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Supported ionic liquid-like phases as efficient solid ionic solvents for the immobilisation of alcohol dehydrogenases towards the development of stereoselective bioreductions
Polymeric materials containing ionic liquid fragments, like those found in bulk ILs, are excellent solid media for the immobilisation of biocatalysts. Herein, the entrapment of the enzymatic system formed by alcohol dehydrogenase from Rhodococcus ruber (ADH-A) overexpressed in E. coli and its coenzyme has been studied. The activity, stability and reusability of these preparations have been investigated in the bioreduction of prochiral ketones finding excellent levels of conversion and selectivity. Interestingly, the immobilised enzyme remained active and exhibited excellent stability in aqueous solutions after several recycling uses. More importantly, these biopolymer materials retained most of their activity after consecutive reaction cycles, prolonged storage and under flow conditions.
Altava, Belen,García-Verdugo, Eduardo,Gotor-Fernández, Vicente,Lavandera, Iván,Lozano, Pedro,Luis, Santiago V.,Porcar, Raul
p. 5609 - 5617
(2021/08/16)

Amino Acid-Functionalized Metal-Organic Frameworks for Asymmetric Base–Metal Catalysis
We report a strategy to develop heterogeneous single-site enantioselective catalysts based on naturally occurring amino acids and earth-abundant metals for eco-friendly asymmetric catalysis. The grafting of amino acids within the pores of a metal-organic framework (MOF), followed by post-synthetic metalation with iron precursor, affords highly active and enantioselective (>99 % ee for 10 examples) catalysts for hydrosilylation and hydroboration of carbonyl compounds. Impressively, the MOF-Fe catalyst displayed high turnover numbers of up to 10 000 and was recycled and reused more than 15 times without diminishing the enantioselectivity. MOF-Fe displayed much higher activity and enantioselectivity than its homogeneous control catalyst, likely due to the formation of robust single-site catalyst in the MOF through site-isolation.
Newar, Rajashree,Akhtar, Naved,Antil, Neha,Kumar, Ajay,Shukla, Sakshi,Begum, Wahida,Manna, Kuntal
supporting information
p. 10964 - 10970
(2021/03/29)

METHODS OF MAKING HIGH ENANTIOSELECTIVE SECONDARY ALCOHOLS
A new process to synthesis of compound OBI-3424 R-form and S-form products is provided. The "R-form" compound OBI-3423 was first synthesized with 48% overall yield from compound OBI-3424-5 by installation of the labile phosphate motif at later stage. The stereo chemistry is established by 5 steps chemo-enzyme combination synthesis to afford 99% optical purity, After then, the "S-form" compound OBI-3424 is prepared with improving overall yield of 54% from compound OBI-3424-5. The stereo chemistry is established by 4 steps combination of chemo-enzyme synthesis with excellent optical purity of 99%.
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(2020/09/08)

Chiral Imidazo[1,5- a]pyridine-Oxazolines: A Versatile Family of NHC Ligands for the Highly Enantioselective Hydrosilylation of Ketones
Herein we report the synthesis and application of a versatile class of N-heterocyclic carbene ligands based on an imidazo[1,5-a]pyridine-3-ylidine backbone that is fused to a chiral oxazoline auxiliary. The key step in the synthesis of these ligands involves the installation of the oxazoline functionality via a microwave-assisted condensation of a cyano-azolium salt with a wide variety of 2-amino alcohols. The resulting chiral bidentate NHC-oxazoline ligands form stable complexes with rhodium(I) that are efficient catalysts for the enantioselective hydrosilylation of structurally diverse ketones. The corresponding secondary alcohols are isolated in good yields (typically >90%) with good to excellent enantioselectivities (80-93% ee). The reported hydrosilylation occurs at ambient temperatures (40 °C), with excellent functional group tolerability. Even ketones bearing heterocyclic substituents (e.g., pyridine or thiophene) or complex organic architectures are hydrosilylated efficiently, which is discussed further in this report.
Chinna Ayya Swamy,Varenikov, Andrii,Ruiter, Graham De
supporting information
p. 247 - 257
(2020/02/04)

Efficient Asymmetric Synthesis of Ethyl (S)-4-Chloro-3-hydroxybutyrate Using Alcohol Dehydrogenase SmADH31 with High Tolerance of Substrate and Product in a Monophasic Aqueous System
Bioreductions catalyzed by alcohol dehydrogenases (ADHs) play an important role in the synthesis of chiral alcohols. However, the synthesis of ethyl (S)-4-chloro-3-hydroxybutyrate [(S)-CHBE], an important drug intermediate, has significant challenges concerning high substrate or product inhibition toward ADHs, which complicates its production. Herein, we evaluated a novel ADH, SmADH31, obtained from the Stenotrophomonas maltophilia genome, which can tolerate extremely high concentrations (6 M) of both substrate and product. The coexpression of SmADH31 and glucose dehydrogenase from Bacillus subtilis in Escherichia coli meant that as much as 660 g L-1 (4.0 M) ethyl 4-chloroacetoacetate was completely converted into (S)-CHBE in a monophasic aqueous system with a >99.9% ee value and a high space-time yield (2664 g L-1 d-1). Molecular dynamics simulation shed light on the high activity and stereoselectivity of SmADH31. Moreover, five other optically pure chiral alcohols were synthesized at high concentrations (100-462 g L-1) as a result of the broad substrate spectrum of SmADH31. All these compounds act as important drug intermediates, demonstrating the industrial potential of SmADH31-mediated bioreductions.
Chen, Rong,Liu, Qinghai,Wang, Hualei,Wei, Dongzhi,Xie, Youyu,Yang, Zeyu,Ye, Wenjie
p. 1068 - 1076
(2020/07/06)

Organic-inorganic nanocrystal reductase to promote green asymmetric synthesis
An acetophenone reductase from Geotrichum candidum (GcAPRD) was immobilized by the organic-inorganic nanocrystal method. The GcAPRD nanocrystal presented improved stability and recyclability compared with those of the free GcAPRD. Moreover, the GcAPRD nanocrystal reduced broad kinds of ketones with excellent enantioselectivities to produce beneficial chiral alcohols such as (S)-1-(3′,4′-dichlorophenyl)ethanol with >99% yield and >99% ee. The robust and versatile properties of the GcAPRD nanocrystal demonstrated an approach to promote green asymmetric synthesis and sustainable chemistry. This journal is
Koesoema, Afifa Ayu,Matsuda, Tomoko,Tsriwong, Kotchakorn
p. 30953 - 30960
(2020/09/11)

