- Stereostructure of komodoquinone A, a neuritogenic anthracycline, from marine Streptomyces sp. KS3
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The absolute stereostructure of komodoquinone A (1), a neuritogenic anthracycline, which was isolated from a cultured marine Streptomyces sp. KS3, has been determined on the basis of chemical derivatization. Komodoquinone A (1) induces neuronal cell differentiation in the neuroblastoma cell line, Neuro 2A and arrests the cell cycle at the G1 phase. The effect of a solid-state medium on the production of 1 and its aglycone, komodoquinone B (2), was examined.
- Itoh, Takuya,Kinoshita, Masahiro,Wei, Hong,Kobayashi, Motomasa
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- Biocatalytic Construction of Quaternary Centers by Aldol Addition of 3,3-Disubstituted 2-Oxoacid Derivatives to Aldehydes
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The congested nature of quaternary carbons hinders their preparation, most notably when stereocontrol is required. Here we report a biocatalytic method for the creation of quaternary carbon centers with broad substrate scope, leading to different compound classes bearing this structural feature. The key step comprises the aldol addition of 3,3-disubstituted 2-oxoacids to aldehydes catalyzed by metal dependent 3-methyl-2-oxobutanoate hydroxymethyltransferase from E. coli (KPHMT) and variants thereof. The 3,3,3-trisubstituted 2-oxoacids thus produced were converted into 2-oxolactones and 3-hydroxy acids and directly to ulosonic acid derivatives, all bearing gem-dialkyl, gem-cycloalkyl, and spirocyclic quaternary centers. In addition, some of these reactions use a single enantiomer from racemic nucleophiles to afford stereopure quaternary carbons. The notable substrate tolerance and stereocontrol of these enzymes are indicative of their potential for the synthesis of structurally intricate molecules.
- Marín-Valls, Roser,Hernández, Karel,Bolte, Michael,Parella, Teodor,Joglar, Jesús,Bujons, Jordi,Clapés, Pere
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supporting information
p. 19754 - 19762
(2020/12/01)
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- Stereoselective oxidation of aryl-substituted vicinal diols into chiral α-hydroxy aldehydes by re-engineered propanediol oxidoreductase
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α-Hydroxy aldehydes are chiral building blocks used in synthesis of natural products and synthetic drugs. One route to their production is by regioselective oxidation of vicinal diols and, in this work, we aimed to perform the oxidation of 3-phenyl-1,2-propanediol into the corresponding α-hydroxy aldehyde applying enzyme catalysis. Propanediol oxidoreductase from Escherichia coli efficiently catalyzes the stereoselective oxidation of S-1,2-propanediol into S-lactaldehyde. The enzyme, however, shows no detectable activity with aryl-substituted or other bulky alcohols. We conducted ISM-driven directed evolution on FucO and were able to isolate several mutants that were active with S-3-phenyl-1,2-propanediol. The most efficient variant displayed a kcat/KM of 40 s-1 M-1 and the most enantioselective variant an E-value (S/R) of 80. Furthermore, other isolated variants showed up to 4400-fold increased activity with another bulky substrate, phenylacetaldehyde. The results with engineered propanediol oxidoreductases identified amino acids important for substrate selectivity and asymmetric synthesis of aryl-substituted α-hydroxy aldehydes. In conclusion, our study demonstrates the feasibility of tailoring the catalytic properties of propanediol oxidoreductase for biocatalytic properties.
- Blikstad, Cecilia,Dahlstroem, Kaethe M.,Salminen, Tiina A.,Widersten, Mikael
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p. 3016 - 3025
(2014/01/06)
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- The first practical approach to optically pure cyclopropanes derived from trans γ-hydroxy enones
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The optically pure cyclopropanes derived from trans γ-hydroxy enones were discussed. The trans γ-hydroxy enones were found to be prepared from reaction of stabilized ketoylides on optically pure α hydroxy aldehydes. The analysis showed that the use of light and a triplet sensitizer lead to a dramatic increase in reaction rate and isolated yield.
- Palmer, Francine N.,Taylor, Dennis K.
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p. 1323 - 1325
(2007/10/03)
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- Asymmetric total synthesis of epolactaene
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The first asymmetric total synthesis of epolactaene, a neuritogenic compound, was accomplished in 16 steps and its absolute stereochemistry was determined.
