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Shū Kobayashi

Publications and source records attributed to Shū Kobayashi.

At least 37 records · Page 2Linked to original sources
PubMed2004

Catalytic asymmetric hydroxymethylation of silicon enolates using an aqueous solution of formaldehyde with a chiral scandium complex.

Catalytic asymmetric hydroxymethylation of silicon enolates has been achieved. In this reaction, an aqueous solution of formaldehyde can be used to realize an easy and safe procedure, and high enantioselectivities have been obtained. This is the first example of catalytic asymmetric reactions in aqueous media with a chiral scandium complex.

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PubMed2004

Zirconium-catalyzed enantioselective [3+2] cycloaddition of hydrazones to olefins leading to optically active pyrazolidine, pyrazoline, and 1,3-diamine derivatives.

Asymmetric [3+2] cycloaddition of hydrazones to external olefins has been successfully conducted in high yields with high enantioselectivities using a chiral zirconium catalyst. These reactions open ways to synthetically and biologically important pyrazoline, pyrazolidine, and 1,3-diamine derivatives. Further, several experiments suggested that the reactions proceeded via concerted pathways.

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PubMed2004

Lewis acid catalysis in supercritical carbon dioxide. Use of poly(ethylene glycol) derivatives and perfluoroalkylbenzenes as surfactant molecules which enable efficient catalysis in ScCO2.

Lewis acid catalysis in supercritical carbon dioxide (CO(2)) was investigated. While solubility of most organic materials is low in scCO(2), poly(ethylene glycol) derivatives or perfluoroalkylbenzenes were found to work as surfactants to dissolve organic materials in scCO(2). In the presence of these molecules, Lewis acid catalyzed organic reactions such as aldol-, Mannich-, and Friedel-Crafts-type reactions proceeded smoothly in scCO(2). Formation of emulsions was observed in these reactions, and the systems were studied in detail.

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PubMed2004

Phosphine oxides as efficient neutral coordinate-organocatalysts for stereoselective allylation of N-acylhydrazones.

Phosphine oxides were found to be efficient neutral coordinate-organocatalysts (NCOs) for the allylation of N-acylhydrazones. Among the phosphine oxides tested, a three carbon-tethered bisphosphine oxide (dppp dioxide) was found to be the most effective, and in the presence of dppp dioxide, less reactive aromatic and [small alpha],[small beta]-unsaturated N-acylhydrazones underwent allylation as well as diastereoselective crotylation. Furthermore, a polymer-supported phosphine oxide was also developed as an effective immobilized NCO.

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PubMed2003

Mechanistic studies on the catalytic cycle of metal fluoride-catalyzed allylation using allyltrimethoxysilane in protic solvents.

The catalytic cycles of CdF(2).1-catalyzed and AgF.BINAP-catalyzed allylation using allyltrimethoxysilane in protic solvents were investigated. The experimental and (19)F NMR studies strongly supported that metal fluorides were regenerated from silyl fluoride species, and that these reactions were truly fluoride-catalyzed reactions. It was revealed that these catalytic cycles were much different from that of TBAF-catalyzed allylation using allyltrimethylsilane in THF.

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PubMed2003

Stereoselective synthesis and structure-activity relationship of novel ceramide trafficking inhibitors. (1R,3R)-N-(3-hydroxy-1-hydroxymethyl-3-phenylpropyl)dodecanamide and its analogues.

New ceramide trafficking inhibitors, (1R,3R)-N-(3-hydroxy-1-hydroxymethyl-3-phenylpropyl)dodecanamide (HPA-12) and a series of its analogues, were synthesized in diastereomerically and enantiomerically pure forms, and the structure-activity relationship was investigated. These analogues were stereoselectively synthesized via catalytic enantioselective Mannich-type reactions using a Cu(II)-chiral diamine 4 complex. Analysis of HPA-12 analogues having various lengths of the amide side chain showed that the optimal chain length for the inhibition of sphingomyelin biosynthesis is 13 with an IC(50) of approximately 50 nM. Masking of the hydroxy group at the 2'- or 3-position of HPA-12 was carried out by methylation, and it was revealed that these hydroxy groups were essential for the activity. Installation of another hydroxy group onto HPA-12 at the same position as that in the natural ceramide was also conducted, but no enhancement of the activity was observed.

Amides↗
PubMed2003

Compatibility in vitro of albumin-heme (O(2) carrier) with blood cell components.

Recombinant human serum albumin including 2-[8-[N-(2-methylimidazolyl)]octanoyloxymethyl]-5,10,15,20-tetrakis(alpha,alpha,alpha,alpha-o-pivaloylamino)phenylporphinatoiron(II) (albumin-heme; rHSA-FeP) is a synthetic hemoprotein that has sufficient capability to reversibly bind and release O(2) under physiological conditions (pH 7.3, 37 degrees C) similar to hemoglobin and myoglobin. In order to use this albumin-based O(2) carrier as a new class of red blood cell substitutes, its compatibility with blood cell components carefully was investigated in vitro. After the addition of the rHSA-FeP solution into whole blood at 10, 20, and 44 vol %, the FeP concentration in the plasma phase remained constant for 6 h at 37 degrees C in each group, and no significant time dependence was observed in the numbers of red blood cells, white blood cells, or platelets. The microscopic observations clearly showed that the shapes of the red blood cells had not been deformed during the measurement period. With respect to the blood coagulation parameters (prothrombin time and activated partial thromboplastin time), the coexistence of rHSA-FeP had only a negligibly small influence. Also the blood compatibility under dynamic flow conditions was evaluated using a microchannel array flow analyzer. All these results suggest that the albumin-heme has no effect on the morphology of blood cell components in vitro.

