- Enantioselective Hydrolysis of D,L-Menthyl Benzoate to L-(-)-Menthol by Recombinant Candida rugosa Lipase LIP1
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The stereoselective synthesis of L-menthol is an attractive process in the flavor and fragrance industry. One promising way to obtain optically pure menthol is the enantioselective hydrolysis of menthol esters under enzymatic catalysis. We developed an effective and highly enantioselective method for the synthesis of L-(-)-menthol (>99% EE) by hydrolyzing the key industrial starting compound, D, L-menthyl benzoate. The enzyme of choice was the lipase from Candida rugosa (CRL). While commercially available preparations of this lipase showed only minor selectivity (E=15), excellent enantiomeric purity (E > 100) was achieved using the heterologously expressed isoenzyme LIP1.
- Vorlova, Sandra,Bornscheuer, Uwe T.,Gatfield, Ian,Hilmer, Jens-Michael,Bertram, Heinz-Juergen,Schmid, Rolf D.
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- Stereoselective reduction of menthone by molecularly imprinted polymers
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Polymeric chiral reductants selective for the reduction of (-)-menthone 1 to the diastereomeric products (-)-menthol 2 and (+)-neomenthol 3 were prepared by a covalentmolecular imprinting using 2 as the template. The LiAlH4 derivatized imprinted polymers altered the natural outcome of the reduction reaction (LiAlH4) from 2:1 [(-)-menthol:(+)-neomenthol] to 1:1. The reaction mechanism is discussed in terms of reaction site structure. The molecularly imprinted polymers demonstrated enantioselective recognition for 2 (0.15μmol enantioselective sites/g polymer) in batch binding experiments.
- Hedin-Dahlstroem, Jimmy,Shoravi, Siamak,Wikman, Susanne,Nicholls, Ian A.
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- Enantioselective enzymatic resolution of racemic alcohols by lipases in green organic solvents
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The effects of two eco-friendly solvents, 2-methyltetrahydrofuran (MeTHF) and cyclopentyl methyl ether (CPME), on the enzyme activity and enantioselectivity of Novozym 435, Candida rugosa lipase (CRL), Porcine pancreas lipase (PPL), Lipase AK, Lipase PS, and Lipozyme, a series of commercial lipases, in the enantioselective transesterfications of racemic menthol, racemic sulcatol and racemic α-cyclogeraniol were studied. Vinyl acetate was chosen as the acyl donor and the reactions were carried out at water activity 0.06. The activity of lipases in CPME was similar to that observed in other largely employed organic solvents [toluene and tert-butyl methyl ether (MTBE)], and was slightly lower in MeTHF. However, for most of the lipases tested, the enantioselectivity was higher in the eco-friendly solvents. Lipase AK exhibited a high enantioselectivity (E?=?232) for the resolution of racemic menthol but the reaction rate was low. Lipase formulation (the enzyme was frozen and lyophilized in potassium phosphate buffer without and with 5% (w/v) of sucrose, D-mannitol, or methoxy poly(ethylene glycol)) was tested with this lipase in order to improve its activity, which increased up to 4.5 times, compared to the untreated enzyme. CALB was found to be a useful biocatalyst for the resolution of racemic sulcatol, where high activity and enantioselectivity were obtained (E?≥?1000). For the resolution of the racemic primary alcohol α-cyclogeraniol, most of the lipases tested were active but not enantioselective, except lipase PS which displayed a moderate enantioselectivity (E?=?19). The effect of the presence of a low percentage of two ionic liquids (ILs) 1-Butyl-3-methylimidazolium bis(trifluoromethylsulfonyl)imide ([BMIM][TFSI]) (5% (v/v)) and 1-Butyl-3-methylimidazoliumtetrafluoroborate ([BMIM][BF4]) (1% (v/v)) in the medium was also investigated. Only in the case of CRL the ILs slightly increased the enantioselectivity from E?=?91 to E?=?103 and E?=?120 for [BMIM][TFSI] and [BMIM][BF4], respectively. However, in all cases ILs caused a decrease of enzyme activity.
- Belafriekh, Abderahmane,Secundo, Francesco,Serra, Stefano,Djeghaba, Zeineddine
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- Apple-tree shoots and transformed carrot and apple roots used as biocatalysts in enantioselective acetate hydrolysis, alcohol oxidation and ketone reduction
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(±)-1-Phenylethyl (1), (±)-1-(1-naphthyl)ethyl (2), (±)-1-(2-naphthyl)ethyl (3) and (±)-menthyl (4) acetates were hydrolyzed using apple-tree shoots and hairy roots of carrot and apple-tree to afford alcohols, which, subsequntly, in the same environment, were oxygenated to ketones. Pure (S)-1-(2-naphthyl)ethanol ((S)-(-)-7), (R)-1-phenylethyl acetate ((R)-(+)-1), (R)-1-(1-naphthyl)ethyl acetate ((R)-(+)-2). (S)-1-phenylethanol ((S)-(-)-5) and (-)-menthol (1R,25,5R)-(-)-8) have been produced.
- Mironowicz, Agnieszka,Kromer, Krystyna
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- Continuous synthesis of menthol from citronellal and citral over Ni-beta-zeolite-sepiolite composite catalyst
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One-pot continuous synthesis of menthols both from citronellal and citral was investigated over 5 wt% Ni supported on H-Beta-38-sepiolite composite catalyst at 60–70 °C under 10–29 bar hydrogen pressure. A relatively high menthols yield of 53% and 49% and stereoselectivity to menthol of 71–76% and 72–74% were obtained from citronellal and citral respectively at the contact time 4.2 min, 70 °C and 20 bar. Citral conversion noticeably decreased with time-on-stream under 10 and 15 bar of hydrogen pressure accompanied by accumulation of citronellal, the primary hydrogenation product of citral, practically not affecting selectivity to menthol. A substantial amount of defuctionalization products observed during citral conversion, especially at the beginning of the reaction (ca. 1 h), indicated that all intermediates could contribute to formation of menthanes. Ni/H-Beta-38-sepiolite composite material prepared by extrusion was characterized by TEM, SEM, XPS, XRD, ICP-OES, N2 physisorption and FTIR techniques to perceive the interrelation between the physico-chemical and catalytic properties.