Production of chiral alcohols from racemic mixtures by integrated heterogeneous chemoenzymatic catalysis in fixed bed continuous operation
Valuable chiral alcohols have been obtained from racemic mixtures with an integrated heterogeneous chemoenzymatic catalyst in a two consecutive fixed catalytic bed continuous reactor system. In the first bed the racemic mixture of alcohols is oxidized to the prochiral ketone with a Zr-Beta zeolite and using acetone as the hydrogen acceptor. In the second catalytic bed the prochiral ketone is stereoselectively reduced with an alcohol dehydrogenase (ADH) immobilized on a two dimensional (2D) zeolite. In this process, the alcohol (isopropanol) formed by the reduction of acetone in the first step reduces the cofactor in the second step, and the full reaction cycle is in this way internally closed with 100% atom economy. A conversion of about 95% with ～100% selectivity to either the (R) or the (S) alcohol has been obtained for a variety of racemic mixtures of alcohols.
Carceller, Jose Miguel,Climent, Maria J.,Corma, Avelino,Iborra, Sara,Mifsud, Maria
supporting information
p. 2767 - 2777
(2020/06/17)

Asymmetric Transfer Hydrogenation in Thermomorphic Microemulsions Based on Ionic Liquids
A thermomorphic ionic-liquid-based microemulsion system was successfully applied for the Ru-catalyzed asymmetric transfer hydrogenation of ketones. On the basis of the temperature-dependent multiphase behavior of the targeted microemulsion, simple product separation as well as catalyst recycling could be realized. The use of water-soluble ligands improved the immobilization of the catalyst in the microemulsion phase and significantly decreased the catalyst leaching into the organic layer upon extraction of the product. Eventually, the optimized microemulsion system could be applied to a wide range of aromatic ketones that were reduced with good isolated yields (up to 98%) and enantioselectivities (up to 97%), while aliphatic ketones were less successful.
Hejazifar, Mahtab,Pálv?lgyi, ádám Márk,Bitai, Jacqueline,Lanaridi, Olga,Bica-Schr?der, Katharina
p. 1841 - 1851
(2019/10/11)

Compartmentalized Nanoreactors for One-Pot Redox-Driven Transformations
This contribution introduces poly(2-oxazoline)-based shell cross-linked micelles (SCMs) as nanoreactors to realize one-pot redox-driven deracemizations of secondary alcohols in aqueous media. TEMPO and Rh-TsDPEN moieties are spatially positioned into the hydrophilic corona and the hydrophobic micelle core, respectively. TEMPO catalyzes the oxidation of racemic secondary alcohols into ketones, while Rh-TsDPEN catalyzes the asymmetric transfer hydrogenation (ATH) of these ketones to afford enantioenriched secondary alcohols. Both catalysts, the Rh-TsDPEN complex and TEMPO, are incompatible with each other and the SCMs are designed to provide indispensable catalyst site isolation. Kinetic studies show that the SCMs enhance the reactivity of the immobilized catalysts, in comparison to those for the unsupported analogues under the same reaction conditions. Our nanoreactors can perform deracemizations on a broad range of secondary alcohol substrates and are reusable in a continuous manner while maintaining high activity.
Qu, Peiyuan,Kuepfert, Michael,Jockusch, Steffen,Weck, Marcus
p. 2701 - 2706
(2019/03/08)

A designer natural deep eutectic solvent to recycle the cofactor in alcohol dehydrogenase-catalysed processes
Deep eutectic solvents (DESs) nowadays represent a sustainable alternative to traditional organic solvents in (bio)transformations. Herein, the use of a solvent composed of an aqueous buffer and choline chloride:glucose (1.5:1 mol/mol) is proposed, a natural DES (NADES) serving as both a cosolvent and efficient system to recycle the nicotinamide cofactor. Thus, glucose from the NADES served as a co-substrate required for several alcohol dehydrogenases to reduce different prochiral ketones, and also helped to solubilise the organic compounds to develop effective biotransformations at higher substrate concentrations.
Mourelle-Insua, ángela,Lavandera, Iván,Gotor-Fernández, Vicente
supporting information
p. 2946 - 2951
(2019/06/18)

Structural basis for a highly (S)-enantioselective reductase towards aliphatic ketones with only one carbon difference between side chain
Aliphatic ketones, such as 2-butanone and 3-hexanone, with only one carbon difference among side chains adjacent to the carbonyl carbon are difficult to be reduced enantioselectively. In this study, we utilized an acetophenone reductase from Geotrichum candidum NBRC 4597 (GcAPRD) to reduce challenging aliphatic ketones such as 2-butanone (methyl ethyl ketone) and 3-hexanone (ethyl propyl ketone) to their corresponding (S)-alcohols with 94% ee and > 99% ee, respectively. Through crystallographic structure determination, it was suggested that residue Trp288 limit the size of the small binding pocket. Docking simulations imply that Trp288 plays an important role to form a C-H?π interaction for proper orientation of ketones in the pro-S binding pose in order to produce (S)-alcohols. The excellent (S)-enantioselectivity is due to a non-productive pro-R binding pose, consistent with the observation that the (R)-alcohol acts as an inhibitor of (S)-alcohol oxidation.
Koesoema, Afifa Ayu,Sugiyama, Yosuke,Xu, Zichang,Standley, Daron M.,Senda, Miki,Senda, Toshiya,Matsuda, Tomoko
p. 9543 - 9553
(2019/09/16)

Asymmetric Enzymatic Hydration of Unactivated, Aliphatic Alkenes
The direct enantioselective addition of water to unactivated alkenes could simplify the synthesis of chiral alcohols and solve a long-standing challenge in catalysis. Here we report that an engineered fatty acid hydratase can catalyze the asymmetric hydration of various terminal and internal alkenes. In the presence of a carboxylic acid decoy molecule for activation of the oleate hydratase from E. meningoseptica, asymmetric hydration of unactivated alkenes was achieved with up to 93 % conversion, excellent selectivity (>99 % ee, >95 % regioselectivity), and on a preparative scale.
Demming, Rebecca M.,Hammer, Stephan C.,Nestl, Bettina M.,Gergel, Sebastian,Fademrecht, Silvia,Pleiss, Jürgen,Hauer, Bernhard
supporting information
p. 173 - 177
(2018/12/11)

Enzymatic chemical transformations of aldehydes, ketones, esters and alcohols using plant fragments as the only biocatalyst: Ximenia americana grains
The present study demonstrated the ability of Ximenia american as a biocatalyst in reduction, hydrolysis and esterification reactions. The reduction reactions of aldehydes and ketones, ester hydrolysis and esterification of alcohols were carried out with interesting results. Reduction of ketones afforded yields of 6–60% with ee in the range of 35–>99% and that of aldehydes in yields of 51–99%. On the other hand, ester hydrolysis afforded yields of 58–98% with ee in the range 34–87%, while esterification of alcohols in 18–99% yields. Experimental conditions for all reactions have been defined using standard substrates as indicated in results and discussion. Some of the products are the potential building blocks for the synthesis of molecules which are of pharmaceutical and agrochemical importance.
da Silva, Romézio Alves Carvalho,de Mesquita, Bruna Marques,de Farias, Iolanda Frota,do Nascimento, Patrícia Georgiana Garcia,de Lemos, Telma Leda Gomes,Queiroz Monte, Francisco José
p. 187 - 194
(2018/01/05)

