Faculty Profiles - TSUKAMOTO, Masaki

Papers - TSUKAMOTO, Masaki

Division display 21 - 34 of about 34 ／ All the affair displays >>

Equilibrium of Homochiral Oligomerization of a Mixture of Enantiomers. Its Relevance to Nonlinear Effects in Asymmetric Catalysis Reviewed

M. Tsukamoto, K. Gopalaiah, and H. B. Kagan

J. Phy. Chem. B Vol. 112 ( 48 ) page： 15361-15368 2008.12

Enantiomeric products formed via different mechanisms: asymmetric hydrogenation of an α,β-unsaturated carboxylic acid involving a Ru(CH3COO)2[(R)-binap] catalyst Reviewed

M. Yoshimura, Y. Ishibashi, K. Miyata, Y. Bessho, M. Tsukamoto, and M. Kitamura

Tetrahedron Vol. 63 ( 46 ) page： 11399-11409 2007.11

Mechanism of Catalytic Asymmetric Hydrogenation of 2-Formyl-1-methylene-1,2,3,4-tetrahydroisoquinoline Using Ru(CH3COO)2[(S)-binap] Reviewed

M. Tsukamoto, M. Yoshimura, K. Tsuda, and M. Kitamura

Tetrahedron Vol. 62 ( 23 ) page： 5448-5453 2006.6

Origin of the Minor Enantiomeric Product in a Noyori Asymmetric Hydrogenation Reviewed

Y. Ishibashi, Y. Bessho, M. Yoshimura, M. Tsukamoto, and M. Kitamura

Angew. Chem. Int. Ed. Vol. 44 ( 44 ) page： 7287-7290 2005.11

Language：English Publishing type：Research paper (scientific journal)

The enantiomeric products of the catalytic hydrogenation of an isotopically labeled substrate were separated. The ratios of the isotopomers revealed that the major and minor enantiomers are formed mostly through different mechanisms. Hence, when analyzing the energy profile of an asymmetric catalytic reaction with the Arrhenius equation, two competing diastereomorphic catalytic cycles should be considered.

Recent Advances of Mechanistic Studies on Asymmetric Hydrogenation of Dehydroamino Acid Derivatives Catalyzed by Diphosphine-Rh and -Ru Complexes Reviewed

J. Synth. Org. Chem. Jpn. Vol. 63 ( 9 ) page： 899-910 2005.9

Novel Synthesis and Characterization of Bioconjugate Block Copolymers Having Oligonucleotides Reviewed

A. Noro, Y. Nagata, M. Tsukamoto, Y. Hayakawa, A. Takano, and Y. Matsushita

Biomacromolecules Vol. 6 ( 4 ) page： 2328-2333 2005

Carboxylic Acids as Promoters for Internucleotide-Bond Formation via Condensation of a Nucleoside Phosphoramidite and a Nucleoside: Relationship between the Acidity and the Activity of the Promoter Reviewed

Y. Hayakawa, T. Iwase, E. J. Nurminen, M. Tsukamoto, and M. Kataoka

Tetrahedron Vol. 61 ( 8 ) page： 2203-2209 2005

Language：English Publishing type：Research paper (scientific journal)

The relationship between the activity and the acidity of a carboxylic acid as a promoter for condensation of a nucleoside phosphoramidite and a nucleoside was investigated. The investigation revealed that the acid, the pKa value of which in acetonitrile is less than 18, is capable of promoting the condensation reaction, and acid with a pKa value outside of this range does not serve as a promoter. In carboxylic acids serving as promoters, the ones with higher acidity generally show greater activity. In particular, acids with a pKa value less than ca. 16 (measured by a potentiometric method), such as trichloroacetic acid (pKaZ10.6), trifluoroacetic acid (pKaZ12.7), dichloroacetic acid (pKaZ13.2 or 15.8), and 2,4-dinitrobenzoic acid (pKaZ16.1), show high levels of activity higher than that of conventionally used 1H-tetrazole. These carboxylic acids generally serve as excellent promoters for both the liquid-phase and the solid-phase synthesis of oligonucleotides via phosphoramidite method.

