- Direct Aerobic α-Hydroxylation of Arylacetates for the Synthesis of Mandelates
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Aerobic α-hydroxylation of α-methylene esters has proven challenging due to overoxidation and hydrolysis of the materials. In this article, KOtBu-promoted TBAB-catalyzed α-hydroxylation of α-methylene aryl esters using O2as the oxyge
- Xu, Changming,Li, Xiangfan,Bai, Lei
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p. 4298 - 4304
(2022/03/16)
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- Cobalt-Catalyzed Transfer Hydrogenation of α-Ketoesters and N-Cyclicsulfonylimides Using H2O as Hydrogen Source
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A Co-catalyzed effective transfer hydrogenation of various α-ketoesters and N-cyclicsulfonylimides by safe and environmentally benign H2O as hydrogen source is described. The reaction used easily available and easy to handle zinc metal as a reductant. Interestingly, the catalytic system does not require ligand for reduction of N-cyclicsulfonylimides. (Figure presented.).
- Gao, Yang,Zhang, Xuexin,Laishram, Ronibala Devi,Chen, Jingchao,Li, Kangkui,Zhang, Keyang,Zeng, Guangzhi,Fan, Baomin
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p. 3991 - 3997
(2019/08/02)
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- Ester Formation via Symbiotic Activation Utilizing Trichloroacetimidate Electrophiles
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Trichloroacetimidates are useful reagents for the synthesis of esters under mild conditions that do not require an exogenous promoter. These conditions avoid the undesired decomposition of substrates with sensitive functional groups that are often observed with the use of strong Lewis or Br?nsted acids. With heating, these reactions have been extended to benzyl esters without electron-donating groups. These inexpensive and convenient methods should find application in the formation of esters in complex substrates.
- Mahajani, Nivedita S.,Meador, Rowan I. L.,Smith, Tomas J.,Canarelli, Sarah E.,Adhikari, Arijit A.,Shah, Jigisha P.,Russo, Christopher M.,Wallach, Daniel R.,Howard, Kyle T.,Millimaci, Alexandra M.,Chisholm, John D.
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p. 7871 - 7882
(2019/06/27)
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- Boron-Catalyzed O-H Bond Insertion of α-Aryl α-Diazoesters in Water
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A catalytic, metal-free O-H bond insertion of α-diazoesters in water in the presence of B(C6F5)3·nH2O (2 mol %) was developed, affording a series of α-hydroxyesters in good to excellent yields. The reaction features easy operation and wide substrate scope, and importantly, no metal is needed as compared with the conventional methods. Significantly, this approach further expands the applications of B(C6F5)3 under water-tolerant conditions.
- San, Htet Htet,Wang, Shi-Jun,Jiang, Min,Tang, Xiang-Ying
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p. 4672 - 4676
(2018/08/09)
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- Silica-supported HClO4 promotes catalytic solvent- and metal-free O-H insertion reactions with diazo compounds
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Solvent-free O-H insertion reactions in the presence of diazo carbonyl compounds were carried-out in very mild conditions. Unlike the traditional metal-catalysed version, employing rhodium acetate dimer, this method uses eco-friendly silica-supported HClO4 as the catalyst. Only 0.3 mol% of this Br?nsted acid catalyst, that can also be recycled several times, is necessary to guarantee very good yields (up to 97%) in the O-H insertion reactions. Reaction set-up is simple and permitted the preparation of forty-three α-hydroxy and α-alkoxy esters/ketones in just 1 h and at room temperature.
- Gallo, Rafael Douglas C.,Burtoloso, Antonio C. B.
