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Steric Course of Deprotonation/Substitution of Chelating/Dipole‐Stabilizing‐Group‐Substituted α‐Amino‐ and α‐Oxynitriles

Michiko Sasaki, Rumiko Shimabara, Tomo Takegawa, Yuri Kotomori, więcej

European Journal of Organic Chemistry > 2018 > 30 > 4128 - 4134

The stereochemical course of electrophilic substitutions of α‐nitrile metallocarbanions was investigated through the deprotonation of enantioenriched α‐amino‐ and α‐oxynitriles bearing a carbamoyl or methoxycarbonyl group in the presence of an electrophile. The results suggested that the dipole‐stabilizing substituents not only affected the configurational stability and chemical reactivity of the...

artykuł

Inhibitory effects of antibiofilm compound 1 against Staphylococcus aureus biofilms

Looniva Shrestha, Shizuo Kayama, Michiko Sasaki, Fuminori Kato, więcej

Microbiology and Immunology > 60 > 3 > 148 - 159

A novel benzimidazole molecule that was identified in a small‐molecule screen and is known as antibiofilm compound 1 (ABC‐1) has been found to prevent bacterial biofilm formation by multiple bacterial pathogens, including Staphylococcus aureus, without affecting bacterial growth. Here, the biofilm inhibiting ability of 156 μM ABC‐1 was tested in various biofilm‐forming strains of S. aureus. It was...

rozdział

Brook Rearrangement

Michiko Sasaki, Kei Takeda

Molecular Rearrangements in Organic Synthesis > 1,2‐Migrations > 151 - 182

This chapter presents unique aspects of the rearrangement with a focus on (1) the production of carbanions under mild conditions, (2) the generation of synthetically valuable enol silyl ethers that are often the products, (3) the potential for incorporation of the Brook rearrangement in tandem and sequential anion relay processes, and (4) the utility of the rearrangement in generating chiral, configurationally...

artykuł

Transnitrosation of non-mutagenic N-nitrosoproline forms mutagenic N-nitroso-N-methylurea

Keiko Inami, Junko Shiino, Shin Hagiwara, Kei Takeda, więcej

Bioorganic & Medicinal Chemistry > 2015 > 23 > 13 > 3297-3302

N-Nitroso-N-methylurea (NMU) is a potent carcinogen and suspected as a cause of human cancer. In this study, mutagenic NMU was detected by HPLC after the transnitrosation of non-mutagenic N-nitrosoproline (NP) to N-methylurea in the presence of thiourea (TU) under acidic conditions. The structure of NMU was confirmed by comparing ¹H NMR and IR spectra with that of authentic NMU after fractionation...

artykuł

Enantiodivergent Deprotonation/Acylation of α‐Amino Nitriles

Michiko Sasaki, Tomo Takegawa, Kunihiro Sakamoto, Yuri Kotomori, więcej

Angewandte Chemie > 125 > 49 > 13194 - 13198

Basische Prinzipien: Die Titelreaktion von enantiomerenangereicherten α‐Ureidonitrilen verläuft hoch enantiodivergent, obgleich stereolabile, in α‐Stellung metallierte Nitrile als Intermediate auftreten. Die Enantiodivergenz hängt dabei von der verwendeten Base ab. Im Fall der schwächer basischen Hexamethyldisilazide (HMDS) wird vorgeschlagen, dass das Metallkation (M) vor der Deprotonierung durch...

artykuł

Enantiodivergent Deprotonation/Acylation of α‐Amino Nitriles

Michiko Sasaki, Tomo Takegawa, Kunihiro Sakamoto, Yuri Kotomori, więcej

Angewandte Chemie International Edition > 52 > 49 > 12956 - 12960

Back to ‘base'ics: The title reaction of enantioenriched α‐ureidonitriles was found to proceed in a highly enantiodivergent manner despite the intermediacy of stereolabile α‐nitrile metallocarbanions. Enantiodivergence is dependent upon the base used. For the less basic hexamethyldisilazides (HMDS), deprotonation in which a metal (M) cation is precomplexed with an electrophile is proposed. LDA=lithium...