Is It Possible to Estimate the Enantioselectivity of a Chiral Catalyst from Its Racemic Mixture? Reviewed

F. Lagasse, M. Tsukamoto, C. J. Welch, and H. B. Kagan

J. Am. Chem. Soc. Vol. 125 ( 25 ) page： 7490-7491 2003

Recent Advances in the Measurement of Enantiomeric Excesses Reviewed

M. Tsukamoto and H. B. Kagan

Adv. Synth. Catal. Vol. 344 ( 5 ) page： 453-463 2002

Mechanism of Asymmetric Hydrogenation of α-(Acylamino)acrylic Esters Catalyzed by BINAP-Ruthenium(II) Diacetate Reviewed

M. Kitamura, M. Tsukamoto, Y. Bessho, M. Yoshimura, U. Kobs, M. Widhalm, and R. Noyori

J. Am. Chem. Soc. Vol. 124 ( 23 ) page： 6649-6667 2002

Language：English Publishing type：Research paper (scientific journal)

The mechanism of asymmetric hydrogenation of R-(acylamino)acrylic esters with Ru(CH3COO)2[(S)-binap] (BINAP ) 2,2′-bis(diphenylphosphino)-1,1′-binaphthyl), giving the S saturated products in more than 90 per cent enantiomeric excess, has been investigated by means of a kinetic study, deuterium labeling experiments, isotope effect measurements, and NMR and X-ray analysis of certain Ru complexes. The hydrogenation in methanol under a low H2 pressure proceeds via a monohydride-unsaturate mechanism that involves the initial RuH formation followed by a reaction with an olefinic substrate. The migratory insertion in the enamide-RuH chelate complex occurs reversibly and endergonically in an exo manner, giving a five-membered metallacycle intermediate. The cleavage of the Ru-C bond is achieved with either H2 (major) or CH3OH (minor). Both of the pathways result in overall cis hydrogenation products. The hydrogen at C(3) is mainly from an H2 molecule, and the C(2) hydrogen is from another H2 or protic CH3OH. The major S and minor R enantiomers are produced via the same mechanism involving diastereomeric intermediates. The turnover rate is limited by the step of hydrogenolysis of a half-hydrogenated metallacyclic intermediate. The participation of two different hydrogen donor molecules is in contrast to the pairwise dihydrogenation using a single H2 molecule in the Rh(I)-catalyzed reaction which occurs via a dihydride mechanism. In addition, the sense of asymmetric induction is opposite to that observed with (S)-BINAP-Rh(I) catalysts. The origin of this phenomenon is interpreted in terms of stereocomplementary models of the enamide/metal chelate complexes. A series of model stoichiometric reactions mimicking the catalytic steps has indicated that most NMR-observable Ru complexes are not directly involved in the catalytic hydrogenation but are reservoirs of real catalytic complexes or even side products that retard the reaction.

Synthesis of α-Amino Phosphonic Acids by Asymmetric Hydrogenation Reviewed

M. Kitamura, M. Yoshimura, M. Tsukamoto, and R. Noyori

Enantiomer Vol. 1 ( 4-6 ) page： 281-303 1996

Conformational Study on 2-Acyl-1-alkylidene-1,2,3,4-tetrahydroisoquinolines Reviewed

M. Kitamura, M. Tsukamoto, H. Takaya, and R. Noyori

Bull. Chem. Soc. Jpn. Vol. 69 ( 6 ) page： 1695-1700 1996

General Asymmetric Synthesis of Isoquinoline Alkaloids. Enantioselective Hydrogenation of Enamides Catalyzed by BINAP-Ruthenium(II) Complexes Reviewed

M. Kitamura, Yi Hsiao, M. Ohta, M. Tsukamoto, T. Ohta, H. Takaya, and R. Noyori

J. Org. Chem. Vol. 59 ( 2 ) page： 297-310 1994

Applicability of a Standardized Discrete Cosine Transform Coding Method to Character Images Reviewed

Y. Hoshino, D. Ando, S. Higashino, and M. Tsukamoto

J. Electronic Imaging Vol. 1 ( 3 ) page： 322-327 1992

　 PREV - NEXT 　

<TSUKAMOTO, Masaki>

Papers - TSUKAMOTO, Masaki