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p. 4547 - 4556
(2018/10/17)
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- Zirconocene-catalyzed direct (trans)esterification of acyl acids (esters) and alcohols in a strict 1:1 ratio under solvent-free conditions
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A highly efficient way for the direct (trans)esterification of acyl acids (esters) and alcohols in a strict 1:1 ratio using a zirconocene complex (1, 1 mol%), a strong Lewis acid of good water tolerance, as a catalyst under solvent-free conditions has been developed. A wide range of acid and alcohol (esters) substrates undergo (trans)esterification to produce carboxylic ester motifs in moderate to good or excellent yields with good functional tolerance, such as that towards C-Br as well as CC and CC bonds. And complex 1 can be recycled six times without showing a significant decline in catalytic efficiency. It was demonstrated that cyclandelate, which is used to treat high blood pressure as well as heart and blood-vessel diseases, can be directly synthesized on a gram scale with 81% yield (6.70 g) using complex 1.
- Tang, Zhi,Jiang, Qiutao,Peng, Lifen,Xu, Xinhua,Li, Jie,Qiu, Renhua,Au, Chak-Tong
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supporting information
p. 5396 - 5402
(2017/11/22)
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- Ester manufacturing method (by machine translation)
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PROBLEM TO BE SOLVED: To produce an ester compound by transesterification using an inexpensive and low toxic inorganic compound. SOLUTION: Transesterification of an ester compound and an alcohol compound is carried out under the presence of lanthanum nitrate (for example, lanthanum nitrate hexahydrate) and a phosphine compound (for example, tri-n-octylphosphine), thereby obtaining the ester product. For example, transesterification of dimethyl carbonate and benzyl alcohol is carried out under the presence of 1 mol% of lanthanum nitrate hexahydrate, and 2 mol% of tri-n-octylphosphine, thereby obtaining benzyl methylcarbonate at a yield of >99%. COPYRIGHT: (C)2012,JPO&INPIT
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Paragraph 0083; 0084
(2017/02/17)
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- Enantio- and chemoselective Br?nsted-acid/Mg(nBu) 2 catalysed reduction of α-keto esters with catecholborane
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The first enantio- and chemoselective Br?nsted-acid catalysed reduction of α-keto esters with catecholborane has been developed. The α-hydroxy esters were obtained under mild reaction conditions in virtually quantitative yields and excellent enantioselectivities. With slight modifications both enantiomers can be obtained without any loss of selectivity. This journal is the Partner Organisations 2014.
- Enders, Dieter,St?ckel, Bianca A.,Rembiak, Andreas
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p. 4489 - 4491
(2014/04/17)
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- A homochiral porous metal-organic framework for enantioselective adsorption of mandelates and photocyclizaton of tropolone ethers
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A chiral porous metal-organic framework of an axially C2- symmetric 1,1′-biphenol ligand is constructed and can be used as a solid-state host to enanioselectively adsorb mandelates with up to 93.1% ee and to entrap achiral tropolone ethers and
- Peng, Yongwu,Gong, Tengfei,Cui, Yong
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supporting information
p. 8253 - 8255
(2013/09/12)
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- Chemoselective esterification of α-hydroxyacids catalyzed by salicylaldehyde through induced intramolecularity
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A new, direct and chemoselective esterification of α-hydroxyacids was developed using a reversible covalent-binding strategy. By taking advantage of acetal chemistry, simple aldehydes can be used to efficiently catalyze the esterification of α-hydroxy carboxylic acids in the presence of β-hydroxyacid moieties or other carboxylic acids in amounts equal to or in excess of the alcohols. A diverse array of α-aryl, α-alkyl, α-heteroaryl, and functionalized α-hydroxyacids were smoothly esterified with 1° and 2° alcohols catalyzed by 10 mol% inexpensive and commercially available salicylaldehyde, furnishing the resultant esterification products in 83-95% yields after a simple basic aqueous workup to remove the unreacted hydroxyacids. In addition, the salicylaldehyde can be recovered through vacuum distillation or silica gel purification, thereby meeting the standards of green chemistry. A mechanistic study proved that the formation of covalent adduct III during our proposed catalytic cycle (Scheme 1A) is responsible for the real catalysis.
- Weng, Shiue-Shien,Li, Hsin-Chun,Yang, Teng-Mao
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p. 1976 - 1986
(2013/03/13)
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- In situ generated "lanthanum(iii) nitrate alkoxide" as a highly active and nearly neutral transesterification catalyst
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In situ generated lanthanum(iii) nitrate alkoxide is a highly active and nearly neutral transesterification catalyst, which can promote non-epimerized transesterification of α-substituted chiral carboxylic esters under reflux conditions.