artykuł

Chirality transfer in Brook rearrangement-mediated SE2′ solvolytic protonation and its use in estimation of the propensity for racemization of the α-lithiocarbanions of the substituents

Michiko Sasaki, Misato Fujiwara, Yuri Kotomori, Masatoshi Kawahata, więcej

Tetrahedron > 2013 > 69 > 29 > 5823-5828

Chirality transfer from an α-silylalcohol to α-carbmoyloxy- and α-siloxyallyl-carbanions was investigated using a Brook rearrangement-mediated S _E 2′ protonation in γ-carbamoyloxy- and γ-siloxy-α-silylallyl alcohols. We proposed a hypothesis that the reaction proceeds along one of two pathways that involves (1) a concerted protonation of a silicate intermediate and (2) a concerted lithiation...

artykuł

Regio- and Stereoselective Multisubstituted Enol Ester Synthesis

Noriko Okamoto, Yoshihisa Miwa, Hideki Minami, Kei Takeda, więcej

The Journal of Organic Chemistry > 2011 > 76 > 21 > 9133 - 9138

artykuł

One-Pot Approach to 2,3-Disubstituted-2,3-dihydro-4-quinolones from 2-Alkynylbenzamides

Noriko Okamoto, Kei Takeda, Minoru Ishikura, Reiko Yanada

The Journal of Organic Chemistry > 2011 > 76 > 21 > 9139 - 9143

artykuł

Steric Course of the Electrophilic Substitution of a Lithiocarbanion Generated from (S,E)‐1‐Phenylbut‐2‐en‐1‐yl Diisopropylcarbamate and Solvent Effects

Hidaka Ikemoto, Michiko Sasaki, Masatoshi Kawahata, Kentaro Yamaguchi, więcej

European Journal of Organic Chemistry > 2011 > 32 > 6553 - 6557

The effects of electrophiles and solvents on the stereochemistry of electrophilic substitution of a lithiocarbanion generated from (S,E)‐1‐phenylbut‐2‐en‐1‐yl diisopropylcarbamate were examined using various acids and carbon electrophiles. The stereochemical outcomes were influenced by the relative ability of the electrophiles and solvents to coordinate to lithium.

artykuł

Enantioselective Synthesis of Siloxyallenes from Alkynoylsilanes by Reduction and a Brook Rearrangement and Their Subsequent Trapping in a [4+2] Cycloaddition

Michiko Sasaki, Yasuhiro Kondo, Masatoshi Kawahata, Kentaro Yamaguchi, więcej

Angewandte Chemie > 123 > 28 > 6499 - 6502

In einem Eintopfprozess aus enantioselektiver Meerwein‐Ponndorf‐Verley‐Reduktion von Alkinoylsilanen durch ein chirales Lithiumamid, Brook‐Umlagerung und elektrophiler S_E2′‐Substitution entstehen die Titelverbindungen. Im Fall von Eninoylsilanen reagieren die gebildeten Vinylallene in situ in einer [4+2]‐Cycloaddition mit ungewöhnlicher Seitenselektivität zu hochfunktionalisierten Polycyclen.

artykuł

Enantioselective Synthesis of Siloxyallenes from Alkynoylsilanes by Reduction and a Brook Rearrangement and Their Subsequent Trapping in a [4+2] Cycloaddition

Michiko Sasaki, Yasuhiro Kondo, Masatoshi Kawahata, Kentaro Yamaguchi, więcej

Angewandte Chemie International Edition > 50 > 28 > 6375 - 6378

Two flavors of selectivity: An enantioselective Meerwein–Ponndorf–Verley‐type reduction of alkynoylsilanes by a chiral lithium amide followed by a Brook rearrangement and S_E2′ electrophilic substitution provides the title compounds in a one‐pot process. In the case of enynoylsilanes, the generated vinylallenes undergo in situ [4+2] cycloaddition to afford highly functionalized polycyclic compounds...

artykuł

Solvent Effects on the Steric Course of the [2,3]‐Wittig Rearrangement of (S,E)‐[3‐(Allyloxy)prop‐1‐ene‐1,3‐diyl]dibenzene and Derivatives