Enantioselective hydrogenation of ketones over a tartaric acid-modified raney nickel catalyst: Substrate-modifier interaction strength and enantioselectivity
Chiral (R,R)-tartaric acid and NaBr-doubly modified Raney nickel (TA-MRNi) is a promising heterogeneous catalyst for enantioselective hydrogenation of prochiral β-keto esters. To obtain deeper insights into the factors ruling the enantioselectivity, enantiodifferentiating hydrogenation of substituted ketones was studied over TA-MRNi and NaBr-modified RNi by use of combined individual-competitive hydrogenation techniques. Relative equilibrium adsorption constants of the substrates were estimated to evaluate their relative interaction strength with adsorbed tartaric acid moiety. DFT calculations were also performed to estimate the interaction energy through hydrogen bonding, providing clear support to the kinetic analysis and surface model. It is concluded with the enantioselective hydrogenation of ketones over TA-MRNi that the enantioselectivity increases as the substrate-modifier interaction strength increases: Methyl acetoacetate (MAA) > acetylacetone (AA) ～ 4-hydroxy-2-butanone (HB) > 2-octanone (2O).
Choliq, Azka Azkiya,Murakami, Eitaro,Yamamoto, Shota,Misaki, Tomonori,Fujita, Morifumi,Okamoto, Yasuaki,Sugimura, Takashi
p. 1325 - 1332
(2018/09/21)

Biocatalytic Racemization Employing TeSADH: Substrate Scope and Organic Solvent Compatibility for Dynamic Kinetic Resolution
Racemization in combination with a kinetic resolution is the base for a dynamic kinetic resolution (DKR). Biocatalytic racemization was successfully performed for a broad scope of sec-alcohols by employing a single alcohol dehydrogenase (ADH) variant from Thermoanaerobacter pseudoethanolicus (formerly T. ethanolicus; TeSADH W110A I86A C295A). The catalyst employed as a lyophilized whole cell preparation or cell free extract, which tolerated various non-water miscible organic solvents under micro-aqueous or two-phase conditions, whereby cyclohexane and n-hexane suited best. Various concepts for combining the enzymatic racemization with an enzymatic kinetic resolution to achieve overall a bis-enzymatic DKR were evaluated. A proof of concept showed a successful DKR with racemization in aqueous phase combined with acylation in the organic phase.
Pop?oński, Jaros?aw,Reiter, Tamara,Kroutil, Wolfgang
p. 763 - 768
(2018/02/27)

Chiral terpene auxiliaries IV: new monoterpene PHOX ligands and their application in the catalytic asymmetric transfer hydrogenation of ketones
New PHOX ligands, derived in three steps from (1R, 2S, 3R, 5R)-3-amino-apopinan-2-ol 1 and (1R, 2R, 3S, 5R)-3-amino-pinan-2-ol 2 were applied as chiral ligands for the formation of ruthenium catalysts. The catalysts were used in asymmetric transfer hydrogenations of prochiral ketones producing the corresponding alcohols in moderate to high yields and enantioselectivity.
Kmieciak, Anna,Krzemiński, Marek P.
p. 467 - 472
(2017/03/24)

Use of the Trost Ligand in the Ruthenium-Catalyzed Asymmetric Hydrogenation of Ketones
The Trost ligand, (1S,2S)-1,2-diaminocyclohexane-N,N′-bis(2′-diphenylphosphinobenzoyl) (L), is reported for the first time as a ligand for the asymmetric hydrogenation (AH) of ketones. Ligand (S,S)-L was screened in the presence of several metal salts and was found to form active catalysts if combined with ruthenium sources in the presence of hydrogen and a base. Reaction optimization was performed by screening different Ru sources, solvents, and bases. Under the optimized conditions, the complex formed by the combination of (S,S)-L with RuCl3(H2O)x in the presence of Na2CO3 was able to promote the AH of several ketones at room temperature in good yields with up to 96 % ee. The reaction kinetics measured under the optimized conditions revealed the presence of a long induction period, during which the initially formed Ru species was transformed into the catalytically active complex by reaction with hydrogen. Remarkably, a ketone that is a precursor of the antiemetic drug aprepitant was hydrogenated in excellent yield with a good ee value.
Cettolin, Mattia,Puylaert, Pim,Pignataro, Luca,Hinze, Sandra,Gennari, Cesare,de Vries, Johannes G.
p. 3125 - 3130
(2017/08/29)

Identification of a Robust Carbonyl Reductase for Diastereoselectively Building syn-3,5-Dihydroxy Hexanoate: A Bulky Side Chain of Atorvastatin
t-Butyl-6-cyano-(3R,5R)-dihydroxyhexanoate is an advanced chiral precursor for the synthesis of the side chain pharmacophore of cholesterol-lowering drug atorvastatin. Herein, a robust carbonyl reductase (LbCR) was newly identified from Lactobacillus brevis, which displays high activity and excellent diastereoselectivity toward bulky t-butyl 6-cyano-(5R)-hydroxy-3-oxo-hexanoate (7). The engineered Escherichia coli cells harboring LbCR and glucose dehydrogenase (for cofactor regeneration) were employed as biocatalysts for the asymmetric reduction of substrate 7. As a result, as much as 300 g L-1 of water-insoluble substrate was completely converted to the corresponding chiral diol with >99.5% de in a space-time yield of 351 g L-1 d-1, indicating a great potential of LbCR for practical synthesis of the very bulky and bi-chiral 3,5-dihydroxy carboxylate side chain of best-selling statin drugs.
Gong, Xu-Min,Zheng, Gao-Wei,Liu, You-Yan,Xu, Jian-He
supporting information
p. 1349 - 1354
(2017/09/23)

Asymmetric transfer hydrogenation of aryl ketoesters with a chiral double-chain surfactant-type catalyst in water
A chiral double-chain surfactant-type ligand was designed and synthesized. The rhodium catalyst formed from the ligand can self-assemble into chiral vesicular aggregates in water, which was applied to the ATH of a broad range of aromatic ketoesters in neat water and gave up to 99% yield and 99% ee. In addition, this double-chain surfactant-type catalyst could also be applied to the dynamic kinetic resolution (DKR) of bicyclic β-ketoesters in water.
Li, Jiahong,Lin, Zechao,Huang, Qingfei,Wang, Qiwei,Tang, Lei,Zhu, Jin,Deng, Jingen
p. 5367 - 5370
(2017/11/22)