- Hatano, Manabu,Kamiya, Sho,Ishihara, Kazuaki
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supporting information
p. 9465 - 9467
(2012/10/29)
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- Selective reduction of aldehydes and ketones to alcohols with ammonia borane in neat water
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Chemoselective reduction of various carbonyl compounds to alcohols with ammonia borane (AB), a nontoxic, environmentally benign, and easily handled reagent, in neat water was achieved in quantitative conversions and high isolated yields. Interestingly, α- and β-keto esters were selectively reduced to corresponding hydroxyl esters by AB, while diols were obtained when sodium borohydride was used as a reducing agent. The procedure is also compatible with the presence of a variety of base-labile protecting groups, such as tosyl, acetyl, benzoyl, ester groups, and acid-labile protecting groups such as trityl and TBDMS groups, and others, such as the unsaturated double bond, nitro and cyano groups. Finally, a kilo scale reaction of methyl benzoylformate with AB was conducted in water and gave methyl mandelate in 94% yield.
- Shi, Lei,Liu, Yingying,Liu, Qingfeng,Wei, Bin,Zhang, Guisheng
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experimental part
p. 1372 - 1375
(2012/06/04)
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- Asymmetric aerobic oxidation of α-hydroxy acid derivatives catalyzed by reusable, polystyrene-supported chiral N-salicylidene oxidovanadium tert-leucinates
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The direct immobilization of two different C-5-propargyl ether-modified, chiral N-salicylidene vanadyl(V) tert-leucinates onto 4-azidomethyl-substituted polystyrene by click chemistry was examined. Among the eight different solvents investigated, the resulting polystyrene-supported catalysts promote the asymmetric, aerobic oxidation of α-hydroxy (thio)esters and amides with enantioselectivities of up to 99% ee (selectivity factor up to 41) in chloroform. These polystyrene-supported catalysts can be readily recovered by filtration and reused for at least four consecutive runs without discernible loss of reactivity and enantioselectivity.
- Salunke, Santosh B.,Babu, N.Seshu,Chen, Chien-Tien
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p. 1234 - 1240
(2011/06/26)
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- Transesterification catalyzed by iron(III) β-diketonate species
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A practical and clean protocol for transesterification catalyzed by a 5 mol % cheap, non-toxic and moisture stable Fe(acac)3 or other iron(III) β-diketonate species in solvent, such as heptane under azeotropic condition is developed. A remarkable rate enhancement was observed upon the addition of 5 mol % of an inorganic base, such as Na2CO3, which suggests that faster formation of a dimeric μ-alkoxy-bridged iron(III) species under alkaline conditions facilitates catalytic turnover. This system provides smooth transesterification over a wide range of structurally diverse esters and alcohols without disturbing functional groups. In addition, the use of iron β-diketonate complexes as catalysts is more environmentally friendly, safer, and economical than other transition-metal catalysts. Preliminary mechanistic studies indicate that the active catalyst is likely a dimeric μ-alkoxy-bridged iron(III) species, as determined by X-ray crystallography of [Fe(dbm)2(O-n-Bu)]2 derived from the alcoholysis of Fe(dbm)3 under alkaline conditions.
