- Stereoselective synthesis of thienyl and furyl analogues of ephedrine
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The stereoselective syntheses of thienyl and furyl analogues of ephedrine starting from (R)- and (S)-cyanohydrins, respectively, are described. Addition of methyl Grignard to the O-trimethylsilyl protected optically active cyanohydrins (R)- and (S)-3 and hydrogenation of the resulting imino intermediates gives the erythro-2-amino alcohols 4 with high diastereoselectivity. Their reductive methylation leads to the enantiomerically pure thiophene analogues (1S,2S)- and (1R,2R)-6a, (1R,2S)- and (1S,2R)-6b as well as to the furan analogues (1S,2S)-6c and (1R,2S)-6d of ephedrine, The biological activity of the new compounds is under investigation.
- Effenberger, Franz,Eichhorn, Joachim
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- A simple separation method for (S)-hydroxynitrile lyase from cassava and its application in asymmetric cyanohydrination
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Using an acetone precipitation method, crude (S)-hydroxynitrile lyase [(S)-MeHNL] was separated from Munihot esculenta (cassava) leaves, and used directly as biocatalyst to catalyze asymmetric cyanohydrination and produce cyanohydrins with enantiomeric purities (≥90% ee) significantly greater than those previously reported. The use of a water/i-Pr2O system with an enzyme, NaCN, and appropriate amounts of acetic acid is crucial in improving the stereoselectivity of cyanohydrin formation by minimizing the non-enzymatic reaction and the racemization of the chiral products. The proposed isolation method for crude (S)-MeHNL has a high value because of its simplicity, and low cost as well as the high activity of the crude (S)-MeHNL.
- Zheng, Zubiao,Zi, Yan,Li, Zhongzhou,Zou, Xinzhuo
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p. 434 - 439
(2013/06/27)
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- Purification and characterization of a novel (R)-hydroxynitrile lyase from Eriobotrya japonica (Loquat)
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A hydroxynitrile lyase was isolated and purified to homogeneity from seeds of Eriobotrya japonica (loquat). The final yield, of 36% with 49-fold purification, was obtained by 30-80% (NH4)2SO4 fractionation and column chromatography on DEAE-Toyopearl and Concanavalin A Sepharose 4B, which suggested the presence of a carbohydrate side chain. The purified enzyme was a monomer with a molecular mass of 72 kDa as determined by gel filtration, and 62.3 kDa as determined by SDS-gel electrophoresis. The N-terminal sequence is reported. The enzyme was a flavoprotein containing FAD as a prosthetic group, and it exhibited a Km of 161 μM and a k cat/Km of 348 s-1 mM-1 for mandelonitrile. The optimum pH and temperature were pH 5.5 and 40°C respectively. The enzyme showed excellent stability with regard to pH and temperature. Metal ions were not required for its activity, while activity was significantly inhibited by CuSO4, HgCl2, AgNO3, FeCl3, β-mercaptoethanol, iodoacetic acid, phenylmethylsulfonylfluoride, and diethylpyrocarbonate. The specificity constant (kcat/Km) of the enzyme was investigated for the first time using various aldehydes as substrates. The enzyme was active toward aromatic and aliphatic aldehydes, and showed a preference for smaller substrates over bulky one.
- Ueatrongchit, Techawaree,Kayo, Ai,Komeda, Hidenobu,Asano, Yasuhisa,H-Kittikun, Aran
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p. 1513 - 1522
(2008/12/21)
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- A new (R)-hydroxynitrile lyase from Prunus mume: Asymmetric synthesis of cyanohydrins
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A new hydroxynitrile lyase (HNL) was isolated from the seed of Japanese apricot (Prunus mume). The enzyme has similar properties with HNL isolated from other Prunus species and is FAD containing enzyme. It accepts a large number of unnatural substrates (benzaldehyde and its variant) for the addition of HCN to produce the corresponding cyanohydrins in excellent optical and chemical yields. A new HPLC based enantioselective assay technique was developed for the enzyme, which promotes the addition of KCN to benzaldehyde in a buffered solution (pH=4.5).