Hidaka Ikemoto, Michiko Sasaki, Kei Takeda

European Journal of Organic Chemistry > 2010 > 34 > 6643 - 6650

The effect of solvents and additives on the steric course of [2,3]‐Wittig rearrangement of the chiral 1,3‐diphenyl‐1‐propenyloxy‐2‐propen‐1‐yl carbanion and its derivatives wasexamined on the basis of chirality transfer in intramolecular trapping.

artykuł

Platinum-Catalyzed, One-Pot Tandem Synthesis of Indoles and Isoquinolines via Sequential Rearrangement of Amides and Aminocyclization

Noriko Okamoto, Kei Takeda, Reiko Yanada

The Journal of Organic Chemistry > 2010 > 75 > 22 > 7615 - 7625

artykuł

Formal Total Syntheses of (+)-Prelaureatin and (+)-Laurallene by Diastereoselective Brook Rearrangement-Mediated [3 + 4] Annulation

Michiko Sasaki, Kazuhisa Oyamada, Kei Takeda

The Journal of Organic Chemistry > 2010 > 75 > 11 > 3941 - 3943

artykuł

Design and Synthesis of a Stable Supramolecular Trigonal Prism Formed by the Self-Assembly of a Linear Tetrakis(Zn ²⁺ −cyclen) Complex and Trianionic Trithiocyanuric Acid in Aqueous Solution and Its Complexation with DNA (Cyclen = 1,4,7,10-Tetraazacyclododecane)

Mohd Zulkefeli, Tetsuya Sogon, Kei Takeda, Eiichi Kimura, więcej

Inorganic Chemistry > 2009 > 48 > 19 > 9567 - 9578

artykuł

One-pot concise syntheses of benzimidazo[2,1-a]isoquinolines by a microwave-accelerated tandem process

Noriko Okamoto, Keisuke Sakurai, Minoru Ishikura, Kei Takeda, więcej

Tetrahedron Letters > 2009 > 50 > 28 > 4167-4169

Direct, efficient syntheses of the benzimidazo[2,1-a]isoquinoline ring system have been achieved with 2-bromoarylaldehydes, terminal alkynes, and 1,2-phenylenediamines by a microwave-accelerated tandem process in which a Sonogashira coupling, 5-endo cyclization, oxidative aromatization, and 6-endo cyclization can be performed in a single synthetic operation.

artykuł

Crystal structures of the Apo and Holo form of rat catechol-O-methyltransferase

Eiichi Tsuji, Kosuke Okazaki, Masayuki Isaji, Kei Takeda

Journal of Structural Biology > 2009 > 165 > 3 > 133-139

Catechol-O-methyltransferase (COMT, EC 2.1.1.6) is a monomeric enzyme that catalyzes the transfer of a methyl group from S-adenosyl-l-methionine (AdoMet) to the phenolic oxygen of substituted catechols. Although the inhibitor recognition pattern and AdoMet site have already been studied crystallographically, structural information on the catalytic cycle of COMT has not yet been obtained. In this study,...

artykuł

Crystal structures of rat catechol-O-methyltransferase complexed with coumarine-based inhibitor

Eiichi Tsuji, Kosuke Okazaki, Kei Takeda

Biochemical and Biophysical Research Communications > 2009 > 378 > 3 > 494-497

In human, catechol-O-methyltransferase (COMT: E.C. 2.1.1.6) is responsible for metabolism of catechol neurotransmitter and xenobiotics. The main clinical interest in COMT results from the possibility of using COMT inhibitors as adjuncts in the therapy of Parkinson’s disease (PD) with l-DOPA. COMT is therefore a target for inhibitor development aiming at PD treatment and has been submitted to extensive...

artykuł

Biginelli reactions catalyzed by hydrazine type organocatalyst

Ichiro Suzuki, Yukari Iwata, Kei Takeda

Tetrahedron Letters > 2008 > 49 > 20 > 3238-3241

Pyrazolidine dihydrochloride can be used in the acceleration of Biginelli reactions between urea, ethyl acetoacetate and various aldehydes to provide DHPMs in good to excellent yields.

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