Animals↗
PubMed2003

Catalytic, asymmetric Mannich-type reactions of alpha-imino esters bearing readily removable substituents on nitrogen.

[reaction: see text] Catalytic, enantioselective Mannich-type reactions of alpha-imino esters bearing readily removable substituents on nitrogen are described. Several N-carbamate-protected alpha-imino esters, which are readily prepared from 2-bromoglycine esters using a polymer-supported amine, reacted with silicon enolates to afford the desired adducts in high yields with high enantioselectivity using a copper(II)-diamine complex. Easy deprotection of the product amine and transformation to free alpha-amino acid derivatives have also been demonstrated.

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PubMed2003

Chiral sulfoxides as neutral coordinate-organocatalysts in asymmetric allylation of N-acylhydrazones using allyltrichlorosilanes.

Sulfoxides were first introduced to the allylation of N-acylhydrazones with allyltrichlorosilanes as effective neutral coordinate-organocatalysts (NCOs). Both high diastereo- and enantioselectivity were attained when optically active chiral sulfoxides were used. Asymmetric crotylations using (Z)- and (E)-crotyltrichlorosilanes showed a high level of stereospecificity (Z --> anti and E --> syn) with high enantioselectivity.

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PubMed2003

Chiral hetero Diels-Alder products by enantioselective and diastereoselective zirconium catalysis. Scope, limitation, mechanism, and application to the concise synthesis of (+)-Prelactone C and (+)-9-deoxygoniopypyrone.

Catalytic asymmetric hetero Diels-Alder (HDA) reactions using a chiral zirconium complex have been developed. The reactions of aldehydes with Danishefsky's dienes proceeded smoothly to afford the corresponding pyranone derivatives in high yields with high diastereo- and enantioselectivities in the presence of a chiral zirconium complex, which was prepared from zirconium tert-butoxide, (R)-3,3'-diiodobinaphthol or its derivative, a primary alcohol, and a small amount of water. It is noted that 2,3-trans-pyranone derivatives were obtained with remarkably high diastereo- and enantioselectivities in the reaction with 4-methyl Danishefsky's diene. This is the first example of catalytic asymmetric trans-selective hetero Diels-Alder reactions of aldehydes. Furthermore, asymmetric HDA reactions with 4-benzyloxy Danishefsky's dienes were conducted to afford 2,3-cis-pyranone derivatives in high selectivities. Isolation of an intermediate of this asymmetric hetero Diels-Alder reaction indicated that the reaction proceeded in a stepwise cycloaddition pathway. Finally, these catalytic, asymmetric hetero Diels-Alder reactions were successfully applied to concise syntheses of biologically important natural pyranone derivatives, (+)-Prelactone C and (+)-9-deoxygoniopypyrone.

Aldehydes↗
PubMed2003

The polymer incarcerated method for the preparation of highly active heterogeneous palladium catalysts.

A new method named "the polymer incarcerated (PI) method" for preparing a heterogeneous palladium catalyst has been developed. The method is operationally simple, and the Pd catalyst prepared (PI Pd) is highly active for hydrogenation, carbon-carbon, and carbon-oxygen bond-forming reactions. Remarkable points are that the activity of PI Pd is higher than that of homogeneous Pd catalysts and that PI Pd is recovered by simple filtration and reused several times without loss of activity. The catalyst is expected to replace many heterogeneous palladium catalysts, especially Pd/C, which is often used in academia and industry, but recovery of which is difficult.

Journal Article↗
PubMed2003

Catalytic asymmetric aldol reactions in aqueous media using chiral bis-pyridino-18-crown-6-rare earth metal triflate complexes.

Catalytic asymmetric aldol reactions in aqueous media have been developed using Pr(OTf)(3) and chiral bis-pyridino-18-crown-6 1. In the asymmetric aldol reaction using rare earth metal triflates (RE(OTf)(3)) and 1, slight changes in the ionic diameters of the metal cations greatly affected the diastereo- and enantioselectivities of the products. The substituents (MeO, Br) at the 4-position of the pyridine rings of the crown ether did not significantly affect the selectivities in the asymmetric aldol reaction, although they affected the binding ability of the crown ether with RE cations and the catalytic activity of Pr(OTf)(3)-crown ether complexes. From X-ray structures of RE(NO(3))(3)-crown ether complexes, it was found that they had similar structures regardless of the RE cations and the crown ethers used. Accordingly, the binding ability of the crown ether with the RE cation and the catalytic activity of the complex are important for attaining high selectivity in the asymmetric aldol reaction. Various aromatic and alpha,beta-unsaturated aldehydes and silyl enol ethers derived from ketones and a thioester can be employed in the catalytic asymmetric aldol reactions using Pr(OTf)(3) and 1, to provide the aldol adducts in good to high yields and stereoselectivities. In the case using the silyl enol ether derived from the thioester, 2,6-di-tert-butylpyridine significantly improved the yields of the aldol adducts.

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