Enzymatic Kinetic Resolution of Secondary Alcohols Using an Ionic Anhydride Generated In Situ
We developed a method for the resolution of secondary alcohols using an ionic anhydride acylating agent prepared directly in the reaction medium containing the biocatalyst Candida antarctica lipase B (CALB). NMR studies showed that mixing all components at the same time does not interfere with the coupling reaction or the enzymatic activity. After optimization of the reaction conditions, the method allowed the resolution of a number of substrates in very high conversions (46–48 %) and enantiomeric ratios (E>170) along with an easy recovery of both enantiomers without the need for preparative chromatographic separation. Additionally, both the starting ionic acid and the biocatalyst could be recovered and reused up to nine cycles without significant loss of enantioselectivity.
Rocha, ?ngelo,Teixeira, Raquel,Louren?o, Nuno M. T.,Afonso, Carlos A. M.
p. 296 - 302
(2017/01/17)

NHTs Effect on the Enantioselectivity of Ru(II) Complex Catalysts Bearing a Chiral Bis(NHTs)-Substituted Imidazolyl-Oxazolinyl-Pyridine Ligand for Asymmetric Transfer Hydrogenation of Ketones
Pincer-type ruthenium(II)-NNN complex catalysts bearing a chiral bis(NHTs)-substituted imidazolyl-oxazolinyl-pyridine ligand were synthesized and structurally characterized by NMR, IR, elemental analysis, and X-ray single-crystal crystallographic determinations. The two NHTs groups substituted on the imidazolyl moiety of the chiral NNN ligand exhibited a remarkable effect on the enantioselectivity of the Ru(II)-NNN complexes for the asymmetric transfer hydrogenation (ATH) of ketones. The Ru(II)-NNN complex bearing a chiral (NHTs)2-substituted imidazolyl-(isopropyl)oxazolinyl-pyridine ligand exhibited excellent catalytic activity, reaching an enantioselectivity up to 99.9% ee for the target alcohol products.
Chai, Huining,Liu, Tingting,Yu, Zhengkun
p. 4136 - 4144
(2017/11/21)

Alternatives to Phosphinooxazoline (t-BuPHOX) Ligands in the Metal-Catalyzed Hydrogenation of Minimally Functionalized Olefins and Cyclic β-Enamides
This study presents a new series of readily accessible iridium- and rhodium-phosphite/oxazoline catalytic systems that can efficiently hydrogenate, for the first time, both minimally functionalized olefins and functionalized olefins (62 examples in total) in high enantioselectivities (ees up to >99%) and conversions. The phosphite-oxazoline ligands, which are readily available in only two synthetic steps, are derived from previous privileged 4-alkyl-2-[2-(diphenylphosphino)phenyl]-2-oxazoline (PHOX) ligands by replacing the phosphine moiety by a biaryl phosphite group and/or the introduction of a methylene spacer between the oxazoline and the phenyl ring. The modular design of the ligands has given us the opportunity not only to overcome the limitations of the iridium-PHOX catalytic systems in the hydrogenation of minimally functionalized Z-olefins and 1,1-disubstituted olefins, but also to expand their use to unfunctionalized olefins containing other challenging scaffolds (e.g., exocyclic benzofused and triaryl-substituted olefins) and also to olefins with poorly coordinative groups (e.g., α,β-unsaturated lactams, lactones, alkenylboronic esters, etc.) with enantioselectivities typically >95% ee. Moreover, both enantiomers of the hydrogenation product could be obtained by simply changing the configuration of the biaryl phosphite moiety. Remarkably, the new catalytic systems also provided excellent enantioselectivities (up to 99% ee) in the asymmetric hydrogenation of another challenging class of olefins – the functionalized cyclic β-enamides. Again, both enantiomers of the reduced amides could be obtained by changing the metal from Ir to Rh. We also demonstrated that environmentally friendly propylene carbonate can be used with no loss of enantioselectivity. Another advantage of the new ligands over the PHOX ligands is that the best ligands are derived from the affordable (S)-phenylglycinol rather than from the expensive (S)-tert-leucinol. (Figure presented.).
Biosca, Maria,Magre, Marc,Coll, Mercè,Pàmies, Oscar,Diéguez, Montserrat
supporting information
p. 2801 - 2814
(2017/08/23)

Mechanism-Based Enantiodivergence in Manganese Reduction Catalysis: A Chiral Pincer Complex for the Highly Enantioselective Hydroboration of Ketones
A manganese alkyl complex containing a chiral bis(oxazolinyl-methylidene)isoindoline pincer ligand is a precatalyst for a catalytic system of unprecedented activity and selectivity in the enantioselective hydroboration of ketones, thus producing preparatively useful chiral alcohols in excellent yields with up to greater than 99 % ee. It is applicable for both aryl alkyl and dialkyl ketone reduction under mild reaction conditions (TOF >450 h?1 at ?40 °C). The earth-abundant base-metal catalyst operates at very low catalyst loadings (as low as 0.1 mol %) and with a high level of functional-group tolerance. There is evidence for the existence of two distinct mechanistic pathways for manganese-catalyzed hydride transfer and their role for enantiocontrol in the selectivity-determining step is presented.
Vasilenko, Vladislav,Blasius, Clemens K.,Wadepohl, Hubert,Gade, Lutz H.
supporting information
p. 8393 - 8397
(2017/07/11)

CO2-expanded bio-based liquids as novel solvents for enantioselective biocatalysis
For the first time, CO2-expanded bio-based liquids were reported as novel and sustainable solvents for biocatalysis. Herein, it was found that by expansion with CO2, 2-methyltetrahydrofuran (MeTHF), and other bio-based liquids, which were not favorable solvents for immobilized Candida antarctica lipase B (Novozym 435) catalyzed transesterification, were tuned into excellent reaction media. Especially, for the kinetic resolution of challenging bulky secondary substrates such as rac-1-adamantylethanol, the lipase displayed very high activity with excellent enantioselectivity (E value > 200) in CO2-expanded MeTHF (MeTHF concentration 10% v/v, 6 MPa), whereas there was almost no activity observed in conventional organic solvents.
Hoang, Hai Nam,Nagashima, Yoshihiro,Mori, Shuichi,Kagechika, Hiroyuki,Matsuda, Tomoko
p. 2984 - 2989
(2017/04/26)

Selective Activation of C?H Bonds in a Cascade Process Combining Photochemistry and Biocatalysis
Selective oxyfunctionalizations of inert C?H bonds can be achieved under mild conditions by using peroxygenases. This approach, however, suffers from the poor robustness of these enzymes in the presence of hydrogen peroxide as the stoichiometric oxidant. Herein, we demonstrate that inorganic photocatalysts such as gold–titanium dioxide efficiently provide H2O2 through the methanol-driven reductive activation of ambient oxygen in amounts that ensure that the enzyme remains highly active and stable. Using this approach, the stereoselective hydroxylation of ethylbenzene to (R)-1-phenylethanol was achieved with high enantioselectivity (>98 % ee) and excellent turnover numbers for the biocatalyst (>71 000).
Zhang, Wuyuan,Burek, Bastien O.,Fernández-Fueyo, Elena,Alcalde, Miguel,Bloh, Jonathan Z.,Hollmann, Frank
p. 15451 - 15455
(2017/11/13)

