Masaki Tomizawa
Tohoku University
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Publication
Featured researches published by Masaki Tomizawa.
Molecular Cancer Therapeutics | 2006
Hisatsugu Ohori; Hiroyuki Yamakoshi; Masaki Tomizawa; Masatoshi Shibuya; Yuichi Kakudo; Atsuko Takahashi; Shin Takahashi; Satoshi Kato; Takao Suzuki; Chikashi Ishioka; Yoshiharu Iwabuchi; Hiroyuki Shibata
Curcumin (diferuloylmethane) is a dietary phytochemical with low toxicity that exhibits growth-suppressive activity against a variety of cancer cells and possesses certain chemopreventive properties. Curcumin has already been the subject of several clinical trials for use as a treatment in human cancers. Synthetic chemical modifications of curcumin have been studied intensively in an attempt to find a molecule with similar but enhanced properties of curcumin. In this study, a series of novel curcumin analogues were synthesized and screened for anticancer activity. New analogues that exhibit growth-suppressive activity 30 times that of curcumin and other commonly used anticancer drugs were identified. Structurally, the new analogues are symmetrical 1,5-diarylpentadienone whose aromatic rings possess an alkoxy substitution at each of the positions 3 and 5. Analysis of the effects of the analogues on the expression of cancer-related genes usually affected by curcumin indicated that some induced the down-regulation of β-catenin, Ki-ras, cyclin D1, c-Myc, and ErbB-2 at as low as one eighth the concentration at which curcumin normally has an effect. The analogues, however, exhibited neither harmful nor growth-suppressive effects on normal hepatocytes where oncogene products are not activated. They also exhibited no toxicities in vivo that they may provide effective alternative therapies for the prevention and treatment of some human cancers. [Mol Cancer Ther 2006;5(10):2563–71]
Journal of the American Chemical Society | 2011
Masatoshi Shibuya; Yuji Osada; Yusuke Sasano; Masaki Tomizawa; Yoshiharu Iwabuchi
5-Fluoro-2-azaadamantane N-oxyl (5-F-AZADO) realizes a simple, organocatalytic aerobic alcohol oxidation system that has a wide scope under mild conditions at ambient pressure and temperature and is weakly acidic and halogen- and transition-metal-free. The oxoammonium nitrate (5-F-AZADO(+)NO(3)(-)) works as a bifunctional catalyst of 5-F-AZADO and NO(x) that enables the catalytic aerobic oxidation of alcohols by itself (a metal-salt-free system).
Journal of Organic Chemistry | 2009
Masatoshi Shibuya; Masaki Tomizawa; Yusuke Sasano; Yoshiharu Iwabuchi
A practical, three-step synthetic route to 9-azabicyclo[3.3.1]nonane N-oxyl (ABNO, 3), an unhindered, stable class of nitroxyl radical, has been developed. ABNO exhibits a highly active nature compared with TEMPO in the catalytic oxidation of alcohols to their corresponding carbonyl compounds.
Journal of Organic Chemistry | 2008
Masatoshi Shibuya; Masaki Tomizawa; Yoshiharu Iwabuchi
Practical and highly efficient methods for oxidative rearrangement of tertiary allylic alcohols to beta-substituted alpha,beta-unsaturated carbonyl compounds employing oxoammonium salts are described. The methods developed are applicable to acyclic substrates as well as medium membered ring substrates and macrocyclic substrates. The counteranion of the oxoammonium salt plays crucial roles on this oxidative rearrangement.
Organic Letters | 2009
Masaki Tomizawa; Masatoshi Shibuya; Yoshiharu Iwabuchi
A highly enantioselective organocatalytic oxidative kinetic resolution (OKR) of racemic secondary alcohols has been accomplished using asymmetric organocatalysis. A panel of chirally modified 2-azaadamantane N-oxyls (AZADOs) exhibit superior catalytic activity and high enantioselectivity, allowing us to obtain optically active secondary alcohols with a k(rel) value up to 82.2.
Organic Letters | 2008
Masatoshi Shibuya; Masaki Tomizawa; Yoshiharu Iwabuchi
The novel catalytic method for the oxidative rearrangement of tertiary allylic alcohols to beta-substituted alpha,beta-unsaturated ketones is described. TEMPO/NaIO4-SiO2 causes facile and efficient oxidative rearrangement of various acyclic substrates as well as medium-sized and macrocyclic substrates.
Journal of the American Chemical Society | 2014
Keiichi Murakami; Yusuke Sasano; Masaki Tomizawa; Masatoshi Shibuya; Eunsang Kwon; Yoshiharu Iwabuchi
The development and characterization of enantioselective organocatalytic oxidative kinetic resolution (OKR) of racemic secondary alcohols using chiral alkoxyamines as precatalysts are described. A number of chiral alkoxyamines have been synthesized, and their structure-enantioselectivity correlation study in OKR has led us to identify a promising precatalyst, namely, 7-benzyl-3-n-butyl-4-oxa-5-azahomoadamantane, which affords various chiral aliphatic secondary alcohols (ee up to >99%, k(rel) up to 296). In a mechanistic study, chlorine-containing oxoammonium species were identified as the active species generated in situ from the alkoxyamine precatalyst, and it was revealed that the chlorine atom is crucial for high reactivity and enantioselectivity. The present OKR is the first successful example applicable to various unactivated aliphatic secondary alcohols, including heterocyclic alcohols with high enantioselectivity, the synthetic application of which is demonstrated by the synthesis of a bioactive compound.
Heterocycles | 2010
Yoshiharu Iwabuchi; Yosuke Sato; Hayato Fukuda; Masaki Tomizawa; Tomohito Masaki; Masatoshi Shibuya; Naoki Kanoh
The enantio- and diastereocontrolled total synthesis of (―)-salinosporamide A, a potent 20S proteasome inhibitor, was accomplished through organocatalytic aldolization, diastereoselective Claisen condensation, a Rh-catalyzed Reformatsky reaction, and an AZADO-catalyzed oxidative β-lactonization reaction as the key reactions.
Journal of the American Chemical Society | 2006
Masatoshi Shibuya; Masaki Tomizawa; Iwao Suzuki; Yoshiharu Iwabuchi
Tetrahedron Letters | 2012
Masatoshi Shibuya; Fabio Pichierri; Masaki Tomizawa; Shota Nagasawa; Iwao Suzuki; Yoshiharu Iwabuchi