- Hayashi, Yujiro,Narasaka, Koichi
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p. 313 - 314
(2007/10/03)
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- New insight into the pyruvate decarboxylase-catalysed formation of lactaldehyde from H-D exchange experiments: A 'water proof' active site
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Pyruvate decarboxylase from Saccharomyces cerevisiae catalyses the formation of lactaldehyde from sodium glyoxylate and acetaldehyde. By using deuteriated sodium glyoxylate (sodium [2-2H]glyoxylate monohydrate) as a substrate it was verified that the lactaldehyde formed retains the deuterium atom. The implications of the observed result for the enzyme mechanism are discussed in the light of conclusions derived from recent molecular modelling studies.
- Lobell, Mario,Crout, David H. G.
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p. 1577 - 1581
(2007/10/03)
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- Kinetics and Mechanism of Oxidative Decarboxylation and Deamination of Amino Acids by N-Chloro-N-sodio-p-tuluenesulphonamide at Low Acid Concentrations
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Kinetics of oxidation of seven amino acids by chloramine-T has been investigated in low acid medium.The rate followed first order kinetics in and zero order each in and +>.Effect of added reaction product, p-toluenesulphonamide and variation of ionic strength and dielectric constant of the reaction medium on the rate have also been investigated.Activation parameters have been computed from the Arrhenius plots.Suitable mechanism has been proposed to account for the observed kinetics.
- Gowda, B. Thimme,Sherigara, B. S.
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p. 158 - 162
(2007/10/02)
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- Kinetics of Oxidation of Amino Acids by Chloramine-T. A Reinvestigation on the Oxidation of Alanine, 2-Aminobutyric Acid, Valine, Serine, and Threonine
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The kinetics of oxidation of amino acids in aqueous medium were reinvestigated.The rate of oxidation follows second order with respect to chloramine-T (CAT) and an inverse dependence on (RNH2).At constant the rate of the reaction can be represented as (in the absence of chloride ion) .A linear relationship exists between pK1 and the rate constants.This shows the electrophilic attack of the oxidant at the carboxylato group of the amino acid.The effect of chloride ion on kobsd is catalytic.The mechanisms of the reactions are discussed in terms of the kinetic results.
- Ramachandran, M. Shanmugam,Vivekanandam, T. Subburamiyer
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p. 3397 - 3404
(2007/10/02)
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- Kinetics and Mechanism of Oxidation of Amino Acids by Bromamine-T in Acid Medium
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Kinetics of oxidation of L-serine, L-threonine, L-glutamic acid, L-glutamine, L-arginine and L-histidine by bromamine-T has been investigated in perchloric acid medium.In general the rate is first order in , fractional order in and inverse fractional order in .Added bromide and p-toluenesulphonamide and varying ionic strength and dielectric constant of the medium have no effect on the rate of the reaction.The kinetic and thermodynamic parameters have been computed and suitable rate laws consistent with the experimental results have been deduced.
- Gowda, B. Thimme,Rao, R. Vijayalakshmi
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p. 578 - 581
(2007/10/02)
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- Enzymatic vs. Fermentative Synthesis: Thermostable Glucose Dehydrogenase Catalyzed Regeneration of NAD(P)H for use in Enzymatic Synthesis
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Procedures are described for regeneration of reduced nicotinamide cofactors NADH and NADPH from NAD(P) based on glucose and a thermostable glucose dehydrogenase from Bacillus cereus immobilized in polyacrylamide gels.The turnover number for NAD in a synthesis of 200 mmol of D-lactate is 40000.Application of this system to other syntheses is demonstrated with preparations of ethyl (R)-4-chloro-3-hydroxybutanoate, (R)-2,2,2-trifluoro-1-phenylethanol, ethyl (S)-3-hydroxyvalerate, (S)-lactaldehyde dimethyl acetal, and (S)-3-hydroxybutanal dimethyl acetal.Further investigation of the kinetics regarding the thermoresistance of glucose dehydrogenase in the presence of NaCl has been carried out, and it appears that the enhancement by NaCl of the thermal stability of the enzyme is approximately third order.The immobilized glucose dehydrogenase incubated at 55 deg C, pH 7.5, for 7 days is still fully active while many other enzymes are completely inactivated in 1-2 days.Addition of NaCl enhances the thermal stability more significantly than the immobilization does, and a remarkable increase in thermal stability was observed with these two combined factors.The half-life of the immobilized glucose dehydrogenase at 55 deg C in a buffer (pH 7.0-7.5) containing 1 M NaCl is more than 30 days compared to 3 min for the free enzyme, corresponding to an overall ca. 50000-fold increase in thermal stability.
- Wong, Chi-Huey,Drueckhammer, Dale G.,Sweers, Henri M.
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p. 4028 - 4031
(2007/10/02)
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