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Rika Obata

Kitasato University

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Publication

Featured researches published by Rika Obata.

Bioorganic & Medicinal Chemistry Letters | 1995

Chemical modification and structure-activity relationships of pyripyropenes; potent, bioavailable inhibitor of acyl-CoA: Cholesterol O-acyltransferase (ACAT)

Rika Obata; Toshiaki Sunazuka; Hiroshi Tomoda; Yoshihiro Harigaya; Satoshi Ōmura

Abstract Modification and structure-activity relationships of ACAT inhibitor pyripyropene were examined. PR-109 (7g) showed the most potent (IC50 = 6 nM) inhibitory activity. PR-86 (2e) also had strong inhibitory activity (IC50 = 19 nM) and its in vivo activity improved 10 times better (ED50 = 10 mg/kg) than that of pyripyropene A.

Bioorganic & Medicinal Chemistry Letters | 2000

Synthetic conversion of ACAT inhibitor to acetylcholinesterase inhibitor

Rika Obata; Toshiaki Sunazuka; Kazuhiko Otoguro; Hiroshi Tomoda; Yoshihiro Harigaya; Satoshi Ōmura

Natural product acyl-CoA:cholesterol acyltransferase (ACAT) inhibitor pyripyropene A was synthetically converted to acetylcholinesterase (AChE) inhibitor via heterolitic cleavage of the 2-pyrone ring, followed by gamma-acylation/cyclization with several aroyl chlorides. The 4-pyridyl analogue selectively showed AChE inhibitory activity (IC50 7.9 microM) and no ACAT inhibitory activity IC50 = >1000 microM.

Journal of the American Chemical Society | 1994

RELATIVE AND ABSOLUTE STEREOCHEMISTRY OF PYRIPYROPENE A, A POTENT, BIOAVAILABLE INHIBITOR OF ACYL-COA : CHOLESTEROL ACYLTRANSFERASE (ACAT)

Hiroshi Tomoda; Hiroyuki Nishida; Young Kook Kim; Rika Obata; Toshiaki Sunazuka; Satoshi Omura; Jon Bordner; Mark A. Guadliana; Peter G. Dormer; Amos B. Smith

Journal of Organic Chemistry | 1995

Total Synthesis of (+)-Pyripyropene A, a Potent, Orally Bioavailable Inhibitor of Acyl-CoA:Cholesterol Acyltransferase

Tohru Nagamitsu; Toshiaki Sunazuka; Rika Obata; Hiroshi Tomoda; Haruo Tanaka; Yoshihiro Harigaya; Satoshi Omura; Amos B. Smith

The Journal of Antibiotics | 1996

Chemical modification and structure-activity relationships of pyripyropenes. 1. Modification at the four hydroxyl groups

Rika Obata; Toshiaki Sunazuka; Zhuorong Li; Zhiming Tian; Yoshihiro Harigaya; Noriko Tabata; Hiroshi Tomoda; Satoshi Omura

Journal of Organic Chemistry | 1996

BIOSYNTHESIS OF PYRIPYROPENE A

Hiroshi Tomoda; N. Tabata; Y. Nakata; Hiroyuki Nishida; Takushi Kaneko; Rika Obata; Toshiaki Sunazuka; Satoshi Omura

The Journal of Antibiotics | 2000

Structure-activity relationships study of pyripyropenes: Reversal of cancer cell multidrug resistance

Rika Obata; Toshiaki Sunazuka; Yoshihiro Harigaya; Masahiko Hayashi; Mun Chual Rho; Hiroshi Tomoda; Satoshi Omura

The Journal of Antibiotics | 1996

Chemical modification and structure-activity relationships of pyripyropenes. 2. 1,11-cyclic analogs

Rika Obata; Toshiaki Sunazuka; Yumiko Kato; Hiroshi Tomoda; Yoshihiro Harigaya; Satoshi Omura

The Journal of Antibiotics | 1997

Chemical Modification and Structure-activity Relationships of Pyripyropenes 3. Synthetic Conversion of Pyridine-pyrone Moiety

Rika Obata; Toshiaki Sunazuka; Zhiming Tian; Hiroshi Tomoda; Yoshihiro Harigaya; Satoshi Omura

The Journal of Antibiotics | 1995

Structure-activity relationships of pyripyropenes fungal acyl-CoA: cholesterol acyltransferase inhibitors.

Rika Obata; Toshiaki Sunazuka; Li Zhuorong; Hiroshi Tomoda; Satoshi Omura

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Toshiaki Sunazuka

Kitasato University

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Hiroshi Tomoda

Kitasato University

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Satoshi Omura

Kitasato University

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Yoshihiro Harigaya

Kitasato University

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Zhiming Tian

Kitasato University

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Amos B. Smith

University of Pennsylvania

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Haruo Tanaka

Kitasato University

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Hiroyuki Nishida

Kitasato University

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Masahiko Hayashi

Kitasato University

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Satoshi Ōmura

Kitasato University

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