyzes the hydrolysis of epoxides by a rare one-step mechanism in contrast to the usual two-step sequence. From a synthetic organic viewpoint it is unfortunate that LEH shows acceptable stereoselectivity essentially only in the hydrolysis of the natural substrate limonene epoxide, which means that this EH cannot be exploited as a catalyst in asymmetric transformations of other substrates. In the present study, directed evolution using iterative saturation mutagenesis (ISM) has been tested as a means to engineer LEH mutants showing broad substrate scope with high stereoselectivity. By grouping individual residues aligning the binding pocket correctly into randomization sites and performing saturation mutagenesis iteratively using a reduced amino acid alphabet, mutants were obtained which catalyze the desymmetrization of cyclopentene-oxide with stereoselective formation of either the (R,R)- or the (S,S)-diol on an optional basis. The mutants prove to be excellent catalysts for the desymmetrization of other meso-epoxides and for the hydrolytic kinetic resolution of racemic substrates, without performing new mutagenesis experiments. Since less than 5000 tranformants had to be screened for achieving these results, this study contributes to the generalization of ISM as a fast and reliable method for protein engineering. In order to explain some of the stereoselective consequences of the observed mutations, a simple model based on molecular dynamics simulations has been proposed.
Zheng, Huabao,Reetz, Manfred T.
supporting information; experimental part
p. 15744 - 15751
(2011/02/21)