Asymmetric Transfer Hydrogenation of Ketones with Modified Grubbs Metathesis Catalysts: On the Way to a Tandem Process
Herein, we report the successful transformation of a 1st generation Grubbs metathesis catalyst into an asymmetric transfer hydrogenation (ATH) catalyst. Upon addition of a chiral amine ligand, an alcohol and a base, the 1st generation Hoveyda-Grubbs catalyst (HG-I) was found to promote the enantioselective reduction of acetophenone to 1-phenylethanol. After optimizing the order of addition and the reaction conditions, the substrate scope was assessed leading to enantiomeric excesses up to 97% ee. NMR experiments were run in order to get information about the in situ-generated ATH catalyst. Furthermore, the possibility to perform olefin metathesis and ketone transfer hydrogenation sequentially in one pot was demonstrated, and the first tandem olefin metathesis-ketone asymmetric transfer hydrogenation was carried out.
Renom-Carrasco, Marc,Gajewski, Piotr,Pignataro, Luca,De Vries, Johannes G.,Piarulli, Umberto,Gennari, Cesare,Lefort, Laurent
supporting information
p. 515 - 519
(2016/02/27)

Screening, Molecular Cloning, and Biochemical Characterization of an Alcohol Dehydrogenase from Pichia pastoris Useful for the Kinetic Resolution of a Racemic β-Hydroxy-β-trifluoromethyl Ketone
The stereoselective synthesis of chiral 1,3-diols with the aid of biocatalysts is an attractive tool in organic chemistry. Besides the reduction of diketones, an alternative approach consists of the stereoselective reduction of β-hydroxy ketones (aldols). Thus, we screened for an alcohol dehydrogenase (ADH) that would selectively reduce a β-hydroxy-β-trifluoromethyl ketone. One potential starting material for this process is readily available by aldol addition of acetone to 2,2,2-trifluoroacetophenone. Over 200 strains were screened, and only a few yeast strains showed stereoselective reduction activities. The enzyme responsible for the reduction of the β-hydroxy-β-trifluoromethyl ketone was identified after purification and subsequent MALDI-TOF mass spectrometric analysis. As a result, a new NADP+-dependent ADH from Pichia pastoris (PPADH) was identified and confirmed to be capable of stereospecific and diastereoselective reduction of the β-hydroxy-β-trifluoromethyl ketone to its corresponding 1,3-diol. The gene encoding PPADH was cloned and heterologously expressed in Escherichia coli BL21(DE3). To determine the influence of an N- or C-terminal His-tag fusion, three different recombinant plasmids were constructed. Interestingly, the variant with the N-terminal His-tag showed the highest activity; consequently, this variant was purified and characterized. Kinetic parameters and the dependency of activity on pH and temperature were determined. PPADH shows a substrate preference for the reduction of linear and branched aliphatic aldehydes. Surprisingly, the enzyme shows no comparable activity towards ketones other than the β-hydroxy-β-trifluoromethyl ketone.
Bulut, Dalia,Hummel, Werner,Gr?ger, Harald,Duangdee, Nongnaphat,Berkessel, Albrecht
p. 1349 - 1358
(2016/12/24)

Enzymatic kinetic resolution of aliphatic sec-alcohols by LipG9, a metagenomic lipase
Bioprospection for new enantioselective enzymes for application in organic synthesis is a prominent area of investigation in biocatalysis. In this context, here we present the evaluation of an immobilized lipase isolated from a metagenomic library (LipG9) for the enzymatic kinetic resolution (EKR) of aliphatic sec-alcohols, which are still challenging substrates, since low enantioselectivity values are usually observed for these resolutions. LipG9 was successfully employed in EKR of aliphatic alcohols, which were resolved with satisfactory conversions (19-59%) and enantiomeric excesses for alcohols (26-88%) and esters (30-96%) by transesterification reactions, demonstrating that its performance is equal to or better than commercially available enzymes for the same reaction.
Bandeira, Pamela T.,Alnoch, Robson C.,De Oliveira, Alfredo R.M.,De Souza, Emanuel M.,De O.P., Fábio,Krieger, Nadia,Piovan, Leandro
p. 58 - 63
(2016/01/30)

ALKANE OXIDATION BY MODIFIED HYDROXYLASES
This invention relates to modified hydroxylases. The invention further relates to cells expressing such modified hydroxylases and methods of producing hydroxylated alkanes by contacting a suitable substrate with such cells.
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Paragraph 0323; 0324

(2016/02/16)

Asymmetric Synthesis of Secondary Alcohols and 1,2-Disubstituted Epoxides via Organocatalytic Sulfenylation
Enantioenriched secondary alcohols can be prepared via a short reaction sequence involving asymmetric organocatalytic sulfenylation of an aldehyde, organometallic addition, and desulfurization. This process provides access to enantioenriched alcohols with sterically similar groups attached to the alcohol carbon atom. The intermediate β-hydroxysulfides can also serve as precursors to enantioenriched 1,2-disubstituted epoxides via alkylation of the sulfur and subsequent base-mediated ring closure.
Rota, Filippo,Benhamou, Laure,Sheppard, Tom D.
supporting information
p. 33 - 36
(2015/12/26)

Iron achieves noble metal reactivity and selectivity: Highly reactive and enantioselective iron complexes as catalysts in the hydrosilylation of ketones
Chiral iron alkyl and iron alkoxide complexes bearing boxmi pincers as stereodirecting ligands have been employed as catalysts for enantioselective hydrosilylation reactions with unprecedented activity and selectivity (TOF = 240 h-1 at -40 °C, ee up to 99% for alkyl aryl ketones), which match the performance of previously established noble-metal-based catalysts. This shows the potential of earth-abundant metals such as iron for replacing platinum-metals without any drawbacks for the reaction design.
Bleith, Tim,Wadepohl, Hubert,Gade, Lutz H.
supporting information
p. 2456 - 2459
(2015/03/04)