- Weng, Shiue-Shien,Ke, Chih-Shueh,Chen, Fong-Kuang,Lyu, You-Fu,Lin, Guan-Ying
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experimental part
p. 1640 - 1648
(2011/04/17)
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- Polymer and silica supported tridentate schiff base vanadium catalysts for the asymmetric oxidation of ethyl mandelate - Activity, stability and recyclability
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Homogeneous tridentate Schiff base vanadium catalysts derived from salicylaldehydes and tert-leucinol or tert-leucine are known to be excellent catalysts for the asymmetric oxidation of α-hydroxy esters including ethyl mandelate. Herein, new analogous supported, semi-soluble and insoluble catalysts are synthesized and their activities relative to the homogeneous catalyst are reported. The new catalysts are characterized by 1H and 13C NMR spectroscopy, mass spectrometry (EI, ESI, FAB), X-ray crystallography, elemental analysis, gel permeation chromatography (GPC), Fourier transform infrared (FT-IR) spectroscopy, and nitrogen physisorption. The effects of support material, synthesis procedure, and reaction solvent are examined to probe the utility of these catalysts. Linear poly(styrene) supported catalysts are partially soluble under the reaction conditions, and it is shown that the soluble species contribute significantly to the catalytic reactivity. Insoluble catalysts based on the same vanadyl complexes supported on cross-linked poly(styrene) resin or mesoporous silica allow for catalyst recovery and recycle, showing equivalent selectivities over multiple reaction cycles. The mesoporous silica supported catalyst exhibits greater selectivity than the analogous homogeneous and polymer supported catalysts. Rigorous recycle studies show a loss of activity in each recycle, which is attributed to the decomposition of some portion of the vanadyl complexes in each cycle.
- Shiels, Rebecca A.,Venkatasubbaiah, Krishnan,Jones, Christopher W.
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experimental part
p. 2823 - 2834
(2009/11/30)
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- Asymmetrie aerobic oxidation of α-hydroxy acid derivatives by C 4-symmetric, vanadate-centered, tetrakisvanadyl(V) clusters derived from N-salicylidene-α-aminocarboxylates
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(Chemical Equation Presented) A series of chiral vanadyl(V) methoxides bearing 3-t-butyl-5-substituted N-salicylene-L-valinate and L-t-leucinate as chiral auxiliaries has been prepared. In all cases except the 3,5-di-t-butyl analogue, they exist as monomers both in solution and in the single crystal state. In the case of the 3,5-di-t-butyl analogue, the architectural nature of the vanadyl(V) complex highly depends on the base used during the complex formation event. A pentanuclear C4-symmetric complex was formed when potassium salts were employed instead of the corresponding sodium salts. A central vanadate(V) unit serves to grip four identical chiral monomelic vanadyl(V) units together, by which a potassium ion sits on top of the four flanking units through carbonyl coordinations and serves to hold the whole cluster by cooperation with the central vanadate(V) unit. In comparison with the corresponding monomelic vanadyl(V) methoxide complex, the cluster complex was utilized to facilitate the asymmetric aerobic oxidations of various racemic α-hydroxyesters, -amides, and -thioesters with excellent selectivity factors (krel 40 to >500).
- Chen, Chien-Tien,Bettigeri, Sampada,Weng, Shiue-Shien,Pawar, Vijay D.,Lin, Ya-Hui,Liu, Cheng-Yuan,Lee, Way-Zen
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p. 8175 - 8185
(2008/02/13)
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- Catalytic asymmetric transfer hydrogenation of α-ketoesters with hantzsch esters
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C2-symmetric chiral copper(II)-bisoxazolines function as alcohol dehydrogenase mimics and catalyze highly enantioselective transfer hydrogenations of α-ketoesters with Hantzsch esters as a synthetic NADH analogue to give α-hydroxy esters in excellent enantioselectivities.
- Yang, Jung Woon,List, Benjamin
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p. 5653 - 5655
(2007/10/03)
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- Direct atom-efficient esterification between carboxylic acids and alcohols catalyzed by amphoteric, water-tolerant TiO(acac)2
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A diverse array of oxometallic species were examined as catalysts for a test direct condensation of benzoic acid and 2-phenylethanol in 1:1 stoichiometry. Besides group IVB MOCl2-XH2O and TiOX 2-xH2O, group VB VOCl2-xTHF and group IVB TiO(acac)2 were found to be the most efficient and water-tolerant catalysts for the test reaction. The new neutral catalytic protocol with the optimal TiO(acac)2 tolerates many stereo/electronic structural variations in both (di)-acid (1°-3° alkyl and aryl) and (di)alcohol (1°, 2° alkyl, and aryl) components with high chemoselectivity.
- Chen, Chien-Tien,Munot, Yogesh S.