- Er?nen, Kari,M?ki-Arvela, P?ivi,Martinez-Klimov, Mark,Muller, Joseph,Murzin, Dmitry Yu.,Peurla, Markus,Simakova, Irina,Vajglova, Zuzana
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- Novel highly efficient absolute optical resolution method by serial combination of two asymmetric reactions from acetylene monomers having racemic substituents
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For general optical resolution, an optical resolution agent is necessary, and the best agent should be selected for each racemic compound. In this study, we will report that a novel optical resolution method by circularly polarized light (CPL) without any
- Aoki, Toshiki,Kaneko, Takashi,Liu, Lijia,Suzuki, Junpei,Tang, Yanan,Teraguchi, Masahiro
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supporting information
p. 450 - 461
(2022/01/15)
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- Light-Induced Formation/Scission of C-N, C-O, and C-S Bonds Enables Switchable Stability/Degradability in Covalent Systems
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The manipulation of covalent bonds could be directed toward degradable, recyclable, and sustainable materials. However, there is an intrinsic conflict between properties of stability and degradability. Here we report light-controlled formation/scission of three types of covalent bonds (C-N, C-O, and C-S) through photoswitching between equilibrium and nonequilibrium states of dynamic covalent systems, achieving dual benefits of photoaddressable stability and cleavability. The photocyclization of dithienylethene fused aldehyde ring-chain tautomers turns on the reactivity, incorporating/releasing amines, alcohols, and thiols reversibly with high efficiency, respectively. Upon photocycloreversion the system is shifted to kinetically locked out-of-equilibrium form, enabling remarkable robustness of covalent assemblies. Reaction coupling allows remote and directional control of a diverse range of equilibria and further broadens the scope. Through locking and unlocking covalent linkages with light when needed, the utility is demonstrated with capture/release of bioactive molecules, modification of surfaces, and creation of polymers exhibiting tailored stability and degradability/recyclability. The versatile toolbox for photoswitchable dynamic covalent reactions to toggle matters on and off should be appealing to many endeavors.
- Hai, Yu,Li, Ziyi,Lu, Hanwei,Ye, Hebo,You, Lei,Zou, Hanxun
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supporting information
p. 20368 - 20376
(2021/12/03)
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- Heterogeneous Hydroxyl-Directed Hydrogenation: Control of Diastereoselectivity through Bimetallic Surface Composition
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Directed hydrogenation, in which product selectivity is dictated by the binding of an ancillary directing group on the substrate to the catalyst, is typically catalyzed by homogeneous Rh and Ir complexes. No heterogeneous catalyst has been able to achieve equivalently high directivity due to a lack of control over substrate binding orientation at the catalyst surface. In this work, we demonstrate that Pd-Cu bimetallic nanoparticles with both Pd and Cu atoms distributed across the surface are capable of high conversion and diastereoselectivity in the hydroxyl-directed hydrogenation reaction of terpinen-4-ol. We postulate that the OH directing group adsorbs to the more oxophilic Cu atom while the olefin and hydrogen bind to adjacent Pd atoms, thus enabling selective delivery of hydrogen to the olefin from the same face as the directing group with a 16:1 diastereomeric ratio.
- Shumski, Alexander J.,Swann, William A.,Escorcia, Nicole J.,Li, Christina W.
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p. 6128 - 6134
(2021/05/29)
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- Continuous flow synthesis of menthol: Via tandem cyclisation-hydrogenation of citronellal catalysed by scrap catalytic converters
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A continuous flow synthesis of menthol starting from citronellal catalysed by scrap catalytic converters is reported. The reaction was conducted in a tandem system connecting in series two catalytic systems, with the first having Lewis acid properties (favouring the cyclisation of citronellal to isopulegols) and the second having hydrogenation catalytic activity (catalysing the hydrogenation of isopulegols to menthols). A Lewis acid catalyst was prepared by supporting iron oxide nanoparticles over a waste material, i.e. the ceramic core of scrap catalytic converters (SCATs) via a microwave assisted method. Most importantly, SCATs, containing a low residual noble metal content, could be directly employed in the second step as hydrogenation catalysts. The reaction was performed studying the influence on the yield and selectivity to (-)-menthol of various reaction parameters (T, p and flow rate). Under the best reaction conditions (at a flow rate of 0.1 mL min-1 and at 373 K and 413 K for cyclisation and hydrogenation steps respectively) a conversion of >99% of (+)-citronellal to (-)-menthol with 77% final yield was achieved.
- Zuliani, Alessio,Cova, Camilla Maria,Manno, Roberta,Sebastian, Victor,Romero, Antonio A.,Luque, Rafael
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p. 379 - 387
(2020/02/13)
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- Production of l-menthyl acetate through kinetic resolution by?Candida cylindracea lipase: effects of alkaloids as additives
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Abstract: Enzymatic transesterification of dl-menthol with vinyl acetate in tert-Butyl methyl ether (TBME) catalyzed by Candida cylindracea lipase (CCL) was carried out in the presence of cinchona alkaloid as additive. The effects of various reaction parameters, such as lipase nature and loading, acylating agent, molecular sieves, solvents and various additives, on the reactivity as well as on the enantioselectivity were investigated. A significant improvement of CCL reactivity has been recorded after using cinchona alkaloid as additive in TBME. A high enantiomeric ratio (E = 80) was achieved when 30?mol% of quinidine was added, and l-(-)-menthyl acetate was obtained with 93% optical purity and 49% conversion. This process was easily applied to gram-scale quantities, using commercially inexpensive lipase, providing high yield optically active menthol under mild experimental conditions. Graphical abstract: [Figure not available: see fulltext.].