- Nanda, Samik,Kato, Yasuo,Asano, Yasuhisa
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p. 10908 - 10916
(2007/10/03)
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- Preparation of optically active cyanohydrins using the (S)-hydroxynitrile lyase from Hevea brasiliensis
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Several aliphatic, aromatic and heteroaromatic aldehydes have been converted into the chiral cyanohydrins using the (S) hydroxynitrile lyase from Hevea brasiliensis. The corresponding cyanohydrins were obtained in moderate to good yield and high enantiomeric excess with the exeption of phenyloxyacetaldehyde, benzyloxyacetaldehyde and the pyrrole-, pyridine- and indolealdehydes investigated. In contrast to previously reported results, cinnamaldehyde could be converted into (S)-(-)-2-hydroxy-4-phenyl-(E)-but-3- enenitrile with good selectivity by means of optimized reaction conditions.
- Schmidt, Michael,Herve, Stephanie,Klempier, Norbert,Griengl, Herfried
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p. 7833 - 7840
(2007/10/03)
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- Ueber die erste rekombinante Hydroxynitril-Lyase und ihre Anwendung in der Synthese von (S)-Cyanhydrinen
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Keywords: Asymmetrische Synthesen; (S)-Cyanhydrine; Enzymkatalyse; Lyasen
- Foerster, Siegfried,Roos, Juergen,Effenberger, Franz,Wajant, Harald,Sprauer, Achim
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p. 493 - 494
(2007/10/03)
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- Asymmetric Carbon-Carbon Bond Forming Reactions Catalyzed by Chiral Schiff Base-Titanium Alkoxide Complexes
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The enantioselective addition of trimethylsilyl cyanide to a variety of aldehydes proceeded by the aid of a catalyst prepared in situ from titanium tetraisopropoxide and chiral Schiff bases and gave the corresponding cyanohydrins in high optical yield (up to 96percent e.e.).A remarkable rate enhancement was brought about by the addition of the Schiff base to the titanium alkoxide mediated silylcyanation of aldehydes.This catalyst system also promoted the highly enantioselective reaction of diketene with aldehydes, which led to the formation of optically active 5-hydroxy-3-oxoesters.
- Hayashi, Masahiko,Inoue, Tetsuya,Miyamoto, Yasunori,Oguni, Nobuki
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p. 4385 - 4398
(2007/10/02)
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- Enantioselective Trimethylsilylcyanation of Some Aldehydes Catalyzed by Chiral Schiff Base-Titanium Alkoxide Complexes
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A variety of aldehydes (aromatic, heteroaromatic, α,β-unsaturated, and nonconjugate aliphatic aldehydes) has been trimethylsilylcyanated in highly enantiomeric excess (ee) with a catalyst prepared in situ from titanium tetraisopropoxide and chiral Schiff bases.A remarkable rate enhancement was brought about by the addition of the Schiff base into the titanium alkoxide mediated silylcyanation of aldehydes.The chemical structure of chiral Schiff base-titanium alkoxide complexes is discussed based on their 13C NMR spectra, field desorption (FD) mass spectra, and molecular weights.
- Hayashi, Masahiko,Miyamoto, Yasunori,Inoue, Tetsuya,Oguni, Nobuki
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p. 1515 - 1522
(2007/10/02)
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- Enantioselective Trimethylsilylcyanation of some Aldehydes Catalysed by Titanium Alkoxide-Chiral Dialkyl Tartrate Complexes
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Highly enantioselective trimethylsilylcyanation of various aldehydes with trimethylsilyl cyanide has been achieved with a modified Sharpless catalyst, consisting of titanium tetraisopropoxide i)4> and chiral diisopropyl tartrate (DIPT).Asymmetric amplification was also observed in the trimethylsilylcyanation of benzaldehyde with a catalyst composed of Ti(OPri)4 and partially resolved DIPT.
- Hayashi, Masahiko,Matsuda, Tohru,Oguni, Nobuki
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p. 3135 - 3140
(2007/10/02)
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- Enantioselective Trimethylsilylcyanation of Some Aldehydes by Chiral Titanium Schiff's Base Complexes
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The complexes formed between titanium tetraalkoxide and chiral Schiff's bases make excellent catalysts for enantioselective trimethylsilylcyanation of aldehydes to optically active cyanohydrins in high optical yield.
- Hayashi, Masahiko,Miyamoto, Yasunori,Inoue, Tetsuya,Oguni, Nobuki
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p. 1752 - 1753
(2007/10/02)
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