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p. 8625 - 8627
(2007/10/03)
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- Expanding the utility of proteases in synthesis: Broadening the substrate acceptance in non-coded amide bond formation using chemically modified mutants of subtilisin
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The strategy of combined site directed mutagenesis and chemical modification creates chemically modified mutants (CMMs) with greatly broadened substrate specificities. We have previously reported that the CMMs of subtilisin Bacillus lentus (SBL) are efficient catalysts for the coupling of both L- and D-amino acids. We now report that these powerful catalysts also allow amide bond formation between a variety of non-coded carboxylic acids, including β-alanine and β-amino homologues of phenylalanine, with both L- and D-amino acid nucleophiles. As a guide to enzyme efficiency, a hydrolysis assay indicating pH change has been employed. CMMs selected by this screen furnished higher yields of coupling products compared to the wild-type enzyme (WT). Furthermore, both WT and CMM enzymes allow highly stereoselective aminolysis of a meso diester with an amino acid amine. These results highlight the utility of CMMs in the efficient formation of non-coded amides as potential peptide isosteres.
- Khumtaveeporn, Kanjai,Ullmann, Astrid,Matsumoto, Kazutsugu,Davis, Benjamin G.,Jones
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p. 249 - 261
(2007/10/03)
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- An efficient and convenient procedure for preparation of mandelates catalysed by TiO2/SO4/2- solid superacid
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An easy and efficient synthesis of mandelates in excellent yields from mandelic acid with alcohols catalysed by TiO2/SO42- solid superacid.
- Jin,Ma,Li,Sun,Li
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p. 2051 - 2054
(2007/10/03)
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- Improved Cs2CO3 promoted O-alkylation of acids
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Cesium carbonate mediated O-alkylation of carboxylic acids was efficiently carried out under mild in situ conditions to give the corresponding esters exclusively. Chiral templates including α-hydroxy and α-alkoxy acids were also converted to their corresponding esters with no observed racemization.
- Parrish, Jay P.,Dueno, Eric E.,Kim, Seok-In,Jung, Kyung Woon
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p. 2687 - 2700
(2007/10/03)
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- Fe2(SO4)3 · xH2O in synthesis: A new and convenient catalyst for the esterification of mandelic acid with alcohols
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Treatment of various of alcohols with mandelic acid in the presence of a catalytic amount of Fe2(SO4)3 · xH2O to give the corresponding esters in good yields.
- Zhang, Gui-Sheng,Gong, Hui
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p. 1547 - 1551
(2007/10/03)
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- A general and simple synthesis of phenylglyoxylic esters via the oxidation of mandelic esters with ammonium chlorochromate adsorbed on alumina
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A general method for preparation of phenylglyoxylic esters by oxidation of mandelic esters with readily available ammonium chlorochromate adsorbed on alumina is described.
- Zhang, Gui-Sheng,Gong, Hui
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p. 3149 - 3153
(2007/10/03)
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- A CONVENIENT METHOD FOR ENZYMATIC BENZYL-ALKYL TRANSESTERIFICATION UNDER MILD NEUTRAL CONDITIONS
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Lipases from Candida cylindracea and from Pseudomonas fluorescens efficiently catalyse the benzyl to alkyl transesterification in organic solvents under mild conditions in nearly quantitative yields.
- Gutman, Arie L.,Shkolnik, Eleonora,Shapira, Michal
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p. 8775 - 8780
(2007/10/02)
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- Certain optically active mono esters of dicarboxylic acids
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Optically active mono-esters of dicarboxylic acid of the formula III: STR1 being useful as intermediates for preparing optically active natural products or medicines; asymmetric synthesis process for preparing thereof being characterized by the reaction of an acid anhydride with an (R)- or (S)-arylacetic acid derivative; and the key substances therefor are also claimed.
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- Synthetic cephalotaxine esters having antileukemic activity
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Six acyl esters of cephalotaxine have been synthesized by ordinary and standard procedures, and all have demonstrated chemotherapeutic activity against leukemia in animals.
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