- Belkacemi, Fatima Zohra,Merabet-Khelassi, Mounia,Aribi-Zouioueche, Louisa,Riant, Olivier
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p. 6847 - 6860
(2018/07/15)
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- Electrochemical Deprotection of para-Methoxybenzyl Ethers in a Flow Electrolysis Cell
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Electrochemical deprotection of p-methoxybenzyl (PMB) ethers was performed in an undivided electrochemical flow reactor in MeOH solution, leading to the unmasked alcohol and p-methoxybenzaldehyde dimethyl acetal as a byproduct. The electrochemical method removes the need for chemical oxidants, and added electrolyte (BF4NEt4) can be recovered and reused. The method was applied to 17 substrates with high conversions in a single pass, yields up to 92%, and up to 7.5 g h-1 productivity. The PMB protecting group was also selectively removed in the presence of some other common alcohol protecting groups.
- Green, Robert A.,Jolley, Katherine E.,Al-Hadedi, Azzam A. M.,Pletcher, Derek,Harrowven, David C.,De Frutos, Oscar,Mateos, Carlos,Klauber, David J.,Rincón, Juan A.,Brown, Richard C. D.
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supporting information
p. 2050 - 2053
(2017/04/27)
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- A synthetic process of L-menthol
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The invention relates to the field of spice synthesis and particularly relates to a synthetic process of L-menthol. The process includes steps of d,l-menthol synthesizing, d,l-menthol rectification, d,l-menthol esterification, d,l-menthyl benzoate rectification, d,l-menthyl benzoate resolution, D-menthol synthesizing, menthol isomerization and L-menthol synthesizing. The process adopts thymol that is a simple, easily available and cheap chemical product as a raw material. Esterification conditions are optimized and the esterification and rectification are performed at the same time so as to allow the esterification to be converted into a way beneficial to d,l-menthyl benzoate production, thus increasing the esterification yield. Crystallization and resolution are optimized by utilization of the d,l-menthyl benzoate. Preparation of the L-menthol by the process is characterized by being high in yield, low in cost, simple and convenient in operation, suitable for continuous and large-scale production, and the like. According to the process, operation of the process is cyclic with a whole system being sealed, and the process is free of waste water, energy-saving and environmental friendly.
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Paragraph 0076; 0077; 0078
(2017/02/24)
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- Highly Productive and Enantioselective Enzyme Catalysis under Continuous Supported Liquid–Liquid Conditions Using a Hybrid Monolithic Bioreactor
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Enzyme-containing ionic liquids (ILs) were immobilized in cellulose-2.5-acetate microbeads particles embedded in a porous monolithic polyurethane matrix. This bioreactor was used under continuous liquid-liquid conditions by dissolving the substrates in a nonpolar organic phase immiscible with the ILs, thereby creating a biphasic system. Lipases (candida antarctica lipase B, CALB, candida rugosa lipase, CRL) were used to catalyze the enantioselective transesterification of racemic (R,S)-1-phenylethanol with vinyl butyrate and vinyl acetate, the esterification of (+/-)-2-isopropyl-5-methylcyclohexanol with propionic anhydride and the amidation of (R,S)-1-phenylethylamine with ethyl methoxyacetate. With this unique setup, very high productivities, that is, turnover numbers (TONs) up to 5.1×106 and space-time yields (STYs) up to 28 g product L?1 h?1, exceeding the corresponding values for batch-type reactions by a factor of 3100 and 40, respectively, were achieved while maintaining or even enhancing enantioselectivity compared to batch reactions via kinetic resolution. To our best knowledge, this is the first continuously operated bioreactor using supported liquid-liquid conditions that shows these features in the synthesis of chiral esters and amides.
- Sandig, Bernhard,Buchmeiser, Michael R.
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p. 2917 - 2921
(2016/11/02)
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- 2,3-Dichloro-5,6-dicyano-1,4-benzoquinone-catalyzed aerobic oxidation reactions via multistep electron transfers with iron(II) phthalocyanine as an electron-transfer mediator
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A new biomimetic catalytic oxidation system which employs 2,3-dichloro-5,6-dicyano-1,4-benzoquinone (DDQ) as the catalyst, molecular oxygen as the terminal oxidant and iron(ii) phthalocyanine (FeIIPc) as the electron-transfer mediator has been developed. This system can be applied for oxidative deprotection of PMB ethers, alcohol oxidation, aromatization and α,β-unsaturated aldehyde formation. After immobilizing FeIIPc on multi-walled carbon nanotubes, it can be reused without loss of activity.
- Hong, Yiming,Fang, Tiantian,Li, Meichao,Shen, Zhenlu,Hu, Xinquan,Mo, Weimin,Hu, Baoxiang,Sun, Nan,Jin, Liqun
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p. 51908 - 51913
(2016/06/13)
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- Facile Protocol for Catalytic Frustrated Lewis Pair Hydrogenation and Reductive Deoxygenation of Ketones and Aldehydes
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A series of ketones and aldehydes are reduced in toluene under H2 in the presence of 5 mol % B(C6F5)3 and either cyclodextrin or molecular sieves affording a facile metal-free protocol for reduction to alcohols. Similar treatment of aryl ketones resulted in metal-free deoxygenation yielding aromatic hydrocarbons.
- Mahdi, Tayseer,Stephan, Douglas W.
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supporting information
p. 8511 - 8514
(2015/11/27)
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- P450-catalyzed regio- and stereoselective oxidative hydroxylation of disubstituted cyclohexanes: Creation of three centers of chirality in a single CH-activation event This paper is dedicated to the memory of Harry H. Wasserman
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Wild-type P450-BM3 is able to catalyze in a highly regio- and diastereoselective manner the oxidative hydroxylation of non-activated disubstituted cyclohexane derivatives lacking any functional groups, including cis- and trans-1,2-dimethylcyclohexane, cis- and trans-1,4-dimethylcyclohexane, and trans-1,4-methylisopropylcyclohexane. In all cases except chiral trans-1,2-dimethylcyclohexane as substrate, the single hydroxylation event at a methylene group induces desymmetrization with simultaneous creation of three centers of chirality. Certain mutants increase selectivity, setting the stage for future directed evolution work.