Majority-Rules-Type Helical Poly(quinoxaline-2,3-diyl)s as Highly Efficient Chirality-Amplification Systems for Asymmetric Catalysis
A highly efficient majority-rules effect of poly(quinoxaline-2,3-diyl)s (PQXs) bearing 2-butoxymethyl chiral side chains at the 6- and 7-positions was established and attributed to large ΔGh values (0.22-0.41 kJmol-1), which are defined as the energy difference between P- and M-helical conformations per chiral unit. A PQX copolymer prepared from a monomer derived from (R)-2-octanol (23% ee) and a monomer bearing a PPh2 group adopted a single-handed helical structure (>99%) and could be used as a highly enantioselective chiral ligand in palladium-catalyzed asymmetric reactions (products formed with up to 94% ee), in which the enantioselectivity could be switched by solvent-dependent inversion of the helical PQX backbone. Bowing to the majority: Poly(quinoxaline-2,3-diyl) containing PPh2 groups and chiral side chains derived from (R)-2-octanol with 23% ee exhibited a single-handed-helical conformation and served as a highly enantioselective chiral ligand in palladium-catalyzed reactions (see scheme; se=screw-sense excess). The chirality of the polymer could be switched by a solvent effect to enable the synthesis of the enantiomeric products.
Ke, Yuan-Zhen,Nagata, Yuuya,Yamada, Tetsuya,Suginome, Michinori
supporting information
p. 9333 - 9337
(2015/08/06)

Chiral terpene auxiliaries III: Spiroborate esters from (1R,2S,3R,5R)-3-amino-apopinan-2-ol as highly effective catalysts for asymmetric reduction of ketones with borane
New spiroborate esters, derived from terpene amino alcohols, (S)-prolinol, and 2-aminoethanol, were employed as catalysts in the borane reduction of acetophenone and other aryl alkyl and halogenated ketones. The corresponding alcohols were obtained in high yields and with enantioselectivities up to 98% ee. The influence of the amino alcohol and the diol moieties of spiroborate on the reaction selectivity was examined. The catalyst load, the nature of the solvent, the borane source, and the reaction conditions were also investigated.
?wiklińska, Marta,Krzemiński, Marek P.,Tafelska-Kaczmarek, Agnieszka
p. 1453 - 1458
(2015/12/09)

Chemoenzymatic Deracemization of Secondary Alcohols by using a TEMPO-Iodine-Alcohol Dehydrogenase System
A deracemization system for secondary alcohols was established after the analysis of individual steps and their compatibility in one pot. The chemical oxidation and bioreduction occurred in a sequential manner to yield 1-arylethanols and lineal aliphatic alcohols with excellent conversions and enantiomeric excess values. The oxidation step was performed by using 2,2,6,6-tetramethylpiperidin-1-oxyl and iodine. This chemical process was extremely favored by sonication, which allowed quantitative formation of the corresponding ketone intermediates after just 1 h. Simple destruction of iodine in the same pot allowed sequential bioreduction of the ketones by using either Prelog or antiPrelog enzymes, which led to the preparation of the enantiopure alcohols in excellent yields. Just a sec: The one-pot deracemization of secondary alcohols involving oxidation with 2,2,6,6-tetramethylpiperidin-1-oxyl (TEMPO) and iodine followed by alcohol dehydrogenase (ADH)-catalyzed bioreduction is described. 1-Arylethanols and lineal aliphatic alcohols are obtained with excellent conversions and enantiomeric excess values. LBADH=alcohol dehydrogenase from Lactobacillus brevis.
Méndez-Sánchez, Daniel,Mangas-Sánchez, Juan,Lavandera, Iván,Gotor, Vicente,Gotor-Fernández, Vicente
p. 4016 - 4020
(2015/12/26)

Iridium-Catalyzed Asymmetric Hydrogenation with Simple Cyclohexane-Based P/S Ligands: In Situ HP-NMR and DFT Calculations for the Characterization of Reaction Intermediates
We report a reduced but structurally valuable phosphite/phosphinite-thioether ligand library for the Ir-hydrogenation of 40 minimally functionalized alkenes, including relevant examples with poorly coordinative groups. We found that enantiomeric excesses are mainly dependent on the substrate structure and on some ligand parameters (i.e., the type of thioether/phosphorus moieties and the configuration of the phosphite group), whereas the substituents of the biaryl phosphite moiety had little impact. By tuning the ligand parameters we were able to find highly selective catalysts for a range of substrates (ees up to 99%). These phosphite/phosphinite-thioether ligands have a simple backbone and thus yield simple NMR spectra that reduce signal overlap and facilitate the identification of relevant intermediates. Therefore, by combining HP-NMR spectroscopy and theoretical studies, we were also able to identify the catalytically competent Ir-dihydride alkene species, which made it possible to explain the enantioselectivity obtained.
Borràs, Carlota,Biosca, Maria,Pàmies, Oscar,Diéguez, Montserrat
supporting information
p. 5321 - 5334
(2015/11/18)

Discrimination of the prochiral hydrogens at the C-2 position of n-alkanes by the methane/ammonia monooxygenase family proteins
The selectivity of ammonia monooxygenase from Nitrosomonas europaea (AMO-Ne) for the oxidation of C4-C8n-alkanes to the corresponding alcohol isomers was examined to show the ability of AMO-Ne to recognize the n-alkane orientation within the catalytic site. AMO-Ne in whole cells produces 1- and 2-alcohols from C4-C8n-alkanes, and the regioselectivity is dependent on the length of the carbon chain. 2-Alcohols produced from C4-C7n-alkanes were predominantly either the R- or S-enantiomers, while 2-octanol produced from n-octane was racemic. These results indicate that AMO-Ne can discriminate between the prochiral hydrogens at the C-2 position, with the degree of discrimination varying according to the n-alkane. Compared to the particulate methane monooxygenase (pMMO) of Methylococcus capsulatus (Bath) and that of Methylosinus trichosporium OB3b, AMO-Ne showed a distinct ability to discriminate between the orientation of n-butane and n-pentane in the catalytic site.
Miyaji, Akimitsu,Miyoshi, Teppei,Motokura, Ken,Baba, Toshihide
p. 8261 - 8270
(2015/08/03)

Genomic mining-based identification of novel stereospecific aldo-keto reductases toolbox from Candida parapsilosis for highly enantioselective reduction of carbonyl compounds
Biocatalytic reduction of prochiral ketones offers significant potential in synthesis of optically active alcohols. However, so far the application of aldo-keto reductases (AKRs) in asymmetric reduction has been hampered due to limited availability of AKRs with high enantioselectivity and catalytic efficiency. Based on the genome sequence of Candida parapsilosis, a versatile bioresource for asymmetric reduction, eight open reading frames encoding putative AKRs were discovered and expressed, and the resulted enzymes (CPARs), comprising an AKR toolbox, were evaluated toward various carbonyl substrates. The CPARs were active to the selected substrates, especially 2-hydroxyacetophenone and ethyl 4-chloro-3-oxobutyrate. Additionally, most of them were obviously enantioselective to the substrates and gave alcohol products with optical purity up to 99%e.e. Of the enzymes, CPAR4 was outstanding with excellent enantioselectivity and broad substrate spectrum. All these positive features demonstrate that genomic mining is powerful in searching for novel and efficient biocatalysts of desired reactions for pharmaceuticals and fine chemicals synthesis.
Guo, Rongyun,Nie, Yao,Mu, Xiao Qing,Xu, Yan,Xiao, Rong
p. 66 - 73
(2014/05/20)