- Ilie, Adriana,Agudo, Rubén,Roiban, Gheorghe-Doru,Reetz, Manfred T.
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p. 470 - 475
(2015/02/02)
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- Sustainable, mild and efficient p-methoxybenzyl ether deprotections utilizing catalytic DDQ
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A procedure for the selective deprotection of p-methoxybenzyl ethers using catalytic amounts of DDQ and of sodium nitrite, with oxygen as the terminal oxidant, is reported.
- Walsh, Katie,Sneddon, Helen F.,Moody, Christopher J.
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p. 7380 - 7387
(2017/09/13)
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- Metal-organic framework Co(D-cam)1/2(bdc)1/2(tmdpy) for improved enantioseparations on a chiral cyclodextrin stationary phase in gas chromatography
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Initial efforts to combine a chiral metal-organic framework (MOF), Co(D-Cam)1/2(bdc)1/2(tmdpy) (D-Cam=D-camphoric acid, bdc=1,4-benzenedicarboxylic acid, tmdpy=4,4′-trimethylenedipyridine), with peramylated β-cyclodextrins to investigate whether the use of a MOF can enhance enantioseparations on a cyclodextrin stationary phase are reported. Compared with columns of peramylated β-cyclodextrin incorporated in a MOF containing sodium chloride, the column of peramylated β-cyclodextrin+MOF shows excellent selectivity for the recognition of racemates, and higher resolutions are achieved on the peramylated β-cyclodextrin+MOF stationary phase. Experimental results indicate that the use of Co(D-Cam) 1/2(bdc)1/2(tmdpy) can improve enantioseparations on peramylated β-cyclodextrins. This is the first report that chiral MOFs can improve enantioseparations on a chiral stationary phase for chromatography. Copyright
- Liu, Hong,Xie, Sheng-Ming,Ai, Ping,Zhang, Jun-Hui,Zhang, Mei,Yuan, Li-Ming
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p. 1103 - 1108
(2014/11/07)
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- Highly enantioselective organocatalytic oxidative kinetic resolution of secondary alcohols using chiral alkoxyamines as precatalysts: Catalyst structure, active species, and substrate scope
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The development and characterization of enantioselective organocatalytic oxidative kinetic resolution (OKR) of racemic secondary alcohols using chiral alkoxyamines as precatalysts are described. A number of chiral alkoxyamines have been synthesized, and their structure-enantioselectivity correlation study in OKR has led us to identify a promising precatalyst, namely, 7-benzyl-3-n-butyl-4-oxa-5-azahomoadamantane, which affords various chiral aliphatic secondary alcohols (ee up to >99%, krel up to 296). In a mechanistic study, chlorine-containing oxoammonium species were identified as the active species generated in situ from the alkoxyamine precatalyst, and it was revealed that the chlorine atom is crucial for high reactivity and enantioselectivity. The present OKR is the first successful example applicable to various unactivated aliphatic secondary alcohols, including heterocyclic alcohols with high enantioselectivity, the synthetic application of which is demonstrated by the synthesis of a bioactive compound.
- Murakami, Keiichi,Sasano, Yusuke,Tomizawa, Masaki,Shibuya, Masatoshi,Kwon, Eunsang,Iwabuchi, Yoshiharu
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supporting information
p. 17591 - 17600
(2015/02/19)
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- PROCESS FOR THE PREPARATION OF MENTHOL
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The invention relates to a process for the preparation of 2-isopropyl-5-methylcyclohexanol (D,L-menthol) via the hydrogenation of thymol to menthone and subsequent further hydrogenation to give D,L-menthol.
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Paragraph 0085-0086
(2014/03/25)
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- PROCESS FOR THE PREPARATION OF MENTHOL
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The invention relates to a process for the preparation of 2-isopropyl-5-methylcyclohexanol (menthol) via the hydrogenation of thymol to neomenthol and the subsequent isomerization to give D/L (+/?)-menthol.
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Paragraph 0049-0053
(2014/03/25)
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- Highly practical iron-catalyzed C-O cleavage reactions
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Facile iron-catalyzed cleavage of various allyl, cinnamyl and benzyl C-O linkages has been effected in the presence of ethylmagnesium chloride. The protocol is operationally simple (xylene-THF, r.t., 1 h), requires low catalyst loading (1 mol% FeCl2) and tolerates halides, esters, amines, ethers and olefins. The allyl moiety is converted to volatile hydrocarbons which renders laborious product separation unnecessary.
- Gaertner, Dominik,Konnerth, Hannelore,Von Wangelin, Axel Jacobi
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p. 2541 - 2545
(2013/09/24)
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- MOFs as multifunctional catalysts: One-pot synthesis of menthol from citronellal over a bifunctional MIL-101 catalyst
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A bifunctional MOF catalyst containing coordinatively unsaturated Cr 3+ sites and palladium nanoparticles (Pd@MIL-101) has been used for the cyclization of citronellal to isopulegol and for the one-pot tandem isomerization/hydrogenation of citronellal to menthol. The MOF was found to be stable under the reaction conditions used, and the results obtained indicate that the performance of this bifunctional solid catalyst is comparable with other state-of-the-art materials for the tandem reaction: Full citronellal conversion was attained over Pd@MIL-101 in 18 h, with 86% selectivity to menthols and a diastereoselectivity of 81% to the desired (-)-menthol, while up to 30 h were necessary for attaining similar values over Ir/H-beta under analogous reaction conditions. The Royal Society of Chemistry 2012.
- Cirujano,Llabres I Xamena,Corma
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scheme or table
p. 4249 - 4254
(2012/05/07)
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- Microwave-assisted rapid and efficient deprotection and direct esterification and silylation of MOM and EOM ethers catalyzed by [Hmim][HSO 4] as a Bronsted acidic ionic liquid
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1-Methylimidazolium hydrogensulfate, [Hmim] [HSO4], a Bronsted acidic room temperature ionic liquid, is used as a catalyst and reaction medium for facile and ecofriendly deprotection of methoxymethyl (MOM) and ethoxymethyl (EOM) ethers to their corresponding alcohols under thermal conditions (Δ) and microwave irradiation (MW). Furthermore, one-pot interconversion to the respective acetates and trimethylsilyl (TMS) ethers was also achieved. Springer-Verlag 2010.
- Mohammadpoor-Baltork, Iraj,Moghadam, Majid,Tangestaninejad, Shahram,Mirkhani, Valiollah,Khosropour, Ahmad Reza,Mirjafari, Arsalan
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experimental part
p. 1083 - 1088
(2012/06/18)
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- CATALYST FOR ASYMMETRIC HYDROGENATION
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This invention aims at providing a catalyst for producing an optically active aldehyde or an optically active ketone, which is an optically active carbonyl compound, by carrying out selective asymmetric hydrogenation of an α,β-unsaturated carbonyl compound, particularly a catalyst which is insoluble in a reaction mixture for obtaining optically active citronellal which is useful as a flavor or fragrance, by carrying out selective asymmetric hydrogenation of citral, geranial or neral; and a method for producing a corresponding optically active carbonyl compound. The invention relates to a catalyst for asymmetric hydrogenation of an α,β-unsaturated carbonyl compound, which comprises a powder of at least one metal selected from metals belonging to Group 8 to Group 10 of the Periodic Table, or a metal-supported substance in which at least one metal selected from metals belonging to Group 8 to Group 10 of the Periodic Table is supported on a support, an optically active cyclic nitrogen-containing compound and an acid.
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Page/Page column 64
(2010/12/31)
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- A tetranuclear-zinc-cluster-catalyzed practical and versatile deprotection of acetates and benzoates
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A new catalytic deacylation of acetates and benzoates through transesterification with methanol was developed (see scheme). Reactions with various acidand nucleophile-sensitive functional groups proceeded efficiently in the presence of a catalytic amount of the tetranuclear zinc cluster. The present catalysis is applicable to less-reactive tertiary acetates, the deacylation of which is difficult to achieve by transesterification with other catalysts.
- Iwasaki, Takanori,Agura, Kazushi,Maegawa, Yusuke,Hayashi, Yukiko,Ohshima, Takashi,Mashima, Kazushi
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supporting information; experimental part
p. 11567 - 11571
(2010/11/24)
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- METHOD FOR PRODUCING OPTICALLY ACTIVE, RACEMIC MENTHOL
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The present invention relates to a particularly economic overall method for producing menthol, specifically for producing optically active, essentially enantiomerically and diastereomerically pure L-menthol and racemic menthol, starting from the starting material citral which is available inexpensively on an industrial scale. The method comprises the following steps a.1) catalytic hydrogenation of neral and/or geranial to give citronellal, b.1) cyclization of citronellal to isopulegol in the presence of an acidic catalyst, c.1) purification of isopulegol by crystallization and d.1) catalytic hydrogenation of isopulegol to give menthol.
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Page/Page column 41-42
(2010/10/19)
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- One-pot synthesis of menthol catalyzed by a highly diastereoselective Au/MgF2 catalyst
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No toxic compounds such as KCN and no thermal activation is required for the preparation of Au/MgF2 complexes by a simple and facile incipient wetness impregnation method in which hydrogen tetrachloroaurate (HAuCl 4) is the gold precursor. One of the complexes prepared exhibits unique catalytic properties and serves as a heterogeneous catalyst for the highly diastereoselective one-pot synthesis of (±)-menthol from citronellal (see picture).
- Negoi, Alina,Wuttke, Stefan,Kemnitz, Erhard,MacOvei, Dan,Parvulescu, Vasile I.,Teodorescu,Coman, Simona M.
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supporting information; experimental part
p. 8134 - 8138
(2011/02/24)
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- One-step microwave-assisted asymmetric cyclisation/hydrogenation of citronellal to menthols using supported nanoparticles on mesoporous materials
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The selective conversion of citronellal to menthols, with good diastereoselectivities to (-)-menthol for the case of (+)-citronellal as starting material, can effectively be carried out in a one-step reaction under microwave irradiation catalysed by supported nanoparticles on mesoporous materials. 2% Pt/Ga-MCM-41 was found to be the optimum catalyst for the reaction, with a quantitative conversion of starting material and selectivities above 85% to menthols obtained in short reaction times (typically 15 min). These results constitute the first report of a simple microwave-assisted one-step cyclisation/hydrogenation process for the production of menthols.
- Balu, Alina Mariana,Campelo, Juan Manuel,Luque, Rafael,Romero, Antonio Angel
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experimental part
p. 2845 - 2849
(2010/08/21)
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- Effects of methyl substituents on the activity and enantioselectivity of homobenzotetramisole-based catalysts in the kinetic resolution of alcohols
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Substitution of the tetrahydropyrimidine ring in the enantioselective acyl transfer catalyst homobenzotetramisole (HBTM) 6 with methyl groups exerts a dramatic influence on its performance in the kinetic resolution of secondary alcohols. The syn-3-methyl analogue of HBTM (9a) has proved to be superior to the parent compound in terms of catalytic activity, enantioselectivity, and synthetic accessibility.
- Zhang, Yuhua,Birman, Vladimir B.