Enantioselective Hydrosilylation of Ketones Catalyzed by a Readily Accessible N-Heterocyclic Carbene-Ir Complex at Room Temperature
A series of functionalized azolium compounds were synthesized from chiral α-amino acid derivatives such as β-amino alcohols. of hydroxy-amide-functionalized azolium salts thus obtained with Ag2O afforded N-heterocyclic carbene-Ag (NHC-Ag) complexes. Subsequent treatment of the resulting silver compound with [IrCl(cod)]2 yielded monodentate IrCl(cod)(NHC), which was stable in air. The NHC-Ir complex facilitated efficient asymmetric hydrosilylation of ketones using (EtO)2MeSiH under ambient conditions. A chiral ligand containing an isobutyl stereodirecting group was found to be the best ligand for the functionalized NHC-Ir complexes that were examined. A linear relationship was found between the catalyst ee and the product ee. The hydroxy functional group on the NHC ligand side-arm not only induced stereocontrol but also enhanced the reaction rate.
Shinohara, Kanako,Kawabata, Shun,Nakamura, Hanako,Manabe, Yoshiki,Sakaguchi, Satoshi
p. 5532 - 5539
(2014/10/16)

Enzymatic kinetic resolution of sec-alcohols using an ionic liquid anhydride as acylating agent
A task-specific ionic liquid bearing an anhydride moiety was synthesized for the first time in good yield (83%) through a carbodiimide-mediated coupling reaction. The enantiomeric separation of a series of sec-alcohols was performed via enzymatic kinetic resolution, employing an ionic anhydride as acylating agent and Candida antarctica Lipase B as a biocatalyst. A fast and efficient recovery of both enantiomers was achieved separately due to the ionic nature of the acyl donor, combined with the possibility of carrying out the enzymatic step in an organic solvent.
Teixeira, Raquel,Lourenco, Nuno M.T.
p. 944 - 948
(2014/07/22)

Dynamic double kinetic resolution of amines and alcohols under the cocatalysis of Raney nickel/Candida antarctica lipase B: From concept to application
Herein, we have established a dynamic double kinetic resolution (DDKR) strategy under the co-catalysis of Raney nickel and Candida antarctica lipase B (CAL-B) for the one-pot simultaneous resolution of primary amines and secondary alcohols (or esters). The DDKR strategy was successfully applied to the resolution of a series of racemic amines and secondary alcohols (or esters) as well as mexiletine, an important antiarrhythmic agent. The catalysts could be recycled and reused several times with the same high activity. Scale-up experiments were also successful. As a more atom-economical and efficient process than traditional simple kinetic resolutions, the DDKR strategy can be widely used to prepare optically pure amines and alcohols.
Xia, Bo,Cheng, Guilin,Lin, Xianfu,Wu, Qi
supporting information
p. 2917 - 2923
(2014/05/20)

A novel P450-based biocatalyst for the selective production of chiral 2-alkanols
A P450 monooxygenase from Nocardia farcinica (CYP154A8) catalyses the stereo- and regioselective hydroxylation of n-alkanes, still a challenging task in chemical catalysis. In a biphasic reaction system, the regioselectivity for the C2-position of C7-C9 alkanes was over 90%. The enzyme showed strict S-selectivity for all tested substrates, with enantiomeric excess (ee) of up to 91%. This journal is the Partner Organisations 2014.
Von Bühler, Clemens J.,Urlacher, Vlada B.
supporting information
p. 4089 - 4091
(2014/04/03)

Development of a mixed solvent system for the efficient resolution of (R, S)-2-octanol catalyzed by magnetite-immobilized lipase
In order to find a suitable reaction system for the enzymatic resolution of (R, S)-2-octanol, the effects of the molecular structure of the solvent on the enantioselectivity (E) and enzymatic activity of Yarrowia lipolytica lipase (YLL) immobilized onto magnetic nanoparticles were systematically analyzed. Both the E and enzymatic activity of the reaction in an acyclic, structurally linear solvent were higher than those in the corresponding branched chain solvent or cyclic solvent. In a mixed solvent system with acetone and carbon tetrachloride (v/v = 3:7), the immobilized YLL exhibited high enantioselectivity, activity, and reusability. The thermodynamic analysis showed that the enantiomer discrimination was enthalpy-driven at all temperatures tested. These results present new opportunities and challenges for understanding and intensifying the enzymatic resolution process of (R, S)-2-octanol by designing suitable solvent system.
Liu, Ying,Guo, Chen,Liu, Chun-Zhao
p. 23 - 27
(2014/02/14)

Engineering of P450pyr hydroxylase for the highly regio- and enantioselective subterminal hydroxylation of alkanes
Terminal-selective cytochrome P450pyr has been successfully engineered through directed evolution for the subterminal hydroxylation of alkanes with excellent regio- and enantioselectivity. A sensitive colorimetric high-throughput screening (HTS) assay was developed for the measurement of both the regioselectivity and the enantioselectivity of a hydroxylation reaction. By using the HTS assay and iterative saturation mutagenesis, sextuple-mutant P450pyrSM1 was created for the hydroxylation of n-octane (1) to give (S)-2-octanol (2) with 98 % ee and >99 % subterminal selectivity. The engineered P450 is the first enzyme for this type of highly selective alkane hydroxylation, being useful for the Ci-H activation and functionalization of alkanes and the preparation of enantiopure alcohols. Molecular modeling provided structure-based understanding of the fully altered regioselectivity and the excellent enantioselectivity. Another sextuple-mutant P450pyrSM2 catalyzed the hydroxylation of propylbenzene (3) to afford (S)-1-phenyl-2-propanol (4) with 95 % ee and 98 % subterminal selectivity. Get a handle on it: Highly regio- and enantioselective subterminal hydroxylation of n-octane and propylbenzene was observed with P450 enzymes obtained by the directed evolution of terminal-selective P450pyr hydroxylase (see scheme). The engineered enzymes with their fully altered selectivities are useful for the functionalization of alkanes and the preparation of enantiomerically pure alcohols.
Yang, Yi,Liu, Ji,Li, Zhi
supporting information
p. 3120 - 3124
(2014/04/03)

A green resolution-separation process for aliphatic secondary alcohols
In order to obtain both enantiomers of aliphatic secondary alcohols via a greener method, the four-step resolution-separation process involving lipase-catalyzed enantioselective esterification and hydrolysis as well as two separation procedures both via heterogeneous azeotropic distillation was developed. (S)-2-Pentanol (ee = 98.6%), (R)-2-pentanol (ee >99%), (S)-2-octanol (ee = 98.2%), and (R)-2-octanol (ee = 98.5%) were all produced in high purity (>98%) and high yield (>90%). In addition to the two model substrates, this method could also be applied to the resolution of other aliphatic secondary alcohols.
Ren, Liwei,Xu, Tian,He, Ruoping,Jiang, Zhenhua,Zhou, Hua,Wei, Ping
p. 249 - 253
(2013/05/09)