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supporting information; scheme or table
p. 2525 - 2529
(2009/12/28)
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- Enzymatic production of l-menthol by a high substrate concentration tolerable esterase from newly isolated Bacillus subtilis ECU0554
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Enzymatic preparation of l-menthol has been attracting much attention in the flavor and fragrance industry. A new ideal strain, Bacillus subtilis ECU0554, which exhibited high hydrolytic activity and excellent enantioselectivity towards l-menthyl ester, has been successfully isolated from soil samples through enrichment culture and identified as Bacillus subtilis by 16S rDNA gene sequencing. The esterase extracted from B. subtilis ECU0554 (BSE) showed the best catalytic properties (E > 200) for dl-menthyl acetate among the five menthyl esters examined. Enantioselective hydrolysis of 100 mM dl-menthyl acetate at 30°C and pH 7.0, using crude BSE as biocatalyst and 10% ethanol (v/v) as cosolvent, resulted in 49.0% conversion (3 h) and 98.0% ee for the l-menthol produced, which were much better than those using commercial enzymes tested. Moreover, BSE exhibited strong tolerance against high substrate concentration (up to 500 mM), and the concentration of l-menthol produced could reach as high as 182 mM, and more importantly, the optical purity of l-menthol produced was kept above 97% ee, which were not found in previous reports. These results imply that BSE is a potentially promising bio-catalyst for the large-scale enzymatic preparation of l-menthol. Using this excellent biocatalyst, the enzymatic production of l-menthol will become a mild, efficient, inexpensive and easy-to-use "green chemistry" methodology.
- Zheng, Gao-Wei,Yu, Hui-Lei,Zhang, Jian-Dong,Xu, Jian-He
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experimental part
p. 405 - 414
(2009/11/30)
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- Highly enantioselective organocatalytic oxidative kinetic resolution of secondary alcohols using chirally Modified AZADOs
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A highly enantioselective organocatalytic oxidative kinetic resolution (OKR) of racemic secondary alcohols has been accomplished using asymmetric organocatalysis. A panel of chirally modified 2-azaadamantane N-oxyls (AZADOs) exhibit superior catalytic act
- Tomizawa, Masaki,Shibuya, Masatoshi,Iwabuchi, Yoshiharu
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supporting information; experimental part
p. 1828 - 1831
(2009/09/06)
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- Esters of pyromellitic acid. Part II. Esters of chiral alcohols: Para pyromellitate diesters as a novel class of resolving agents and use of pyromellitates as duplicands for chiral purification
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(Chemical Equation Presented) Methods are presented for the preparation of pyromellitate esters of chiral terpene alcohols, including d-(3) or l-menthol (4), d-isomenthol (7), l-borneol (8), or d- (5) or l-isopinocampheol (6). Alcoholysis of PMDA in CH2Cl2/Et3N led to the formation of monoesters (e.g., 18) or diesters (11, 12), as needed, relying on the differential reactivity of the two anhydride groups. The easily isolated para diester (11) crystallized before the meta diester (12) from HOAc. Nicotine (1, 14) was efficiently resolved as 1:1 salts with the menthyl (11a, 11b) or bornyl (11f) para diesters, prototypes of what promises to be a large class of novel resolving agents. Recrystallization of para-di-d-menthyl pyromellitate (11a) greatly improved the chiral purity of the contained d-menthol (3), an example of purification by "duplication". An alternative synthesis of specific diesters took advantage of the easily separated benzyl diesters and their derived acid chlorides (19, 21), with the benzyl esters serving as temporary blocking groups removable by catalytic hydrogenolysis. Pyromellitate tetraesters (26) were prepared by base-catalyzed transesterification of the tetraethyl ester (25). Tri-l-menthyl pyromellitate (27b) was obtained by catalytic hydrogenolysis of benzyl tri-l-menthyl pyromellitate (31b), itself prepared from the alcoholysis of benzyl pyromellitate triacid chloride (30) with l-menthol (4).
- Paine III, John B.
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p. 4939 - 4948
(2008/12/21)
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- Homobenzotetramisole: An effective catalyst for kinetic resolution of aryl-cycloalkanols
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Homobenzotetramisole (HBTM), a ring-expanded analogue of the previously reported catalyst BTM, displays higher catalytic activity and a different structure-selectivity profile. It displays good enantioselectivities in kinetic resolution of secondary benzylic alcohols but is particularly effective for 2-aryl-substituted cycloalkanols.
- Birman, Vladimir B.,Li, Ximin
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supporting information; experimental part
p. 1115 - 1118
(2009/04/07)
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- Hydrogen-transfer reduction of carbonyl compounds promoted by nickel nanoparticles
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Nickel(0) nanoparticles, generated from nickel(II) chloride, lithium powder and a catalytic amount of 4,4-di-tert-butylbiphenyl (DTBB) in THF at room temperature, have been found to promote the reduction of a variety of ketones and aldehydes by transfer hydrogenation using isopropanol as the hydrogen donor. The nickel nanoparticles were characterised and could be re-utilised with a good performance in the absence of a base. A mechanistic study demonstrates that the reaction proceeds through a dihydride-type mechanism.
- Alonso, Francisco,Riente, Paola,Yus, Miguel
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p. 1847 - 1852
(2008/09/18)
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- Design of catalyst systems for the one-pot synthesis of menthols from citral
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Stable, active, and highly selective bifunctional Ni/Al-MCM-41 catalysts were developed for the one-pot synthesis of menthols from citral. The liquid-phase hydrogenation of citral to citronellal was studied on silica-supported noble (Pt, Pd, Ir) and nonnoble (Ni, Co, Cu) metals. It was found that citronellal is selectively formed at the beginning of the reaction only on Pd and Ni catalysts. The consecutive ene-cyclization of citronellal to isopulegols was investigated on solid acids containing exclusively Lewis (ZnO/SiO2) or strong Broensted (CsHPA) acid sites, and also on catalysts containing both Lewis and Broensted acid sites of either strong (zeolites, SiO2-Al2O3) or moderate (Al-MCM-41) strength. The isopulegol formation rate was higher on samples exhibiting dual Lewis/Broensted acidity, such as SiO2-Al2O3, Al-MCM-41, and zeolite HBEA. Based on these previous results, bifunctional catalysts containing Pd or Ni supported on SiO2-Al2O3, Al-MCM-41, or zeolite HBEA were prepared and tested for citral conversion to menthols. The catalyst stability and the effect of hydrogen pressure and metal loading on menthol productivity were also investigated. The best catalyst was Ni(8%)/Al-MCM-41, which yielded more than 90% menthols at 2026.0 kPa and showed no significant deactivation after two consecutive catalytic tests.
- Trasarti,Marchi,Apesteguia
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p. 155 - 165
(2008/02/03)
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- Carbonyl reduction with CaH2 and R3SiCl catalyzed by ZnCl2
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Ketones and aldehydes were effectively reduced to the corresponding alcohols (or their silyl ethers) by the reaction with CaH2 and R3SiCl in the presence of a catalytic amount of ZnCl2. In the absence of the carbonyl substrate, the reagent reduced R3SiCl to the corresponding hydrosilane under mild reaction conditions.
- Tsuhako, Akiko,He, Jing-Qian,Mihara, Mariko,Saino, Naoko,Okamoto, Sentaro
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p. 9120 - 9123
(2008/09/17)
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- Domino-cyclisation and hydrogenation of citronellal to menthol over bifunctional Ni/Zr-Beta and Zr-beta/Ni-MCM-41 catalysts
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The one-pot conversion of (±)-citronellal to menthol can be selectively catalysed by either a bifunctional Ni/Zr-zeolite beta catalyst or a dual catalyst system of Zr-beta and Ni/MCM-41, giving a high diastereoselectivity to (±)-menthol of 90-94%. The Royal Society of Chemistry 2006.
- Nie, Yuntong,Chuah, Gaik-Khuan,Jaenicke, Stephan
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p. 790 - 792
(2008/02/03)
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- Insight into the mechanism of oxidative kinetic resolution of racemic secondary alcohols by using manganese(III)(salen) complexes as catalysts
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The oxidative kinetic resolution of various racemic secondary alcohols with PhI(OAc)2 catalyzed by chiral [MnIII(salen)] complexes in the presence of KBr was studied in a water/organic solvent mixture. The dramatic, synergetic effect of additives, organic solvent, and the substituents of chiral salen ligands on the enantioselectivities of the reactions is reported. Results from UV/Vis spectroscopy and ESI-MS studies provide evidence that these reactions are induced by the formation of a high-valent manganese intermediate.
- Li, Zhen,Tang, Zhong H.,Hu, Xiao X.,Xia, Chun G.
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p. 1210 - 1216
(2007/10/03)
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- Enantioselective glucosylation of (±)-secondary alcohols with plant glucosyltransferases
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Two glucosyltransferases were isolated from plant cell cultures of Catharanthus roseus and Nicotiana tabacum. The enzyme from C. roseus enantioselectively glucosylated (±)-secondary alcohols to give the glucosides of (R)-alcohols, while the glucosylation with that from N. tabacum gave preferentially the glucosides of (S)-alcohols.
- Shimoda, Kei,Kubota, Naoji,Hamada, Hiroki
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p. 2319 - 2321
(2007/10/03)
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- Hydrolysis of Alkenyl Esters and Ethers Catalyzed by Metal Complexes
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(Equation presented) Various kinds of transition metals catalyzed the hydrolysis of alkenyl esters and ethers under buffer-free, high concentration conditions compared to usual biocatalysts. Hydrolytic kinetic resolution of cis-2-tert-butylcyclohexyl vinyl ether was achieved by chiral (salen)Co complexes with good selectivity (krel = 10.0).
- Aoyama, Hiroshi,Tokunaga, Makoto,Hiraiwa, Shin-Ichiro,Shirogane, Yuki,Obora, Yasushi,Tsuji, Yasushi
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p. 509 - 512
(2007/10/03)
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- METHOD FOR PRODUCING MENTHOL
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To the invention relates to a method for producing menthol by catalytically hydrogenating compounds, which comprise the carbon skeleton of methane having at least one double bond and which are substituted at the 3-position by oxygen, and/or by catalytically rearranging stereoisomers of methanol in the presence of hydrogen and doped nickel catalysts.
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Page/Page column 11-12
(2008/06/13)
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- Lipase-catalyzed resolution of p-menthan-3-ols monoterpenes: Preparation of the enantiomer-enriched forms of menthol, isopulegol, trans- and cis-piperitol, and cis-isopiperitenol
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A study on the enzymic resolution of the most common p-menthan-3-ol monoterpene isomers is described. Enantioenriched alcohols 1, 5, 10, 11 and 12 are obtained by means of the lipase-mediated kinetic acetylation of the corresponding racemic materials. The stereochemical aspects of the enzymic process have been investigated. We found that the structural features of the starting p-menthan-3-ol as well as the kind of lipase used, impacted strongly on the enantioselectivity of the resolution. The potentialities of this approach for preparative purposes are discussed.
- Serra, Stefano,Brenna, Elisabetta,Fuganti, Claudio,Maggioni, Francesco
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p. 3313 - 3319
(2007/10/03)
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- Lipase-catalyzed Irreversible Transesterification of Secondary Alcohols Using Isopropenyl Acetate
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Asymmetric acetylation of a set of secondary alcohols with the innocuous acyl donor isopropenyl acetate catalyzed by a lipase from Pseudomonas cepacia immobilized on ceramic particles (PSL-C) in toluene as organic medium afforded the chiral alcohols and the corresponding acetates in high enantiomeric excess (up to 99%). An effective baseline separation of the enantiomers of both substrate and product was performed in one analysis without derivatization using gas chromatography on a new chiral stationary phase (CSP) Chirasil-β-Dex containing an undecamethylene spacer (C11-Chirasil-Dex).
- Ghanem, Ashraf,Schurig, Volker
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p. 1151 - 1157
(2007/10/03)
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- Entrapment of Pseudomonas cepacia lipase with peracetylated β-cyclodextrin in sol-gel: Application to the kinetic resolution of secondary alcohols
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Co-lyophilized Pseudomonas cepacia lipase with peracetylated β-cyclodextrin was immobilized by the sol-gel process. The gel-entrapped lipase/cyclodextrin was prepared by the hydrolysis of methyltrimethoxysilane (MTMS) in the presence of the co-lyophilized lipase with peracetylated β-cyclodextrin prepared with different weight ratios (enzyme to CD). This type of enzyme preparation was subsequently used in the kinetic resolution of a set of secondary alcohols using isopropenyl acetate as an innocuous acyl donor in toluene as the organic medium. The resulting chiral alcohols (substrate) and the corresponding acetates (product) were baseline separated in one analysis without derivatization using gas chromatography on a new chiral stationary phase (CSP) Chirasil-β-Dex containing an undecamethylene spacer (C11-Chirasil-Dex).