C2 symmetrical nickel complexes derived from α-amino amides as efficient catalysts for the enantioselective addition of dialkylzinc reagents to aldehydes
A series of C2 symmetrical 1:2 Ni:L complexes derived from α-amino amides were studied for the enantioselective addition of dialkylzinc reagents to aldehydes. Different structural elements on the ligands seem to play an important role in determining the observed enantioselectivity. Through optimization of structure and reaction conditions, the best ligand provided secondary alcohols in excellent yields (up to 98%) and enantioselectivity of up to 99% ee for (R)-enantiomer. A transition state model has been proposed to explain the observed enantioselectivities based on computational calculations at the DFT level. Very interestingly, calculations suggest a coordination model of the aldehyde to the metal complex through association of a lone pair of the carbonyl oxygen to the hydrogen atom of an amino group.
Escorihuela, Jorge,Altava, Belen,Burguete, M. Isabel,Luis, Santiago V.
p. 551 - 558
(2013/07/27)

Escherichia coli/ADH-A: An all-inclusive catalyst for the selective biooxidation and deracemisation of secondary alcohols
The nicotinamide adenine dinucleotide regeneration system present in Escherichia coli cells was exploited for the oxidation and deracemisation of secondary alcohols with the overexpressed alcohol dehydrogenase from Rhodococcus ruber DSM 44541 (E. coli/ADH-A). Thus, various racemic alcohols were selectively oxidised with lyophilised or resting E. coli/ADH-A cells without need for an external cofactor or co-substrate. The addition of these substrates to the E. coli/ADH-A cells in buffer afforded the corresponding ketones and the remaining enantioenriched (R)-alcohols. This methodology was used for the desymmetrisation of a meso-diol and for the synthesis of the highly valuable raspberry ketone. Moreover, a biocatalytic concurrent process was developed with the resting cells of E. coli/ADH-A, ADH from Lactobacillus brevis, and glucose dehydrogenase for the deracemisation of various secondary alcohols, which afforded the desired enantiopure alcohols in more than 99 % ee starting from the racemic mixture. The reaction time of deracemisation of 1-phenylethanol was estimated to be less than 30 min. The stereoinversion of (S)-1-phenylethanol to its pure (R)-enantiomer was also achieved, which provided a biocatalytic alternative to the chemical Mitsunobu inversion reaction. An integrated recycling system: A nicotinamide adenine dinucleotide regeneration system present in Escherichia coli cells is exploited for the oxidation of secondary alcohols with E. coli/alcohol dehydrogenase (ADH-A). Racemic alcohols are oxidized selectively without need for an external cofactor or cosubstrate, which affords the remaining enantioenriched (R)-alcohols. Deracemization, desymmetrization, and stereoinversion processes are developed, which leads to optically pure high value-added compounds. Copyright
Paul, Caroline E.,Lavandera, Ivan,Gotor-Fernandez, Vicente,Kroutil, Wolfgang,Gotor, Vicente
p. 3875 - 3881
(2014/01/06)

Asymmetric 1,2-reduction of enones with potassium borohydride catalyzed by chiral N,N′-dioxide-scandium(III) complexes
The first catalytic enantioselective 1,2-reduction of enones with 0.45 mol equiv potassium borohydride solution catalyzed by a chiral N,N′-dioxide- Sc(III) complex catalyst was accomplished under mild reaction conditions. A number of optically active allylic alcohols were obtained in good to excellent enantioselectivities (up to 95% ee) with nearly quantitative yields.
He, Peng,Liu, Xiaohua,Zheng, Haifeng,Li, Wei,Lin, Lili,Feng, Xiaoming
supporting information
p. 5134 - 5137,4
(2020/09/15)

Syntheses of enantiopure aliphatic secondary alcohols and acetates by bioresolution with lipase B from candida antarctica
The lipase B from Candida antarctica (Novozym 435, CALB) efficiently catalyzed the kinetic resolution of some aliphatic secondary alcohols: (±)-4-methylpentan- 2-ol (1), (±)-5-methylhexan-2-ol (3), (±)-octan-2-ol (4), (±)-heptan-3-ol (5) and (±)-oct-1- en-3-ol (6). The lipase showed excellent enantioselectivities in the transesterifications of racemic aliphatic secondary alcohols producing the enantiopure alcohols (>99% ee) and acetates (>99% ee) with good yields. Kinetic resolution of rac-alcohols was successfully achieved with CALB lipase using simple conditions, vinyl acetate as acylating agent, and hexane as non-polar solvent.
Ferreira, Hercules V.,Rocha, Lenilson C.,Severino, Richele P.,Porto, Andre L. M.
p. 8955 - 8967,13
(2020/08/31)

Chiral surfactant-type catalyst for asymmetric reduction of aliphatic ketones in water
A novel chiral surfactant-type catalyst is developed. Micelles formed in water by association of the catalysts themselves, and this was confirmed by TEM analyses. Asymmetric transfer hydrogenation of aliphatic ketones catalyzed by the chiral metallomicellar catalyst gave good to excellent conversions and remarkable stereoselectivities (up to 95% ee). Synergistic effects between the metal-catalyzed center and the hydrophobic microenvironment of the core in the metallomicelle led to high enantioselectivities.
Li, Jiahong,Tang, Yuanfu,Wang, Qiwei,Li, Xuefeng,Cun, Linfeng,Zhang, Xiaomei,Zhu, Jin,Li, Liangchun,Deng, Jingen
supporting information
p. 18522 - 18525
(2013/01/15)

The substrate spectrum of the inverting sec-alkylsulfatase Pisa1
The substrate spectrum of the inverting alkylsulfatase Pisa1 was investigated using a range of sec-alkyl sulfate esters bearing aromatic, olefinic and acetylenic moieties. Perfect enantioselectivities were obtained for substrates bearing groups of different size adjacent to the sulfate ester moiety. Insufficient selectivities could be doubled by using dimethyl sulfoxide (DMSO) as co-solvent. Hydrolytically unstable benzylic sulfate esters could be sufficiently stabilised by introduction of electron-withdrawing substituents. Overall, Pisa1 appears to be a very useful inverting alkylsulfatase for the deracemisation of rac-sec-alcohols via enzymatic hydrolysis of their corresponding sulfate esters, which furnishes homochiral products possessing the 'anti-Kazlauskas' configuration. Copyright
Schober, Markus,Knaus, Tanja,Toesch, Michael,MacHeroux, Peter,Wagner, Ulrike,Faber, Kurt
experimental part
p. 1737 - 1742
(2012/07/31)