- Ghanem, Ashraf,Schurig, Volker
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p. 2547 - 2555
(2007/10/03)
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- Facile and Chemo-selective Cleavages of Allyl Ethers Utilizing Tetrabutylammonium Sulfate Radical Species
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Allyl ethers containing various functional groups reacted with tetrabutylammonium peroxydisulfate in acetonitrile under mild conditions to afford the corresponding cleaved alcohols in excellent yields.
- Yang, Seung Gak,Park, Min Young,Kim, Yong Hae
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p. 492 - 494
(2007/10/03)
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- Mapping the substrate selectivity of new hydrolases using colorimetric screening: Lipases from Bacillus thermocatenulatus and Ophiostoma piliferum, esterases from Pseudomonas fluorescens and Streptomyces diastatochromogenes
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Recent advances in biochemistry and molecular biology have simplified the discovery and preparation of new hydrolases. Although these hydrolases might solve problems in organic synthesis, measuring their selectivity, especially enantioselectivity, remains tedious and time consuming. Recently, we developed a colorimetric screening method to measure the enantioselectivity of hydrolases. Here we apply this rapid screening method to map the substrate selectivity of four new hydrolases: lipases from the thermophilic Bacillus thermocatenulatus (DSM 730, BTL2) and a filamentous fungus Ophiostoma piliferum (NRRL 18917, OPL) and esterases from two bacteria, Pseudomonas fluorescens (SIK-W1, esterase I, PFE) and Streptomyces diastatochromogenes (Tue 20, SDE). We screened a general library of 29 substrates and a chiral library of 23 pairs of enantiomers. All four hydrolases catalysed the hydrolysis of unnatural substrates, but the two lipases accepted a broader range of substrates than the two esterases. As expected, the two lipases favoured more hydrophobic substrates, while the two esterases showed a preference for smaller substrates. Several moderately enantioselective reactions were identified for the solketal esters: BTL2, butyrate, E = 7.9 (R); octanoate, E = 4.9 (R) and 3-bromo-2-methyl propionate methyl esters, PFE, E = 12 (S); SDE, E = 5.6 (S). OPL showed low enantioselectivity toward all substrates tested. The current colorimetric screen could not measure the selectivity for several slow-reacting substrates. Traditional screening identified high enantioselectivity of BTL2 and PFE toward one of these slow substrates, 1-phenylethyl acetate (E>50).
- Liu, Andrew Man Fai,Somers, Neil A.,Kazlauskas, Romas J.,Brush, Terry S.,Zocher, Frank,Enzelberger, Markus M.,Bornscheuer, Uwe T.,Horsman, Geoff P.,Mezzetti, Alessandra,Schmidt-Dannert, Claudia,Schmid, Rolf D.
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p. 545 - 556
(2007/10/03)
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- Chiral aminoalcohols with a menthane skeleton as catalysts for the enantioselective addition of diethylzinc to benzaldehyde
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Novel chiral aminoalcohols were synthesized by highly diastereoselective addition of Me3SiCN and LiCH2CN to (-)-menthone followed by LiAlH4 reduction. The addition of CH2=CH-MgBr and PhCH=CH-MgBr to menthone and the following epoxidation, provided useful hydroxy epoxides, one of which could be aminolyzed to afford an aminodiol. In one case, the configuration of the newly formed epoxidic stereogenic center was determined by X-ray crystallography. When applied as catalysts in the enantioselective addition of Et2Zn to benzaldehyde, the aminoalcohols induced enantiomeric excesses (e.e.s) of up to 77%.
- Panev, Stefan,Linden, Anthony,Dimitrov, Vladimir
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p. 1313 - 1321
(2007/10/03)
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- Molecular recognition study on supramolecular systems. Part 19. Circular dichroism studies of inclusion complexation of aliphatic alcohols by organoselenium modified β-cyclodextrins
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Complex stability constants for the stoichiometric 1 : 1 inclusion complexation of various aliphatic alcohols with mono[6-(benzylseleno)-6-deoxy]-β-cyclodextrin (1). mono[6-(phenylseleno)-6-deoxy]-β-cyclodextrin (2), and mono-[6-(o-, m-, or p-tolylseleno)-6-deoxy]-β-cyclodextrin (3-5) have been obtained by spectrophotometric titrations at 25°C in phosphate buffer solution (pH = 7.2). The Cotton effects observed indicate that the aromatic moiety penetrates shallowly into the hydrophobia cavity of cyclodextrin. Therefore, the aromatic moiety can be taken as an induced circular dichroism (ICD) probe to investigate the inclusion phenomena. The results obtained demonstrate that the modified β-cyclodextrin (1) is highly sensitive to the size/shape and conformational rigidity of guest molecules, giving fairly good molecular selectivity up to 114 for adamantan-1-ol/cyclopentanol and relatively high EIZ selectivity up to 2.7 for geraniol/nerol. Interestingly, all of the modified β-cyclodextrins employed displayed relatively good enantioselectivity for (+)-enantiomers of borneol and menthol. The molecular recognition ability and enantioselectivity for aliphatic alcohols of the modified β-cyclodextrins (1-5) are discussed from the viewpoints of the size/shape-fit relationship and the multipoint recognition mechanism.
- Liu, Yu,Li, Bin,Han, Bao-Hang,Wada, Takehiko,Inoue, Yoshihisa
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p. 563 - 568
(2007/10/03)
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- Expedient and simple method for regeneration of alcohols from toluenesulfonates using Mg-MeOH
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Efficient conversion of toluenesulfonates to corresponding alcohols with Mg-MeOH is described.
- Sridhar, Madabhushi,Kumar, B. Ashok,Narender
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p. 2847 - 2850
(2007/10/03)
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